CRAM Flashcards

Question

What is the function of the nucleus?

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

- 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

Answer 5

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)

Answer 6

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

Answer 7

to help your body grow and repair itself

Answer 8

The division of existing cells

Answer 9

Movement of mucus in the trachea and bronchi

Answer 10

Sending and recieving neurotransmitters

Answer 11

Transport of oxygen

Answer 12

- 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

Answer 13

- 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

Answer 14

- 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

Answer 15

- 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

Answer 16

- 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

Answer 17

Absorbtion of water and mineral ions from water

Answer 18

Conduction of water through the plant; support of the plant

Answer 19

- 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

Answer 20

Photosynthesis

Answer 21

- 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

Answer 22

- 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

Answer 23

Cell. Basic functional and structural units in a living organism

Answer 24

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

Answer 25

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

Answer 26

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

Answer 27

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

Answer 28

the kinetic energy of random movement of molecules and ions

Answer 29

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)

Answer 30

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

Answer 31

- 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

Answer 32

By osmosis through the partially permeable membrane

Answer 33

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

Answer 34

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

Answer 35

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

Answer 36

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

Answer 37

So plants stay upright and have exposure to sunlight

Answer 38

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.

Answer 39

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

Answer 40

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

Answer 41

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

Answer 42

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

Answer 43

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

Answer 44

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

Answer 45

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

Answer 46

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.

Answer 47

When the substrate and enzyme collide

Answer 48

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

Answer 49

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

Answer 50

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

Answer 51

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

Answer 52

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

Answer 53

It’s needed to make chlorophyll

Answer 54

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

Answer 55

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

Answer 56

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

Answer 57

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.

Answer 58

- The more light a plant receives, the faster the rate of 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

Answer 59

- Carbon dioxide is one of the raw materials required for photosynthesis - This means the more carbon dioxide that is present, the faster the reaction can 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

Answer 60

- As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes - However, as the reaction is controlled by enzymes, this trend only continues up to the optimum temperature beyond there the enzymes begin to denature and the rate of reaction decreases

Answer 61

During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net 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

Answer 62

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

Answer 63

Concentration of carbon dioxide is atmospheric level. Photosynthesis=respiration

Answer 64

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

Answer 65

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

Answer 66

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

Answer 67

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

Answer 68

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

Answer 69

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

Answer 70

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.

Answer 71

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

Answer 72

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

Answer 73

Allows carbon dioxide to diffuse to palisade mesophyll cells quickly

Answer 74

Absorbs light energy so photosynthesis can take place

Answer 75

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

Answer 76

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

Answer 77

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

Answer 78

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.

Answer 79

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

Answer 80

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

Answer 81

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

Answer 82

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

Answer 83

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

Answer 84

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

Answer 85

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

Answer 86

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

Answer 87

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

Answer 88

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

Answer 89

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

Answer 90

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

Answer 91

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.

Answer 92

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.

Answer 93

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.

Answer 94

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.

Answer 95

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.

Answer 96

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

Answer 97

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.

Answer 98

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

Answer 99

Stores bile to release into the duodenum as required.

Answer 100

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

Answer 101

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

Answer 102

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

Answer 103

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

Answer 104

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

Answer 105

increase the surface area of food for the action of enzymes during chemical digestion

Answer 106

chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum

Answer 107

The stomach lining contains muscles which contract to physically squeeze and mix the food with the strong digestive juices that are present (also known as "stomach churning")

Answer 108

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

Answer 109

Work to bring the food into the mouth and cut it

Answer 110

Cut and tear food up

Answer 111

Help incisors and canines grind and mix food while chewing

Answer 112

the breakdown of large insoluble molecules into small soluble molecules

Answer 113

to produce small soluble molecules that can be absorbed

Answer 114

- Breaks down starch to simple reducing sugars - Amylases are produced in the mouth and the pancreas (secreted into the duodenum)

Answer 115

- 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)

Answer 116

- Breaks down fats and oils to fatty acids and glycerol - Lipase enzymes are produced in the pancreas and secreted into the duodenum

Answer 117

- The stomach produces several fluids which together are known as gastric juice. One of the fluids produced is hydrochloric 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 it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life

Answer 118

- Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas) and digests starch to maltose (a disaccharide) - Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium lining of the small intestine

