Biology paper 1

Question 1

what are living things made of

Answer 1

cells

Question 2

what are the two types of cells

Answer 2

eukaryotic:

• have a nucleus
• complex cells including all animal and plant cells

prokaryotic:
- smaller and simpler like bacteria

Question 3

what are eukaryotes and prokaryotes

Answer 3

eukaryote:
- organisms made of eukaryotic cells (have a nucleus/ animal and plant cells)

prokaryote:

• singe celled organisms
• a prokaryotic cell (small and simple like bacteria)

Question 4

what subcellular structures does an animal cell have

Answer 4

• nucleus
• cytoplasm
• cell membrane
• mitochondria
• ribosomes

Question 5

what subcellular structures does a plant cell have

Answer 5

• rigid cell wall
• large vacuole
• chloroplasts

Question 6

what subcellular structures does a bacterial cell have

Answer 6

• chromosomal DNA
• ribosomes
• cell membrane
• plasmid DNA
• flagella
• slime capsule

Question 7

what is the function of a nucleus, cytoplasm and mitochondria

Answer 7

nucleus - contains the genetic material that controls the activities of the cell, genetic material is arranged into chromosomes

cytoplasm - gel like substance where most of the chemical reactions take place and contains enzymes to control these reactions

mitochondria - energy released from respiration reactions

Question 8

what is the function of the cell membrane and cell wall and ribosomes

Answer 8

cell membrane - holds the cell together and controls what substances move in and out of the cell

cell wall - made of cellulose it supports the cell and strengthens it

ribosomes - involved in the translation of genetic material to make proteins in protein synthesis

Question 9

what is the function of the vacuole and chloroplasts

Answer 9

vacuole - contains cell sap, a weak solution of sugar and salts and it maintains the internal pressure to support the cell

chloroplasts - contain chlorophyll which absorbs light for photosynthesis reactions to happen

Question 10

what is the function of chromosomal and plasmid DNA and flagella

Answer 10

chromosomal DNA - one long circular chromosome that controls the cell’s activities and replication, it floats free in the cytoplasm not in a nucleus

plasmid DNA - small loops of extra DNA that aren’t part of the chromosome and plasmids contain genes for things like drug resistance and can be passed between bacteria

flagella - a long hair like structure that rotates to make the bacterium move. It can be used to move away from toxins or towards things like nutrients or oxygen which are beneficial

Question 11

what happens in sexual reproduction

Answer 11

the nucleus of an egg cell fuses with the nucleus of a sperm cell to create a fertilised egg which develops into an embryo

sperm and egg cells are haploid which means they only contain half the number of chromosomes needed for a normal body cell

Question 12

what are the adaptations and function of the an egg cell or ovum

Answer 12

function:
- to carry the female DNA and to nourish the developing embryo in the early stages

adaptations:

• contains lots of nutrients in a large cytoplasm to be able to feed the embryo
• haploid nucleus
• straight after fertilisation, its membrane change structure to stop any more sperm getting in and this ensures the offspring has the right amount of DNA

Question 13

what are the adaptations and function of a sperm cell

Answer 13

function:
- to transport the males DNA to the females egg

adaptations:

• long flagellum tail to swim to the egg
• packed with mitochondria in the middle section to provide energy from respiration to be able to swim the large distance to swim to the egg
• has an acrosome at the front of the head where it stores enzymes needed to digest its way through the membrane of the egg cell
• haploid nucleus

Question 14

what are the adaptations and function of epithelial cells

Answer 14

function:
- the line the surface of cells to help move substances

adaptations:

• cilia ( hair like structures on the top) that beat in one direction along the surface of the tissue
• the lining of the airways has lot of ciliated epithelial cells which help to move the mucus and all of the particles from the air that it has trapped up the throat so it can be swallowed and doesn’t reach the lungs

Question 15

what is the resolution of a microscope

Answer 15

how well it distinguishes between two points that are close together
a higher resolution means that the image can be seen more clearly and in more detail

Question 16

how do light microscopes work

Answer 16

they pass light through the specimen and let us see things like nuclei and chloroplasts and we can also use them to study living cells
hence the need to take a thin slice of the cell to allow light to pass through

Question 17

what are the advantages and disadvantages of using an electron microscope

Answer 17

advantages:

