CRAM

Question 1

What is sensitivity?

Answer 1

sensitivity is the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.

Question 2

What is excretion?

Answer 2

The removal from organisms of toxic materials, the waste products of metabolism and substances in excess of requirements

Question 3

What is egestion?

Answer 3

The passing out of undigested food through the anus

Question 4

What is nutrition?

Answer 4

The taking in of materials for energy, growth and development.

Question 5

What is a species?

Answer 5

A group of organisms that can reproduce to produce fertile offspring

Question 6

What is the binomial system?

Answer 6

An internationally agreed system in which the scientific name of an organism is divided into two parts showing the genus and species

Question 7

What is classification?

Answer 7

The way biologists group organisms to determine things like their family groups and species, evolutionary relationships and study their morphology and specific characteristics

Question 8

What is the modern method of classification?

Answer 8

Base sequences in DNA. Groups of organisms that share a more recent ancestor have more similar base sequences meaning they are more closely related

Question 9

What are the 5 main kingdoms?

Answer 9

• Animals
• Plants
• Fungi
• Prokaryotes
• Protoctists

Question 10

What are the main features of reptiles?

Answer 10

• Cold blooded
• Have dry scaly skin
• Lay eggs on dry land
• (Snake, crocodile, lizards)

Question 11

What are the main features of fish?

Answer 11

• Have scales on their bodies
• Have gills for breathing
• Cold blooded
• (Shark, tuna, salmon)

Question 12

What are the main features of amphibians?

Answer 12

• Have moist, slimy skin
• Cold blooded
• Lay eggs in water
• (Frog, newt, salamander)

Question 13

What are the main features of birds?

Answer 13

• Have feathers and wings
• Have beaks and lay eggs
• Warm blooded
• (Eagle, swan, sparrow)

Question 14

What are the main features of mammals?

Answer 14

• Have fur or hair
• Feed young on milk
• Warm blooded
• external ears
• (Cow, human, bear)

Question 15

What are the main groups of arthropods?

Answer 15

Arachnids, crustaceans, insects and myriapods

Question 16

What is an arthropod?

Answer 16

All invertebrates with jointed legs, segmented bodies and a hard exoskeleton made of chitin

Question 17

What is a virus’s structure?

Answer 17

Genetic material (RNA or DNA) inside a protein coat

Question 18

What are the features of flowering plants?

Answer 18

• Reproduce sexually by means of flowers and seeds
• Seeds are produced inside the ovary found at the base of the flower
• Can be divided into two groups: monocotyledons and dicotyledons

Question 19

What are the features of monocotyledons?

Answer 19

• Contain petals in a multiple of 3
• Leaves have parallel leaf veins
• Vascular bodies are randomly arranged
• Fibrous root system

Question 20

What are the features of dicotyledons?

Answer 20

• Contains petals in multiples of 4 or 5
• Leaves have branched veins
• Vascular bodies arranged in rings
• Roots are taproot

Question 21

What are the main features of insects?

Answer 21

Three body sections and six legs

Question 22

What are the main features of arachnids?

Answer 22

Two body sections and eight legs

Question 23

What are the main features of crustaceans?

Answer 23

two body sections and at least ten legs

Question 24

What are the main features of myriapods?

Answer 24

Many segments with lots of legs

Question 25

What is the function of the nucleus?

Answer 25

Contains the genetic material (DNA) which controls the activities of the cell

Question 26

What is the function of ribosomes?

Answer 26

• Can be free floating in the cytoplasm or associated with the ER
• Site of protein synthesis (makes proteins)

Question 27

What is the function of chloroplasts?

Answer 27

• Contains green chlorophyll pigment (to absorb light energy) and the enzymes needed for photosynthesis
• Uses light energy to produce glucose as a food source

Question 28

What is the function of a vacuole?

Answer 28

• Plant cells have a large central vacuole
• Animal cells have several small vacuoles or absent
• Important for storage of compounds, water and nutrients
• Maintains turgidity

Question 29

What are the features of bacteria?

Answer 29

Cell membrane, cytoplasm, ribosomes, cell wall (made of peptidoglycan), circular loop of DNA
Some may also have plasmids (small loops of DNA) and flagella (thread like structures that allow them to move in liquids)

Question 30

What are specialised cells?

Answer 30

Specialised cells are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus

Question 31

Why do cells need to divide?

Answer 31

to help your body grow and repair itself

Question 32

How are new cells produced?

Answer 32

The division of existing cells

Question 33

What’s the function of a ciliated cell?

Answer 33

Movement of mucus in the trachea and bronchi

Question 34

What’s the function of a neuron?

Answer 34

Sending and recieving neurotransmitters

Question 35

What’s the function of a red blood cell?

Answer 35

Transport of oxygen

Question 36

What are the adaptations of a ciliated cell?

Answer 36

• Extensions of the cytoplasm at the surface of the cell form hair-like structures called cilia which beat to move mucus and trapped particles up the throat

Question 37

What are the adaptations of nerve cells?

Answer 37

• Long so nerves can run to and from different parts of the body to central nervous systems
• The cell has extensions and branches, so that it can communicate with other nerve cells, muscles and glands
• The axon (extension of cytoplasm away from the cell body) is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse

Question 38

What are the adaptations of red blood cells?

Answer 38

• Biconcave disc shape increases surface area for more efficient diffusion of oxygen
• Contains haemoglobin which joins with oxygen to transport it
• Contains no nucleus to increase amount of space available for haemoglobin inside cell

Question 39

What are the adaptations of a sperm cell?

Answer 39

• The head contains the genetic material for reproduction in a haploid nucleus (nucleus with half the normal number of chromosomes)
• The acrosome in the head contains digestive enzymes so that a sperm can penetrate an egg
• The mid-piece is packed with mitochondria to release energy needed to swim and fertilise the egg
• The tail enables the sperm to swim

Question 40

What are the adaptations of an ovum?

Answer 40

• Contains a lot of cytoplasm which has nutrients for the growth of the early embryo
• Haploid nucleus contains the genetic material for fertilisation
• Cell membrane changes after fertilisation by a single sperm so no more sperm can enter

Question 41

What is the function of root hair cells?

Answer 41

Absorbtion of water and mineral ions from water

Question 42

What is the function of the xylem vessel?

Answer 42

Conduction of water through the plant; support of the plant

Question 43

What are the adaptations of a root hair cell?

Answer 43

• Root hair increases surface area of cell to ensure maximum absorption of water and mineral ions
• Walls are thin enough to ensure that water moves through quickly
• No chloroplasts present

Question 44

What is the function of a palisade mesophyll cell?

Answer 44

Photosynthesis

Question 45

What are the adaptations of the xylem vessel?

Answer 45

• No top and bottom walls between xylem vessels so there is a continuous column of water running through them
• Cells are dead without organelles or cytoplasm to allow free passage of water
• Their walls become thickened with a substance called lignin which means they are able to help support the plant

Question 46

What are the adaptations of the palisade mesophyll cell?

Answer 46

• Column shaped to maximize absorption of sunlight and fit as many in a layer under the epidermis of the leaf as possible
• Contains many chloroplasts for maximum photosynthesis

Question 47

What’s the first level of organisation in an organism? describe it.

Answer 47

Cell. Basic functional and structural units in a living organism

Question 48

What’s the second level of organisation in an organism? describe it.

Answer 48

Tissue. Groups of similar cells working together to carry out a specific function

Question 49

What’s the third level of organisation in an organism? describe it.

Answer 49

Organs. Groups of tissue working together to carry out a specific function.

Question 50

What’s the fourth level of organisation in an organism? describe it.

Answer 50

Organ system. Groups of organs working together to carry out a specific function.

Question 51

How many micrometers is a millimeter?

Answer 51

1000μm

Question 52

What is diffusion?

Answer 52

The net movement of particles from a region of higher concentration to a region of lower concentration (i.e. down a concentration gradient), as a result of their random movement requiring no energy to do so

Question 53

Where does the energy for diffusion come from?

Answer 53

the kinetic energy of random movement of
molecules and ions

Question 54

What are the factors that affect diffusion?

Answer 54

1. Concentration gradient (the larger it is, the faster the rate of diffusion)
2. Temperature (More energy associated with the particle at higher temperatures means faster rate of diffusion)
3. Surface area (The larger the surface area in contact between the two regions the faster the diffusion)
4. Distance (The larger the distance, the longer time to diffuse)

Question 55

What is the importance of the diffusion of gases and solutes in living organisms?

Answer 55

• Getting raw materials for respiration or photosynthesis
• Removing waste products
• Importing or exporting products

Question 56

Name some situations where water is important as a solvent in organisms?

Answer 56

• Dissolved substances can be easily transported around organisms
• Digested food molecules in the alimentary canal dissolve in water to be absorbed into the blood (for transport to cells
• Toxic substances can dissolve in water to be (easily) excreted in urine
• Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells

Question 57

How does water move into cells?

Answer 57

By osmosis through the partially permeable membrane

Question 58

What is osmosis?

Answer 58

the net movement of water molecules from a region of higher water
potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Question 59

What’s active transport?

Answer 59

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration

Question 60

What’s the importance of active transport?

Answer 60

Active transport is vital process for the movement of molecules or ions across membranes. Including:
- uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron
- uptake of ions from soil water by root hair cells in plants

Question 61

What is turgor pressure?

Answer 61

The pressure within cells that pushes at the cell wall or membrane, more water inside the cell means higher turgor pressure

Question 62

Why is turgor pressure important to plants?

Answer 62

So plants stay upright and have exposure to sunlight

Question 63

What happens to a plant cell in a hypertonic solution?

Answer 63

There’s a net movement of water out of the cell, causing a reduction in turgor pressure. This first makes the cell flaccid then after some time the cell membrane begins to pull back from the cell wall and the cell becomes plasmolysed.

Question 64

What happens to a plant cell in a hypotonic solution?

Answer 64

There’s a net movement of water into the cell, causing an increase in turgor pressure and the cell membrane to push against the cell wall. This makes the cell turgid

Question 65

What happens to a plant cell in an isotonic solution?

Answer 65

There is no net movement of water so the cell stays the same

Question 66

What large molecules are made from glucose?

Answer 66

Cellulose- plants use to make cell wall
Starch- plants use to store energy
Glycogen- animals use to store energy in the liver

Question 67

What is the function of glucose?

Answer 67

To produce energy from respiration. Plants transport sucrose which is then converted into glucose and used for respiration

Question 68

What is the function of protein?

Answer 68

It’s used to make new proteins and enzymes, used for growth and repair of cells and used to make antibodies which are used to kill bacteria and viruses

Question 69

What is the structure of DNA?

Answer 69

Two strands coiled together to form a double helix. The backbone is made of sugar and phosphate while on the inside the double helix contains chemicals called bases which determine the code of the DNA. The bonds between pairs of bases hold the
strands together

Question 70

Why are enzymes important in all living
organisms?

Answer 70

they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life. Without enzymes, reactions are so slow to occur, that the cells would die from not being able to do life processes

Question 71

Explain enzyme action with reference to: active site, enzyme-substrate complex, substrate and product

Answer 71

Enzymes are specific to one particular substrate as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate. They fit together like a lock (enzyme) and key (substrate). When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex. After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and the enzyme remains unchanged and takes on another substrate.

Question 72

When do enzyme reactions occur?

Answer 72

When the substrate and enzyme collide

Question 73

Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation

Answer 73

At lower temperatures, there are fewer successful collisions because the enzymes and the substrates have less kinetic energy. When the temperature is increasing, the enzymes and substrates have more kinetic energy resulting in more successful collisions. At the optimum temperature, the enzymes work the fastest they can. Above the optimum temperature, there are more collisions but the active site becomes denatured by the high temperature and the active site and substrate are no longer complementary so there are fewer successful collisions

Question 74

What is photosynthesis?

Answer 74

the process by which plants synthesise carbohydrates from raw materials using energy from light

Question 75

What is chlorophyll?

Answer 75

The protein found within chloroplasts that catalyses the reaction, it’s also what causes the plant to be green.

Question 76

What does chlorophyll do?

Answer 76

transfers energy from light into energy in chemicals, for the synthesis of carbohydrates

Question 77

What are the 5 uses and storage of the carbohydrates made in photosynthesis?