Answer 119

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

Answer 120

Protein digestion takes place in the stomach and duodenum with two main enzymes produced: - Pepsin is produced in the stomach and breaks down protein in acidic conditions in the stomach (optimum pH of 3) - Trypsin is produced in the pancreas and secreted into the duodenum where it breaks down protein in alkaline conditions (optimum pH of 8)

Answer 121

- The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger like projections). These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently. Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients. - Wall of the villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport - Villus contains a network of blood capillaries that 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 - Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph

Answer 122

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

Answer 123

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

Answer 124

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

Answer 125

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

Answer 126

- 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 by osmosis - The large surface area of root hairs increases the uptake of water and mineral ions because it increases the rate of osmosis/diffusion

Answer 127

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

Answer 128

the loss of water vapour from leaves

Answer 129

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

Answer 130

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.

Answer 131

- 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.

Answer 132

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

Answer 133

- Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from the source (where it’s made) to sink (where it’s stored or used) - During winter, 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 a growth 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

Answer 134

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.

Answer 135

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

Answer 136

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

Answer 137

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.

Answer 138

- Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it by the pumping of the heart, meaning it cannot travel as fast. By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster 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.

Answer 139

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.

Answer 140

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

Answer 141

separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood

Answer 142

to prevent backflow of blood

Answer 143

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

Answer 144

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

Answer 145

These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood from flowing back into the atria

Answer 146

These valves open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart

Answer 147

- 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 that sufficient blood is taken to the working muscles to provide them with enough nutrients and oxygen for increased respiration. An increase in heart rate also allows for waste products to be removed at a faster rate

Answer 148

- Following exercise, the heart continues to beat faster for a while to ensure that all excess waste products are removed from muscle cells. - It is also likely that muscle cells have been respiring anaerobically during exercise and so have built up an oxygen debt. This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure that extra oxygen is still being delivered to muscle cells - The extra oxygen is used to break down the lactic acid that has been built up in cells as a result of anaerobic respiration

Answer 149

- The blood is supplied by the coronary arteries. If a coronary artery becomes partially or completely blocked by fatty deposits called ‘plaques’ (mainly formed from cholesterol), the arteries are not as elastic as they should be and therefore cannot stretch to accommodate the blood which is being forced through them - leading to coronary heart disease - Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina - Complete blockage means cells in that area of the heart will not be able to respire and can no longer contract, leading to a heart attack

Answer 150

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

Answer 151

Deoxygenated blood coming from the body flows into the right atrium via the vena cava. Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle. The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which 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 blood returns to the left atrium via the pulmonary vein. It passes through the bicuspid (atrioventricular) valve into the left ventricle. The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body. The semilunar valve in the aorta prevents the blood flowing back down into the heart

Answer 152

- Carry blood at low pressure towards the heart - Carry deoxygenated blood (other than the pulmonary vein) - Have thin walls - Have a large lumen as blood pressure is low - Contain valves 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 is slow

Answer 153

- Carry blood at high pressure away from the heart (dangerous to cut as blood will spurt out) - Carry oxygenated blood (other than the pulmonary artery) - Have thick muscular walls containing 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 a narrow lumen to maintain high blood pressure - Speed of flow is fast

Answer 154

- Carry blood at low pressure within tissues - Forms a huge network linking arteries to veins (allowing blood to access every cell in our body) - Carry both oxygenated and deoxygenated blood - Have walls that are one 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 is slow

Answer 155

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

Answer 156

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

Answer 157

The hepatic portal vein transports deoxygenated blood from the gut to the liver (nutrient-rich blood)

Answer 158

Red blood cells, plasma, platelets, white blood cells

Answer 159

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

Answer 160

- Large cells containing big nucleus, different types have slightly different structures and functions - Function is to defend the body against infection by pathogens by carrying out phagocytosis and antibody production - There are two main types, phagocytes and lymphocytes

Answer 161

engulfing pathogens by phagocytosis

Answer 162

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 and release digestive enzymes to digest it.

Answer 163

antibody production

Answer 164

Produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by pathogens

Answer 165

Platelets are fragments of cells which are involved in blood clotting and forming scabs where the skin has been cut or punctured

Answer 166

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

Answer 167

Role is to prevent blood loss and the entry of pathogens

Answer 168

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 cause soluble fibrinogen proteins to convert into insoluble fibrin and form an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot. The clot eventually dries and develops into a scab to protect the wound from bacteria entering.