• higher resolution
• higher magnification
• more detail
• see internal structure of chloroplasts and mitochondria
• allow understanding of how cells work and the role of subcellular structures

disadvantages;

• expensive
• can’t be used to see living cells

Question 18

how would you view a specimen using a light microscope

Answer 18

1) thin slice of specimen to light through
2) take a clean slide and put a drop of water on using a pipette to hold the specimen in place and place specimen on using tweezers
3) add stain if your specimen is completely transparent or colourless to make it easier to see e.g methylene blue for DNA
4) place cover slip at on end of the cover slip holding it at an angle with a mounted needle and carefully lower onto the slide. Press it down gently so that no air bubbles are trapped under it the clip slide to stage
5) select lowest objective lens
6) use the coarse adjustment knob to move the stage up so that the slide is just underneath the objective lens
7) look down the eyepiece and move stage downwards till specimen is nearly in focus
8) adjust the focus with the fine adjustment knob until you get a clear image
9) position a clear ruler on the stage and use it to measure the diameter of the circular area visible - your field of view
10) repeat with different objective lens

Question 19

what are the two magnification calculations

Answer 19

total magnification = eyepiece lens x objective lens

magnification = image size divided by actual real size

Question 20

convert mm to micrometres (um)

Answer 20

x 1000

Question 21

what are enzymes

Answer 21

biological catalysts that reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body

Question 22

what do chemical reactions normally involve

Answer 22

things being split apart or joined together

catalysed or synthesised

Question 23

what molecule is changed in an enzyme reaction

Answer 23

substrate

Question 24

discuss how temperature affects the rate of enzyme reaction

Answer 24

an increasing temperature will increase the rate of reaction at first until it reaches the enzymes optimum temperature. After this temperature the bonds holding the enzyme together begin to break so the shape of the enzymes active site changes and becomes denatured so it can no longer bind with its specific substrate. After the optimum activity decreases and stops.

Question 25

discuss how pH affects the rate of enzyme controlled reaction

Answer 25

the pH must be at the optimum, either side of the optimum the enzyme won’t work as well because it will be denatured as the bonds holding the active site together will change shape

Question 26

discuss how substrate concentration will affect the rate of an enzyme controlled reaction

Answer 26

the higher the substrate concentration, the faster the rate of reaction because it is more likely that an enzyme will meet up with a substrate molecule and react
however this is only up to a point. after that there are so many substrate molecules that there isn’t enough enzymes to react because all the active sites are full so the rate of reaction won’t change

Question 27

what is the core practical for investigating the effect of pH on enzyme activity

Answer 27

the enzyme amylase catalyses the breakdown of starch to maltose and you can detect the starch using iodine
if starch is present it will turn from browny-orange to blue-black
1) a drop of iodine into every well of a spotting tile
2) place a Bunsen burner on a heat proof mat and a tripod and gauze over the top. Put a beaker of 25ml of water and heat till 35 degrees use thermometer to keep temp throughout the same
3) use a syringe to add 3cm cubed of amylase solution and 1 cm cubed of buffer solution of pH 5 to a boiling tube. Using test tube holders place the tube in the water for 5 mins
4) next use a different syringe to add 3cm of starch solution to the boiling tube
5) immediately mix the contents of the boiling tube and start a stop clock
6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch. to do this use a dropping pipette to take a fresh sample from the boiling tube every ten seconds and put a drop into a well. When the solution remains browny-orange starch is no longer present
7) repeat with different pH values

Question 28

how do you calculate the rate of reaction

Answer 28

rate = 1000/time
the unit of rate is s to the -1

or if an experiment measures how much something changes over time you can use
amount of product formed = change
change/ time

Question 29

why is it important that organisms can break big molecules like proteins, lipids and carbohydrates into smaller molecules

Answer 29

so they can be used for growth and other life processes

many of the molecules we eat in food are too big to pass through the walls of our digestive system so digestive enzymes break them down into smaller soluble molecules.
these can easily pass through the walls of our digestive system allowing them to be absorbed into the bloodstream and pass into cells to be used by the body.

plants store energy in the form of starch (a carbohydrate) and when plants need energy enzymes break down starch into smaller sugar molecules. These can then be respired to transfer energy to be used by the cells

