Question 1:-
Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.
Plants to the rescue
Since the early 20th century, the concentration of carbon dioxide in the atmosphere has increased rapidly. This has further increased in recent years due to more cars and the increased demand for electricity for homes and industry.
5 Scientists have found that plants play a critical part in removing this excess carbon dioxide from the atmosphere. Using computer models, the scientists concluded that photosynthesis has increased by 30 per cent.
10 The scientists measured carbonyl sulfide found in ice cores and air samples. In addition to carbon dioxide, plants take in carbonyl sulfide gas during their natural carbon cycle, and this is frequently used as a measure of photosynthesis on a global scale. Terrestrial plants are removing about 29 per cent of carbon dioxide emissions that would otherwise contribute to an increase in the atmospheric carbon dioxide concentration.
15 A carbon sink is an ecosystem, such as a forest, that absorbs more carbon dioxide than it releases. The size of the carbon sink depends on the rate of photosynthesis but also on the levels of deforestation and respiration. The model the scientists used showed that the role of photosynthesis in producing a carbon sink in land plants is larger than estimated in most other models.
20 Other scientists are less confident about using carbonyl sulfide as a measure of photosynthesis. Plant absorption of carbonyl sulfide can vary depending upon the amount of light the plants receive. Therefore, the measure of global photosynthesis could be overestimated.
25 Regardless of the rate at which photosynthesis has increased, scientists agree that excess carbon dioxide is boosting the growth of plants. Trees are becoming leafier, and there is more wood. The wood is where most of the carbon is stored in the plant.
30 In experimental research, scientists exposed plants to double the normal concentration of carbon dioxide found in the atmosphere. Under these increased carbon dioxide conditions, the composition of the leaf tissues changed. This made the leaves tougher for herbivores to eat and made it harder for insect larvae to grow.
Scientists have also observed that when plants are exposed to increasing levels of carbon dioxide, the size of the stomatal pores on a leaf increases.
(a) Explain why more cars would result in an increase in atmospheric carbon dioxide. (Lines 1-3)
(b) Explain how increased carbon dioxide can cause climate change.
(c) Explain why increasing carbon dioxide concentration can increase photosynthesis in plants.
(d) Explain why the carbon sink depends upon respiration and deforestation as well as photosynthesis. (Lines 13 to 15)
(e) Light affects gas exchange in leaves. (Lines 19 and 20) Describe an experiment that shows how the net gas exchange from a leaf varies with light intensity.
(f) The photograph shows stomata on a small square of the lower surface of a leaf.
The total area of the lower surface of the leaf is 150cm2.
Using the photograph and the total lower surface area of the leaf, estimate the number of stomata on the lower surface of the leaf.
number of stomata = ……………………………………………………..
(g) Stomata also have a role in water transport in the plant.
Explain the role of stomata in water transport.
▶️Answer/Explanation
Ans : 1(a)(i) The only correct answer is
C (oak tree)
A is not the answer as caterpillar is not a producer
B is not the answer as earthworm is not a producer
D is not the answer as stoat is not a producer
1(a)(ii) The only correct answer is
D (ladybird)
A is not the answer as caterpillar is not a secondary
consumer
B is not the answer as earthworm is not a secondary
consumer
C is not the answer as fox is not a secondary consumer
1(a)(iii) The only correct answer is
A (blackbird)
B is not the answer as earthworm is not a secondary and
a tertiary consumer
C is not the answer as fox is not a secondary and a
tertiary consumer
D is not the answer as stoat is not a secondary and a
tertiary consumer
1 (b)(i) An explanation that makes reference to three of the following:
• fewer blackbirds / numbers fall / population
reduces / die / migrate /eq (1)
• less food (for blackbirds) fewer (caterpillars)
to eat / fewer ladybirds / eq (1)
• less food for ladybirds / fewer greenfly for
ladybirds to eat/ eq (1)
• (blackbirds) will eat more earthworms / will
eat only earthworms / eq (1)
• blackbirds consume pesticide /