Answer 169

- 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

Answer 170

1. Large surface area to allow faster diffusion of gases across the surface 2. Thin walls to ensure diffusion distances remain short 3. Good ventilation with air so that diffusion gradients can be maintained 4. Good blood supply to maintain a high concentration gradient so diffusion occurs faster

Answer 171

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

Answer 172

- 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.

Answer 173

- 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

Answer 174

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

Answer 175

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

Answer 176

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

Answer 177

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 airways and keep them open during breathing. If they were not present then the sides could collapse inwards when the air pressure inside the tubes drops

Answer 178

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

Answer 179

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

Answer 180

Tiny air sacs where gas exchange takes place

Answer 181

Inspired air: 21% Expired air: 16%

Answer 182

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

Answer 183

Inspired air: 0.04% Expired air: 4%

Answer 184

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

Answer 185

Inspired air: Lower Expired air: Higher

Answer 186

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

Answer 187

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

Answer 188

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 contracts meaning it flattens and this increases the volume of the chest cavity (thorax), which also leads to a decrease in air pressure inside the lungs relative to outside the body, meaning air enters the lungs to equilibrate the pressure

Answer 189

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 and moves upwards back into its domed shape and this decreases the volume of the chest cavity (thorax), which consequently leads to an increase in air pressure inside the lungs relative to outside the body, forcing air out

Answer 190

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

Answer 191

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.

Answer 192

- The rate of respiration increases in muscle cells when exercising heavily - CO2 is a product of aerobic respiration, so CO2 levels increase in the muscle cells. This CO2 diffuses out of the cells into the blood plasma, CO2 in 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 by chemoreceptors (cells that detect chemical changes in the body) in the brain

Answer 193

- 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 they need 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 also respire anaerobically, producing lactic acid

Answer 194

After exercise has finished, the lactic acid that has built up in muscles needs to be removed as it lowers the pH of cells and can denature enzymes catalysing 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

Answer 195

- The brain sends nerve impulses to the diaphragm and the intercostal muscles to increase the rate and depth of muscle contraction. The rate of inspiration increases, along with the the volume of air moved 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 is greater absorption of oxygen and removal rate of carbon dioxide

Answer 196

Goblet cells in the lung epithelium produce and secrete mucus

Answer 197

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

Answer 198

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

Answer 199

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

Answer 200

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

Answer 201

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

Answer 202

C6H12O6 → 2C2H5OH + 2CO2

Answer 203

glucose → lactic acid

Answer 204

Anaerobic respiration mainly takes place in muscle cells during vigorous exercise. When we exercise vigorously, our muscles have a higher demand for energy than 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

Answer 205

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

Answer 206

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 we continue to breath heavily and our heart rate remains high even 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

Answer 207

- 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

Answer 208

Tube that transports urine from kidneys to bladder

Answer 209

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

Answer 210

- 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)

Answer 211

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

Answer 212

The glomerulus is a knot of blood vessels surrounded by the renal capsule. The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta). This forces water, ions, urea and glucose to be forced 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)

Answer 213

After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the renal tubule. This takes place by active transport and the nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules. Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the renal tubule. As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion and active transport and as salts are reabsorbed back into the blood, water follows by osmosis. 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.

Answer 214

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 contains carbon is turned into glycogen and stored. The other part, which contains nitrogen, is turned into ammonia, which is highly toxic, and so is immediately converted into urea, which is less toxic. The urea dissolves in the blood and is taken to the kidney to be excreted. A small amount is also excreted in sweat

Answer 215

Excretion is important because it 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

Answer 216

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

Answer 217

bundle of neurons

Answer 218

1. central nervous system (CNS) - the brain 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).

Answer 219

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

Answer 220

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

Answer 221

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.

