Edexcel iGCSE Biology 4BI1 - Paper 2B -Genetic modification- Exam Style Questions- New Syllabus

Question

Apples contain an enzyme called phenol oxidase.

When apple tissue is exposed to oxygen in the air, this enzyme turns the apple tissue brown.

(a) A student uses this method to investigate the effect of pH on the time taken for apple tissue to turn brown.

mash an apple to produce a pulp
place 25 g of this pulp into a beaker
mix a pH 7 buffer with the pulp to maintain the pH
check the colour of the pulp every five minutes
record the time when the pulp turns brown

The student repeats this method using pH buffers of 3, 5, 9, and 11.

The graph shows the student’s results.

(i) Calculate the percentage increase in time taken for the apple pulp to turn brown at pH 11 compared with the time taken at pH 7.
(ii) Explain why the change in pH affects the time taken for the apple pulp to turn brown.
(iii) Explain how the student could modify this method to give a more accurate measure of the time taken for the apple pulp to turn brown.

(b) A genetically modified (GM) variety of apple has been produced that does not turn brown when exposed to air.

These apples have a gene in their DNA that produces a section of mRNA with a complementary sequence to the mRNA for the phenol oxidase gene.

(i) State two differences between DNA and mRNA.
(ii) Explain why these GM apples do not turn brown when the apple tissue is exposed to air. Use your knowledge of protein synthesis to support your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(c): Biological molecules — parts (a)(ii), (b)(ii)
• 2(c): Enzymes as biological catalysts — parts (a)(ii), (a)(iii)
• 3(b): Inheritance — parts (b)(i), (b)(ii)
• 5(c): Genetic modification (genetic engineering) — part (b)(ii)
• Appendix 3: Mathematical skills — part (a)(i)

▶️ Answer/Explanation

Solution

(a)(i)

• 1400 (%) (2)

One mark for 75 ÷ 5 = 15 OR 70 ÷ 5 = 14

Calculation: Time at pH 11 = 75 minutes, Time at pH 7 = 5 minutes

Percentage increase = \(\frac{75 – 5}{5} \times 100 = \frac{70}{5} \times 100 = 14 \times 100 = 1400\%\)

(a)(ii)

An explanation that makes reference to three of the following points:

1. optimum pH is 7 (1)

2. (pH causes) enzyme to denature (1)

3. shape of enzyme changes / shape of active site changes (1)

4. substrate does not fit active site / enzyme no longer complementary / cannot form enzyme-substrate complexes (1)

(a)(iii)

An explanation that makes reference to two of the following points:

1. use a colour matching chart / light sensor / colorimeter (1)

2. (because) colour change is subjective / to standardise the end colour / so colour is always same (1)

3. use intervals of shorter than 5 minutes / shorter intervals / check more often / check colour constantly (1)

(b)(i)

An answer that makes reference to two of the following points:

1. DNA is double stranded / RNA is single stranded (1)

2. DNA has T (thymine) / RNA has U (uracil) (1)

3. DNA is a helix / RNA is not a helix (1)

4. DNA has deoxyribose / RNA has ribose (1)

(b)(ii)

An explanation that makes reference to four of the following points:

1. (complementary) RNA binds to the phenol oxidase RNA (1)

2. translation cannot occur (1)

3. so enzyme / phenol oxidase not made (1)

AND

Maximum three from:

4. transcription makes mRNA (1)

5. RNA leaves nucleus and enters cytoplasm / RNA moves to ribosome (1)

6. tRNA brings / carries / transports amino acids (1)

7. (during translation) tRNA binds mRNA / anticodons bind codons (1)

8. amino acids join / amino acid chain / makes polypeptide / peptide bonds form (1)

Question

The photograph shows a fish called tilapia. This type of fish is often grown in fish farms.

(a) Tilapia are a good source of nutrients for humans.

The table shows the percentage of the daily requirements for humans of three nutrients provided by a portion of tilapia.

Nutrient group	Percentage of daily requirement provided by a portion of tilapia
lipids	16
protein	38
carbohydrate	16

(i) Use the table to determine the ratio of lipid to protein to carbohydrate.

Give your answer in the form \(1 : n : 1\)

(ii) Describe how to test a sample of tilapia to show the presence of lipid.

(iii) State one function of protein in the human body.

(b) Scientists have produced genetically modified (GM) tilapia that grow faster.

Scientists investigate the growth of these GM tilapia compared with non-genetically modified (non-GM) tilapia.

This is the scientists’ method.

set up two equally sized tanks containing water
put non-GM tilapia into one tank
put an equal mass of GM tilapia into the second tank
feed the fish in each tank the same mass of protein pellets

The mass of each type of fish was measured at the start of the investigation and after seven months.

A measure called the feed conversion index was also calculated for each type of fish.

The table shows the scientists’ results.

Type of fish	Total starting mass of fish in g	Total mass of fish after seven months in g	Feed conversion index
non-GM	1250	2830	1.9
GM	1250	3750	1.2

(i) The mean rate of increase in mass of the non-GM tilapia during the seven months is \(226 \, \text{g}\) per month.

Calculate the mean rate of increase in mass, in g per month, of the GM tilapia.