bioaccumulation / pesticide kills blackbirds / eq (1)
1 (b)(ii) A description that makes reference to the following:
• biological control (1)
• introduce predator / increase ladybirds / eq (1)
• to eat / consume / prey on greenfly / eq (1)
1(d) An explanation that makes reference to two of the following points:
• (carbon sink) absorbs more CO2 (than it releases) / eq (1)
• respiration releases carbon dioxide / eq (1)
• deforestation releases carbon dioxide by decomposition / decay / combustion / eq (1)
1(e) A description that makes reference to three of the following points:
• place leaves in test tubes / eq with hydrogen-carbonate indicator (1)
• leaf in light and leaf in dark / eq (1)
• in light, indicator turns purple / dark red / eq / in dark turns yellow / eq (1)
• same size leaf / species leaf / same age of leaf / same time / same temperature / same volume of indicator / same concentration of indicator / eq (1)
1(f) 2 stomata in area of 0.4mm × 0.4mm
= 0.04 cm × 0.04 cm
2 in 0.0016cm2
therefore density = 2 ÷ 0.0016
stomata per cm2
total number in 150 cm2
= 150 × (2÷ 0.0016)
=150 × 1250
= 187500 stomata (3)
OR
150 / 0.0016 = 93750
93750 x 2 = 187500
1(g) An explanation that makes reference to the following points:
• water loss / transpiration / evaporation / diffusion (through stomata) / (set up) transpiration stream / eq (1)
• draws water up from roots / up stem / up xylem / into leaf / creates a (water potential) gradient / eq (1)
Question 2:-
Catalase is an enzyme found in many cells.
This enzyme controls the breakdown of hydrogen peroxide into water and oxygen.
2H2O2 → 2H2O + O2
hydrogen water oxygen
peroxide
A teacher uses this method to investigate the effect of pH on catalase.
Step 1 cut a cylinder of potato tissue into six equal sized discs
Step 2 measure 10cm3 of hydrogen peroxide solution and place into a boiling tube
Step 3 add a pH buffer solution to the tube to keep the pH at 7
Step 4 add the six potato discs to the boiling tube
Step 5 collect the gas given off by the reaction in an inverted 20cm3 measuring cylinder
Step 6 measure the total volume of gas collected after five minutes Repeat steps 1 to 6 using four different pH buffers (pH 4, pH 5, pH 6 and pH 8).
The diagram shows the teacher’s apparatus.
(a) State what is meant by the term enzyme.
(b) Suggest why each potato cylinder was cut into six discs rather than left as one cylinder.
(c) (i) Give the dependent variable in this experiment.
(ii) The teacher controls the time for gas collection and also the volume of hydrogen peroxide used.
State two other abiotic variables the teacher should control in this experiment.
1 …………………………………………………………………………..
2 …………………………………………………………………………..
(d) The table shows the teacher’s results.
(i) Calculate the percentage change in the mean rate of reaction as the pH is changed from pH 4 to pH 7.
(ii) The teacher calculated the mean rate of reaction by collecting the oxygen released for the first five minutes of the reaction.
Explain why the mean rate of reaction changes beyond the first five minutes.
(iii) Explain the effect of changing pH on an enzyme-controlled reaction.
▶️Answer/Explanation
Ans : 2(a) An answer that makes reference to:
• (biological) catalyst / substance that speeds up reactions / protein that speeds up reactions / eq (1)
2(b) An answer that makes reference to:
• increased surface area / so more catalase exposed to the H2O2 / speeds up reaction / eq (1)
2(c)(i) An answer that makes reference to:
• volume of gas (released in 5 minutes) / eq (1)
2(c)(ii) An answer that refers to two of the following:
• concentration of peroxide / eq (1)
• temperature (1)
• volume of (pH) buffer / eq (1)
2(d)(i) 2.4- 0.8
= 1.6 ÷ 0.8 × 100
= 200% (2)
2(d)(ii) An explanation that makes reference to two of the following points:
• substrate / H2O2 is being used up / reaction complete / concentration of H2O2 decreases / eq (1)
• so fewer enzyme substrate-complexes / fewer collisions / eq(1)
• water formed dilutes H2O2 / eq (1)
2(d)(iii) An explanation that makes reference to the following points:
• pH changes from optimum pH / enzymes have
optimum pH / eq (1)
• pH denatures enzyme / alters the bonding / alters shape of active site / eq (1)
• substrate and enzyme no longer fit / ES complexes cannot form / substrate cannot bind / enzyme and substrate are no longer complementary / eq (1)
Question 3:-
The diagram shows a nephron from a human kidney with some structures labelled.