Question 30

how are proteins made

Answer 30

by joining amino acids together using enzymes that synthesise

Question 31

what is the test for sugars

Answer 31

BENEDICTS REAGENT

there are lots of different types of sugar molecules. due to their chemical properties many sugars are called reducing sugars

add Benedict’s reagent (which is blue) to a sample and heat it in a water bath that’s set to 75 degrees. If the test is positive it will form a coloured precipitate

the higher the concentration of reducing sugars the further the colour change goes

blue - green - yellow - orange - brick red

Question 32

what is the test for starch

Answer 32

IODINE

add iodine
if starch is present the sample changes from browny-orange to blue-black

Question 33

what is the test for lipids

Answer 33

ETHANOL SHAKE WATER MILKY EMULSION

add 20ml of ice cold ethanol and shake for about a minute until it dissolves and pour the solution in water

if there are any lipids present they will precipitate out of the liquid and show up as a milky emulsion

the more lipid the more noticeable the milky colour will be

Question 34

what is the test for proteins

Answer 34

BIURET TEST

add a few drops of potassium hydroxide solution to make the solution alkaline
then add 10ml of copper (II) sulphate solution which is bright blue

if there are no protein the solution will stay blue
if proteins are PRESENT the solution will turn purple

Question 35

what is the core practical for seeing how much energy food contains

Answer 35

CALORIMETRY

1) collect some food that will burn easily - something that is dry like pasta, dried beans or crisps
2) weigh 2grams of the food and then skewer it on a mounted needle
3) add 50ml of water to a boiling tube (held with a clamp) so you can measure the amount of energy that is transferred when the food is burnt
4) measure the temperature of the water, then set fire to the food using a Bunsen burner but make sure the Bunsen isn’t near the water or your results will be inaccurate
5) immediately hold the burning food under the boiling tube until it goes out. Then relight the food and hold it under the tube and repeat until the food won’t catch fire again
6) measure the end temperature of the water

then do…
energy in food = mass of water x temperature change of water x 4.2

then do…
energy per gram of food = energy in food / mass of food

Question 36

how can you reduce energy loss to the surroundings in the food energy (calorimetry) core practical?

Answer 36

insulate the boiling tube with foil or cotton wool

Question 37

discuss osmosis

Answer 37

a partially permeable membrane is just one with very small holes in it so bigger molecules like sucrose can’t pass through

the water molecules actually pass both ways through the membrane during osmosis because the water molecules move about randomly all the time

but because there are more water molecules on one side than the other, there’s a steady net flow of water into the region with fewer water molecules, e.g the more concentrated solute solution

this means the solute solution gets more dilute and the water acts like it is trying ‘even up’ the concentration either side of the membrane

Question 38

define diffusion

Answer 38

passive process
no energy needed
ya know the rest :)

Question 39

define active transport

Answer 39

active transport is the net movement of particles across a membrane against a concentration gradient (from an area of low concentration to an area of high concentration) using energy transferred during respiration
the process requires energy

Question 40

discuss active transport with nutrient in the blood

Answer 40

when there’s a higher chance of nutrients in the gut than in the blood the nutrients diffuse naturally into the blood
but sometimes there’s a lower concentration of nutrients in the gut than in the blood
active transport allows nutrients to be taken into the blood despite the fact that it is against the concentration gradient to stop us from starving

Question 41

what is the core practical for investigating osmosis

Answer 41

1) prepare sucrose solutions of different concentrations ranging from pure water to a very concentrated sucrose solution
2) use a cork borer to cut potato into the same sized pieces of about 1cm diameter and from the same potato
3) divide the cylinders into groups of three and use a mass balance to measure the mass of each group
4) place on group in each solution
5) leave the cylinders in the solution for at least 40 minutes
6) remove the cylinders and pat dry gently with a paper towel to remove excess water from the surface of the cylinders so you get a more accurate measurement of their final masses
7) weight each group again and record your results
8) the only thing you should change in this experiment is sucrose solution concentration. Everything else must stay the same

then do percentage change = final mass - initial mass over initial mass and times your answer by 100
positive = gained mass
negative = lost mass

Question 42

what does the nucleus contain

Answer 42

genetic information in the form of chromosomes which are coiled up lengths of DNA molecules