Answer 77

1. Glucose is commonly stored in plants as starch (as an energy source)
2. Glucose can be used to form cellulose to build cell walls
3. Glucose can be used in respiration to provide energy
4. Glucose can be converted to sucrose and transported through phloem vessels from source to sink
5. Glucose can be converted into nectar and used to attract insects for pollination

Question 78

Function of magnesium in plants

Answer 78

It’s needed to make chlorophyll

Question 79

Function of nitrate in plants

Answer 79

A source of nitrogen needed to make amino acids (build proteins)

Question 80

Deficiency of magnesium in plants

Answer 80

Yellowing between the veins of leaves (known as chlorosis) due to lack of chlorophyll production

Question 81

Deficiency of nitrate in plants

Answer 81

Stunted growth, leaves (usually near growing tip) start to turn yellow, old leaves start to dry out

Question 82

What is a limiting factor?

Answer 82

something that is in short supply that restricts a process. When a process depends on two or more variables, the rate of that process is determined by the factor that is in shortest supply.

Question 83

How does light intensity affect the rate of photosynthesis?

Answer 83

• Themore lighta plant receives, thefaster the rateof photosynthesis
• At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate

Question 84

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 84

• Carbon dioxide is one of the raw materials required for photosynthesis
• This means themore carbon dioxidethat is present, thefaster the reactioncan occur
• This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply

Question 85

How does temperature affect the rate of photosynthesis?

Answer 85

• As temperature increases the rate of photosynthesis increases as the reaction iscontrolled by enzymes
• However, as the reaction is controlled by enzymes, this trend only continues up to the optimum temperature beyond there the enzymes begin todenatureand the rate of reactiondecreases

Question 86

What is the net effect of the carbon dioxide in plants during the day and night?

Answer 86

During the day, especially when the sun is bright,plants are photosynthesising at a faster rate than they are respiring, so there is anet intake of carbon dioxide and a net output of oxygen. During the night, plants respire more than they photosynthesise so there is a net release of carbon dioxide

Question 87

What does yellow and orange colour of hydrogen carbonate indicator mean?

Answer 87

Highest and high concentration of carbon dioxide, respectively. More respiration>photosynthesis (lower pH, more acidic)

Question 88

What does red colour of hydrogen carbonate indicator mean?

Answer 88

Concentration of carbon dioxide is atmospheric level. Photosynthesis=respiration

Question 89

What does purple and magenta colour of hydrogen carbonate indicator mean?

Answer 89

Lowest and low concentration of carbon dioxide, respectively. More photosynthesis>respiration (higher pH, more alkaline)

Question 90

What does upper epidermis do in a leaf?

Answer 90

Offer protection but thin and transparent to allow light to enter the palisade mesophyll layer

Question 91

What does palisade mesophyll do in a leaf?

Answer 91

Column shaped cells tightly packed together with many chloroplasts to absorb more light, maximising photosynthesis

Question 92

What does a waxy cuticle do in a leaf?

Answer 92

Protective layer on top of the leaf that prevents water from evaporating. It also allows light to pass through whilst protecting the leaf’s surface

Question 93

What does spongey mesophyll do in a leaf?

Answer 93

Irregular shape, fewer chloroplasts and contain internal air spaces to increase the surface area to volume ratio for the diffusion of gases

Question 94

What do guard cells do in a leaf?

Answer 94

Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in and oxygen to diffuse out

Question 95

What do the stomata do in a leaf?

Answer 95

Where gas exchange takes place; opens during the day and closes during the night. Evaporation of water also takes place here. In most plants they are located on the underside of the lead to reduce water loss.

Question 96

What does the vascular bundle do in a leaf?

Answer 96

Contains xylem and phloem to transport substances to and from the leaf. Xylem transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from the stomata. Phloem transports sucrose and amino acids around the plant

Question 97

Why does a large surface area adapt a leaf for photosynthesis?

Answer 97

Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis

Question 98

Why does the leaf being thin adapt a leaf for photosynthesis?

Answer 98

Allows carbon dioxide to diffuse to palisade mesophyll cells quickly

Question 99

How does chlorophyll adapt a leaf for photosynthesis?

Answer 99

Absorbs light energy so photosynthesis can take place

Question 100

How do the epidermal cells adapt a leaf for photosynthesis?

Answer 100

They are thin and transparent which allows more light to reach the palisade cells

Question 101

How does the spongey mesophyll layer adapt a leaf for photosynthesis?

Answer 101

Airspaces allow carbon dioxide to diffuse through the leaf, increasing the surface area

Question 102

How does the vascular bundle adapt a leaf for photosynthesis?

Answer 102

Thick cell walls of the tissue in the bundles help to support the stem and leaf

Question 103

What is a balanced diet?

Answer 103

A balanced diet has the correct amount of each group of nutrients (carbohydrates, fats, proteins, vitamins, minerals, dietary fibre and water). We need a balanced diet to stay healthy.

Question 104

What are the 7 main food groups?

Answer 104

Carbohydrates
Protein
Fats
Dietary fibre
Vitamins (C and D)
Minerals (Iron and calcium)
Water

Question 105

Function and sources of carbohydrates

Answer 105

Function: Source of energy, nutrient for producing energy
Sources: Bread, cereals, pasta, rice, potatoes

Question 106

Function and sources of protein

Answer 106

Function: Growth (getting bigger by growing new cells), repair (replacing damaged or worn out cells)
Sources: Meat, fish, eggs, beans, nuts

Question 107

Function and sources of lipids

Answer 107

Function: Insulation and energy storage, making cell membranes of cells
Sources: Butter, oil, cheese, margarine

Question 108

Function and sources of dietary fibre

Answer 108

Function: Ensures food moves through intestines at the correct rate
Sources: Vegetables, whole grains

Question 109

Function and sources of vitamins

Answer 109

Function: Needed in small quantities to maintain health
Sources: Fruit and vegetables

Question 110

Function and sources of vitamin C

Answer 110

Function: Used in creating connective tissue, blood vessels, bones and cartilage. It’s required for wound healing.
Sources: Citrus fruits (lemon, lime, orange), strawberries, kiwifruit

Question 111

Function and sources of vitamin D

Answer 111

Function: Helps the body to absorb calcium. Needed to maintain strong, healthy bones and teeth
Sources: Main source is sunlight but can also be gained from fatty fish, egg yolks and dairy products

Question 112

Function and sources of calcium

Answer 112

Function: Needed for strong bones and teeth and maintaining blood clotting
Sources: Milk, cheese, eggs, fish with bones

Question 113

Function and sources of iron

Answer 113

Function: Required for making haemoglobin in red blood cells which is used to bind oxygen
Sources: Red meat, whole grains, leafy green vegetables

Question 114

Function and sources of water

Answer 114

Function: Acts as a solvent for cellular reactions, circulatory system and digestion system, helps to maintain body temperature
Sources: Water, juice, milk, fruits and vegetables

Question 115

Main organs in digestive system

Answer 115

mouth, salivary glands, oesophagus,
stomach, small intestine (duodenum and ileum), large intestine (colon, rectum,
anus), pancreas,
liver and gall bladder

Question 116

Function of mouth

Answer 116

The mouth is where mechanical digestion takes place. The teeth grind the food into small pieces to increase its surface area to volume ratio. The salivary glands release saliva in the mouth. The saliva contains amylase enzymes which break down starch into maltose. Another enzyme maltase breaks down maltose to glucose. At the back of the mouth, the food is made into a ball called bolus by the tongue and lubricated in saliva so it can be swallowed easily.

Question 117

What is the function of the oesophagus?

Answer 117

The tube that connects the mouth to the stomach. The bolus goes here after being swallowed and is pushed down the oesophagus by wave-like muscle contractions called peristalsis.

Question 118

What is the function of the stomach?

Answer 118

The main organ where food is digested as it does both mechanical and chemical digestion. Food is mechanically digested by muscles that churn the food. Protease enzymes start to chemically digest proteins and hydrochloric acid is added to kill bacteria in food and provide the optimum pH for the enzymes to work.

Question 119

What is the function of the small intestine?

Answer 119

Where nutrients are absorbed. The first section is the duodenum where food goes when it goes out of the stomach. This is where bile and digestive enzymes are added to further digest the food. At this point the pH of the small intestine is slightly alkaline at 8-9 because bile is basic. The second section is called the ileum and it’s where the absorption of digested food molecules takes place. The ileum is long and lined with villi to increase the surface area over which absorption takes place.

Question 120

What is the function of the large intestine?

Answer 120

Mainly indigestible food and water enter the large intestine. Here water is absorbed back into the body to produce faeces. Faeces are stored in the rectum. The anus is the opening at the end of the digestive system and is where the faeces are removed.

Question 121

What is the function of the salivary glands?

Answer 121

Release saliva in the mouth. The saliva contains amylase enzymes which break down starch into maltose.

Question 122

What is the function of the pancreas?

Answer 122

Produces the enzymes involved in digestion: amylase, protease and lipase. It secretes these enzymes in an alkaline fluid into the duodenum to raise the pH of food coming out of the stomach. It also produces insulin and glycogen which are hormones that regulate blood sugar levels.

Question 123

What is the function of the liver?

Answer 123

Produces bile which emulsifies fats (breaking large droplets into smaller droplets, mechanical digestion) helping to digest them. Bile contains lipase and neutralises the pH. Amino acids that aren’t used to make protein are broken down here which produces urea

Question 124

What is the function of the gall bladder?

Answer 124

Stores bile to release into the duodenum as required.

Question 125

What is ingestion and where in the body does it happen?

Answer 125

the taking of substances, e.g. food and drink, into the body
Part of body: mouth (eating the food)

Question 126

What is digestion and where in the body does it happen?

Answer 126

What is digestion and where in the body does it happen?

Question 127

What is absorption and where in the body does it happen?

Answer 127

the movement of nutrients from the intestines into the blood
Part of body: small intestine (ileum) and large intestine

Question 128

What is assimilation and where in the body does it happen?

Answer 128

uptake and use of nutrients by cells
Part of body: small intestine

Question 129

What is physical digestion?

Answer 129

the breakdown of food into smaller pieces without chemical change to the food molecules

Question 130

What do the processes that happen in physical digestion help to do?

Answer 130

increase the surface areaof food for the action ofenzymesduring chemical digestion

Question 131

Where physical digestion occurs

Answer 131

chewingaction of theteeth, thechurningaction of thestomachand theemulsification of fatsbybilein the duodenum

Question 132

How does the stomach do physical digestion?

Answer 132

The stomach lining containsmuscleswhich contract tophysically squeezeand mix the food with the strong digestive juices that are present (also known as “stomachchurning”)

Question 133

How does bile do physical digestion?

Answer 133

Bile is used to emulsify (break down large fat molecules into smaller ones) fats and oils to increase the surface area for chemical digestion

Question 134

What do incisors do?

Answer 134

Work to bring the food into the mouth and cut it

Question 135

What do canines do?

Answer 135

Cut and tear food up

Question 136

What do premolars do?

Answer 136

Help incisors and canines grind and mix food while chewing

Question 137

What is chemical digestion?

Answer 137

the breakdown of large insoluble molecules into small soluble molecules

Question 138

What is the role of chemical digestion?

Answer 138

to produce small soluble molecules that can be absorbed

Question 139

What does amylase do in digestion?

Answer 139

• Breaks down starch to simple reducing sugars
• Amylasesare produced in themouthand thepancreas(secreted into theduodenum)

Question 140

What does protease do in digestion?

Answer 140

• Break down protein to amino acids
• Proteases are in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas)

Question 141

What does lipase do in digestion?

Answer 141

• Breaks down fats and oils to fatty acids and glycerol
• Lipaseenzymes are produced in thepancreasand secreted into theduodenum

Question 142

Function of hydrochloric acid

Answer 142

• The stomach produces several fluids which together are known asgastric juice. One of the fluids produced ishydrochloric acid
• The hydrochloric acid is used in killing harmful microorganisms in food and providing an acidic pH for optimum enzyme activity
• The low pH kills bacteria in food that we have ingested as itdenatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life

Question 143

What happens in the digestion of starch?

Answer 143

• Amylaseis secreted into the alimentary canal in themouthand theduodenum(from the pancreas) and digestsstarch to maltose(a disaccharide)
• Maltoseis digested by the enzymemaltaseintoglucoseon the membranes of the epithelium lining of the small intestine

Question 144

What is bile?

Answer 144

Bile is an alkaline mixture that neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action

Question 145

What happens in the digestion of protein?

Answer 145

Protein digestion takes place in the stomach and duodenum with two main enzymes produced:

• Pepsinis produced in thestomach and breaks down protein in acidic conditions in the stomach (optimum pH of 3)
• Trypsinis produced in thepancreasand secreted into theduodenumwhere it breaks down protein inalkaline conditions (optimum pH of 8)

Question 146

How is the small intestine adapted for its function?

