Past Paper Question Errors

Question 1

When setting up a simple respometer to investigate rate of respiration of yeast
Suggest one reason why it is important that the student left the apparatus for an hour after yeast culture reaches a constant temperature
(1 mark)

Answer 1

To allow oxygen to be respired

Question 2

Explain why a log scale might be used to record the number of cells
(1 mark)

Answer 2

Large range/ difference/ increase in number

Question 3

If a graph decreases then plateaus at 1000 years
Use the evidence from this graph, what can you conclude about the net primary productivity in sand dunes older than 1000 years
(2 marks)

Answer 3

1) NPP remains constant
2) GPP/ photosynthesis and respiration remain constant

OR

3) NPP low/decreases
4) less light so less photosynthesis/GPP

Question 4

Furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons
Explain how flurosemide causes an increase in volume of urine produced
(3 marks)

Answer 4

1) water potential of filtrate/ tubule decreases
2) less water (reabsorbed) by osmosis ( from filtrate/tubule)
3) collecting duct (is where osmosis occurs)

Question 5

Suggest two features of the structure of different proteins that enable them to be separate by gel electrophoresis
(2 marks)

Answer 5

1) mass/ number of amino acids/ polypeptides
2) charge
3) R groups differ

Question 6

Lactase persistence (LP) is caused by mutation in DNA. This mutation does not occur in the gene coding for lactase
Suggest and explain how this mutation causes LP
(2 marks)

Answer 6

1) mutation in promoter for transcription factors or promoter regions for the gene
2) lactase gene continues to be transcribed

Question 7

Achromatopsia is a form of colour blindness when only rod cells and no functional cone cells in the eye. People with complete achromatopsia have difficulty in seeing detail
Explain why
(3 marks)

Answer 7

1) no functional cones/ only rod cells
2) cones are connected to a single neurone/ several rods connected to a single neurone
3) cones separate impulses to brain/ rods single impulse to brain

Question 8

Red-green colourblindness= sex-linked recessive allele. They have green sensitive cones but the photoreceptive pigment they contain does not function
People with red- green colour blindness are unable to distinguish between red and green and also between other colours. Explain why
(3 marks)

Answer 8

1) green sensitive pigments/ cones are non-functional
2) three different types of pigment/cones
3) different colours due to stimulation of more than one pigment/cones

Question 9

The scientists observed the chloroplast from sample of leaves using electron microscope. Suggest why iron deficient plants have a reduced growth rate if a thinner thylakoid membrane was observed
(3 marks)

Answer 9

With less thylakoid membrane
1) smaller surface area/ less chlorophyll
2) so reduced light absorption
3) slower rates of photosynthesis

Question 10

If drug trial test have been done on mice
Suggest and explain two further investigations that should be done before this ADC is tested on human breast cancer patients
(2 marks)

Answer 10

• test on other mammals to check for side effects
• test on healthy humans to check side effects
• see if repeat doses stop tumours regrowing

Question 11

Succession occurs in natural ecosystems. Describe and explain how succession occurs
( 4 marks)

Answer 11

1) pioneer species developed
2) changes the environmental factors to become less hostile so other species can develop
3) other species better adapted so out complete pioneer species
4) increase in biodiversity
5) until climax community reached

Question 12

Explain how a single base substitution causes a change in the structure of this polpeptide.
Do Not include details of transcription and translation in your answer.
(3 mark)

Answer 12

1) change in sequence of amino acid/primary structure
2) change in hydrogen/ionic/disulfate bonds
3) Alters tertiary structures

Question 13

Explain why the lids were kept on the Petri dishes when growing sample of shoot
(2 marks:

Answer 13

1) prevent/ reduce evaporation
2) which alters concentration of IAA solution

Question 14

Another group of scientists suggested that a decrease in the force of muscle concentration is caused by an increase in concentration of inorganic phosphate, in muscle tissue.
Their hypothesis is that an increase in the conc of Pi prevents the release of Ca ions in muscle tissue.
Explain how a decrease in the conc of Ca2+ in muscle tissue could decrease the force of muscle contraction
(3 marks)

Answer 14

1) shape of tropomyosin not changed so binding site not exposed
2) fewer cross bridges formed
3) myosin head doesn’t move/ myosin does not pull actin

Question 15

In muscles, Pyruvate is converted to lactate during prolonged exercise.
Explain why converting Pyruvate to lactate allows the continued production of ATP by anaerobic respiration
( 2 marks)

Answer 15

Pyruvate oxides by reduced NAD producing NAD+
So glycolysis can continue

Question 16

Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration
(3 marks)

Answer 16

1) less/no ATP is converted to cyclic AMP/ cAMP
2) less/no kinase is activated
3) less/no glycogen is converted to glucose (glycogenolysis)

Question 17

Describe what happens during photoionisation in the light dependent reaction

Answer 17

1) chrolophyll absorbs light energy
2) causing electrons to be lost

Question 18

Describe the methods the student used to separate the pigments after the solution of pigments has been applied to the origin
(2 marks)

Answer 18

1) water added just below the origin line
2) remove the paper before solvent reaches the top
3) draw pencil line where solvent reached and allow to dry

Question 19

Describe how the DNA is broken down into smaller fragments
( 2 marks)

Answer 19

1) restriction enzymes/endonuclease
2) cuts DNA at specific base sequences

Question 20

Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients
(2 marks)