Give your answer to three significant figures.

(ii) The feed conversion index is a measure of the mass of protein pellets used compared with the increase in mass of tilapia.

It is calculated using this formula.

\(\text{feed conversion index} = \frac{\text{total mass of protein pellets used}}{\text{increase in mass of tilapia}}\)

Use the information in the table to calculate the mass of protein pellets given to the non-GM tilapia.

(iii) Suggest why the GM tilapia have a lower feed conversion index than the non-GM tilapia.

(iv) Both groups of fish were fed the same mass of pellets and placed into the same sized tanks of water.

Give one other abiotic factor that the scientists should keep constant.

(v) The scientists conclude that farming GM tilapia is better for the environment than farming non-GM tilapia. This is because the GM tilapia would result in less nitrate in the water and cause less spread of disease. Evaluate this conclusion.

Use the information in the table and your own knowledge in your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(c): Biological molecules — parts (a)(ii), (a)(iii)
• 2(e): Nutrition — part (a)(i), (a)(iii)
• 5(a): Food production (Fish farming) — parts (b)(i), (b)(ii), (b)(iii), (b)(iv), (b)(v)
• 5(c): Genetic modification (genetic engineering) — parts (b)(i), (b)(iii), (b)(v)
• 4(a): The organism in the environment (Abiotic factors) — part (b)(iv)

▶️ Answer/Explanation

Solution

(a)(i) \(1 : 2.4 : 1\)
Accept \(1: 2.375: 1\)

(a)(ii) A description that makes reference to the following points:
• ethanol / alcohol and add water (1)
• goes white / cloudy / white emulsion forms / milky / eq (1)
OR
• add Sudan III (1)
• red colour (in top layer) (1)
Accept alternative method: rub on paper / eq (1); paper goes transparent / clear / eq (1)

(a)(iii) • growth / repair / enzymes / build muscle / antibodies / eq (1)

(b)(i) • \(357 \, \text{g per month}\) (2)
Correct answer gains both marks.
Accept one mark for:
\(2500\) (increase) or division by \(7\) or \((3750-1250)\) or \(357.14…\)

(b)(ii) • \(3002 / 3000 \, \text{g}\) (1)

(b)(iii) An answer that makes reference to two of the following points (1 mark each):
• (GM fish) grow more / bigger / faster / eq
• produce less faeces / can digest more efficiently / absorb more / eq
• less respiration / lower metabolic rate / eq
• move less / slower swimming / eq
• eat more food / less food wasted / eq

(b)(iv) • temperature / light (intensity) / oxygen / salinity / pH / eq (1)

(b)(v) An evaluation that makes reference to the following points (up to 5 marks):
1. GM fish grow bigger/faster/harvest sooner / eq (1)
2. less food wasted / more food eaten / eq (1)
3. less faeces / urea / excretion / ammonia / eq (1)
4. less decomposition / fewer decomposers / eq (1)
5. less nitrification / fewer nitrifying bacteria / eq (1)
6. less eutrophication / algal growth / plant growth / eq (1)
7. less oxygen loss / more oxygen in water / eq (1)
8. due to less (bacterial) respiration / (more oxygen for) respiration of animals / eq (1)
9. no information about disease spread / pathogen spread / eq (1)
10. GM fish are (genetically) similar so may be more likely to catch/spread disease / eq (1)
11. not repeated / need more experiments / no idea of sample size / eq (1)
12. (GM) fish that escape may harm food chains / outcompete wild fish / may breed with wild fish / eq (1)
13. did not measure nitrates / eq (1)

Question

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Offshore or freshwater fish farming

Fish farming in fresh water and in the sea offers the potential to increase the amount of fish harvested whilst protecting wild fish stocks. Offshore or fish farming at sea has less risk of serious injury or death to people than catching fish by deep sea fishing.

Some scientists predict that smart fish farming at sea could increase ocean fish production by an estimated 21 million tonnes from the 2020 value to 44 million tonnes by 2050. Other estimates suggest that fish farming at sea, using an area the size of Lake Michigan, might produce the same amount of seafood as all of the world’s wild-caught fisheries.

Fish farming at sea is done anywhere from three to 200 miles away from the coast. The fish produced are often Atlantic salmon, seabass and cobia. The aim is to reduce the environmental impact of fish farming near the coast by moving them further away from sensitive shorelines. This limits the impact of disease, pollution and pests such as sea lice. Further out to sea, and at deeper depths, the water movement is often faster.

Critics of fish farming at sea claim that it will be more difficult to monitor and regulate any environmental impact and that pollution, disease and pests would still impact the surrounding waters. A major risk of farming at sea is the exposure to high winds and water speeds, increasing the risk of all the fish escaping. In 1997, 300 000 farmed Atlantic salmon escaped into the Pacific Ocean. Wild fish are attracted to the farms by the scent of fish food. These wild fish are at risk of being hit by ships travelling to and from the large fish farms.

In contrast, other scientists support the development of fish farming in fresh water. Freshwater fish farms have increased in numbers steadily in the past 30 years. Asia is the main part of the world where this has happened. It is relatively cheap and easy to grow freshwater fish in small ponds. Fish farming provides incomes for many family farms, workers and small businesses, as well as jobs.

