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Question 1

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

Extinctions

During the evolution of living organisms, most species have become extinct. Evolution by natural selection means that species constantly replace each other. The photograph shows the fossilised jaws of a shark called megalodon. Megalodon was a giant, predatory shark that became extinct 2.6 million years ago.

Some scientists think megalodon was replaced by giant, predatory toothed whales. These whales were the ancestors of modern orcas. Any sharks that remained evolved to become smaller. As well as the steady loss of species over time, there have been mass extinction events. Approximately 250 million years ago 90% of all animals and plants became extinct. The cause of this mass extinction is not known, but one theory is that it was due to the eruptions of volcanoes. The volcanoes released sulfur dioxide, carbon dioxide and dust into the atmosphere. This caused populations of producer species to fall, atmospheric carbon dioxide levels to rise, and oxygen levels to fall.

Human activity is now causing another mass extinction. Some scientists estimate that approximately one million animal and plant species are at risk. To prevent species loss, cryozoos are being developed. Cryozoos are storage tanks containing samples of body cells from animals and are kept at a temperature of -170 oC. The cells are put in a salt and sugar solution and then frozen. If a species becomes extinct, the frozen cells can be used to clone new animals. The banteng is an endangered breed of cattle. Banteng body cells have been stored in a cryozoo. These cells have been used with eggs from another species to successfully produce a living banteng.

In the future we may be able to bring back extinct species such as mammoths by making clones using the remains of frozen mammoths. Scientists need to consider the advantages and disadvantages of bringing back extinct animals. Currently, the biodiversity of the world is different from the time when mammoths were alive. Many natural predators of mammoths are now extinct. Mammoths may have helped to keep methane-releasing soil frozen, reducing the release of the methane. Mammoths were also an important part of the nitrogen cycle and increased the nutrient content of low-nutrient Arctic soil.

(a) Megalodon was an animal.

Which of these features does megalodon share with the fungus yeast?

nuclei present in cells
nervous coordination
stores carbohydrate as glycogen

A) 1 and 2 only
B) 1 and 3 only
C) 2 and 3 only
D) 1, 2 and 3

(b) Scientists think that the giant, predatory toothed whales that replaced the extinct megalodon consumed the same sources of food. Explain how the evolution of giant, predatory toothed whales may have caused the extinction of megalodon. (lines 5 to 7)

(c) (i) Volcanoes release sulfur dioxide into the atmosphere. Describe the biological consequences of sulfur dioxide release. (lines 10 to 12)
(ii) The release of large amounts of dust into the atmosphere reduced light intensity. Explain why this would cause a loss of food chains. (lines 9 to 11)

(d) (i) Explain why the cells in cryozoos are put in salt and sugar solution rather than pure water. (lines 16 to 18)
(ii) Describe how scientists could clone a bantering. (lines 18 to 20)

(e) Explain why releasing cloned mammoths could have negative and positive effects on Arctic biodiversity. (lines 22 to 28)

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 1(b): Variety of living organisms — part (a)
• 5(d): Human influences on the environment — part (c)(i)
• 5(a), 5(b): The organism in the environment, Feeding relationships — part (c)(ii)
• 2(d): Movement of substances into and out of cells — part (d)(i)
• 6(d): Cloning — part (d)(ii)
• 5(d), 6(d): Human influences on the environment, Cloning — part (e)

▶️ Answer/Explanation

Solution

(a) B (1 and 3 only)
A is incorrect as yeast has no nervous system
C is incorrect as yeast has no nervous system
D is incorrect as yeast has no nervous system

(b) An explanation that makes reference to three of the following:
• competition (between megalodon and whales) (1)
• whales ate more food / eq (1)
• whales better adapted / swam faster / better at feeding / better at hunting / eq (1)
• whales survived / eq (1)
• whales reproduced more / had more offspring / eq (1)
Accept less food left for megalodon / no food / megalodon starve. Accept megalodon less well adapted. Accept megalodon did not survive/died (out). Ignore extinct.

(c) (i) A description that makes reference to two of the following:
• acid rain (1)
• deforestation / death of trees / death of plants / eq (1)
• death of fish / death of animals in lakes / loss of species in lakes or rivers / eq (1)
Accept sulphuric acid. Accept damages plants/trees. Accept loss of food chains/biodiversity.

(ii) An explanation that makes reference to three of the following:
• (less) photosynthesis (1)
• so less glucose / sugar / starch / eq (1)
• fewer producers / fewer plants / less mass of producers / producers die / plants do not grow as much / eq (1)
• less food for consumers / less energy for consumers / eq (1)
Ignore ‘cannot produce food’ for mp2. Accept fewer consumers/herbivores/carnivores.

(d) (i) An answer that makes reference to two of the following:
• prevents osmosis / less osmosis (1)
• so water will not enter cells / eq (1)
• so cells do not burst / eq (1)
Accept osmosis would occur if in water. Accept cells burst if in water.