Answer 222

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

Answer 223

- Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord) - Sensory neurones are long and have a cell body branching off the middle of the axon

Answer 224

- Motor neurones carry impulses from the CNS to effectors (muscles or glands) - Motor neurones are long and have a large cell body at one end with long dendrites branching off it

Answer 225

- Relay neurones are found inside the CNS and connect sensory and motor neurones - Relay neurones are short and have a small cell body at one end with many dendrites branching off it

Answer 226

1. Voluntary response (one where you make a conscious decision to carry out a particular action therefore it starts with your brain) 2. Involuntary response or reflex response (does not involve the brain as the coordinator of the reaction and you are not aware you have completed it

Answer 227

Involuntary actions are usually ones which are essential to basic survival and are rapid, whereas voluntary responses often take longer as we consider what the consequences might be before doing it.

Answer 228

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

Answer 229

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

Answer 230

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 are chemical as opposed to electrical, it is the only place where drugs can act to affect the nervous system

Answer 231

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.

Answer 232

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 stimulation of the second neurone which would cause repeated impulses to be sent)

Answer 233

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

Answer 234

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

Answer 235

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

Answer 236

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

Answer 237

Sensory neurone that carries impulses from the eye to the brain

Answer 238

Opening in eye that allows light to enter

Answer 239

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

Answer 240

Attaches lens to ciliary muscles

Answer 241

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 cells are found and there are no rod cells

Answer 242

This is a reflex action carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light.

Answer 243

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.

Answer 244

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.

Answer 245

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

Answer 246

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

Answer 247

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

Answer 248

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

Answer 249

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

Answer 250

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

Answer 251

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.

Answer 252

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)

Answer 253

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)

Answer 254

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

Answer 255

- 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 muscles and 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)

Answer 256

- Homeostasis is the maintenance of a constant internal environment - Homeostasis means that internal conditions within the body (such as temperature, blood pressure, water concentration, glucose concentration etc) need to be kept within set limits in 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 the body will not function properly and the eventual consequence without medical intervention will be death

Answer 257

- 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.

Answer 258

- Blood glucose levels are controlled by a negative feedback mechanism involving the production of two hormones - insulin and glucagon. Both hormones which control blood glucose concentration are made in the pancreas - Insulin is produced when blood glucose rises and stimulates 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. - Glucagon is produced when blood glucose falls and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood

Answer 259

Type 1 diabetes is a condition where the blood glucose levels are not able to be regulated as the insulin-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 often far too high

Answer 260

The human body maintains the temperature at which enzymes work best, around 37°C. If body temperature increases over this temperature, enzymes will denature and become less effective at catalysing reactions such as respiration

Answer 261

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.

Answer 262

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.

Answer 263

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

Answer 264

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

Answer 265

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.

Answer 266

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.

Answer 267

- 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)

Answer 268

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)

Answer 269

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)

Answer 270

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.

Answer 271

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

Answer 272

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.

Answer 273

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

Answer 274

- 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.

Answer 275

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

Answer 276

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

Answer 277

Antibiotics are chemical substances made by certain fungi or bacteria that affect the working of bacterial cells, either by disrupting their structure or function or by preventing them from reproducing (kill infective bacteria without harming body cells)

Answer 278

Antibiotics kill bacteria but do not affect viruses

Answer 279

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)

Answer 280

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

Answer 281

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.

Answer 282

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)

Answer 283

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

Answer 284

he transmission of genetic information from generation to generation

Answer 285

A length of DNA that codes for a protein

Answer 286

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

Answer 287

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

Answer 288

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.

Answer 289

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.

Answer 290

- 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)

Answer 291

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

Answer 292

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

Answer 293

nuclear division giving rise to genetically identical cells

Answer 294

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.

Answer 295

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

Answer 296

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

Answer 297

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)

Answer 298

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.

Answer 299

The number of chromosomes must be halved when the gametes (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

Answer 300

- 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

Answer 301

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

Answer 302

the observable features of an organism

Answer 303

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

Answer 304

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

Answer 305

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

Answer 306

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

Answer 307

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

Answer 308

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

Answer 309

Monohybrid inheritance is the inheritance of characteristics controlled by a single gene

Answer 310

Breeders can use a test cross to 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 the ratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

Answer 311

differences between individuals of the same species

Answer 312

In almost all cases, there are only alleles on the X chromosome as the Y chromosome is much smaller - Because males only have one X chromosome, they are much 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 a carrier; she doesn’t have the disease, but she has a 50% chance of passing it on to her offspring

Answer 313

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

Answer 314

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

Answer 315

Ionising radiation and some chemicals increase the rate of mutation

Answer 316

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

Answer 317

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

Answer 318

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

Answer 319

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

Answer 320

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

Answer 321

- 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 rolled with stomata inside and an inner surface covered 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 roots allow for the quick absorption of large quantities of water when it rains - Thickened leaves or stems which contain cells that store water

Answer 322

**(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 a change in the characteristics of the species - it will produce evolution

Answer 323

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

Answer 324

**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.

Answer 325

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

Answer 326

**(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

Answer 327

- 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

Answer 328

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.