Question 43

why are body cells normally diploid

Answer 43

because it has two copies of each chromosomes one from your mother and one from your father

Question 44

discuss interphase in mitosis

Answer 44

in a cell that’s not dividing the DNA is all spread out in long strings. Before it divides the cell has to grow and to increase the amount of subcellular structure such as mitochondria and ribosomes.

it then duplicates its DNA so there is one copy for each new cell. The DNA is copied and forms X-shaped chromosomes. Each arm of the chromosomes is an exact duplicate of the other

Question 45

explain the stages of mitosis from prophase to cytokinesis

Answer 45

prophase - the chromosomes condense getting shorter and fatter. The membrane around the nucleus breaks down and the chromosome lie free in the cytoplasm

metaphase - the chromosomes line up at the centre of the cell

anaphase - spindle fibres pull the chromosomes apart. The two arms of each chromosome go to opposite arms of the cell

telophase - membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided

cytokinesis - the cytoplasm and cell membrane divides to form new cells

Question 46

what is produced by mitosis and what is mitosis used for

Answer 46

2 diploid genetically identical daughter cells

growth and repair

Question 47

describe mitosis

Answer 47

the division of a cell to form 2 diploid genetically identical daughter cells that are used for growth and repair

Question 48

how do you calculate the number of cells after multiple divisions

Answer 48

2 to the power of n where n is the number of divisions

Question 49

how does a cell grow

Answer 49

cell DIVISION by mitosis
cell ELONGATION where a plant cell expands making the cells bigger and the plant grow
cell DIFFERENTIATION - the process by which a cell changes to become specialised for its job. having specialised cells allows multicellular organisms to work more efficiently

Question 50

discuss growth in animals

Answer 50

all growth in animals happens by cell division. Animals tend to grow while they’re young and then they reach full growth and stop growing. So when you’re young cells divide at a fast rate but once you’re an adult most cell division is for repair - the cells divide to replace old or damaged cells. This also means in most animals cell differentiation is lost at an early stage

Question 51

discuss growth in plants

Answer 51

in plants growth in height is mainly due to cell elongation - cell division usually just happens in the tips of the roots and shoots (in areas in called meristems) but plants often grow continuously - even really old trees will keep putting out new branches. So, plants continue to differentiation to develop new parts e.g leaves or roots

Question 52

how is cancer caused

Answer 52

uncontrolled cell division

the rate at which cells divide by mitosis is controlled by the chemical instructions (genes) in an organisms DNA

If there’s a change in one of the genes that controls cell division (a mutation), the cell may start dividing uncontrollably

this can result in a mass of abnormal cells called a tumour

if the tumour invade and destroys surrounding tissue it is called cancer

Question 53

what chart is used to measure growth

why do we use these charts

what does it mean to be on the 75th percentile

Answer 53

percentile chart

assess a child’s growth over time so that an overall pattern in development can be seen and any problems like obesity, malnutrition and obesity can be highlighted

25% of babies are bigger at that age
75% of babies are smaller at that age

Question 54

what are stem cells

Answer 54

undifferentiated cells

Question 55

why can embryonic stem cells divide into any type of cell

Answer 55

because the first few cells of the human embryo need to develop into all of our body cells

Question 56

what can adult stem cells do

Answer 56

only divide into some cells
only found in certain places like bone marrow
used to replace damaged cells like skin or blood cells

Question 57

what are the cells in plants that divide by mitosis

Answer 57

meristems
meristem tissue is found in the areas of a plant that are growing e.g tips of roots and shoots
meristems produce unspecialised cells that are able to divide and form any cell type in the plant - they act like embryonic stem cells but unlike human stem cells these cells can divide and differentiate to generate any type of cell for as long as the plant lives
the unspecialised cells go on to form specialised tissues like xylem and phloem

Question 58

how do doctors use stem cells in medicine

Answer 58

• doctors use adult stem cells to cure some diseases
• scientists have experimented with extracting stem cells from very early human embryos and growing them. Under certain conditions the stem cells can be stimulated to differentiate into specialised cells
• it might be possible to use stem cells to create specialised cells to replace those which have been damaged by disease or injury e.g new cardiac muscle cells could be transplanted into someone with heart disease
• this potential for new cures is the reason for the huge scientific interest in stem cells

Question 59

what are the potential risks associated with stem cells treatment

Answer 59

tumour development:
stem cells divide very quickly. If scientists are unable to control the rate at which the transplanted cells divide inside a patient, a tumour may develop

Disease transmission:
viruses live inside cells. If donor cells are infected with a virus and this isn’t picked up the virus could be passed on to the recipient and make them sicker

Rejection:
if the transplanted cells aren’t grown using the patients own stem cells the patients body may recognise the cells as foreign and trigger an immune response to try to get rid of them. The patient can take drugs to suppress this response but this makes them susceptible disease.

