Question 1
1 Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.
Supercharging plants to reduce global warming
The proportion of carbon dioxide in the atmosphere has increased in the last 100 years. In 2020, a mass of 727 gigatonnes of carbon dioxide was released into the atmosphere from natural processes, along with a mass of 37 gigatonnes from human activities. Scientists have estimated that plants naturally remove a mass of 746 gigatonnes of carbon dioxide from the atmosphere every year. The difference between what is removed and what is released causes atmospheric carbon dioxide to rise every year. Carbon dioxide is a greenhouse gas, and a significant rise will cause global warming.
To help solve the problem of rising concentrations of atmospheric carbon dioxide, scientists are planning to produce transgenic, supercharged plants that can remove atmospheric carbon dioxide and store it in their roots. The scientists estimate that if these plants can be developed, the plants could remove a mass of carbon dioxide equivalent to 50% of the emissions from human activities.
Coastal plants that have their roots in seawater contain a substance called suberin in the cell walls of the outer layer of the roots. Suberin is a waterproof substance that contains a high proportion of carbon atoms. Suberin is decomposed very slowly so remains in the soil for a long time.
The photograph shows a coastal plant called a mangrove.
To produce the supercharged plants, scientists intend to take the gene that codes for high suberin production from a coastal plant and insert it into crop plants. The crop plants used are perennial plants. Perennial plants live for many years rather than dying each winter. The transgenic crops would take in large amounts of carbon dioxide and use the carbon atoms to make suberin. The carbon would then be locked up and stored as suberin in the roots. After successfully producing one plant, they will use micropropagation rather than pollination to produce others.
These supercharged crop plants may have other uses. Suberin in roots helps to make them tolerant to soil with a high salt concentration, helping to produce higher crop yields in areas that have difficult growing conditions.
(a) (i) Carbon dioxide is a greenhouse gas.
State the name of another greenhouse gas (line 7).
(ii) Calculate the increase in mass, in kg, of atmospheric carbon dioxide in 2020 (lines 2 to 7).
Give your answer in standard form.
[1 gigatonne = 1000000000 000kg]
Increase in mass = …………………………………………………….. kg
(iii) State two consequences of global warming for the environment.
(b) Explain why producing genetically engineered plants with additional suberin in their roots could reduce atmospheric carbon dioxide (lines 14 to 17 and lines 19 to 24).
(c) Which enzyme is used to remove a gene from a section of DNA?
A amylase
B ligase
C lipase
D restriction
(d) Explain why the additional suberin in the cell walls of the roots will make the transgenic plants tolerant to soil with a high salt concentration (lines 26 to 28).
(e) Give three reasons why the scientists use micropropagation to reproduce the transgenic crop plants (lines 24 to 25).
▶️Answer/Explanation
1 (a)(i) methane / nitrous oxides / CFCs / water vapour / eq (1)
1 (a)(ii) 1.8 x 1013 (3)
1(a)(iii) An answer that makes reference to two of the following.
- ice (caps) melt / glaciers melt / eq (1)
- flooding / sea level rises / eq (1)
- loss of habitat / desertification / droughts (1)
- extinctions / disrupted food chains / migration of species / damaged ecosystems / decreased plant yields / decreased productivity / eq (1)
- destruction of coral reefs / coral bleaching / eq (1)
- spread of disease / pests / pathogens / eq (1)
- extreme weather / climate change / changes in weather patterns / eq (1)
1 (b) An explanation that makes reference to four of the following.
- plants take in / absorb, carbon dioxide (1)
- for photosynthesis (1)
- carbon (dioxide) is converted into / stored as suberin / locked up in suberin / eq (1)
- suberin does not decay for long periods / suberin decomposes slowly / suberin remains for long period of time / eq (1)
- perennial plants remain for long periods of time / do not die off / grow for many years / don’t die each year / don’t have to be replanted / eq (1)
- slower / less carbon dioxide is released from decomposition / decay / (respiration of) decomposers (1)
1 (c) The only correct answer is D
A is incorrect as the amylase digests starch
B is incorrect as ligase sticks DNA
C is incorrect as lipase digests fats
1 (d) An answer that makes reference to two of the following.