Answer 20

1) break down proteins
2) provides amino acids
OR
3) digestion of DNA
4) provides nucleotides for growth

Question 21

Explain how damage to the myelin sheath of neurones can cause muscular paralysis
( 3 marks)

Answer 21

1) saltatory conduction or impulses pass to other neurones
2) nerve impulse slowed
3) refer to neuromuscular junctions then not receiving impulse

Question 22

Explain why there is a decrease in gross productivity as woodland matures
(2 marks)

Answer 22

1) less light due to more trees
2) reduces photosynthesis

Question 23

One farmer stated that the increase in use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other specifies of insects. Was he correct? Explain your answer
(4 marks)

Answer 23

1) mutation in one species occurs randomly
2) only the rate of mutation is affected by environment
3) genes are not spread to members of other species
4) organism from other species an not breed together to produce fertile offspring

Question 24

There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin.
Explain why there was a time lag
(3 marks)

Answer 24

1) initially one individual with favoured mutations
2) individuals with mutations will have more offspring
3) takes many generations for mutations to become most common allele

Question 25

What id meant by uniformly distributed (1 mark)

Answer 25

Same number of organism in each region/ equally spread

Question 26

How do the assumptions made in proportional sampling differ from those made in mark-release-recapture? (2 marks)

Answer 26

1) no assumption that organisms are uniformly distributed 2) size of total area size of sample region not required

Question 27

Give one assumption about the animals caught that is made in both mark-release-recapture and proportional sampling (1 mark)

Answer 27

Animals are from same population

Question 28

When preparing the cells for observations they were placed in a slightly higher (less negative) water potential that cytoplasm. This did not cause cells to burst bu moved the chromosomes further apart in order to reduce the overlapping of chromosomes when observed with an optical microscope. Suggest how this procedure moved the chromosomes apart (2 marks)

Answer 28

1) water moves into the cell by osmosis 2) cell gets bigger separating chromosomes

Question 29

What is a homologous pair of chromosomes (1 mark)

Answer 29

Two chromosomes that carry the same genes

Question 30

The scientists tested their null hypothesis using the chi-squared statistical test. After 1 cycle their calculated chi-squared value was 350. The critical value at P=0.05 is 3.841 What does this result suggest about the difference between the observed and expected results and what can the scientists therefore conclude (2 marks )

Answer 30

1) less that 5% probability that difference occurred by chance 2) calculated value is greater than critical value so null hypothesis can be rejected

Question 31

Explain why fertilisers are needed in an agricultural ecosystem

Answer 31

- mineral ions taken up by crops, which are transported and consumed away from the land preventing nutrients being replaced and therefore fertilisers are needed to provide nutrients needed for crops to grow.

Question 32

At night, it is often easier to see a star in the sky by looking slightly to the side of it rather than directly at it. Suggest why this is so

Answer 32

Light reaches earth from a star is of low intensity. Looking directly at a star light focuses the light on the fovea where there are only cone cells not rod cells. Cone cells can only respond to high light intensity and therefore makes it hard to see the star

Question 33

When walking along a street we barely notice the background noise of traffic. However, we often respond to louder traffic noises, such as the sound of a horn. From knowledge of summation, explain this difference

Answer 33

Relatively quiet noise produces lower level frequency of action potential in sensory neurone. Amount of neurotransmitter released into the synapse is insufficient to exceed threshold and to trigger an action potential so filtured out. Louder noise created higher frequency so neurotransmitter released is enough to be above threshold and trigger an action potential

Question 34

State why it is necessary for acetylcholine to be hydrolysed by acetylcholinesterase

Answer 34

To recycle choking and ethanol acid: To prevent acetylcholine from continuously generating a new action potential in post synaptic neurone

Question 35

Dead cells can no longer produce ATP. Soon after death, muscles contract, making the body stiff. From your knowledge of muscle contraction, explain the reason why this stiffness occurs after death

Answer 35

One one of the roles of ATP in muscle contraction is to attach the myosin heads, therefby abusing them to detach from actin filamanets and making the muscle relax. As no ATP is produced after death, there is none to attach to the myosin, which therefore remains attached to actin, leaving the muscle in a contracted state

Question 36

Explain why there will be a colour change if the blood sample contains target gene in ELISA test

Answer 36

1) antibody with enzyme only attaches if gene is present 2) no colour change occurs without enzyme bound

Question 37

Using knowledge of enzymes to explain why restriction enzymes can only cut DNA at specific restriction sites

Answer 37

Different lengths of DNA have different base sequences resulting in different shapes

Question 38

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical microscope (4 marks)

Answer 38

1) cut into thin sections of plant tissue 2) add drop of water to the glass slide 3) stain the tissue samples with iodine to make the starch visible 4) lower cover slip with mounted needle

Question 39

A diabetic person and a non-diabetic person each ate the same amount of glucose. One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why (3 marks)

Answer 39

In diabetic persons 1) lack of insulin 2) reduced uptake of glucose by cells 3) reduced conversion of glucose to glycogen

Question 40

The urine of a non-diabetic person does not constrain glucose. Explain why (2 marks)

Answer 40

Leaves the blood at kidney Taken back into blood/reabsorbed In 1st convoluted tubule

Question 41

A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how (2 marks )

Answer 41

Large amount/ high concentration of glucose in filtrate Cannot all be reabsorbed - saturation of carriers/ 1st convoluted tube too short to reabsorbed all glucose