(ii) A description that makes reference to four of the following:
• place diploid nucleus into enucleated egg cell / place body cell nucleus into enucleated egg cell / eq (1)
• electric shock / eq (1)
• mitosis / cell division / eq (1)
• place embryo into uterus / womb (1)
• of surrogate (mother) (1)
Accept fuse body cell with enucleated egg. Accept empty egg cell for enucleated egg cell.

(e) A description that makes reference to three of the following:
Negative:
• mammoth population increases / over-population occurs / eq (1)
• mammoth eats too much food / less food for other species / eq (1)
Positive:
• less global warming / less greenhouse effect / eq (1)
• decomposition of faeces / decay of dead mammoths (1)
• more amino acid / protein / DNA / chlorophyll synthesis in plants / eq (1)
• (soil nutrients means) more plants / increased plant growth / eq (1)
Accept high mammoth reproduction rate. Accept overeats prey / prey could go extinct. Accept less greenhouse gas. Accept better plant growth.

Question 2

Transpiration (water loss) is affected by several environmental factors.

A student investigates the effect of light intensity on water loss from a plant shoot. The diagram shows some of the apparatus the student uses.

The student predicts that water loss from a plant shoot will increase as light intensity increases.

(a) (i) Describe how to set up and use the student’s apparatus to test this prediction.
(ii) State the dependent variable in this investigation.

(b) Another student uses the apparatus to collect and process the data. Table 1 shows their results.

Table 1
Light intensity in arbitrary units	Mean volume of water lost by shoot in 10 minutes in mm³
0	2
5	8
10	12
15	12

(i) Explain why light intensity changes the mean volume of water lost by the shoot.

(ii) The student repeats the experiment with a plant that is adapted to live in desert environments. Table 2 shows the results for this desert plant.

Table 2
Light intensity in arbitrary units	Mean volume of water lost by shoot in 10 minutes in mm³
0	6
5	4
10	0
15	0

The desert plant has adaptations to survive in desert environments where not much water is available.

Explain why the results for this desert plant, in table 2, are different from the results in table 1.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(h): Transport — parts (a)(i), (a)(ii), (b)(i), (b)(ii) [focus on transpiration]
• 2(g): Gas exchange in plants — parts (b)(i), (b)(ii) [link to stomatal behavior]
• 3(b): Structure and functions in living organisms: Part 1 (Nutrition in plants) — implicit link to water uptake
• 5(a): Ecology and the environment — part (b)(ii) [adaptations to environment]

▶️ Answer/Explanation

Solution

(a)(i) Mark Scheme Summary: A description that makes reference to four of the following points (1 mark each):

Cut shoot underwater / cut shoot diagonally.
Ensure apparatus is airtight (e.g., dry leaves, check seals, use petroleum jelly).
Measure distance bubble moves / distance water moves in capillary tube.
Measure this movement over a set time.
Place lamp at different distances from the shoot (to vary light intensity).
Control other variables (e.g., temperature, humidity).
Repeat readings / use reservoir to reset bubble.

(a)(ii) Water loss / distance moved by bubble / volume of water taken up / time taken to move bubble / rate of bubble movement.
Accept: water uptake / transpiration speed.

(b)(i) An explanation that makes reference to two of the following (1 mark each):

More water loss as light intensity increases (more transpiration/evaporation).
Because (more) stomata open / stomata open wider.
Until all stomata are open (completely) / until stomata are fully open.

(b)(ii) An explanation that makes reference to three of the following (1 mark each):

Desert plant loses less water in total / retains/conserves water.
Water is lost in low light / water is not lost in high light (water loss decreases as light intensity increases for desert plant).
Stomata close in light/day / stomata open in dark/night (reverse of normal plants).
Desert plants have fewer stomata.
This adaptation reduces wilting / stops plant going flaccid.

Question 3

Isotonic drinks are often used to rehydrate athletes after exercise.

(a) Explain why athletes lose water during exercise.

(b) Isotonic drinks contain salt and sugar solutions that are the same concentration as normal blood plasma.

A scientist uses this method to investigate how well an isotonic drink rehydrates athletes.

three athletes exercise for one hour
one athlete has no drink
the second athlete drinks \(1000\ \text{cm}^3\) of pure water
the third athlete drinks \(1000\ \text{cm}^3\) of isotonic drink
the volume and colour of urine produced by each athlete are measured one hour later

The table shows the scientist’s results.