The main species produced by freshwater farming are carp, tilapia and catfish. These fish are herbivores or omnivores. In the farms they are fed small amounts of fish to speed up growth, but their main diet is the by-products of crops like rice, groundnut and soy. Farmed freshwater fish are an affordable food for millions of low- and middle-income consumers.

(a) Suggest why deep sea fishing has a risk of serious injury or death to people. (lines 2 to 3)

(b) Give three reasons why the scientists’ prediction of an increase in ocean fish production to 44 million tonnes by 2050 is only an estimate. (lines 4 to 6)

(c) Explain how fish farms cause pollution. (lines 12 to 16)

(d) Fish farmers use methods to control disease in their fish farms.

(i) Describe the methods a fish farmer could use to reduce the incidence of disease in a fish farm.
(ii) Explain how these methods may affect the local ecosystem.

(e) Explain why locating the fish farms further out to sea may help reduce the effects on the local ecosystem. (lines 12 to 16)

(f) Suggest why fish farming further out at sea will be more difficult to monitor and regulate. (lines 14 to 16)

(g) Give a reason why farming fish that are herbivores is an advantage for the fish farmer. (lines 27 and 28)

(h) Explain why small, local freshwater fish farms would have less impact on global warming than large fish farms at sea.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 4(d): Human influences on the environment — parts (c), (e)
• 5(a): Food production (Fish farming) — parts (a), (b), (d)(i), (d)(ii), (f), (g), (h)
• 5(b): Selective breeding — part (d)(i)
• 5(c): Genetic modification — part (d)(i)

▶️ Answer/Explanation

Solution

(a) • drowning / being washed overboard / sinking / storms / (bad) weather / attacked / killed by sharks by predators / eq (1)

(b) An explanation that makes reference to three of the following points: (3)
1. only based on forecasts / model / not happened yet / can’t predict future / 30 years is a long way off / not guaranteed / eq (1)
2. other (scientists) have different view / only an opinion / government policy may change / eq (1)
3. amount of sea farms may change / may not work / unproven / untested / eq (1)
4. peoples’ tastes may changes / diet / choices / demand for fish may change / eq (1)
5. effect of climate change / sea temperature rising / levels rising / global warming /eq (1)
6. effect of pollution / eq (1)

(c) An explanation that makes reference to three of the following points: (3)
1. (fish) faeces / waste / uneaten food /eq (1)
2. nitrate / phosphate levels increase / eq (1)
3. leads to algal growth / eutrophication / (eq)
4. less oxygen (for respiration)/ oxygen used (by bacteria) / eq (1)
5. chemicals / hormones /eq (1)
6. bacteria / decomposers / eq (1)

(d)(i) A description that makes reference to two of the following points: (2)
1. pesticide / insecticide / fungicide / eq (1)
2. antibiotics / vaccinate fish / eq (1)
3. selective breeding / GM fish / eq (1)
4. separating / isolating diseased fish / removing sick / dead fish / eq (1)
5. low stocking density /eq (1)

(d)(ii) An explanation that makes reference to two of the following points: (2)
1. pesticide / insecticide / fungicide/ antibiotic / kill other organisms / disrupt food chain /eq (1)
2. (pesticide / insecticide / fungicide / antibiotics ) can (bio)accumulate / eq (1)
3. (antibiotics) lead to antibiotic resistance / eq (1)
4. selective bred / GM organisms may escape and interbreed / eq (1)

(e) An explanation that makes reference to two of the following points: (2)
1. deep water / greater volume / eq (1)
2. (so) dilution / reduces concentration / eq (1)
3. fast water flowing / eq (1)
4. (so) dispersed / carried away / eq (1)

(f) An answer that includes: (1)
• further from shore / further from land / isolated / longer distance to travel / no population nearby / need to use boat to reach / take a long time to get there / eq (1)

(g) An answer that includes one of: (1)
• is cheaper / use cheaper food (readily available) / surplus food / crop waste /eq (1)
• more efficient energy transfer / eq (1)
• will not eat each other / other fish / eq(1)

(h) An explanation that makes reference to two of the following points: (2)
• less fuel / less transport of equipment /supplies / workers / less food miles / eq (1)
• less energy used / less electricity / less machinery (in running / building) / eq (1)
• less carbon dioxide released (from burning the fossil fuel) / eq (1)

Total = 17 marks

Question

Scientists have genetically modified soya plants so that the soya beans they produce contain less saturated fat.

The scientists produced one transgenic soya plant. Micropropagation was then used to make multiple copies of this transgenic soya plant.

(a) Explain why micropropagation was used to produce copies of the transgenic soya plant.

(b) A student uses this equipment to compare the energy content of transgenic soya beans with the energy content of non-transgenic soya beans.

(i) Describe how the student could use the equipment to make a valid comparison of the energy content of the two types of soya bean.

(ii) Give one safety precaution that the student should take when using the apparatus.

(iii) The diagram shows a different type of apparatus that can be used for the investigation.