Answer 329

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

Answer 330

a network of interconnected food chains

Answer 331

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

Answer 332

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

Answer 333

an animal that gets its energy by eating plants

Answer 334

an animal that gets its energy by eating other animals

Answer 335

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

Answer 336

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

Answer 337

as a result of human impact - either by overharvesting of food species or by the introduction of foreign species to a habitat

Answer 338

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

Answer 339

Pyramids of biomass are more accurate than pyramids of number because they provide a much better idea of the quantity of 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

Answer 340

- 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

Answer 341

- 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 cells that can be eaten. Only the energy that is made into new cells remains with the organism to be passed on.

Answer 342

- making waste products that 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

Answer 343

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

Answer 344

- Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much more energy available to them than if they eat the cows that eat the wheat - This is because 90% of energy is lost each trophic level so the higher you go there is less available to pass on to humans. Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores

Answer 345

- Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis - It is passed on to animals (and microorganisms) by feeding - It is returned to the atmosphere in the form of carbon dioxide by plants and animals as a result of respiration - 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, into fossil fuels - When fossil fuels are burned in combustion, the carbon combines with oxygen and carbon dioxide is released into the atmosphere - Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere. - In addition, mass deforestation is reducing the number of producers available 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 are burnt 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

Answer 346

- Nitrogen fixing bacteria convert N2 gas into ammonium compounds, which can then be converted to usable nitrates - Nitrogen fixing bacteria can be free-living in the soil or can live within the root nodules of some plants - Lightning can split the bond between the two N atoms combining it with water (H2O) to form ammonia (NH3) and nitrates (NO3)

Answer 347

- The plants can’t absorb ammonium compounds, so nitrifying bacteria convert 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 of nitrates and use it to build proteins - Animals eat the plants and get the nitrogen they need from the plant proteins - This nitrogen is passed up the food chain through 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 animals decay and all the proteins inside them are broken down into ammonium compounds by decomposers - Denitrifying bacteria take nitrates out of the soil and convert them back into N2 gas - This process reduces soil fertility and 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

Answer 348

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

Answer 349

all of the populations of different species in an ecosystem

Answer 350

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

Answer 351

- Food supply - Competition - Predation - Disease

Answer 352

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

Answer 353

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

Answer 354

Stationary phase- population stays the same size due to a factor 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

Answer 355

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

Answer 356

- 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

Answer 357

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

Answer 358

- 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

Answer 359

- 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)

Answer 360

In developed countries, large numbers of livestock are often kept in an area that would not normally be able to support more than a very small number. They are often fed high energy foods, regularly given medication such as antibiotics as a preventative measure against disease and kept in artificially warm temperatures and small spaces that do not allow for much movement

Answer 361

- 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

Answer 362

- 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

Answer 363

the number of different species that live in an area

Answer 364

**Increased area for housing, crop plant production and livestock production* **Extraction of natural resources** **Freshwater and marine pollution**

Answer 365

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

Answer 366

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

Answer 367

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.

Answer 368

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.

Answer 369

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

Answer 370

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

Answer 371

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

Answer 372

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.

Answer 373

The enhanced greenhouse effect happens when increasing levels of greenhouse gases from human activities cause the Earth's average temperature to rise above normal, leading to global 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.

Answer 374

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

Answer 375

Climate change Habitat destruction Introduction of foreign species Hunting Overharvesting Pollution

Answer 376

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

Answer 377

- Education - Protected areas - Quotas - Replanting

Answer 378

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

Answer 379

- 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

Answer 380

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.

Answer 381

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.

Answer 382

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

Answer 383

- 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)

Answer 384

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.

Answer 385

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

Answer 386

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

Answer 387

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.

Answer 388

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.

Answer 389

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.

Answer 390

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

Answer 391

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

Answer 392

- 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

Answer 393

- 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

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