Answer 146

• The ileum is adapted for absorption as it isvery longand has ahighly folded surface with millions of villi(tiny, finger like projections). These adaptations massivelyincrease the surface areaof the ileum, allowing absorption to take place faster and more efficiently. Microvillion the surface of the villus further increase surface area for faster absorption of nutrients.
• Wall of the villus isone cell thickmeaning that there is only a short distance for absorption to happen by diffusion and active transport
• Villus contains anetwork of blood capillariesthat transport glucose and amino acids away from the small intestine in the blood. Blood flows through the capillaries which maintains the concentration gradient leading to fast diffusion
• Lactealruns through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph

Question 147

What is the function of xylem?

Answer 147

transport of water and mineral ions, and support (transports up from roots to leaves)

Question 148

What is the function of phloem?

Answer 148

transport of sucrose and amino acids (transports in all directions)

Question 149

Where is xylem and phloem in vascular bundle?

Answer 149

cells on top or the bigger cells are xylem and cells on bottom or smaller cells are phloem

Question 150

What are the adaptations of xylem vessels?

Answer 150

• Cells joined end to end withno cross wallsto form a long continuous tube
• Cells have no cell contents
• Thick cell walls that are strengthened by lignin

Question 151

What are root hair cells and what are their function?

Answer 151

• Root hair cells are the ones that have finger-like projections coming out of them
• They grow between soil particles and absorb water and minerals from the soil
• Water enters the root hair cells byosmosis
• The large surface area of root hairs increases the uptake of water and mineral ions because it increases the rate of osmosis/diffusion

Question 152

What is the path of water in a plant?

Answer 152

Water moves through a root hair by osmosis. It then travels by osmosis through the cortex, from cell to cell, until eventually it reaches the xylem vessels in the middle of the root. These transport it all the way up through stem and into the mesophyll layer of leaves and evaporates out through stomata into the atmosphere

Question 153

What is transpiration?

Answer 153

the loss of water vapour from leaves

Question 154

Why does transpiration happen?

Answer 154

Transpiration happens because water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour

Question 155

How does the large surface area in the spongey mesophyll layer increase transpiration?

Answer 155

The many interconnecting air spaces between the mesophyll cells and the stomata creates a large internal surface area. This increases the rate of transpiration as it allows water vapour to move freely and easily meaning evaporation can happen rapidly when stomata are open. The size and number of stomata on a leaf’s surface also affect this process. A larger number of stomata or larger stomata can potentially increase the rate of water vapour loss due to increased opportunities for diffusion.

Question 156

How and why does wilting happen?

Answer 156

• Wilting happens when all the cells of the plant aren’t full of water, so the strength of the cell walls can’t support the plant making it start to collapse. Wilting reduces surface area and conserves water.
• Plants wilt because more water evaporates from a plant than can be absorbed from the soil, the plant cells become flaccid causing the plant to wilt.

Question 157

What is translocation?

Answer 157

the movement of sucrose and amino acids in phloem from sources to sinks

Question 158

Why does the source and sink of a plant change?

Answer 158

• Transport in the phloemgoes in many different directionsdepending on the stage of development of the plant or the time of year; however dissolved food is always transported from thesource(where it’s made) tosink(where it’s stored or used)
• Duringwinter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue. During agrowth period(eg during the spring), the storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks. After the plant has grown(usually during the summer), the leaves are photosynthesizing and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again

Question 159

How does single circulation work in fishes?

Answer 159

They have a two-chambered heart comprising an atrium and a ventricle. In fishes, the heart pumps out the deoxygenated blood which undergoes oxygenation in the gills. In gills, blood receives oxygen and releases carbon dioxide, a process facilitated by the thin walls of gill capillaries allowing efficient gas exchange. The oxygenated blood is then passed to the body parts from where the deoxygenated blood is returned to the heart.

Question 160

What is the circulatory system?

Answer 160

The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow of blood

Question 161

What is double and single circulation?

Answer 161

Double circulation means that the blood flows through two circuits – one low-pressure circuit and one high-pressure circuit.
Single circulation is when the blood passes through a single circuit

Question 162

What is the double circulation of a mammal?

Answer 162

Mammals have a four chamber heart (two atria and two ventricles) and double circulation. Double circulation means that the blood flows through two circuits – one low-pressure circuit and one high-pressure circuit. The right low-pressure circuit is when the deoxygenated blood travels from the heart, to the lungs where it becomes oxygenated, and back. This is also known as the pulmonary circuit. The left high-pressure circuit, or systemic circuit, is when oxygenated blood flows from the heart to the rest of the body, and back. This is higher pressure because the blood has to travel further, so the heart applies a greater force on this blood, this is why the left side of the heart has a thicker muscle wall.

Question 163

What are the advantages of double circulation?

Answer 163

• Blood travelling through the small capillaries in the lungsloses a lot of pressurethat was given to it by the pumping of the heart, meaning itcannot travel as fast. By returning the blood to the heart after going through the lungs itspressure can be raised againbefore sending it to the body, meaningcellscan be supplied with theoxygen and glucosethey need for respirationfaster and more frequently
• Double circulation also helps keep the oxygenated and deoxygenated blood separate and prevents their mixing – this allows a highly efficient supply of oxygen to the body.

Question 164

Why is single circulation inefficient?

Answer 164

Single circulation is inefficient because there lower blood pressure after passing through gills, leading to a slower rate of flow to body tissues and less efficient due to the mixing of blood and the single loop system resulting in reduced oxygenation efficiency.

Question 165

Why do ventricles have thicker muscle walls than the atria?

Answer 165

they are pumping blood out of the heart and so need to generatea higher pressure

Question 166

What does the septum do?

Answer 166

separates the two sides of the heart and soprevents mixing of oxygenated and deoxygenated blood

Question 167

What is the function of valves?

Answer 167

to prevent backflow of blood

Question 168

Where are the atrioventricular valves located?

Answer 168

between the atria and ventricles on both sides of the heart
tricuspid: heart right
bicuspid: heart left

Question 169

Where are the semilunar valves located?

Answer 169

In the two blood arteries that come out of the top of the heart. They are unusual in that they are theonly two arteries in the body that contain valves

Question 170

What is the function of the atrioventricular valves?

Answer 170

These valves are pushedopen when the atria contractbut when theventricles contract they are pushed shutto prevent blood from flowing back into the atria

Question 171

What is the function of the semilunar valves?

Answer 171

These valvesopen when the ventricles contractso blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart

Question 172

Why does physical activity increase heart rate?

Answer 172

• Physical activity increases heart rate. This is because physical activity increases the body’s need for energy, increasing the rate of respiration and thus the demand for oxygen. This means the heart needs to pump blood around the body faster, to deliver oxygen faster to the needy tissues, so the heart rate increases. If the heart rate increases, the number of ‘pulses’ of blood pushed out by the ventricles per minute also increases, so the pulse rate increases.
• The heart rate rises during exercise so thatsufficient bloodis taken to the working muscles to provide them with enoughnutrients and oxygenforincreased respiration. An increase in heart rate also allows forwaste products to be removed at a faster rate

Question 173

Why does the heart continue to beat fast after exercise?

Answer 173

• Following exercise, the heart continues to beat faster for a while to ensure thatall excess waste products are removedfrom muscle cells.
• It is also likely that muscle cells have been respiringanaerobicallyduring exercise and so have built up anoxygen debt. This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure thatextra oxygen is still being delivered to muscle cells
• The extra oxygen is used to break down thelactic acidthat has been built up in cells as a result of anaerobic respiration

Question 174

What happens if a coronary artery is blocked?

Answer 174

• The blood is supplied by thecoronary arteries. If a coronary artery becomes partially or completelyblocked by fatty deposits called ‘plaques’(mainly formed fromcholesterol), the arteries are not aselasticas they should be and therefore cannot stretch to accommodate the blood which is being forced through them - leading tocoronary heart disease
• Partial blockageof the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains calledangina
• Complete blockagemeans cells in that area of the heart will not be able to respire and can no longer contract, leading to aheart attack

Question 175

What are the risk factors for coronary heart disease?

Answer 175

Poor diet- Eating more saturated fat increases cholesterol levels, increasing the chance of the buildup of fatty plaques
Stress- When under stress, hormones produced can increase blood pressure, increasing the chance of a blockage in the coronary arteries
Smoking- Nicotine in cigarettes causes blood vessels to become narrower, increasing blood pressure which causes the buildup of fat globules. If this occurs in the coronary artery, it could cause coronary heart disease
Genetic predisposition- Studies show that people with a history of coronary heart disease in their family are more likely to develop it themselves
Age- The risk of developing coronary heart disease increases as you get older
Gender- Males are more likely to develop it than females

Question 176

How does blood move through the heart?

Answer 176

Deoxygenated bloodcoming from the body flows into theright atriumvia thevena cava. Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through thetricuspid (atrioventricular) valveinto theright ventricle. The walls of the ventriclecontractand the blood is pushed into thepulmonary arterythrough thesemilunar valvewhich prevents blood flowing backwards into the heart. The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure). Oxygen-rich bloodreturns to theleft atriumvia thepulmonary vein. It passes through thebicuspid (atrioventricular) valveinto theleft ventricle. The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into theaortaand all the way around the body. Thesemilunar valvein the aorta prevents the blood flowing back down into the heart

Question 177

Veins characteristics

Answer 177

• Carry blood atlow pressure towards the heart
• Carrydeoxygenatedblood (other than the pulmonary vein)
• Havethinwalls
• Have alarge lumen as blood pressure is low
• Containvalves to prevent the backflow of blood as it is under low pressure
• Blood is squeezed back towards the heart by the action of the skeletal muscles
• Speed of flow isslow

Question 178

Arteries characteristics

Answer 178

• Carry blood athigh pressure away from the heart (dangerous to cut as blood will spurt out)
• Carryoxygenatedblood (other than the pulmonary artery)
• Havethick muscular wallscontaining elastic fibres to withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through
• Can stretch as blood is forced through them and return to original shape. This is felt as a pulse.
• Have anarrow lumen to maintain high blood pressure
• Speed of flow isfast

Question 179

Capillaries characteristics

Answer 179

• Carry blood atlow pressurewithin tissues
• Forms a huge network linking arteries to veins (allowing blood to access every cell in our body)
• Carryboth oxygenated and deoxygenated blood
• Have walls that areone cell thick so substances can easily diffuse in and out of them
• Have ‘leaky’ walls so that blood plasma can leak out and form tissue fluid surrounding cells
• Speed of flow isslow

Question 180

What does the pulmonary artery do?

Answer 180

The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs.

Question 181

What does the pulmonary vein do?

Answer 181

The pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart.

Question 182

What does the hepatic portal vein do?

Answer 182

Thehepatic portal veintransports deoxygenated blood from the gut to the liver (nutrient-rich blood)

Question 183

What are the four components of blood?

Answer 183

Red blood cells, plasma, platelets, white blood cells

Question 184

Red blood cells function and appearance

Answer 184

• Biconcave discs containing no nucleus but plenty of the protein haemoglobin
• Function is to transport oxygenaround the body from the lungs to cells which require it for aerobic respiration

Question 185

White blood cells appearance and function

Answer 185

• Large cells containing big nucleus, different types have slightly different structures and functions
• Function is to defendthe body against infection by pathogens by carrying outphagocytosisandantibody production
• There are two main types,phagocytes and lymphocytes

Question 186

What does a phagocyte’s function?

Answer 186

engulfing pathogens by phagocytosis

Question 187

How do phagocytes engulf pathogens?

Answer 187

Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells. Once they encounter the pathogenic cell, they will engulf it andrelease digestive enzymesto digest it.

Question 188

What is the function of lymphocytes?

Answer 188

antibody production

Question 189

Why do lymphocytes produce antibodies?

Answer 189

Produceantibodiesto destroy pathogenic cells andantitoxinsto neutralise toxins released by pathogens

Question 190

What are platelets?

Answer 190

Platelets arefragments of cells which are involved in blood clottingand forming scabs where the skin has been cut or punctured

Question 191

What is plasma?

Answer 191

• Straw coloured liquid
• Involved in transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide

Question 192

What is the role of blood clotting?

Answer 192

Role is to prevent blood loss and the entry of pathogens

Question 193

What happens when skin is broken?