Explain two reasons why this apparatus will give a more accurate energy value than the apparatus used by the student.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 5(c): Genetic modification (genetic engineering) — part (a)
• 5(d): Cloning — part (a)
• 2(e): Nutrition — part (b)(i), (b)(iii)
• Appendix 6: Suggested practical investigations — part (b)(i), (b)(iii)
• 2.33B practical: investigate the energy content in a food sample — part (b)

▶️ Answer/Explanation

Solution

(a) Micropropagation was used because it produces genetically identical plants (clones) that all contain the modified gene for reduced saturated fat. This ensures consistency in the desired trait without the need to repeat the complex genetic modification process. Additionally, since only one transgenic plant was initially created, micropropagation provides a rapid method to produce many copies regardless of season, avoiding the limitations of traditional breeding.

(b)(i) To make a valid comparison, the student should:

Use the same mass of each type of soya bean (or calculate energy per gram)
Use the same volume (or mass) of water in the boiling tube
Ignite each bean completely and hold it at a consistent distance under the boiling tube to heat the water
Measure the temperature change of the water (initial and highest temperature)
Repeat the experiment multiple times to calculate average values and ensure reliability

(b)(ii) One important safety precaution is to wear eye protection to prevent injury from potential splashes or flying fragments when heating the beans.

(b)(iii) This advanced apparatus provides more accurate results because:

Oxygen supply: The oxygen gas inlet ensures complete combustion of the soya bean, preventing incomplete burning that would yield inaccurate energy measurements.
Insulation: The insulated outer container minimizes heat loss to the surroundings, ensuring that more of the generated heat is transferred to the water and measured.
Stirring mechanism: The stirrer distributes heat evenly throughout the water, preventing hot spots and ensuring a more accurate temperature measurement.
Contained ignition: The internal ignition coil allows the bean to burn completely within the apparatus without needing to be moved, reducing heat loss during transfer.

Question

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.

(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.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(h): Transport — part (a)
• 3(b): Inheritance — parts (b)(i), (b)(ii)
• 5(c): Genetic modification (genetic engineering) — part (b)(i), (b)(ii)
• 5(d): Cloning — part (b) context
• 3(b): Inheritance — part (b)(iii) (evaluation of treatment)

▶️ Answer/Explanation

Solution

(a)

Answer: 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)

Detailed Explanation:

People with beta thalassaemia produce less haemoglobin, which is the protein in red blood cells responsible for carrying oxygen. Since there are fewer red blood cells and less haemoglobin, the blood’s overall oxygen-carrying capacity is significantly reduced. This means that less oxygen is delivered to the body’s tissues, particularly to active muscles.

Oxygen is essential for aerobic respiration, the process that efficiently releases energy (in the form of ATP) from glucose. When oxygen is limited, cells are forced to rely more on anaerobic respiration. Anaerobic respiration releases much less energy per glucose molecule and also produces lactic acid as a waste product, which can lead to muscle fatigue and pain. The combination of reduced ATP (energy) production and the buildup of lactic acid results in the severe tiredness and weakness experienced by individuals with this condition.

(b)(i)

Answer: UUACCGCCGAGU (2)

Detailed Explanation:

To find the complementary RNA sequence, you need to remember the base pairing rules. In RNA, adenine (A) pairs with uracil (U) (instead of thymine, as in DNA), and guanine (G) pairs with cytosine (C).

Let’s go through the DNA strand base by base:

DNA A → RNA U
DNA A → RNA U
DNA T → RNA A
DNA G → RNA C
DNA G → RNA C
DNA C → RNA G
DNA G → RNA C
DNA G → RNA C
DNA C → RNA G
DNA T → RNA A
DNA C → RNA G
DNA A → RNA U

Putting it all together, the complementary RNA strand is U U A C C G C C G A G U.

(b)(ii)

Answer: 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)

Detailed Explanation:

Protein synthesis occurs in two main stages: transcription and translation.

1. Transcription: This first stage takes place inside the nucleus. The DNA double helix unwinds at the specific gene that codes for haemoglobin. The enzyme RNA polymerase uses one strand of the DNA as a template to build a complementary strand of messenger RNA (mRNA). This process follows base-pairing rules (A with U, T with A, G with C, C with G). Once the mRNA strand is complete, it detaches from the DNA, which rewinds, and the mRNA molecule leaves the nucleus through a nuclear pore and enters the cytoplasm.

2. Translation: This second stage occurs on ribosomes in the cytoplasm. The mRNA molecule binds to a ribosome. The ribosome reads the mRNA sequence in groups of three bases called codons. Transfer RNA (tRNA) molecules, each carrying a specific amino acid, have a three-base anticodon that is complementary to the mRNA codon. The tRNA molecules bring the correct amino acids to the ribosome in the order specified by the mRNA sequence. As the ribosome moves along the mRNA, it links the amino acids together with peptide bonds, forming a growing polypeptide chain. This chain continues to grow until a stop codon is reached on the mRNA, at which point the completed haemoglobin polypeptide is released.