(a) (i) Which structure is the Bowman’s capsule?
A P
B R
C S
D T
(ii) Which structure is the loop of Henle?
A P
B Q
C S
D U
(iii) Which structure is affected by ADH?
A P
B Q
C S
D T
(b) (i) Blood plasma contains much glucose, but urine normally does not. Explain what happens to glucose in the kidney.
(ii) Describe how a sample of urine could be tested for glucose.
(c) As a person sweats, they may become dehydrated. Describe the changes in a person’s urine if they become dehydrated.
▶️Answer/Explanation
Ans : 3(a)(i) The only correct answer is
C (S)
A is not the answer as P is not the Bowman’s capsule
B is not the answer as R is not the Bowman’s capsule
D is not the answer as T is not the Bowman’s capsule
3(a)(ii) The only correct answer is
B (Q)
A is not the answer as P is not the Loop of Henle
C is not the answer as S is not the Loop of Henle
D is not the answer as U is not the Loop of Henle
3(a)(iii) The only correct answer is
A (P)
B is not the answer as Q is not affected
C is not the answer as S is not affected
D is not the answer as T is not affected
3(b)(i) An explanation that makes reference to three of the following points:
• glucose passes from glomerulus /
glucose passes into renal / Bowman’s capsule / eq (1)
• reabsorbed / absorbed back into blood / eq (1)
• by active transport / eq (1)
• (reabsorbed) in the proximal convoluted tubule / PCT / first convoluted tubule / eq (1)
3(b)(ii) A description that makes reference to two of the following points:
• add Benedict’s solution (and heat) / eq (1)
• red / orange / yellow / green colour show positive result / eq (1)
3(c) A description that makes reference to the following points:
• less urine / lower volume / less water / eq (1)
• more concentrated / more urea / darker / eq (1)
Question 4:-
Mutation can cause changes in the enzymes produced during protein synthesis.
(a) State what is meant by the term mutation.
(b) Explain the different effects that a single base mutation can have on transcription and translation and the production and activity of an enzyme.
(c) Scientists investigate the rate of spontaneous mutations in yeast.
They record the number of mutations per cell during mitosis and during meiosis.
They count the mutations in three different strains of yeast and repeat each count.
The mutation rates are counted per division per cell.
(i) Calculate the mean mutation rate for strain 5207 during meiosis.
mean rate = …………………………………………………….. × 108 per division per cell
(ii) Suggest why the mutation is calculated per division per cell rather than just per cell.
(iii) Comment on the differences in rates of mutation for mitosis and meiosis in the different yeast strains.
▶️Answer/Explanation
Ans : 4(a) An answer that makes reference to:
• (a rare random) change to DNA / change to gene / change to genetic material / eq (1)
4(b) An explanation that makes reference to five of the following points:
• transcription makes mRNA / eq (1)
• (mRNA will have) different codons / triplets / (base) sequence / order of bases / eq (1)
• different tRNA binds / different amino acids / different anticodon (on tRNA) / eq (1)
• different sequence of amino acids / order of amino acids / chain of amino acids (1)
• different protein / different polypeptide / different structure of protein / different shape of protein / different enzyme / different enzyme properties / eq (1)
• active site no longer fits substrate / ES complexes cannot form / eq (1)
• may have no effect as same amino acid used / similar amino acid used (1)
4(c)(i) 132.6 + 43.2
= 175.8÷2
= 87.9 (× 108) (2)
4(c)(ii) An answer that makes reference to:
• two divisions in meiosis / one division in mitosis / mitosis and meiosis have different numbers of divisions / eq (1)
4(c)(iii) An answer that makes reference to four of the following points:
• meiosis has higher mutation (in all strains) / mitosis has lower mutation / eq (1)
• high(est) difference (between mitosis and meiosis) in 5207 (1)
• small(est) difference between (between mitosis and meiosis) in 5209 (1)
• low(est) mutation rates (for mitosis / meiosis) in 5209 (1)
• high(est) rate for mitosis in 5160 (1)
• high(est) rate for meiosis in 5207 (1)
• differences between repeats of each strain / eq (1)
Question 5:-
The diagram shows the nitrogen cycle with some processes labelled.