- prevent water loss (1)
- (due to) osmosis (1)
- when water moves from a higher water potential to a lower water potential / eq prevents plant cells becoming flaccid / wilting / stay turgid (1)
1 (e) An answer that makes reference to three of the following.
- produce large numbers / large scale /eq (1)
- fast (process) / quick(er) / eq (1)
- all crops produce suberin / all plants are (genetically) identical / all clones / eq / (1)
- less risk of cross pollinating (with wild plants) / pollinating wild plants / spreading (trans)gene into wild / eq (1)
- can be done at, any time of year / all year / eq (1)
Question 2
2 A student uses this method to investigate the nitrogen cycle.
• take two samples of soil, each of mass 100g
• sterilise one sample of soil by heating at 100°C for one hour
• place the sterilised and unsterilised samples into separate filter funnels
• pour 25cm3
of water through each soil sample and collect the filtrate in a
test tube
• test each filtrate for nitrates
• pour water through each soil sample for 5 minutes
• pour another 25cm3
of water through each soil sample and collect the filtrate in a
test tube
• test each filtrate for nitrates
• add 1cm3
of a solution of ammonium salts to each soil and leave for three days
• pour 25cm3
of water through each soil sample again and collect the filtrate in a
test tube
• test each filtrate for nitrates
The diagram shows the student’s apparatus.
The table shows the student’s results.
(a) Give the independent variable in the investigation.
(b) (i) Suggest why the student poured water through the soil samples for five minutes before adding the ammonium salts.
(ii) Comment on the results of the nitrate tests on the two soil samples three days after adding ammonium salts.
▶️Answer/Explanation
2(a) An answer that makes reference to one of the following.
- sterilised / unsterilised / eq (1)
- presence of bacteria / absence of bacteria / eq (1)
- heated / unheated soil / eq (1)
- soil sample / soil used (1)
2 (b)(i) An answer that makes reference to two of the following.
- remove / dissolve / wash away nitrate present / get rid of nitrates / eq (1)
- (so any) nitrate made must have been from the ammonium salt / are due to ammonium salts / eq (1)
- so a fair comparison is made / so the test is valid / so the test is fair (1)
2 (b)(ii) An answer that makes reference to four of the following.
- nitrates present in unsterilised soil(1)
- nitrates produced /made from ammonium / ammonia (1)
- nitrifying bacteria / nitrification (1)
- ammonium is converted into nitrite / nitrite is converted into nitrate (1)
- nitrates not present in sterilised soil because there are no bacteria / bacteria were dead / killed / removed (1)
- not repeated / no measure of quantity of nitrates / qualitative not quantitative (1)
Question 3
The diagram shows a single-celled organism called Chlorella that lives in fresh water.
Chlorella has a chloroplast and can photosynthesise.
(a) (i) Which of these groups of organisms contains Chlorella?
A animals
B bacteria
C plants
D protoctists
(ii) Which of these labelled structures would also be present in an animal cell?
A cell membrane and chloroplast
B cell membrane and mitochondrion
C cell wall and chloroplast
D cell wall and mitochondrion
(b) Complete the balanced chemical symbol equation for photosynthesis.
(c) The graph shows the effect of light intensity on gas exchange by Chlorella.
(i) Explain why Chlorella takes in oxygen at light intensities below 10 arbitrary units.
(ii) Explain the changes in the volume of oxygen released as the light intensity increases from 10 arbitrary units.
(iii) The volume of oxygen released by Chlorella is the difference between the oxygen produced by photosynthesis and the oxygen taken in.
Use the graph to calculate the volume of oxygen produced in five minutes by photosynthesis at a light intensity of 50 arbitrary units.
volume of oxygen = …………………………………………………….. mm3
(d) Describe how hydrogen-carbonate indicator could be used to investigate the
effect of light intensity on carbon dioxide exchange by Chlorella.