(b)(iii)

Answer: 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)

Detailed Explanation:

Advantages of the New Treatment:

The new gene therapy treatment offers significant potential benefits. It appears to be a long-term or even permanent solution, as evidenced by patients not needing transfusions for 15 months post-treatment. This eliminates the lifelong dependency on weekly blood transfusions, freeing patients from frequent hospital visits and the associated disruptions to their daily lives. Using the patient’s own modified cells eliminates the risk of immune rejection, a common problem with organ or tissue transplants. Furthermore, it removes the risk of contracting infectious diseases from donated blood. The results showing patients could exercise normally indicate a vastly improved quality of life and physical capability.

Disadvantages and Risks of the New Treatment:

However, the treatment carries serious risks and limitations. The drugs used to destroy the existing bone marrow caused severe side effects, requiring a long and isolating hospital stay, which is physically and emotionally taxing. The sample size of only two patients is very small, making it difficult to be certain about the treatment’s effectiveness and safety for the wider population. There is a potential risk that the gene editing process could cause unintended mutations in the DNA, which might lead to other health issues, including cancer. The 15-month success period, while promising, is not long enough to confirm it is a true lifelong cure, and longer-term monitoring is essential. In contrast, while weekly transfusions are inconvenient and carry their own risks (like infection or iron overload), they are a well-established and predictable treatment.

In conclusion, the new treatment is a promising potential cure that could greatly improve quality of life, but it is currently associated with significant short-term risks and its long-term safety and efficacy are still unknown due to limited testing.

Question

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 = 1 000 000 000 000 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).

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 4(d): Human influences on the environment — part (a)(i), (a)(iii)
• 4(c): Cycles within ecosystems — part (a)(ii), (b)
• 5(c): Genetic modification (genetic engineering) — part (c)
• 2(d): Movement of substances into and out of cells — part (d)
• 5(d): Cloning — part (e)
• Appendix 4: Mathematical skills — part (a)(ii)

▶️ Answer/Explanation

Solution

(a)(i) Methane / nitrous oxides / CFCs / water vapour

Explanation: Greenhouse gases are those that trap heat in the Earth’s atmosphere, contributing to the greenhouse effect. While carbon dioxide is the most commonly discussed, other significant greenhouse gases include methane (released from livestock and landfills), nitrous oxides (from agriculture and industrial processes), chlorofluorocarbons or CFCs (from refrigerants and aerosols, though now largely phased out), and water vapour. Carbon monoxide is not a significant greenhouse gas and is therefore rejected.

(a)(ii) \( 1.8 \times 10^{13} \) kg

Explanation: To find the net increase in atmospheric carbon dioxide, we calculate the total released minus the total removed. The total released is 727 (natural) + 37 (human) = 764 gigatonnes. The amount removed by plants is 746 gigatonnes. The net increase is therefore 764 – 746 = 18 gigatonnes. Since 1 gigatonne = \( 1 \times 10^{12} \) kg, we convert 18 gigatonnes to kg: 18 × \( 10^{12} \) kg = \( 1.8 \times 10^{1} \) × \( 10^{12} \) kg = \( 1.8 \times 10^{13} \) kg.

(a)(iii) Any two from: ice caps/glaciers melt, sea level rise/flooding, loss of habitat/desertification/droughts, extinctions/disrupted food chains, destruction of coral reefs/coral bleaching, spread of disease/pests, extreme weather/changes in weather patterns.

Explanation: Global warming, driven by an enhanced greenhouse effect, has wide-ranging environmental consequences. Two major effects are the melting of polar ice caps and glaciers, which contributes to rising sea levels and subsequent coastal flooding. Another significant impact is the disruption of ecosystems, leading to habitat loss, species extinction as animals and plants cannot adapt quickly enough, and phenomena like coral bleaching where warmer ocean temperatures cause corals to expel the algae living in their tissues, turning them white and threatening the entire reef ecosystem.

(b) An explanation that makes reference to four of the following points:

Plants take in/absorb carbon dioxide.
This is for the process of photosynthesis.
The carbon (from CO₂) is converted into/stored as suberin/locked up in suberin.
Suberin does not decay for long periods/decomposes slowly/remains for a long time.
Perennial plants remain for long periods/don’t die off each year.
Slower/less carbon dioxide is released from decomposition/decay.

Explanation: Genetically engineered plants with high suberin content act as enhanced carbon sinks. They absorb carbon dioxide from the atmosphere during photosynthesis. Instead of this carbon being used solely for immediate growth or being released back quickly, a significant portion is incorporated into suberin in their root cell walls. Suberin is a very stable, waterproof compound that decomposes extremely slowly, meaning the carbon is effectively “locked away” in the soil for a very long time. Furthermore, because these are perennial plants, they live for many years, continuously performing this carbon sequestration without the need for annual replanting, which could disturb the soil and release stored carbon. This long-term storage reduces the net amount of carbon dioxide in the atmosphere.

(c) D (restriction enzyme)

Explanation: In genetic engineering, specific enzymes are used to cut DNA at precise locations. Restriction enzymes (also called restriction endonucleases) are the enzymes responsible for cutting a gene out of a section of DNA. Amylase digests starch, ligase joins DNA fragments together, and lipase digests lipids (fats).

(d) An explanation that makes reference to two of the following points:

Prevents water loss from the plant roots.
Due to osmosis.
Prevents plant cells from becoming flaccid/wilting; helps them stay turgid by preventing water from moving out to the higher salt concentration in the soil.