(a) (i) Explain why plants need nitrate ions.
(ii) Name the processes V, X and Y.
V…………………………………………………………………………
X ………………………………………………………………………..
Y…………………………………………………………………………
(b) Scientists measure the dissolved nitrate levels in a river that passes through farmland.
They also measure the nitrogen compounds being used on the farmland either as fertiliser or as manure from livestock.
The graph shows how the nitrate levels in the river and the nitrogen compounds applied to the farmland changed from 1950 to 2005.
(i) Comment on the relationship between nitrate levels in the river and the nitrogen compounds applied to the farmland.
(ii) Describe the changes within the river that would have occurred between 1950 and 2000.
▶️Answer/Explanation
Ans : 5(a)(i) An explanation that makes reference to two of the following points:
• to make amino acids / eq (1)
• for protein (synthesis) / eq (1)
• for growth / eq (1)
5(a)(ii) • V nitrogen fixation / nitrogen fixing / nitrogen fixing bacteria (1)
• X nitrification / nitrifying / nitrifying bacteria (1)
• Y denitrification / denitrifying / denitrifying bacteria (1)
5(b)(i) An answer that makes reference to four of the following points:
Descriptions
• both increase / both have similar pattern up to 1970 / eq (1)
• river nitrate more stable than nitrogen on fields / nitrogen on fields fluctuates / nitrogen on fields is more variable / relationship is less clear from 1980 / eq (1)
Explanations
Max 2
• nitrate leaches into river / washed into river / eq (1)
• farmers add different amounts of nitrogen / fertiliser / nitrates to field / eq (1)
• different crops are grown / eq (1)
• river has other sources of nitrate / eq(1)
5(b)(ii) A description that makes reference to three of the following points:
• more algal growth / eutrophication / algal bloom / growth of plants / eq (1)
• (more) decomposers / bacteria / microorganisms / eq (1)
• more turbidity / cloudiness / increased organic waste / less light penetration / eq (1)
• less oxygen in river / anoxic / high BOD / eq (1)
• fewer fish species / death of animals / death of organisms / lower biodiversity / fewer underwater plants / eq (1)
Question 6:-
(a) Describe how stem cells are different from other cell types.
(b) Stem cells from a donor can be used for stem cell therapy.
Human blood cells are produced in bone marrow.
Explain how using stem cells from the bone marrow enables doctors to treat a number of different blood conditions.
(c) One type of stem cell transplant uses a patient’s own stem cells.
They can be used if the patient is producing enough healthy bone marrow cells.
These cells can be collected, frozen and stored for later use.
Explain the advantage of using the patient’s own stem cells rather than using stem cells from a donor.
▶️Answer/Explanation
Ans : 6(a) A description that makes reference to two of the following points:
• undifferentiated / unspecialised / can differentiate / can become specialised cells / eq (1)
• and can become different cell types / eq (1)
• can continue to divide / continue to multiply / can divide several times / eq (1)
6(b) An explanation that makes reference to three of the following points:
• can make different (blood) cells / red cells and white cells / red cells and platelets / white cells and platelets (1)
Max two from:
• red blood cells to treat anaemia / ensure oxygen transport around body / eq (1)
• white blood cells to kill infections / kill bacteria / remove viruses / improve immunity / increase antibodies / eq (1)
• platelets to treat blood clotting problems / eq (1)
• any one blood cell type to treat bone marrow cancer / treat leukaemia / treat lymphoma / treat myeloma / recover from chemotherapy / eq
6(c) An explanation that makes reference to two of the following points:
• have same proteins / antigens / eq (1)
• genetically identical / same genes / eq (1)
• no rejection / immune response / no need for immunosuppressant drugs / cells are accepted by body / cells are compatible / cells have same blood group / eq (1)
• no transfer of other disease / infections / viruses (1)