▶️Answer/Explanation
3 (a)(i) The only correct answer is D (protoctists)
A is incorrect as the animals do not have chloroplasts
B is incorrect as bacteria do not have nuclei
C is incorrect as plants are multicellular
3 (a)(ii) The only correct answer is B (cell membrane and
mitochondrion)
A is incorrect as animal cells do not have chloroplasts
C is incorrect as animal cells do not have chloroplasts
D is incorrect as animal cells do not have cell walls
3 (b)
- one mark for 6CO2 + 6H2O (on LHS) (1)
- one mark for C6H12O6 (on RHS) (1)
3 (c)(i) An explanation that makes reference to two of the following.
- low / less / no light (1)
- photosynthesis is slower than respiration / photosynthesis is less than respiration / respiration is faster than photosynthesis / eq (1)
- more oxygen taken in than released / more oxygen used than produced / there is a net movement of oxygen in / eq (1)
3 (c)(ii) An explanation that makes reference to three of the following.
- at 10 (au) respiration (rate) and photosynthesis (rate) are equal / at the compensation point respiration and photosynthesis are equal (1)
- rate of photosynthesis increases (as light intensity increases) (1)
- photosynthesis rate is greater than respiration rate (1)
- levels off / eq, because another factor / temperature / carbon dioxide is limiting (1)
3(c)(iii) two marks for 48 (2)
3 (d) A description that makes reference to three of the following.
- move lamp different distances / eq(1)
- place same mass / number /volume / concentration Chlorella /algae, in (hydrogen-carbonate indicator) (1)
- same volume / concentration of indicator / same temperature /leave for same or stated time /same starting colour of indicator / use a control tube (with no Chlorella) (1)
- (indicator turns) yellow with low light / covered tube / and red /purple with high light / uncovered tube (1)
Question 4
The diagram shows part of the human urinary system.
(a) Name the structures labelled A and B.
(b) The diagram shows a kidney nephron.
The table shows the relative concentrations of glucose and protein in the areas labelled X, Y and Z on the diagram.
(i) Explain the difference between the concentration of protein in area X and the concentration of protein in area Y.
(ii) Explain the difference between the concentration of glucose in area Y and the concentration of glucose in area Z.
(c) When the body becomes dehydrated, the concentration of urine increases.
Explain the changes that occur in the body that lead to the production of concentrated urine.
▶️Answer/Explanation
4 (a) A: ureter (1)
B: bladder (1)
4 (b)(ii) An answer that makes reference to two of the following.
- glucose is reabsorbed / absorbed into the blood / selectively reabsorbed (1)
- at the proximal convoluted tubule / pct / eq (1)
- by active transport / uptake (1)
4 (c) An explanation that makes reference to four of the following.
- hypothalamus detects /osmoreceptors detect high (salt) concentration of blood / low water of blood (1)
- pituitary releases ADH / eq (1)
- collecting duct (1)
- increased permeability (1)
- more water (re)absorbed / enters blood / eq (1)
Question 5
Pineapple juice contains a protease called bromelain.
A student uses this method to investigate the digestion of solid gelatine protein by bromelain.
• place solid gelatine protein into a test tube up to a height of 5cm
• mix 5cm3 pineapple juice with 1cm3 of pH 4 buffer
• place 1cm3 of the pineapple juice and buffer solution on top of the gelatine
• leave for one hour in a water bath set to 37°C
• measure the height of the solid gelatine and use it to calculate the volume of gelatine that has been digested
Repeat the method three more times.
The diagram shows part of the student’s method.
(a) The table shows the student’s results for the volumes of gelatine digested at pH 4.
(i) Calculate the mean volume of gelatine digested in cm3 .
Give your answer to two decimal places.
mean volume = …………………………………………………….. cm3
(ii) State what substances are produced when the gelatine protein is digested.
(b) The student repeats the investigation with different pH buffers.
The table shows their results.
(i) Give two variables the student should control.
(ii) Explain the effect of changing the pH on the mean volume of gelatine digested.
(c) Describe how to test for the presence of protein.
▶️Answer/Explanation
5 (a)(i) 0.57 (3)
0.57 gains all three marks Accept 0.90 for two marks
OR
Accept 0.56 or 0.56(66666….7) or 0.56
recurring for two marks
Accept 0.9 or 0.8975 or 1.7 or ÷3 for one mark
Example calculation (not mark points):
(0.55 + 0.54 + 0.61) = 1.7
÷ 3
to two dp
Correct answer with no working gains all three marks.