Explanation: Soil with a high salt concentration has a low water potential (a high solute concentration). Water naturally moves by osmosis from areas of high water potential (inside the root cells) to areas of low water potential (the salty soil). This can cause the plant to lose water and wilt. Suberin, being a waterproof substance in the cell walls of the roots, acts as a barrier. It reduces the movement of water out of the root cells into the salty soil, thereby helping the plant to retain water and maintain turgor pressure, which is essential for support and function.

(e) Any three from: produces large numbers/large scale, fast/quick process, all crops produce suberin/are genetically identical/clones, less risk of cross-pollinating with wild plants/spreading the transgene, can be done at any time of year/all year.

Explanation: Micropropagation (tissue culture) is used for several advantages over traditional pollination. Firstly, it allows for the rapid production of a very large number of plants from a single, successfully modified individual. Secondly, the process is much faster than waiting for seeds to develop and grow. Thirdly, all the plants produced are genetically identical clones, guaranteeing that every single plant will have the desired high-suberin trait. Fourthly, since micropropagation is asexual and doesn’t involve pollen, there is no risk of the transgene escaping via cross-pollination and spreading into wild plant populations. Finally, it is not season-dependent and can be carried out in a lab throughout the year.

Question

Scientists can now produce farm animals by cloning. Since Dolly the sheep was born in 1996 many different species have been cloned.

The form of cloning used is called somatic cell cloning.

The first ever clone of a champion racehorse was announced in 2005 in Italy.

The foal was cloned from Pieraz, a world champion in long-distance horse races.

(a) Describe the stages scientists could use to clone a male horse.

(b) Pieraz was castrated (had his testicles removed) at a young age.

Explain why this stopped him reproducing normally but did not stop him being used to produce a foal by cloning.

(c) Suggest why horseracing does not allow the use of non-natural methods of breeding, including cloning.

(d) State one difference between cloning an organism and genetically modifying an organism.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 5(d): Cloning — parts (a), (b), (c), (d)
• 5(c): Genetic modification (genetic engineering) — part (d)
• 3(a): Reproduction — part (b)

▶️ Answer/Explanation

Solution

(a)

Answer: The stages for cloning a male horse involve:

Taking a nucleus from a body (somatic) cell of the male horse.
Inserting this nucleus into an enucleated egg cell (an egg cell that has had its nucleus removed).
Applying an electric shock to stimulate the egg to start dividing.
Allowing the cell to undergo mitosis (cell division) to form an embryo.
Implanting the developing embryo into the uterus (womb) of a surrogate mother horse.

Explanation: This process is known as somatic cell nuclear transfer (SCNT). The key idea is that the genetic material comes entirely from the body cell of the male horse to be cloned, not from the fusion of sperm and egg. The electric shock mimics the natural stimulus of fertilization, triggering the egg to begin development. The surrogate mother provides the environment for the embryo to grow into a foal, which will be a genetic clone of the original male horse.

(b)

Answer: Castration stopped normal reproduction because:

It prevented the production of sperm (gametes).
Therefore, natural fertilization and impregnation of a female horse could not occur.

However, cloning was still possible because:

Cloning uses a body (somatic) cell, which contains the full set of chromosomes (DNA). Since Pieraz’s body cells still contained all his genetic information, a nucleus from one of these cells could be used to create a clone.

Explanation: Normal sexual reproduction requires gametes (sperm and egg). Castration removes the testes, the organs that produce sperm, thus halting this process. Cloning, on the other hand, bypasses the need for gametes altogether. It relies on taking the nucleus from any diploid body cell (like a skin cell), which holds the complete genetic blueprint of the individual. This nucleus is then placed into an empty egg cell to create an embryo that is genetically identical to the original animal.

(c)

Answer: Possible reasons include:

To maintain the value and uniqueness of naturally bred stallions (sires).
To prevent inbreeding and maintain genetic diversity within the horse population, which helps prevent genetic diseases.
To ensure fair competition and prevent cheating.
Due to ethical concerns about the use of cloning technology.

Explanation: Horseracing authorities often have strict rules to preserve the integrity of the sport and the breed. If champion horses could be easily cloned, it could devalue the achievements of individual, naturally bred horses. Furthermore, a population with low genetic diversity is more vulnerable to diseases. Allowing cloning could lead to a situation where many racehorses are genetically identical, which is undesirable for the long-term health of the breed. There are also fairness concerns, as cloning could be seen as an unnatural advantage.

(d)

Answer: Cloning produces organisms that are genetically identical to the original, whereas genetic modification produces organisms with altered DNA (new genes are introduced).

Explanation: The fundamental difference lies in the genetic outcome. Cloning is a form of asexual reproduction that results in an exact genetic copy (a clone) of the parent organism. No new genetic material is added. In contrast, genetic modification (GM) involves deliberately altering the organism’s genome, often by inserting genes from another species, to give the organism a new trait (like disease resistance or faster growth). A clone has the same genotype as its parent, while a genetically modified organism (GMO) has a new, different genotype.

Question

Scientists have produced cloned monkeys.

The diagram shows the procedure used to produce cloned monkeys.

(a) (i) State the meaning of the term enucleated.