Answer 193

When the skin is broken (i.e. there is a wound) platelets arrive to stop the bleeding and stimulate blood clotting. A series of reactions occur within the blood plasma. Platelets release chemicals that causesoluble fibrinogen proteinsto convert intoinsoluble fibrinand form aninsoluble meshacross the wound, trapping red blood cells and thereforeforming a clot. The clot eventually dries and develops into ascabto protect the wound from bacteria entering.

Question 194

How does large surface area increase the rate of gas exchange?

Answer 194

• This large surface area is provided by the numerous alveoli in the lungs and is critical for enhancing the capacity of gas exchange. More alveoli means more space for gases to be exchanged simultaneously, significantly increasing efficiency.
• In terms of individual alveolus, there is a large surface area in contact between capillaries and alveoli

Question 195

What are the main features of gas exchange in humans?

Answer 195

1. Large surface areato allow faster diffusion of gases across the surface
2. Thin wallsto ensure diffusion distances remain short
3. Good ventilation with airso that diffusion gradients can be maintained
4. Good blood supplyto maintain a high concentration gradient so diffusion occurs faster

Question 196

How does good ventilation increase the rate of gas exchange?

Answer 196

Ventilation, the process of air entering and exiting the lungs, is crucial in maintaining a high concentration of oxygen and a low concentration of carbon dioxide in the alveoli. This keeps up concentration gradients for oxygen and carbon dioxide

Question 197

How does thin walls increase the rate of gas exchange?

Answer 197

• The alveoli are only one cell thick, therefore oxygen and carbon dioxide only have to travel a short distance between the alveolar air space and the blood in the capillaries. This minimises the time taken for diffusion, making the process quick and efficient.
• The capillaries are also one cell thick which means to get from the alveoli into the blood the oxygen only has to go through a distance of two cells
• Alveolar walls are also moist, to prevent the cells from drying out and to allow the gases to dissolve in the water on the alveolar walls. This reduces diffusion distance.

Question 198

How does good blood supply increase the rate of gas exchange?

Answer 198

• A dense network of capillaries surrounds each alveolus, providing a continuous flow of blood. This ensures that there is always blood ready to receive oxygen and offload carbon dioxide
• This reduces diffusion distance and maintains the high concentration gradient

Question 199

Function of the ribs

Answer 199

Bone structures that protect vital organs and blood vessels and expand and contract

Question 200

Function of the intercoastal muscles

Answer 200

Muscles between the ribs that control their movement causing inhalation and exhalation

Question 201

Function of the diaphragm

Answer 201

Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation

Question 202

Function of the trachea

Answer 202

Windpipe that connects the mouth and nose to the lungs. It is surrounded by rings of cartilage. The function of the cartilage is to support the airwaysandkeep them openduring breathing. If they were not present then the sides could collapse inwards when the air pressure inside the tubes drops

Question 203

Function of the larynx

Answer 203

Also known as the voice box, when air passes through here we are able to make sounds. It functions as a lid to stop food going down the trachea when swallowing

Question 204

What are bronchi?

Answer 204

Large tubes branching off the trachea with one bronchus going to each lung

Question 205

What are alveoli?

Answer 205

Tiny air sacs where gas exchange takes place

Question 206

What is the concentration of oxygen in the inspired air vs the expired air?

Answer 206

Inspired air: 21%
Expired air: 16%

Question 207

What is the reason that there is more oxygen in inspired air than expired air?

Answer 207

Oxygen is removed from the blood by respiring cells so blood returning to the lungs has a lower concentration than the air in the alveoli meaning oxygen diffuses into the blood in the lungs down the concentration gradient

Question 208

What is the concentration of carbon dioxide in the inspired air vs the expired air?

Answer 208

Inspired air: 0.04%
Expired air: 4%

Question 209

What is the reason that there is more carbon dioxide in expired air than inspired air?

Answer 209

Carbon dioxide is produced by respiration and diffuses into the blood from respiring cells; the blood transports the carbon dioxide to the lungs where it diffuses into the alveoli as it is in a higher concentration in the blood than in the alveoli

Question 210

What is the concentration of water vapour in the inspired air vs the expired air?

Answer 210

Inspired air: Lower
Expired air: Higher

Question 211

What is the reason that there is more water vapour in expired air than inspired air?

Answer 211

Water evaporates from the moist lining of the alveoli into the expired air as a result of the warmth of the body

Question 212

What is the concentration of nitrogen in the inspired air vs the expired air?

Answer 212

78% both

Question 213

What is the reason that there is the same amount of nitrogen in inspired air and expired air?

Answer 213

Nitrogen isn’t a product or reactant for respiration so it isn’t used by the body, this is why the concentration doesn’t change

Question 214

What happens during inhalation?

Answer 214

During inhalation the external set of intercostal muscles contract to pull the ribs up and out (this means the internal intercoastal muscles relax as they are antagonistic pairs). This increases the volume of the chest cavity (thorax), decreasing air pressure which creates a negative pressure which draws air in. Additionally, the diaphragm contractsmeaning it flattens and thisincreases the volumeof the chest cavity (thorax), which also leads to adecrease in air pressureinside the lungs relative to outside the body,meaning air enters the lungs to equilibrate the pressure

Question 215

What happens during exhalation?

Answer 215

During exhalation, the external set of intercostal muscles relax so the ribs drop down and in (this means the internal intercoastal muscles contract because they are antagonistic pairs). This decreases the volume of the chest cavity (thorax) increasing air pressure which creates a positive pressure, forcing air out to equilibrate pressure. Additionally the diaphragm relaxes andmoves upwards back into its domed shape and thisdecreases the volumeof the chest cavity (thorax), which consequently leads to anincrease in air pressureinside the lungs relative to outside the body,forcing air out

Question 216

What is respiration and breathing?

Answer 216

Respiration is a series of chemical reactions that releases energy from food
Breathing is the mechanism for moving air in and out of the lungs; this supports the chemical reactions of respiration

Question 217

Why does frequency and depth of breathing increase when exercising?

Answer 217

The brain detects increasing CO2 levels and sends signals to the lungs to increase breathing and the heart to pump faster. This is to maintain high concentrations of oxygen and low concentrations of carbon dioxide in alveoli, therefore maintaining the steep concentration gradient between blood and alveoli.

Question 218

How does the brain detect that it needs to increase breathing?

Answer 218

• Therate of respirationincreases in muscle cells when exercising heavily
• CO2is aproductof aerobic respiration, soCO2levels increasein the muscle cells. This CO2diffuses out of the cells into theblood plasma, CO2in solution causes a slight drop in pH so the blood becomes slightly more acidic
• The blood flows around the circulatory system and passes to the brain where the increased carbon dioxide levels are detected bychemoreceptors (cells that detect chemical changes in the body)in the brain

Question 219

How does the increased rate of breathing help the body during exercise?

Answer 219

• Increased rate of breathing means you can expel carbon dioxide from your body faster, making the carbon dioxide concentration gradient steeper. This helps carbon dioxide diffuse out of your blood more quickly. Increased depth of breathing means that you can breathe in a higher volume of oxygen per breath, increasing your oxygen concentration gradient. This allows more oxygen to diffuse into your blood.
• This is because muscles are working harder and aerobically respiring more and theyneed more oxygen to be delivered to them(and carbon dioxide removed) to keep up with the energy demand. If they cannot meet the energy demand they will alsorespire anaerobically, producinglactic acid

Question 220

What happens when exercise is finished?

Answer 220

After exercise has finished, the lactic acid that has built up in muscles needs to beremovedas itlowers the pH of cellsand candenature enzymescatalysing cell reactions. It can only be removed by combining it with oxygen - this is known as‘repaying the oxygen debt’. This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal -the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid

Question 221

What does the brain do during exercise to reduce CO2 levels?

Answer 221

• The brain sends nerve impulses to the diaphragm and the intercostal muscles toincrease therate and depth of muscle contraction. Therate of inspiration increases, along with the thevolume of airmoved in and out with each breath. A signal is also sent to the heart to pump faster so that oxygen and nutrients can be transported faster to body cells.
• The result isgreater absorption of oxygenandremoval rate of carbon dioxide

Question 222

What do goblet cells do?

Answer 222

Goblet cells in the lung epithelium produce and secrete mucus

Question 223

What does mucus do to protect the respiratory system?

Answer 223

The mucus traps bacteria, viruses and any particles that enter our lungs. The mucus is pushed out of the lungs by cilia and coughing

Question 224

What does cilia do to protect the respiratory system?

Answer 224

Cilia are the small hairs on the surface of epithelial cells that beat to push mucus and other small trapped particles towards the nose and throat where it can be removed. Cilia doesn’t trap debris it only pushes it out

Question 225

What is aerobic respiration?

Answer 225

The chemical reactions in cells that use oxygen to break down nutrient molecules to release energy

Question 226

What are the 7 uses of energy in living oragnisms?

Answer 226

• Muscle contraction
• Protein synthesis
• Cell division
• Active transport
• Growth
• The passage of nerve impulses
• The maintenance of a constant body temperature

Question 227

What is anaerobic respiration?

Answer 227

The chemical reactions in cells that break down nutrient molecules to release energy without using oxygen. Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration

Question 228

Chemical equation of anaerobic respiration in the yeast

Answer 228

C6H12O6 → 2C2H5OH + 2CO2

Question 229

The word equation for anaerobic respiration in muscles during vigorous exercise

Answer 229

glucose → lactic acid

Question 230

Why does anaerobic respiration take place in muscle cells?

Answer 230

Anaerobic respiration mainly takes place in muscle cells during vigorous exercise. When we exercise vigorously, our muscles have ahigher demand for energythan when we are resting or exercising normally. Our bodies can only deliver so much oxygen to our muscle cells for aerobic respiration. Lactic acid builds up in muscles and blood during vigorous exercise causing an oxygen debt and causes a decrease in pH of cells which could denature enzymes in cells so it needs to be removed

Question 231

What is oxygen debt?

Answer 231

Oxygen debt is the oxygen needed after exercise to remove the lactic acid through aerobic respiration

Question 232

How is oxygen debt repaid?

Answer 232

1. Cells excrete lactic acid into the blood. There is continuation of the fast heart rate to transport lactic acid in the blood from the muscles to the liver
2. Continuation of deeper and faster breathing to supply oxygen for aerobic respiration of lactic acid
3. Aerobic respiration of lactic acid in the liver

This is the reason wecontinue to breath heavilyand ourheart rate remains higheven after finishing exercise - we need to transport the lactic acid from our muscles to the liver, and continue getting larger amounts of oxygen into the blood to oxidise the lactic acid

Question 233

What do kidneys excrete and why?

Answer 233

• Kidneys excrete urea and excess water and ions by producing urine
• Urea is a toxic waste product and must be excreted before it reaches high concentrations in the blood

Question 234

What is a ureter?

Answer 234

Tube that transports urine from kidneys to bladder

Question 235

What is the urethrea?

Answer 235

Tube that connects the bladder to the exterior, facilitates the removal of urine from the body

Question 236

What are the two main functions of the kidneys?

Answer 236

• Maintaining water and ion balance in the body (vital for maintaining blood pressure)
• Excrete toxic waste products of metabolism(filter urea out of blood) and substances in excess of requirements (such as salts)

Question 237

How do kidneys adjust water in the blood?

Answer 237

Too little water in blood

1. Hypothalamus detects and pituitary gland releases ADH
2. More ADH enters kidney (meaning more water is reabsorbed)
3. So less urine which is more concentrated is produced

Too much water in blood

1. Hypothalamus detects and pituitary gland releases less ADH
2. Less ADH enters kidney (meaning less water is reabsorbed)
3. So more urine which is less concentrated is produced

Question 238

How does ultrafiltration work?

Answer 238

The glomerulus is a knot of blood vessels surrounded by the renal capsule. The capillaries getnarroweras they get further into the glomerulus whichincreases the pressureon the blood moving through them (which is already at high pressure because it is coming directly fromthe renal artery which is connected to theaorta). This forces water, ions, urea and glucose to beforced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate (protein and RBC are too large to be filtered)

Question 239

How does selective absorption work?

Answer 239

After the glomerular filtrate enters the Bowman’s Capsule,glucoseis the first substance to be reabsorbed at therenal tubule. This takes place byactive transport and the nephron is adapted for this by havingmany mitochondriato provide energy for the active transport of glucose molecules. Reabsorption of glucosecannot take place anywhere else in the nephronas the gates that facilitate the active transport of glucose are only found in the renal tubule. As the filtrate drips through theLoop of Henlenecessary salts are reabsorbed back into the blood bydiffusionandactive transport and as salts are reabsorbed back into the blood,waterfollows byosmosis. Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time. The final urine contains urea, excess water and excess ions The collecting ducts gather urine from multiple nephrons and deliver it to the renal pelvis, leading to the ureter.