Question 60

discuss the spinal cord

Answer 60

a long column of neurones (nerve cells) that run from the base of the brain down the spine. At several places down the cord, neurones branch off and connect with other parts of the body.
The spinal cord relays information between the brain and the rest of the body

Question 61

what is the brain made up of

Answer 61

billions of interconnected neurones and different parts of the brain have different functions

Question 62

what does the cerebrum part of the brain do

Answer 62

the cerebrum is the largest part of the brain
divided into two halves called cerebral hemispheres.
the right side controls muscles on the left side and vice versa

different parts of the cerebrum are responsible for movement, intelligence, memory, language and vision
[conscious activities]

Question 63

what does the cerebellum part of the brain do

Answer 63

responsible for muscle coordination and balance

Question 64

what does the medulla oblongata part of the brain do

Answer 64

controls unconscious activities like breathing and heart rate

Question 65

how can a CT scanner be used to investigate the brain

Answer 65

• uses an X-ray to produce an image of the brain
• shows the main structures of the brain but doesn’t show the function of them
• However if a CT scan shows a diseased or damaged brain structure and the patient has lost some function, the function of that part of the brain can be worked out. E.g if an area of the brain shows up damaged and the patient can’t see then that area is involved in vision

Question 66

how can a PET scanner be used to investigate the brain

Answer 66

• PET scanners are a bit more fancy than CT scanners
• they use radioactive chemicals to show which parts of the brain are active when the person is inside the scanner
• they are very detailed and can be used to investigate both the structure and the function of the brain in real time
• PET scans can show if areas in the brain are usually inactive and active so they are useful for studying disorders that change the brain’s activity. E.g in Alzheimer’s disease, activity in certain areas of the brain is reduced - PET scans show this reduction when compared to a normal brain

Question 67

what things can go wrong with the CNS and why is this a problem

Answer 67

injuries to the brain or spinal cord, tumours and diseases but these can be difficult to treat

it’s hard to repair damage to the CNS because the neurones in it don’t readily repair themselves and scientists haven’t developed a way to repair nervous tissue in the CNS

If a problem occurs in a part of the nervous system that’s not easy to access it can be hard to treat e.g it’s not possible to surgically remove tumours growing in certain parts of the brain

treatments for problems in the nervous system may lead to permanent damage. For example, a person who has injured their spinal cord may need surgery on their spine near the injury. There is a risk that the spinal cord could be damaged further during the operation leading to permeant damage

Question 68

discuss the CNS response (reflex arc)

Answer 68

the nervous system is made up of neurones which go to all parts of the body

the body has a lot of sensory receptors that detect a stimulus (change in the environment). different receptors detect different stimuli
when a stimulus is detected by receptors the information is converted into electrical impulses and sent along sensory neurones to the CNS
The CNS coordinates a response and impulses travel through the CNS along relay neurones
the CNS sends information along a motor neurone to an effector (muscle or gland)
the effector responds accordingly e.g a muscle may contract or a gland may secrete a hormone

Question 69

what is your reaction time and the typical one of a human

Answer 69

the time it takes you to respond to a stimulus

0.25 seconds

Question 70

what do all neurones have

Answer 70

• a cell body with a nucleus plus cytoplasm and other subcellular structures
• the cell body has extensions that connect to other neurones - dendrites and dendrons carry nerve impulses towards the cell body, and axons carry nerve impulses away from the cell body
• some axons are surrounded by a myelin sheath which acts as an electrical insulator speeding up the electrical impulse and preventing energy loss
• neurones can be very long which also speeds up the impulses because connecting with another neurone slows the impulse down so one long neurone is much quicker than lots of short ones joined together