(a) (ii) Describe how the single cell develops into an embryo.

(b) Scientists can use adult body cells or fetal body cells to clone monkeys.

The table gives information about cloning using body cells from different sources.

Evaluate this data to decide which source of body cells is more successful in cloning monkeys.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 5(d): Cloning — all parts
• 3(a): Reproduction — part (a)(ii)
• 2(b): Cell structure — part (a)(i)
• 5(c): Genetic modification (genetic engineering) — context of cloning technology

▶️ Answer/Explanation

Solution

(a) (i) The nucleus is removed.

Explanation: In the context of cloning, “enucleated” specifically refers to an egg cell that has had its nucleus carefully removed. This is a crucial first step in the somatic cell nuclear transfer (SCNT) process, as it creates a vacant cellular environment ready to receive the nucleus from the donor body cell.

(a) (ii) The single cell divides many times by mitosis, producing a ball of cells, and then the cells differentiate.

Explanation: After the donor nucleus is inserted into the enucleated egg cell and stimulated, the newly formed single cell begins a process of rapid, successive divisions. This type of cell division is called mitosis, which produces genetically identical daughter cells. These divisions lead to the formation of a solid ball of cells. Following this, the process of differentiation begins, where the initially identical cells start to specialize, taking on different structures and functions to form the various tissues that will make up the embryo.

(b) Fetal body cells are more successful.

Explanation: When evaluating the data, we need to look at both the efficiency of the process and the health of the resulting offspring.

Looking at the success rates: For adult cells, 22 out of 42 surrogates resulted in a pregnancy, which is a success rate of approximately 52%. For fetal cells, 6 out of 21 surrogates resulted in a pregnancy, which is a lower success rate of about 29%. Based purely on the number of successful pregnancies, adult cells seem more efficient.

However, the critical factor is the outcome for the offspring. The two offspring produced from adult body cells were “short-lived,” indicating significant health problems. In contrast, the two offspring produced from fetal body cells were “healthy.”

Therefore, while using fetal cells led to fewer successful pregnancies, it resulted in viable, healthy clones. The ultimate goal of cloning is to produce a healthy organism, which makes fetal cells the more successful source in this investigation, despite the lower pregnancy rate.

Question

Blood clotting is an important process in humans. The process is controlled by enzymes.

(a) (i) Give two reasons why blood clotting is important.

(ii) The optimum temperature for the enzymes involved in blood clotting is \(37^\circ C\). Sketch a graph to show how temperature affects the time taken for blood to clot.

(b) Some people cannot make the proteins needed for blood clotting. Cloning is used to produce large numbers of transgenic mammals. These transgenic mammals can make the human blood-clotting proteins. The human blood-clotting proteins can then be removed from the mammals’ milk and injected into people who cannot make the proteins.

(i) Explain why these mammals are described as transgenic.
(ii) Describe how a mammal is cloned.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(h): Transport — Blood clotting (part a(i), a(ii))
• 2(c): Biological molecules — Enzymes (part a(ii))
• 5(c): Genetic modification (genetic engineering) — Transgenic organisms (part b(i))
• 5(d): Cloning — Cloning mammals (part b(ii))

▶️ Answer/Explanation

Solution

(a)(i) Two reasons from:

Prevent loss of blood / stops bleeding (1)
Prevent entry of pathogens / microbes / bacteria / viruses / fungi / prevent infections (1)

(a)(ii) Sketch graph showing a clear minimum (fastest clotting time) at \(37^\circ C\). The line should drop to a low point at \(37^\circ C\) and then rise on both sides.

(b)(i) An explanation that makes reference to:

(They have been given) genetic material / gene / allele / DNA / are genetically altered (1)
From human / a different species (1)

(b)(ii) An answer that makes reference to six of the following points:

Use enucleated egg / empty egg / remove nucleus from egg / eq (1)
Nucleus from body cell / diploid nucleus (placed into empty egg) / fuse adult cell with empty egg (1) (Ignore DNA)
Use of electricity / shock (to fuse cells) (1)
Cell division / mitosis (stimulated) (1)
Embryo forms / develops (1)
Embryo placed into uterus / womb (1)
Surrogate mother (carries embryo to term) (1)

Award marks for any correct and relevant points describing the process of somatic cell nuclear transfer as used in cloning mammals (e.g., Dolly the sheep).

Question

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Schistosomiasis

Schistosomiasis is an infection caused by a parasitic worm called a schistosome. The immature or larvae of the worm live in rivers and lakes in tropical parts of the world. The diagram shows the life cycle of the schistosome worm.

Some people in tropical parts of the world use water from these rivers and lakes for their daily lives. These people risk infection because the larvae burrow into their skin. The larvae are then transported to other parts of the body where they damage organs such as the kidneys, intestines, lungs and brain. The larvae develop into adult worms.

The adult worms lay eggs in the human body. Some of these eggs are destroyed by the immune system, but most eggs survive. These eggs can get into water if faeces or urine from infected people pass into rivers or lakes. In the water, the eggs develop into small larvae which grow inside freshwater snails. Larvae are released from the snails and infect any person they contact. These larvae develop into adult worms inside the human body.