Question 240

What is deamination?

Answer 240

Proteins can’t be stored by the body so excess amino acids are broken down by the liver in a process called deamination. Deamination is the removal of the nitrogen-containing part of amino acids to form urea
- Enzymes in the liver split up the amino acid molecules. The part of the molecule which containscarbonis turned intoglycogenand stored. The other part, which containsnitrogen, is turned intoammonia, which is highly toxic, and so is immediately converted intourea, which is less toxic. The urea dissolves in the blood and is taken to thekidneyto be excreted. A small amount is also excreted insweat

Question 241

What is the importance of excretion?

Answer 241

Excretion is important becauseit helps to maintain the body’s composition of the fluids and prevent toxic substances from building up and killing the body.

The toxic consequences of high urea levels, if it is not excreted effectively, are very serious:
- Cell death
- Reduced response to insulin, leading to diabetes
- Deposits inside blood vessels

Question 242

What are neurons?

Answer 242

nerve cells that carry electrical impulses when stimulated (electrical impulses travel along neurones)

Question 243

What is a nerve?

Answer 243

bundle of neurons

Question 244

What does the human nervous system consist of?

Answer 244

1. central nervous system(CNS) - thebrain and the spinal cord
   The role of the CNS is to coordinate messages travelling through the nervous system. When a receptor detects a stimulus, it sends an electrical impulse to the brain or spinal cord, which then sends an electrical impulse to the appropriate effectors.
2. peripheral nervous system(PNS) - all of the nerves outside of the brain and spinal cord in the body
   This consists of receptor cells (the cells that detect changes in stimuli and send information down the sensory neurones), sensory neurones (the neurones that carry information from receptors) and the motor neurones (the neurones that carry information to the effectors).

Question 245

What does the nervous system allow us to do?

Answer 245

• Make sense of our surroundings and respond to them
• Coordinateandregulate body functions (Ex: muscle contraction, pupil dilating in dark, salivation, stomach digestion, liver releases glucose)

Question 246

What is the function of dendrites?

Answer 246

Dendrites receive signals from surrounding neurones. They are branched to allow connections with many neurones

Question 247

What is the axon?

Answer 247

The axon is a long structure off the cell body that electrical signals can rapidly be sent through. Its long length allows for signals to be sent rapidly. This means that less time is wasted transferring the impulse from one cell to another. The axon is insulated by a fatty sheath with small uninsulated sections along it (called nodes). The electrical signal jumps from one node to the next.

Question 248

What is the axon terminal?

Answer 248

The axon terminal is where signals are passed to the next neuron over the synapse (Nerve impulses can only be sent one way)

Question 249

What do sensory neurones do and look like?

Answer 249

• Sensoryneurones carry impulsesfrom sense organs to the CNS(brain or spinal cord)
• Sensory neurones arelongand have acell body branching off the middle of the axon

Question 250

What do motor neurones do and look like?

Answer 250

• Motorneurones carry impulsesfrom the CNS to effectors(muscles or glands)
• Motor neurones arelongand have alarge cell body at one end with long dendrites branching off it

Question 251

What do relay neurones do and look like?

Answer 251

• Relayneurones are found inside the CNS andconnect sensory and motor neurones
• Relay neurones areshortand have asmall cell body at one endwith many dendrites branching off it

Question 252

What are the two types of responses?

Answer 252

1. Voluntary response (one where you make aconscious decisionto carry out a particular action therefore itstarts with your brain)
2. Involuntary response or reflex response (doesnot involve the brain as the coordinatorof the reaction and you arenot awareyou have completed it

Question 253

Whats the difference between voluntary and involuntary responses?

Answer 253

Involuntary actions are usually ones which areessential to basic survivaland arerapid, whereas voluntary responses oftentake longeras we consider what the consequences might be before doing it.

Question 254

What is a reflex action?

Answer 254

A reflex action is a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)

Question 255

What are the steps in a reflex response?

Answer 255

1. Stimulus is detected by receptor (pain, smell, taste, visual, chemical, pressure) in the skin
2. Signal is transmitted to the sensory neuron
3. Sensory neuron passes to a relay neuron in the central nervous system
4. The relay neuron sends the signal to the motor neuron
5. The motor neuron carries impulse to the effector muscles/gland which is then stimulated to respond

Question 256

What is a synapse?

Answer 256

A junction between two neurones. Synapses ensure that impulses travel in one direction only
- As this is the only part of the nervous system where messages arechemicalas opposed to electrical, it is theonly place where drugs can act to affect the nervous system

Question 257

What does a synapse consist of?

Answer 257

A synapse consists of a presynaptic cell, a synaptic cleft, and a postsynaptic cell. The presynaptic cell releases neurotransmitters into the synaptic cleft, which then bind to receptors on the postsynaptic cell, triggering a response.

Question 258

What events happen at a synapse?

Answer 258

1. An impulse stimulates the release of neurotransmitter molecules from vesicles in the presynaptic neurone into the synaptic gap
2. The neurotransmitter molecules diffuse across the gap (down the concentration gradient
3. Neurotransmitter molecules bind with receptor proteins on the postsynaptic neurone cell surface
4. An impulse is then stimulated in the postsynaptic neurone and is carried along
5. The neurotransmitters are recycled or destroyed once an impulse is sent (destroyed to prevent continued stimulationof the second neurone which would cause repeated impulses to be sent)

Question 259

What is the function of the cornea?

Answer 259

Curved part of eye (transparent lens) that refracts light as it enters the eye

Question 260

What is the function of the lens?

Answer 260

Transparent disc that can change shape to focus light on the retina

Question 261

What is the function of the retina?

Answer 261

Where light is focused in the eye. Contains light receptor cells (rods detect light intensity, cones detect colour)

Question 261

What is the function of the iris?

Answer 261

Coloured part of the eye that controls how much light enters the pupil

Question 262

What is the function of the optic nerve?

Answer 262

Sensory neurone that carries impulses from the eye to the brain

Question 263

What is the function of the pupil?

Answer 263

Opening in eye that allows light to enter

Question 264

What is the function of the ciliary muscles?

Answer 264

Contract or relax to make the suspensory ligaments go slack or tighten respectively, changing the shape of the lens

Question 265

What is the function of the suspensory ligaments?

Answer 265

Attaches lens to ciliary muscles

Question 266

What is the function of the fovea?

Answer 266

A tiny pit located in the retina that provides the clearest vision. The eye lens will focus light on the fovea, almost all of the cone cellsare found and there are no rod cells

Question 267

What is the pupil reflex?

Answer 267

This is areflex actioncarried out toprotect the retina from damagein bright light and protect us from not seeing objects in dim light.

Question 268

What happens to the eye in bright light?

Answer 268

If I was in a brightly lit area, the iris would work to reduce the amount of light able to enter my eye. This would happen as the circular muscles in the iris contract and the radial muscles relax (antagonistic pairs). This would cause the pupil to become smaller, so less light enters the eye. This means the light sensitive cells of the retina would have an appropriate amount of light to be able to send impulses to the brain along the optic nerve to form the image I see.

Question 269

What happens to the eye in dim light?

Answer 269

If I was in a dimly lit area, the iris would work to increase the amount of light able to enter my eye. This would happen as the circular muscles in the iris relax and the radial muscles contract (antagonistic pairs). This would cause the pupil to become larger, so more light enters the eye. This means the light sensitive cells of the retina would have an appropriate amount of light to be able to send impulses to the brain along the optic nerve to form the image I see.

Question 270

What happens to the eyes when you view far objects?

Answer 270

Far objects (range in angle of light is lesser so lens must be thinner)

1. Ciliary muscles relax
2. Suspensory ligaments tighten and are pulled taut
3. Lens becomes thinner

As a result, light is refracted less by lens allowing eye to focus on far object

Question 271

What happens to the eye when you view near objects?

Answer 271

Near objects (range in angle of light is greater so lens needs to be thicker)

1. Ciliary muscles contract inwards
2. Suspensory ligaments slacken
3. Lens becomes fatter

As a result, light is refracted more by lens to focus on the near object

Question 272

What is a hormone?

Answer 272

A hormone is a chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs

Question 273

What is the livers function with hormones?

Answer 273

The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess

Question 274

What is the difference between nervous control and hormonal control?

Answer 274

Nervous control sends signals fast through neurones (electrical impulses) and have a short-term effect, happens until nerve impulses stop (Ex: muscle contraction, gland secretion)
Hormonal control sends signals slowly though blood (chemical messenger). It has a long-term effect, happens until hormone is broken down

Question 275

What is adrenaline’s source, role and effect?

Answer 275

Source: Adrenal gland (on top of kidney)
Role: Causes liver to break down glycogen and release glucose into bloodstream (only fight and flight response)
Effect: Increases heart and breathing rate and dilates pupils

Question 276

What is insulin’s source, role and effect?

Answer 276

Source: Pancreas
Role: Used when blood sugar is high to lower blood glucose levels
Effect: Causes liver to absorb glucose from the bloodstream and convert it into glycogen for later use.

Question 277

What is testosterone’s source, role and effect?

Answer 277

Source: Testes
Role: Main sex hormone in males
Effect: Development of secondary sexual characteristics in males (Growth of penis and testes, growth of facial and body hair, muscles develop, voice breaks, testes start producing sperm)

Question 278

What is oestrogen’s source, role and effect?

Answer 278

Source: Ovaries
Role: Main sex hormone in females
Effect: Development of secondary sexual characteristics in females (Breasts develop, body hair grows, menstrual cycle begins, hips get wider)

Question 279

What is glucagon’s source, role and effect?

Answer 279

Source: Pancreas
Role: Hormone used when blood sugar levels are low but not a fight or flight situation
Effect: Causes the liver to break down glycogen into glucose and release it into the bloodstream

Question 280

Effect of adrenaline on body?

Answer 280

• Increased pupil diameter (pupils dilate so as much light enters the eyes as possible so more information can be sent to the brain)
• Breathing becomes faster and deeper (so more energy for muscle contraction)
• Heart beats faster (to pump more nutrients to cells, ensures muscles are well prepared for high levels of activity in a flight or fight situation)
• Diverting blood flow towards musclesand away from non-essential parts of the body such as the gut (to ensure the reactants of respiration are as available as possible)
• Glucose released from the liver (more nutrients for respiration, increased glucose in the blood and helps deliver more important glucose to muscles for respiration)
• Hair stands on end (goosebumps)

Question 281

What is homeostasis?

Answer 281

• Homeostasis is the maintenance of a constant internal environment
• Homeostasis means thatinternal conditionswithin the body (such as temperature, blood pressure, water concentration, glucose concentration etc)need to be kept within set limitsin order to ensure that reactions in body cells can function and therefore the organism as a whole can live. When one of these conditions deviates far away from the normal if not brought back within set limits thebody will not function properlyand the eventual consequence without medical intervention will be death

Question 282

What is the negative feedback loop and how does it work?

Answer 282

• Homeostasis always tries to keep a variable in our body at a set point using a negative feedback loop. Negative feedback is when a fluctuation in a particular parameter, such as body temperature, is reduced so that it returns to its normal range of functioning. This is done by triggering a sensor that stimulates a response in an effector that reduces the fluctuation. In other words, any change is counteracted so that it returns to its set-point.
• A negative feedback control is when the change in hormone level acts as a signal to cancel out that change, so when the blood hormone level is low, hormone production is stimulated; when it is high, it is inhibited.

Question 283

How are blood glucose levels controlled

Answer 283

• Blood glucose levels are controlled by a negative feedback mechanism involving the production of twohormones-insulinandglucagon. Both hormones which control blood glucose concentration are made in thepancreas
• Insulinis produced whenblood glucose risesandstimulates liver and muscle cells to convert excess glucose into glycogen to be stored (it decreases blood glucose concentration). It’s most often produced directly after eating a carbohydrate rich meal.
• Glucagonis produced whenblood glucose fallsandstimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood

Question 284

What is type 1 diabetes?

Answer 284

Type 1 diabetesis a condition where the blood glucose levels are not able to be regulated as theinsulin-secreting cells in the pancreas are not able to produce insulin (scientists think this is because people’s immune system has destroyed the cells in the pancreas that produce insulin). This means that blood glucose levels are oftenfar too high

Question 285

What internal temperature does the human body maintain and why?