5 (a)(ii)
- amino acids / peptides (1)
5 (b)(i) An answer that makes reference to two of the following.
- temperature (1)
- height / volume / mass /concentration of gelatine / protein/ eq(1)
- volume / concentration, of, enzyme /bromelain / pineapple juice / eq (1)
- volume of buffer (1)
- time (in incubator) (1)
- surface area of gelatine / SA:vol ratio / width of tube (1)
5 (b)(ii) An explanation that makes reference to three of the following.
- volume digested increases up to (pH) 5 then decreases (above 5) / volume digested decreases above and below 5 / eq (1)
- optimal pH / optimum pH (1)
- (away from optimal pH / 5) enzyme denatures / (active site) shape changes / eq (1)
- substrate no longer binds / fits / shape not complementary to substrate (1)
5 (c) A description that makes reference to the following.
- add biuret (reagent) / add biuret A and biuret B / sodium hydroxide & copper sulfate (1)
- turns lilac / purple / pink / mauve / eq (1)
Question 6
Beta thalassaemia is a genetic condition caused by a mutation in a gene for haemoglobin.
People with beta thalassaemia produce less haemoglobin and fewer red blood cells than people without the condition.
(a) Explain why people with beta thalassaemia may experience severe tiredness.
(b) A new treatment for beta thalassaemia has been developed that edits the haemoglobin gene. These are the steps in the treatment.
• remove blood stem cells from a patient’s bone marrow
• put a strand of RNA and an enzyme into the blood stem cells to correct the haemoglobin gene
• use drugs to destroy the patient’s remaining bone marrow cells
• replace the patient’s bone marrow cells with the modified stem cells
The modified stem cells that are in the bone marrow now produce red blood cells containing sufficient haemoglobin.
(i) The strand of RNA used in this treatment is complementary to one strand of the DNA in the haemoglobin gene.
Give the base sequence of RNA that is complementary to this sequence of DNA.
DNA strand A A T G G C G G C T C A
RNA strand
(ii) Protein synthesis of the modified gene will produce haemoglobin.
Describe the stages of this protein synthesis.
(iii) The standard treatment for beta thalassaemia is a weekly blood transfusion.
The new treatment has so far been tested on two patients, with these results.
• both patients started making large numbers of red blood cells with sufficient haemoglobin
• both patients experienced serious side effects from the drugs used, needing to spend several months in isolation in hospital before recovering
• 15 months after the treatment, neither patient required further blood transfusions
• both patients were able to exercise normally without feeling tired
Evaluate the use of the new treatment compared to weekly blood transfusions.
▶️Answer/Explanation
6 (a) An explanation that makes reference to two of the following.
- less oxygen (transported) (1)
- to muscles (1)
- less respiration / less ATP production / less energy release / more lactic acid / more anaerobic respiration (1)
6 (b)(i) UUACCGCCGAGU (2)
6 (b)(ii) A description that makes reference to four of the following.
- transcription occurs in nucleus (1)
- production of messenger RNA / mRNA (from DNA) (1)
- translation occurs on ribosome / mRNA binds to ribosome / mRNA goes to ribosome (1)
- tRNA brings / has amino acids (1)
- codon binds to anticodon / codons are complementary to anticodons / (complementary) triplets on tRNA and mRNA bind / eq (1)
- polypeptide produced / amino acids joined together /amino acid chain produced / eq (1)
6 (b)(iii) An answer that makes reference to four of the following.
Pros (max 3)
- patients produce red blood cells / can exercise / are not breathless / have more energy / eq (1)
- independent life / transfusions not needed / better quality of life / no need to keep visiting hospitals / eq (1)
- no rejection (1)
- less risk of infectious disease (from blood) (1)
- permanent treatment / long lasting / lasts a lifetime / cure /works for at least 15 months (1)
Cons (max 3)
need to spend long time in isolation (for treatment) / eq(1)
side effects (1)
small sample size / only tested on two people / needs further testing / more repeats / eq (1)
could cause mutations in DNA / cause cancers (1)
need to be tested for more than 15 months / for longer / eq (1)