Question 71

discuss sensory neurone

Answer 71

• one long dendron carries nerve impulses from receptor cells to the cell body which is located in the middle of the neurone
• one short axon carries nerve impulses from the cell body to the CNS

Question 72

discuss motor neurone

Answer 72

• many short dendrites carry nerve impulses from the CNS to the cell body
• one long axon carries nerve impulses from the cell body to effector cells

Question 73

discuss relay neurone

Answer 73

• many short dendrites carry nerve impulses from sensory neurones to the cell body
• an axon carries nerve impulses from the cell body to the motor neurones

Question 74

discuss the synapses

Answer 74

the gap between two neurones
the nerve signal is transferred by chemicals called neurotransmitters which diffuse across the gap
the neurotransmitters then set off a new electrical signal in the next neurone
the transmission of a nervous impulse is very fast but it is slowed down a bit at the synapse because the diffusion of neurotransmitters across the gap takes time

Question 75

discuss the reflex to help prevent injury from the sting of a bee

Answer 75

reflexes are automatic, rapid responses to stimuli - they can reduce the chances of being injured. The passage of information in a reflex (from receptor to effector) is called a reflex arc. The neurones in a reflex arc go through the spinal cord or an unconscious part of the brain

1) when a stimulus (a bee sting) is detected by receptors impulses are sent along a sensory neurone to a relay neurone in the CNS
2) when the impulses reach a synapse between the sensory neurone and the relay neurone the trigger neurotransmitters to be released and these carry impulses to be sent along the relay neurone
3) when the impulses reach a synapse between the relay neurone and a motor neurone the same thing happens. Neurotransmitters are released and cause impulses to be sent along the motor neurone
4) the impulses then travel along the motor neurone to the effector of a muscle (in this case but it could be a gland)
5) the muscle then contracts and moves your hand away from the bee
6) because you don’t have to spend time thinking about the response, it’s quicker than normal response

Question 76

how does a reflex help to protect the eye

Answer 76

very bright light can damage the eye so you have a reflex to protect it
light receptors in the eye detect bright light and send a message along a sensory neurone to the brain
the message then travels along a relay neurone to a motor neurone which tells circular muscles in the iris to contract making the pupil smaller

Question 77

what is the function of the cornea

Answer 77

refracts (bends) light into the eye

Question 78

what is the function of the iris

Answer 78

controls how much light enters the pupil

Question 79

what is the function of the lens

Answer 79

refracts light, focusing it onto the retina

Question 80

what is the function of the retina

Answer 80

the light sensitive part of the eye and it is covered in receptor cells called rods and cones

Question 81

what is the function of rods and cones

Answer 81

rods - sensitive in dim light but can’t detect colour

cones - sensitive to different colours but can’t detect light

Question 82

what is the function of the optic nerve

Answer 82

information from light is converted into electrical impulses and the optic nerve carries these impulses from the receptors to the brain

Question 83

what does the eye do to look at distant objects

Answer 83

the ciliary muscle relaxes which allow the suspensory ligaments to pull tight
this pulls the lens into a less rounded shape so light is refracted less

Question 84

what does the eye do to look at close objects

Answer 84

the ciliary muscle contrasts which slackens the suspensory ligaments
the lens becomes a more rounded shape, so light is refracted more

Question 85

why are some people long sighted and what lens can correct this

Answer 85

the lens is the wrong shape and doesn’t bend light enough
the eyeball is too short
light from near objects is brought into focus behind the retina
you can use a convex lens to correct it

Question 86

why are some people short sighted and what lens can correct this

Answer 86

the lens is the wrong shape and bends light too much
the eyeball is too long
light from distant objects is brought into focus in front of the retina
you can use a concave lens to correct this

Question 87

what is colour blindness

Answer 87

can’t tell the difference between certain colours
the most common form of the disorder is red-green colour blindness
caused when red or green cones in the retina are not working properly
there is no cure for colour blindness because the cone cells can’t be replaced

Question 88

what is a cataract

Answer 88

a cloudy patch on the lens which stops light from being able to enter the eye normally
people with cataracts are likely to have blurred vision
they may also experience colours looking less vivid and have difficulty seeing in bright light
a cataract can be treated by replacing the faulty lens with an artificial one