Answer 285

The human body maintains the temperature at which enzymes work best, around37°C. If body temperature increases over this temperature,enzymes will denatureand become less effective at catalysing reactions such as respiration

Question 286

What happens when temperature changes?

Answer 286

When the temperature changes, sensory neurons from heat receptors in the skin detect this information and send it as impulses through nerves to the thermoregulatory centre in the hypothalamus.

Question 287

What is the purpose of the fatty tissue?

Answer 287

Insulation: Fat is an insulator, so when the external temperature fluctuates, it prevents our internal temperature from similarly fluctuating. This is because it traps heat inside our body and slows down the warming up of our body from an external source.

Question 288

What does the body do when temperature increases?

Answer 288

Vasodilation (Widening of arterioles which increases blood flow to the surface capillaries therefore rate of heat loss from the body increases)
Sweating
Hairs lie flat

Question 289

How does vasodilation cool the body down?

Answer 289

When the body temperature rises, the hypothalamus detects this and sends nerve impulses to the arterioles supplying the skin. The smooth muscle in the walls of these arterioles relaxes, causing the arteriole to dilate. This means more blood flows through capillaries closest to the surface of the skin (what causes skin to be red in hot weather) and less blood flows through the shunt vessel so heat can radiate out of the body at an increased rate

Question 290

How does sweating cool the body down?

Answer 290

When the body temperature rises, the hypothalamus detects this and sends signals to sweat glands to increase sweat production. The water in sweat absorbs the heat from the body and evaporates from the surface of the skin taking the heat with it.

Question 291

How does hairs lying flat cool the body down?

Answer 291

The hair erector muscle is relaxed, allowing the hair to lie flat against the skin, so no air is trapped close to the skin, so we are insulated less (more air is circulated). This is less effective in humans as we do not have as much body hair/ fur as some animals.

Question 292

What does the body do when the temperature decreases?

Answer 292

• Vasoconstriction (Narrowing of arterioles which decreases blood flow to the surface capillaries therefore rate of heat loss from the body decreases)
• Shivering (rapid, involuntary contraction and relaxation of the muscles)
• Pilli erection (goosebumps, the hairs stand upright)

Question 293

How does vasoconstriction increase body temperature?

Answer 293

When the body temperature drops, the hypothalamus detects this and sends nerve impulses to the arterioles supplying the skin. The smooth muscle in the walls of the arterioles contracts which constricts the lumen. This causes less blood to flow through capillaries close to the surface of the skin and more blood is shunted away from the surface of the skin so less heat radiates from the body (as there is less blood exposed to the surface of the skin)

Question 294

How does shivering increase body temperature?

Answer 294

When the body temperature drops, the hypothalamus detects this and sends nerve impulses to the muscles to start shivering. Shivering generates heat because muscles require energy to contract and this energy is supplied by respiration. During respiration, some heat is always lost as heat energy. Therefore as the muscles contract more, more heat is generated. (This is also why we breathe deeper when cold because carbon dioxide needs to be excreted)

Question 295

How does pilli erection increase body temperature?

Answer 295

The erector muscle contracts, pulling the hair to stand up straight. This allows the hair to trap air close to the skin. As air is an insulator, it traps heat close to the skin, warming up the body.

Question 296

What is a tropism?

Answer 296

The growth response of an organism towards or away from a stimulus
- Tropisms can be either positive or negative; towards is a positive response and away is a negative response
- These responses are slower than animal responses

Question 297

What is auxin?

Answer 297

A growth regulating hormone that loosens the cell wall and stimulates cell elongation. It is produced in the shoot tip and diffuses through the plant from the shoot tip. It is unequally distributed in response to light and gravity. Auxin moves away from light, accumulating on the shaded side. It is also produced at the root tips and inhibits cell elongation on the bottom side of the root.

Question 298

What is phototropism?

Answer 298

A response in which parts of a plant grow towards or away from the direction of the light source

Question 299

What is a positive and negative phototropic response?

Answer 299

• A positive phototrophic response is shoots as they grow towards light, they must do this so that the leaves can absorb the maximum amount of sunlight
• A negative phototropic response is roots as they grow away from light
• In phototropism, auxin moves to the part of the plant receiving less light. This causes the cells on the shaded part of the plant to elongate, making the plant bend towards the light.

Question 300

What is gravitropism?

Answer 300

A response in which parts of a plant grow towards or away from gravity (also called geotropism)

Question 301

What is a drug?

Answer 301

any substance taken into the body that modifies or affects chemical reactions in the body

Question 302

What are antibiotics?

Answer 302

Antibiotics arechemical substancesmade by certainfungi or bacteriathat affect the working of bacterial cells, either bydisrupting their structure or functionor bypreventing them from reproducing (kill infective bacteria without harming body cells)

Question 303

What do antibiotics kill?

Answer 303

Antibiotics kill bacteria but do not affect viruses

Question 304

How do antibiotics kill bacterial cells?

Answer 304

Antibiotics damage the bacterial cells by inhibiting their cellular processes, but do not damage the host cells. They target the cell wall (stop the growth of cell wall) and target enzymes involved in metabolism (which is why they don’t affect viruses as viruses don’t have any of these)

Question 305

How does antibiotic resistance occur?

Answer 305

Antibiotic resistance occurs when bacteria aren’t affected by an antibiotic due to a mutation in their genetic information

Question 306

How do antibiotic resistant bacteria spread?

Answer 306

When the full population of bacteria isn’t eradicated by the antibiotic, a couple antibiotic resistant bacteria remain. The bacteria reproduce asexually and produce genetic copies of themselves so these antibiotic resistant bacteria multiply and form a larger population that is more difficult to control now that antibiotics don’t work on them.

Question 307

How to reduce rate of antibiotic resistant bacteria forming?

Answer 307

1. Only take antibiotics when its necessary
   - Antibiotics are being overprescribed by doctors leading to them being overused when they aren’t necessary which reduces the effectiveness of the antibiotic and makes the pathogens gain resistance. It creates selective pressure which causes the susceptible bacteria (like good bacteria) to be killed and the resistant bacteria to remain and multiply quickly
2. Finish antibiotic prescription (ensure the entire course is completed even if you feel better)
   - Can lead to traces of antibiotic resistant bacteria remaining and spreading (whole population not killed)

Question 308

MRSA

Answer 308

Superbugs like MRSA (methicillin resistant staphylococcus aureus) which are extremely resistant to antibiotics can be easily spread in hospitals as there is a greater chance of bacteria entering the body in hospital which increases the risk of developing a severe infection

Question 309

Inheritance definition

Answer 309

hetransmission of genetic information from generation to generation

Question 310

Gene definition

Answer 310

A length of DNA that codes for a protein

Question 311

Allele definition

Answer 311

An alternative form of a gene (Alleles give all organisms their characteristics)

Question 312

Chromosomes

Answer 312

Chromosomes are made of DNA which contains genetic information in the form of genes. They are located in the nucleus

Question 313

What does the sequences of bases in a gene decide?

Answer 313

The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein

• Different proteins are made of different combinations of amino acids. The sequence of amino acids in the chain determines how the chain will fold up to make the protein, so different proteins have different three-dimensional shapes. The three-dimensional shape of a protein determines its function.

Question 314

How does DNA control cell function?

Answer 314

DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters

• Proteins are involved in nearly every aspect of cell activity and any change in the DNA sequence (a mutation) can alter the structure and function of the resulting protein.

Question 315

Stages of protein synthesis

Answer 315

• the gene coding for the protein remains in
  the nucleus
• messenger RNA (mRNA) is a copy of a gene
• mRNA molecules are made in the nucleus
  and move to the cytoplasm
• the mRNA passes through ribosomes
• the ribosome assembles amino acids into
  protein molecules
• the specific sequence of amino acids is
  determined by the sequence of bases in the
  mRNA
• Transcription(rewriting the base code of DNA into bases of RNA)
• Translation(using RNA base sequence to build amino acids into a sequence in a protein)

Question 316

What is a haploid nucleus?

Answer 316

A nucleus containing a single set of chromosomes (In humans: 23, only gametes)

Question 317

What is a diploid nucleus?

Answer 317

A nucleus containing two sets of chromosomes (In humans: 46, every other cell in body except gametes)

Question 318

Mitosis definition

Answer 318

nuclear division giving rise to genetically identical cells

Question 319

Roles of mitosis

Answer 319

Since mitosis gives rise to genetically identical daughter cells, mitosis is useful when we need more of the same type of cells

Mitosis is used in:

• Growth
  
  • In growth, body cells divide to form more of the same type of body cells
• Repair of damaged tissues
• Replacement of cells
• Asexual reproduction
  
  • Asexual reproduction relies on mitosis too, because this type of reproduction does not rely on the fusion of gamete nuclei, so mitosis ensures that chromosome number is maintained.

Question 320

Process of mitosis

Answer 320

1. Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x - shaped chromosomes)
2. Chromosomes line up along the centre of the cell where the copies of chromosomes separate, maintaining the chromosome number in each daughter cell

Question 321

Stem cell definition

Answer 321

Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

Question 322

Meiosis definition

Answer 322

A reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells (Meiosis is involved in the production of gametes)

Question 323

How does genetic variation occur in meiosis?

Answer 323

This means that when meiosis occurs, and the chromosomes are split between the daughter cells, some daughter cells will get one of the alleles and the other daughter cells will get the other allele. Therefore, the daughter cells are not genetically identical and there is genetic variation.

Question 324

Process of meiosis

Answer 324

The number of chromosomes must behalvedwhen thegametes(sex cells) are formed. Otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)

1. Each chromosome makes identical copies of itself (forming X-shaped chromosomes)
2. First division: chromosomes pair up along the centre of the cell, recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair
3. Second division: chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)
4. A total of four haploid daughter cells will be produced

Question 325

Differences between mitosis and meiosis

Answer 325

• Mitosis two daughter cells are produced and in meiosis four daughter cells are produced
• In mitosis daughter cells are diploid and is meiosis daughter cells are haploid
• In mitosis daughter cells are genetically identical and in meiosis the daughter cells are genetically different
• In mitosis only one cell division occurs while in meiosis two cell divisions occur

Question 326

Genotype definition

Answer 326

the genetic make-up of an organism and in terms of the alleles present

Question 327

Phenotype definition

Answer 327

the observable features of an organism

Question 328

Homozygous definition

Answer 328

having two identical alleles of a particular gene
- two identical homozygous individuals that breed together will be pure-breeding

Question 329

Heterozygous definition

Answer 329

having two different alleles of a particular gene
- a heterozygous individual will not be pure-breeding

Question 330

Dominant allele definition

Answer 330

an allele that is expressed if it is present in the genotype

Question 331

Recessive allele definition

Answer 331

an allele that is only expressed when there is no dominant allele of the gene present in the genotype

Question 332

Codominance definition

Answer 332

a situation in which both alleles in heterozygous organisms contribute to the phenotype

Question 333

Sex linked characteristic definition

Answer 333

a feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other

Question 334

What is monohybrid inheritance?

Answer 334

Monohybrid inheritanceis the inheritance of characteristics controlled by a single gene

Question 335

What is test cross and what does it involve?

Answer 335

Breeders can use atest crossto find out the genotype of an organism showing the dominant phenotype

• This involves crossing the unknown individual with an individual showing the recessive phenotype
• By looking at theratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

Question 336

Variation definition

Answer 336

differences between individuals of the same species

Question 337

Why are males more likely to have sex linked characteristics?

Answer 337

In almost all cases, there areonly alleles on the X chromosomeas theY chromosome is much smaller

• Because malesonly have one X chromosome, they aremuch more likely to show sex-linked recessive conditions like colourblindness and haemophilia
• Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele
• A female with one recessive allele masked in this way is known as acarrier; she doesn’t have the disease, but she has a 50% chance of passing it on to her offspring

Question 338

Continuous variation vs discontinuous variation

Answer 338

Continuous variation results in a range of phenotypes between two extremes
Discontinuous variation results in a limited number of phenotypes with no intermediates

Question 339

What is mutation?

Answer 339

Mutation is genetic change, it is the way in which new alleles are formed

Question 340

What increases the rate of mutation?

Answer 340

Ionising radiation and some chemicals increase the rate of mutation

Question 341

What is gene mutation?

Answer 341

Gene mutation is a random change in the base sequence of DNA

Question 342

What are sources of genetic variation in populations?

Answer 342

Mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations.