Doctors diagnose schistosomiasis when they find eggs in the faeces or urine of infected people. Infected people also have blood cells in their urine and antibodies for the pathogen in their blood.

At present, the drug praziquantel is used to kill the worms. A dose of \(0.040\ \text{g}\) per kg of body mass is usually effective. With no treatment, affected organs can be permanently damaged, leading to death. It is estimated that 240 million people (in the world) have schistosomiasis. Every year \(8 \times 10^{-4}\) per cent of infected people die from the disease.

A vaccine is being developed using a plasmid. The plasmid has DNA inserted that makes a protein found on the body surface of the adult schistosome worm.

In one investigation, a vaccine made using the DNA plasmid was given to a group of infected people. The results showed a mean number of 21.53 worms per person in this group. In the control group, a mean number of 40.53 worms per person was found.

(a) Which process is affected if kidneys are damaged (line 8)?

A) digestion
B) mutation
C) ultrafiltration
D) vaccination

(b) Suggest three ways to reduce the risk of being infected by schistosomes.

(c) Name two different blood cells that would be found in the urine of infected people (line 17).

(d) An infected person has a body mass of \(120\ \text{kg}\). What dose of drugs would be effective for this person (lines 19 to 20)?

A) \(0.04\ \text{mg}\)
B) \(4.8\ \text{mg}\)
C) \(40\ \text{mg}\)
D) \(4800\ \text{mg}\)

(e) Using the estimated number of people in the world who have schistosomiasis (lines 21 to 22), calculate the number of people who die each year from schistosomiasis.

(f) Which of these is the correct description of a plasmid?

A) a circle of DNA
B) a circle of mRNA
C) a circle of protein
D) a circle of tRNA

(g) Explain how a vaccine could protect people from schistosomiasis (lines 24 to 25).

(h)(i) Suggest what is given to the control group (lines 27 to 29).

(ii) A scientist claims that the investigation proves the vaccine is effective against schistosomiasis (lines 27 to 29). Comment on this claim.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(h): Transport — parts (c) [Blood composition], (g), (h)(i) [Vaccination and immune response]
• 2(i): Excretion — part (a) [Kidney function]
• 1(b): Variety of living organisms / Pathogens — context of parasitic infection
• 5(c): Genetic modification — part (f) [Plasmids as vectors]
• Mathematical Skills (Appendix 3): — parts (d), (e) [Calculations]
• Experimental Skills & Evaluation (Section 4): — part (h)(ii) [Evaluating an investigation]

▶️ Answer/Explanation

Solution

(a) C (ultrafiltration)
A is incorrect because digestion is not a process in the kidneys.
B is incorrect because mutation is not a process in the kidneys.
D is incorrect because vaccination is not a process in the kidneys.

(b) An answer that makes reference to three of the following points:
• treat drinking water / boil water (before drinking) / do not drink water / drink bottled water / eq (1)
• sanitation / no faeces in water / no urine in water / eq (1)
• remove snails / eq (1)
• vaccination (1)
Additional guidance: Allow “do not go in infected rivers or lakes / cover skin when in water / avoid contact with affected water / only wash in clean water”.

(c) An answer that makes reference to two of the following points:
• red blood cells / rbc (1)
• white blood cells / wbc (1)
• lymphocytes (1)
• phagocytes / macrophages (1)

(d) D (4800 mg)
Calculation: \(120\ \text{kg} \times 0.040\ \text{g/kg} = 4.8\ \text{g} = 4800\ \text{mg}\)
A is incorrect because it is the wrong value.
B is incorrect because it is the wrong value.
C is incorrect because it is the wrong value.

(e) \(1920\) people
Working:
• \(8 \times 10^{-4}\% = 0.0008\%\)
• \(0.0008\% \text{ of } 240,000,000 = 0.000008 \times 240,000,000 = 1920\)
Allow 1 mark for: \(19200000 / 1920000 / 192000 / 192200 / 192 / 19.2 / 1.92 / 0.192 / 0.0192\)
Award full marks for correct numerical answer without working.

(f) A (a circle of DNA)
B is incorrect because it is not RNA.
C is incorrect because it is not a protein.
D is incorrect because it is not RNA.

(g) An explanation that makes reference to three of the following points:
• antigen (1)
• memory cells / lymphocytes (1)
• (secondary) immune response (1)
• more antibodies / antibodies made sooner / faster / faster immune response / eq (1)

(h)(i) • (a treatment with) no plasmid / no protein / only water / saline / eq (1)
Allow placebo vaccine / a placebo / plasmid with no gene / plasmid with no DNA / different DNA.

(h)(ii) An answer that makes reference to three of the following points:
• reduced numbers / eq (1)
• by 19 or by 47% / about 50% (1)
• schistosomes / worms, still present in body (1)
• no idea of group size / needs to be repeated (1)
• no idea of age / sex / health (1)
Additional Guidance:
Allow “reduces numbers of worms / worms decrease / lower number of worms after vaccine”.
Allow “more worms in control group”.
Allow “does not completely get rid of them”.
Allow “more testing / more people tested”.

Edexcel iGCSE Biology 4BI1 - Paper 2B -Genetic modification- Exam Style Questions- New Syllabus

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