Question 89

what is mitosis also known as

Answer 89

the cell cycle

Question 90

what are three uses of mitosis

Answer 90

asexual reproduction
growth
repair

Question 91

discuss the process of sexual reproduction

Answer 91

where genetic information from two organisms (a father and a mother) combine to produce offspring which are genetically different to either parent
in sexual reproduction the father and mother produce gametes (egg and sperm) which are reproductive cells
gametes only contain half the number of chromosomes of normal cells and are haploid
at fertilisation a male gamete fuses with a female gamete to produce a fertilised egg known as a zygote ]the zygote ends up with a full set of chromosomes so is diploid
the zygote then undergoes cell division by mitosis and develops into an embryo
the embryo inherits characteristics from both parents as it has received a mixture of chromosomes and therefore genes from its mum and dad

Question 92

how are proteins made

Answer 92

proteins are made by reading the code in DNA

1) DNA controls the production of proteins (protein synthesis) in a cell
2) proteins are made up of chains of amino acid molecules. Each different protein has its own particular number and order of amino acids
3) the amino acid chains fold up to give each protein a different, specific shape which means each protein has a different function
4) remember a section of DNA that codes for a particular protein is called a gene. Its the order of bases in a gene that decides the order of amino acids in a protein
5) each amino acid is coded for by a sequence of three bases in the gene - a base triplet
6) the amino acids are joined together to make proteins following the order of the bases in the gene
7) each gene contains a different sequence of bases - which is what allows it to code for particular protein

Question 93

what is a base triplet

Answer 93

each amino acid is coded for by a sequence of three bases in the gene and this is called the base triplet

Question 94

what is a triplet code

Answer 94

a code based on base triplets

Question 95

discuss non-coding regions in DNA

Answer 95

may regions of DNA are non-coding meaning they don’t code for any amino acids
despite this some of these regions are still involved in protein synthesis
all of an organisms DNA (including the non-coding regions) makes up the organisms genome

Question 96

how can genetic variants arise by mutations

Answer 96

a mutation is a rare random change to an organisms DNA base sequence that can be inherited
if a mutation happens in a gene it produces a genetic variant - a different version of the gene
the genetic variant may code for a different sequence of amino acids which may change the shape of the final protein and so its activity
for an example the activity of an enzyme nay increase, decrease or stop all together
this could end up changing the phenotype of an organism
mutations can also happen in non-coding regions of DNA

Question 97

discuss transcription (stage 1 of protein synthesis)

Answer 97

proteins are made in the cell cytoplasm in the ribosomes
DNA is found in the nucleus and can’t move out because it is too big so the cell needs to get the information from the DNA to the ribosome in the cytoplasm
this is done using a molecule called messenger RNA (mRNA) - like DNA mRNA is a polymer of nucleotides but it is shorter and only a single strand. It also uses uracil (U) for a base instead of thymine (T).
RNA polymerase is the enzyme involved in joining together RNA nucleotides to make mRNA.

1) RNA polymerase binds to a region of non-coding DNA in front of a gene
2) The two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA
3) It uses the coding DNA in the gene as a template to make the mRNA. Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene
4) Once made the mRNA molecule moves out of the nucleus and joins with a ribosome

Question 98

discuss translation (stage 2 of protein synthesis)

Answer 98

Once the mRNA is bound to a ribosome, the protein can be assembled - translation

1) Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA)
2) The order in which the amino acids are brought to the ribosome matches the order of the base triplets in mRNA. Base triplets in mRNA are known as codons
3) Part of tRNA’s structure is called an anticodon - it is complementary to the codon for the amino acid. The pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the correct order.
4) The amino acids are joined together by the ribosome. This makes a polypeptide (protein)

Question 99

how does a mutation of non-coding DNA affect the binding of RNA polymerase

Answer 99

before any transcription can happen RNA polymerase has to bind to a region of non-coding DNA in front of a gene. If a mutation happens in this region of DNA then It could affect the ability of RNA polymerase to bind to it. It might make it easier to bind to or more difficult

how well RNA polymerase can bind to this region of DNA will affect how much mRNA is transcribed and therefore how much of the protein is produced. And depending on the function of the protein, the phenotype of the organism may be affected by how much of it is made

So genetic variants in non-coding regions can still affect the phenotype of an organism even if they don’t code for proteins themselves