Question 343

Adaptive feature definition

Answer 343

Adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment

Question 344

What are the adaptations of hydrophytes?

Answer 344

• Large air spaces in their leavesfor flotation, to keep the leaves close to the surface of the water where there is more light for photosynthesis
• Small rootsas they can also extract nutrients from the surrounding water through their tissues
• Stomata usually open all the time andmainly found on the upper epidermisof the leaf where they can exchange gases much more easily with the air
• Flat leaves maximise photosynthesis and help them float

Question 345

Adaptation definition

Answer 345

Adaptation is the process, resulting from natural selection, by which populations become more suited to their environment over many generations

Question 345

Adaptations of xerophytes

Answer 345

• Thick waxy cuticle: the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers the temperature
• Sunken stomata: stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces the evaporation rate
• Leaf rolledwith stomata inside and an inner surfacecovered in hairs: traps moist air and prevents air movement across stomata which reduces transpiration
• Small leaves: many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
• Extensive shallow rootsallow for the quick absorption of large quantities of water when it rains
• Thickened leaves or stemswhich contain cells that store water

Question 346

Process of natural selection

Answer 346

(a) Genetic Variation Within Populations

Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation arises from mutations, genetic recombination during sexual reproduction, and other processes. It is crucial for natural selection because it provides the raw material upon which selection acts. Without genetic variation, all individuals would be genetically identical, and there would be no differential survival or reproduction among individuals.

(b) Production of Many Offspring

Most species produce more offspring than the environment can support. This overproduction leads to a large number of individuals that must compete for limited resources, such as food, space, and mates. Not all offspring will survive to adulthood or reproduce; this sets the stage for natural selection by ensuring that there is always competition among individuals.

(c) Struggle for Survival, Including Competition for Resources

Due to the overproduction of offspring, there is a constant struggle for survival in nature. Individuals must compete with one another for the resources they need to survive and reproduce. This competition can be for food, water, shelter, and other essentials. Those individuals that are better suited to their environment will have a better chance of surviving and obtaining the resources they need.

(d) A Greater Chance of Reproduction by Individuals that Are Better Adapted to the Environment Than Others

Natural selection favors individuals that have advantageous traits or adaptations that improve their chances of survival and reproduction in a given environment. These individuals are more likely to survive the struggle for existence and more likely to reproduce. As a result, they have a greater chance of passing on their advantageous traits to their offspring.

(e) These Individuals Pass on Their Alleles to the Next Generation

Individuals that survive and reproduce pass their alleles (versions of genes) to their offspring. If these alleles contribute to advantageous traits, they will become more common in the population over generations. Over time, this process can lead to the evolution of populations, as advantageous traits become more widespread and individuals become better adapted to their environments
- Over time, this will bring about achange in the characteristics of the species- it will produceevolution

Question 347

What is evolution?

Answer 347

Evolution is defined as thechange in adaptive features of a population over time as a result of natural selection

Question 348

Natural selection in developing strains of antibiotic resistant bacteria

Answer 348

1. Genetic Variation Within Bacterial Populations

Within any bacterial population, there is genetic variation due to mutations, which are changes in the DNA sequence. Some of these mutations may randomly provide a bacterial cell with resistance to a particular antibiotic.

2. Struggle for Survival

When a population of bacteria is exposed to an antibiotic, the antibiotic works to kill the bacteria or inhibit their growth. However, bacteria with a mutation that gives them resistance to the antibiotic have a survival advantage. The presence of the antibiotic creates a selective pressure in the environment. Bacteria that are susceptible to the antibiotic are more likely to be killed or inhibited, while resistant bacteria are more likely to survive.

3. Reproduction of Resistant Bacteria

Bacteria that survive the antibiotic exposure due to their resistance have the opportunity to reproduce. They replicate rapidly, producing many offspring, these offspring will inherit the resistance genes. As a result, the proportion of antibiotic-resistant bacteria in the population increases over time.

4. Passing on of Resistance Alleles to the Next Generation

As resistant bacteria reproduce, they pass on the alleles that cause resistance to their offspring. Over time, these alleles become more common in the bacterial population. If antibiotic use continues, the population will increasingly be dominated by resistant bacteria, making the antibiotic less effective against the infection.

Question 349

What is selective breeding?

Answer 349

Selective breeding means toselect individuals with desirable characteristics and breed them together.

Question 350

Process of selective breeding

Answer 350

(a) Selection by Humans of Individuals with Desirable Features

The first step in selective breeding involves identifying and selecting individuals within a population that exhibit desirable traits. These traits can vary widely depending on the goals of the breeding program. Humans play a crucial role in this process by choosing which individuals possess the most desirable features to pass on to future generations.

(b) Crossing These Individuals to Produce the Next Generation

Once the individuals with desirable traits have been selected, they are bred together to produce the next generation. This process is called crossing. The goal of this step is to combine the genetic material of two individuals with desirable traits, increasing the likelihood that their offspring will also exhibit these traits. This step may be repeated multiple times across several generations to enhance the desired features in the population.

(c) Selection of Offspring Showing the Desirable Features

After crossing, the offspring produced are evaluated for the presence of the desired traits. Not all offspring will necessarily display these traits due to genetic variation and inheritance patterns. Therefore, only those offspring that show the desirable characteristics are selected for further breeding. This selection process ensures that the desirable traits are concentrated and maintained in the population. Over successive generations, through repeated selection and breeding, these traits can become more pronounced and widespread within the population.

🌟 Selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals

Question 351

Differences between natural and artificial selection

Answer 351

• Natural selection occurs naturally while artificial selection occurs through human intervention
• Natural selection populations have features that are better adapted to suit their environment and survival. Artificial selection have features that are useful to humans not necessarily to the survival of the individual
• Natural selection takes a long time to occur while artificial selection takes less time as only individuals with the desired trait are allowed to reproduce

Question 352

Describe the flow of energy of living organisms

Answer 352

The light energy from the Sun is harnessed by producers (plants and some bacteria) which convert light energy into chemical energy. Some of this energy is used in carrying out life processes but the stored chemical energy is then passed on to the primary consumer through feeding. Some is used up in life processes but when it is consumed by secondary and then tertiary consumers the energy is passed further up the food chain. At every trophic level (producers, consumers, decomposers), energy is lost as heat to the surroundings during metabolic processes like respiration. The energy is returned to the environment through decomposition.

Question 353

Food chain definition

Answer 353

shows the transfer of energy from one organism to the next, beginning with a producer

Question 354

Food web definition

Answer 354

a network of interconnected food chains

Question 355

Producer definition

Answer 355

an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

Question 356

consumer definition

Answer 356

an organism that gets its energy by feeding on other organisms
- Consumers may be classed as primary, secondary, tertiary and quaternary according to their position in a food chain

Question 357

Herbivore definition

Answer 357

an animal that gets its energy by eating plants

Question 358

Carnivore definition

Answer 358

an animal that gets its energy by eating other animals

Question 359

Decomposer definition

Answer 359

an organism that gets its energy from dead or waste organic material

Question 360

Trophic level definition

Answer 360

the position of an organism in a food chain, food web or ecological pyramid
- Producer is trophic level one, quaternary consumer is trophic level five

Question 361

Why do most of the changes in populations of animals and plants happen?

Answer 361

as a result ofhuman impact- either byoverharvesting of food speciesor by theintroduction of foreign species to a habitat

Question 362

How does the introduction of foreign species affect the food chains/web?

Answer 362

Introduction of foreign species into a habitat creates competition for resources which disrupts food chains and food webs. They may have no natural predators in the new environment, allowing them to reproduce rapidly and dominate the ecosystem leading to a decline in native species

Question 363

Why are pyramids of biomass more accurate than the pyramid of number?

Answer 363

Pyramids of biomass are more accurate than pyramids of number because they provide a much better idea of thequantityof the plant or animal material at each level of a food chain and therefore are a better way of representing interdependence within the food chain

Question 364

Pyramid of biomass

Answer 364

• A pyramid of biomass shows the total dry mass of living organisms (biomass) at each trophic level in a food chain.
• Pyramids of biomass are always pyramid shaped because there must always be more biomass in the previous trophic level to support the next

Question 365

What does a pyramid of energy show?

Answer 365

• A pyramid of energy shows the total amount of energy that is transferred through each trophic level in an ecosystem over a certain period of time
• Not all of the energy grass plants receive goes into making new cellsthat can be eaten. Only the energy that is made into new cells remains with the organism to be passed on.

Question 366

Where is the majority of energy used up (90%) in organisms?

Answer 366

• making waste productsthat get removed from the organism
• as movement
• through respiration
• as heat(in mammals and birds that maintain a constant body temperature)
• as undigested waste(faeces) that is removed from the body and provides food for decomposers

Question 367

Why do food chains usually have fewer than five trophic levels

Answer 367

Food chains usually have fewer than five trophic levels because of the significant energy loss that occurs at each trophic level, making it difficult to sustain a large number of higher-level consumers. There is less and less energy available to support organisms as you move up the food chain, at higher trophic levels (e.g., tertiary and quaternary consumers), there is often insufficient energy to support large populations or additional predators.

In order to survive, it would have to:
- eat a huge number of prey every day to get the amount of energy it needed to survive
- not expend much energy itself hunting them

Question 368

Why is it more energy efficient for humans to eat crops?

Answer 368

• Given what we know aboutenergy transfer in food chains, it is clear that if humans eat the wheat there ismuch more energy availableto them than if they eat the cows that eat the wheat
• This is because90% of energy is lost each trophic level so the higher you go there is less available to pass on to humans. Therefore, it ismore energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

Question 369

Explain the carbon cycle

Answer 369

• Carbonis taken out of the atmosphere in the form ofcarbon dioxideby plants to be used for photosynthesis
• It is passed on to animals (and microorganisms) byfeeding
• It is returned to the atmosphere in the form ofcarbon dioxideby plants and animals as a result ofrespiration
• When organisms die decomposers break down the organic molecules through the process of respiration to gain energy, releasing carbon dioxide back into the atmosphere
• If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies is trapped and can be converted, over millions of years and significant pressure, intofossil fuels
• When fossil fuels are burned in combustion, the carbon combines with oxygen andcarbon dioxide is releasedinto the atmosphere
• Increased use of fossil fuelsis contributing to an increase in the carbon dioxide content of the atmosphere.
  
  • In addition,mass deforestationisreducing the number of producersavailable to take carbon dioxide out of the atmosphere by photosynthesis. This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they areburnt down, releasing yet more carbon dioxide into the atmosphere

🌟 Carbon is stored in the atmosphere as CO2, in plants as sugars, in animals as sugars, in dead organisms and in fossil fuels

Question 370

Two ways that Nitrogen gas in the air can be converted into a usable form (called nitrogen fixation)

Answer 370

• Nitrogen fixing bacteriaconvert N2gas into ammonium compounds, which can then be converted to usablenitrates
  
  • Nitrogen fixing bacteria can be free-living in the soil or can live within the root nodules of some plants
• Lightningcan split the bond between the two N atoms combining it with water (H2O) to formammonia (NH3) and nitrates (NO3)

Question 371

Explain the nitrogen cycle without nitrogen fixation

Answer 371

• The plants can’t absorb ammonium compounds, sonitrifying bacteriaconvert the ammonium compounds to nitrites and then to nitrates, which can then be assimilated by plants
• Plants absorb nitrogen from the soil in the form ofnitratesand use it to build proteins
• Animalseatthe plants and get the nitrogen they need from the plant proteins
  
  • This nitrogen ispassed up the food chainthrough feeding
• Waste(urine and faeces) from animals sends nitrogen back into the soil in the form of ammonium compounds
  
  • Ex: Deamination is when excess amino acids are broken down in the liver. The nitrogen-containing part of the amino acid is removed and converted into ammonia (NH₃), which is then quickly converted into urea for safe excretion from the body
• The bodies of dead plants and animalsdecayand all the proteins inside them are broken down into ammonium compounds by decomposers
• Denitrifying bacteriatake nitratesout of the soiland convert them back into N2gas
  
  • This processreduces soil fertilityand is bad for plant growth
  • Denitrifying bacteria are anaerobic so aerating the soil, e.g. by reducing waterlogging and turning over the soil during ploughing, can reduce the rate of denitrification

Question 372

Population definition

Answer 372

a group of organisms of one species, living in the same area, at the same time

Question 373

Community definition

Answer 373

all of the populations of different species in an ecosystem

Question 374

Ecosystem definition

Answer 374

a unit containing the community of organisms and their environment, interacting together

Question 375

Four main factors that affect population growth

Answer 375

• Food supply
• Competition
• Predation
• Disease

Question 376

What is the lag phase?

Answer 376

Lag phase- organisms areadapting to the environment before they are able to reproduce; food is abundant but population size is small limiting the maximum rate of population growth

Question 377

What is the log phase?

Answer 377

Log phase(exponential phase)-food supply is abundant,birth rate is rapidanddeath rate is low;growth is exponentialand only limited by the number of new individuals that can be produced

Question 378

What is the stationary phase?

Answer 378

Stationary phase- populationstays the same sizedue to afactor in the environment normally amount of resources; birth rate and death rate are equal and will remain so until the factor is resolved or becomes more limiting

Question 379

What is the death phase?

Answer 379

Death phase- populationdecreasesas death rate is now greater than birth rate; this is usually due to overpopulation, increased competition and limited resources

Question 380

Ways humans increased food production

Answer 380

• Agricultural machinery to use larger areas of land and increase efficency (by saving manual labour)
• Chemical fertilisers to increase yield
• Insecticides to improve quality and yield
• Herbicides to reduce competition with weeds
• Selective breeding to improve production by crop plants and livestock

Question 381

What is monoculture farming?

Answer 381

Monoculture farming means that on a given area of agricultural landonly one species of crop is grown

Question 382

Advantages of monoculture

Answer 382

• More efficient (only need to buy equipment for one crop type, can harvest at same time)
• Crops can be optimised for highest quality and yield (promotes agricultural technology)
• Higher profits

Question 383

Disadvantages of monoculture

Answer 383

• Pathogens/disease affect the entire crop
• Destroys soil nutrients (different plants use different nutrients)
• Has large impacts on local ecosystem and reduces biodiversity
• Can lead to soil erosion due to lack of established roots in the soil
• Increased pest issues, issues with insecticides (harming the environment)

Question 384

What is intensive livestock production?

Answer 384

In developed countries,large numbers of livestockare often kept in an area that wouldnot normally be able to support more than a very small number. They are often fedhigh energy foods, regularly given medication such asantibioticsas a preventative measure against disease and kept inartificially warm temperaturesand small spaces thatdo not allow for much movement

Question 385

Advantages of intensive livestock production

Answer 385

• Less land is required to produce large amounts of food
• Food can be produced all year round in controlled environments
• Cost of production is lower (therefore food can be sold for cheap prices)
• Lower requirement for labour to produce the food

Question 386

Disadvantages of intensive livestock production

Answer 386

• Higher risk of disease outbreaks
• Herbicides and pesticides tend to be used potentially causing eutrophication and negative effects to food chains
• Reduction in biodiversity
• Large amounts of cattle produce a large amount of methane + overgrazing can lead to soil erosion
• Ethical issues with the cruel treatment of animals

Question 387

Biodiversity definition

Answer 387

the number of different species that live in an area

Question 388

Reasons for habitat destruction

Answer 388

**Increased area for housing, crop plant production and livestock production*

Extraction of natural resources

Freshwater and marine pollution

Question 389

What is deforestation?

Answer 389

Deforestation involves cutting down large amounts of trees to gather as resources for manufacturing or to clear space for other economic activities. It is normally an unsustainable practice

Question 390

Undesirable effects of deforestation

Answer 390

Reducing biodiversity
Extinction
Loss of soil
Flooding
Increase of carbon dioxide in the atmosphere

Question 391

How can water be polluted by untreated sewage?

Answer 391

Untreated sewage contains organic matter, harmful pathogens, and chemicals that can severely impact aquatic ecosystems. Firstly it provides a good food source for bacteria. Bacteria decompose the organic matter in sewage through aerobic respiration, which consumes oxygen in the process. This causes the death of aquatic organisms such as fish. Untreated sewage also often contains harmful bacteria, viruses, and parasites that can contaminate water, posing health risks to both aquatic life and humans.

Question 392

How can water be polluted by excess fertiliser?

Answer 392

Excess nutrients from fertilizers lead to eutrophication, which is an over-enrichment of water with nutrients. This stimulates the rapid growth of algae and other aquatic plants. Algae blooms often form which can block sunlight, preventing aquatic plants from photosynthesizing and producing oxygen. When these algae die and decompose, bacteria consume large amounts of oxygen during decomposition, further depleting oxygen levels in the water. The sudden increase in algae and plant growth disrupts the natural food chains, reducing the diversity of species and altering the balance of the ecosystem.

Question 393

How can water be polluted by non-biodegradable plastics?

Answer 393

Non-biodegradable plastics remain in the environment for hundreds of years causing them to accumulate in the environment. Marine life can become entangled in plastic waste and also ingest the plastic when it’s in smaller pieces (this could block the digestive system, cause internal injuries, and lead to starvation, as the animal feels full without gaining any nutrients). Microplastics (tiny plastic particles) are particularly dangerous as they are consumed by a wide range of organisms, from plankton to fish, and can accumulate up the food chain, ultimately affecting predators

Question 394

Process of eutrophication

Answer 394

Increased availability of nitrates and other ions
Increased growth of producers
Increased decomposition after death of producers
Increased aerobic respiration by decomposers
Reduction in dissolved oxygen
Death of organisms requiring dissolved oxygen in water

Question 395

Main components of air pollution and how they are released

Answer 395

The main pollutants of air are methane (CH4) and carbon dioxide (CO2). They are released into the atmosphere through farming practices and manufacturing especially through the combustion of fossil fuels and keeping of livestock. Additionally, global warming melts the permafrost in sub-polar regions, which results in even more trapped methane being released into the atmosphere

Question 396

Adverse effects of climate change

Answer 396

Ocean temperatures increasing, causing melting of polar ice caps / rising sea levels / flooding / coral bleaching. Increasing temperatures causing extreme weather like super storms, flooding, droughts.

Question 397

What is the enhanced greenhouse effect?

Answer 397

Theenhanced greenhouse effecthappens whenincreasing levels of greenhouse gasesfrom human activities cause the Earth’s average temperature to rise above normal, leading toglobal warming.
Normally, the Sun’s rays enter the Earth’s atmosphere, and while some of the heat is reflected back into space, a portion is absorbed and trapped by greenhouse gases, keeping the planet warm. However, human activities such as burning fossil fuels, deforestation, and industrial processes have increased the concentration of these gases, leading to the trapping of excess heat, which contributes to global warming.

Question 398

Sustainable resource definition

Answer 398

a resource that is produced as rapidly as it is removed from the environment so that it does not run out

Question 399

Why do organisms become endangered or extinct

Answer 399

Climate change
Habitat destruction
Introduction of foreign species
Hunting
Overharvesting
Pollution

Question 400

Methods of conservation for endangered species

Answer 400

• Monitoring and protecting species and habitats
• Education
• Captive breeding programmes
• Seed banks

Question 401

Ways forests can be conserved

Answer 401

• Education
• Protected areas
• Quotas
• Replanting

Question 402

Ways fish stocks are conserved

Answer 402

• Education
• Closed seasons
• Protected areas
• Controlled net types and mesh sizes
• Quota
• Monitoring

Question 403

Reasons for conservation programmes

Answer 403

• Maintaining or increasing biodiversity
• Reducing extinction
• Protecting vulnerable ecosystems
• Maintaining ecosystem functions, limited to nutrient cycling and resource provision, including food, drugs, fuel and genes

Question 404

What is artificial insemination?

Answer 404

Artificial insemination (AI) involves collecting sperm from a male and manually inserting it into a female’s reproductive tract to fertilize her egg. This method is commonly used in captive breeding programs when natural mating is difficult or impossible.

Question 405

What is in vitro fertilisation?

Answer 405

In vitro fertilisation (IVF) involves the fertilization of an egg by sperm outside the body (in a laboratory) before the resulting embryo is implanted into the female for development. It is often used when a female is infertile, or a male doesn’t produce enough functional sperm.

Question 406

Risks to a species if its population size decreases

Answer 406

This reduces genetic variation. This could reduce the ability of the species to adapt to environmental changes especially disease leading to extinction

Question 407

Why are bacteria useful in biotechnology and genetic modification?

Answer 407

• Their rapid reproduction rate
• Ability to make complex molecules
• Few ethical concerns over their manipulation and growth
• The presence of plasmids (plasmids are small, circular loops of DNA which can be an ideal way of transferring DNA from one cell to another during genetic manipulation)

Question 408

Use of pectinase in fruit juice production

Answer 408

Pectinase is an enzyme which is added to the chopped up fruit to break down the pectin in the cell walls. It makes fruit juice clear by breaking down pectin which makes fruit juices cloudy and thick. Additionally, by breaking down the fruit’s cell walls, pectinase helps release more juice from the fruit, increasing the total yield.

Question 409

How is lactase used to produce lactose free milk?

Answer 409

When lactase is added to milk after leaving it for a while it breaks down the lactose into molecules that are fine for the gut

Question 410

Examples of genetic modification

Answer 410

1. the insertion of human genes into bacteria to
   produce human proteins
2. the insertion of genes into crop plants to
   confer resistance to herbicides
3. the insertion of genes into crop plants to
   confer resistance to insect pests
4. the insertion of genes into crop plants to
   improve nutritional qualities

Question 411

How is insulin grown in a fermenter?

Answer 411

Insulin (by bacteria):
Genetically engineered bacteria, often E. coli, are used to produce human insulin.
The gene for human insulin is inserted into bacterial DNA, allowing the bacteria to synthesize insulin, which is then harvested, purified, and used for medical purposes in the treatment of diabetes.

Question 412

How is penicillin grown in a fermenter?

Answer 412

Penicillin (by fungi):
The fungus Penicillium is grown in fermenters to produce penicillin, a widely used antibiotic.
Penicillin is secreted by the fungus during growth and is extracted from the fermenter for purification and use in medicine.

Question 413

Conditions that need to be controlled in a fermenter

Answer 413

Temperature
Why it needs to be controlled: Enzymes within microorganisms work best at an optimum temperature. Too high a temperature can denature enzymes, stopping growth, while too low a temperature slows down metabolic processes.
How it is controlled: Cooling jackets or heaters are used to maintain the ideal temperature for the microorganisms.

pH
Why it needs to be controlled: Microorganisms have an optimum pH range at which their enzymes function efficiently. If the pH becomes too acidic or too alkaline, enzyme activity is affected, and growth may stop.
How it is controlled: pH sensors monitor the acidity or alkalinity of the fermentation broth, and acids or bases are added to maintain the correct pH.

Oxygen Supply
Why it needs to be controlled: Many microorganisms, including those used in the production of insulin and mycoprotein, require oxygen for aerobic respiration. Insufficient oxygen can slow down growth and reduce product yield.
How it is controlled: Air is pumped into the fermenter, and stirrers or paddles ensure that oxygen is evenly distributed throughout the culture.

Nutrient Supply
Why it needs to be controlled: Microorganisms need nutrients (such as glucose, nitrogen, and minerals) for growth and product synthesis. A continuous supply ensures that the microorganisms remain active and productive.
How it is controlled: Nutrients are continuously added to the fermenter to keep the microorganisms in the growth phase and to maximize product yield.

Waste Product Removal
Why it needs to be controlled: As microorganisms grow and metabolize, they produce waste products (such as carbon dioxide, acids, or alcohols) that can build up and inhibit growth if not removed.
How it is controlled: Fermenters are equipped with systems to remove or neutralize waste products to prevent toxicity or adverse effects on the microorganisms.

Question 414

Genetic modification definition

Answer 414

genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes

Question 415

Process of genetic modification using
bacterial production of a human protein

Answer 415

1. isolation of the DNA making up a human gene using restriction enzymes, forming sticky ends
2. cutting of bacterial plasmid DNA with the same restriction enzymes, forming complementary sticky ends
3. insertion of human DNA into bacterial plasmid DNA using DNA ligase to form a recombinant plasmid
4. insertion of recombinant plasmids into bacteria
5. multiplication of bacteria containing
   recombinant plasmids
6. expression in bacteria of the human gene to make the human protein

Question 416

Advantages of genetically modifying crops

Answer 416

• Reduced use of chemicals such as herbicides and pesticides (better for the environment)
• Increased yields from the crops as they aren’t competing with the weeds

Question 417

Disadvantages of genetically modifying crops

Answer 417

• Increased costs of seeds meaning smaller farmers can’t compete with large farms
• Increased dependancy on certain chemicals
• Risk of inserted genes being transferred to wild plants by pollination
• Reduced biodiversity