Drink consumed by athlete	Volume of urine produced in \(\text{cm}^3\)	Colour of urine
no drink	100	very dark yellow
pure water	750	very light yellow
isotonic drink	500	yellow

(i) Explain the results shown in the table for the athlete who consumed no drink.
(ii) Explain the differences in urine volume and urine colour produced by the athlete who consumed the isotonic drink and the athlete who consumed pure water.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 1(a): Characteristics of living organisms — part (a)
• 3(h): Transport (Humans) — part (a, b)
• 3(i): Excretion (Humans) — parts (b)(i), (b)(ii)
• 3(j): Co-ordination and response (Homeostasis) — parts (b)(i), (b)(ii)

▶️ Answer/Explanation

Solution

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

Exercise increases body temperature / eq (1)
(More) sweat / eq (1)
To cool down / lose heat / eq (1)
By evaporation (of sweat) (1)

(b)(i) An explanation that makes reference to three of the following:

Blood concentration increases / less water in blood / eq (1)
(Detected by) hypothalamus / osmoreceptors / pituitary gland (1)
Releases ADH (1)
Collecting duct becomes more permeable / eq (1)
Increased water reabsorption (so less urine produced) (1)

(b)(ii) An explanation that makes reference to two of the following:

With (pure water) blood becomes more dilute / less concentrated / has high water concentration / eq (1)
Less / no ADH released when drinking water / eq (1)
Less water reabsorbed (by kidney) when water drunk / eq (1)
Salt / sugar absorbed into blood (in intestine) (from isotonic drink) / eq (1)

Accept converse arguments for the isotonic drink (e.g., more ADH released, more water reabsorbed).

Question 4

The diagram shows four glands in the human body labelled W, X, Y and Z.

(a) LH is a hormone involved in the menstrual cycle.

(i) Which labelled gland produces LH?

A) W
B) X
C) Y
D) Z

(ii) Describe the functions of LH during the menstrual cycle.

(b) The diagram shows a fetus developing in a uterus.

Explain how the amniotic fluid and placenta enable the safe growth of the fetus.

(c) Scientists investigated the effects of tobacco smoking and taking mineral ion supplements on the growth of developing babies during pregnancy.

The scientists looked at four groups of mothers.

Group A non-smokers taking mineral ion supplements
Group B non-smokers not taking mineral ion supplements
Group C smokers taking mineral ion supplements
Group D smokers not taking mineral ion supplements

The graph shows the mean masses of developing babies at 12 weeks of pregnancy, at 24 weeks of pregnancy and at birth (36 weeks).

(i) Calculate the percentage difference at 36 weeks of the mean mass of babies from mothers in group A compared with the mean mass of babies from mothers in group D.
Give your answer to the nearest whole number.

(ii) Comment on the effect of smoking and the effect of taking mineral ion supplements on the growth of babies. Use the graph and your own knowledge to help your answer.

Most-appropriate topic codes (Pearson Edexcel IGCSE Biology):

• 4(a): Reproduction (Humans) — parts (a)(i), (a)(ii)
• 4(a): Reproduction (Humans) — part (b)
• 2(e): Nutrition (Humans) — part (c)(ii) – mineral function
• 2(g): Gas exchange (Humans) — part (c)(ii) – smoking effects
• Mathematical skills — part (c)(i)

▶️ Answer/Explanation

Solution

(a)(i) A (W) — the pituitary gland.
B is incorrect as X (the pancreas) does not release LH.
C is incorrect as Y (the adrenal) does not release LH.
D is incorrect as Z (the ovary) does not release LH.

(a)(ii) A description that makes reference to the following:
• ovulation / release of egg / oocyte (1)
• (stimulates) progesterone release (1)
Accept: stimulates oestrogen release.

(b) An explanation that makes reference to the following:
• (amniotic fluid) prevents physical damage / bumps / equalizes pressure / acts as a shock absorber / cushioning (1)
and two from:
• (placenta) allows diffusion / active transport (1)
• gives the fetus amino acids / glucose / oxygen / antibodies / vitamins / minerals (1)
• removes from the fetus urea / carbon dioxide (1)
• makes sure mother’s and baby’s blood do not mix (1)

(c)(i) • 27% (3 marks)
Working:
Mass difference = \(2800 – 2200 = 600\) g
Percentage difference = \(\frac{600}{2200} \times 100 = 27.27…\%\) ≈ 27% (nearest whole number)
One mark for (2800 – 2200) or 600; one mark for division by 2200; one mark for correct answer.

(c)(ii) An answer that makes reference to four of the following points (4 marks):
1. smoking results in slower growth / lower mass (1)
2. taking minerals results in faster growth / higher mass (1)
3. biggest increase in mass / fastest growth is non-smokers with minerals (Group A) (1)
4. smoking has a bigger (negative) impact than not taking mineral supplements (1)
5. carbon monoxide (in smoke) binds to haemoglobin / reduces oxygen transport (1)
6. less respiration / energy release for growth (1)
7. minerals (e.g., iron) are needed for haemoglobin / red blood cells (1)
8. minerals (e.g., calcium) are needed for bone growth (1)
Accept converse statements for points 1-3.

Question 5

The sequence of bases on one strand of a section of DNA is:

TAC CGT AAT TAT

(a) (i) Which of these is the complementary sequence of DNA on the other strand of the double helix?

A) ATG GCA TTA ATA
B) AUG GCA UUA AUA
C) CGT TAC GGC CGC
D) CGU UAC GGC CGC

(ii) Which of these is the correct summary of the processes occurring during protein synthesis?

A) DNA transcription → RNA translation → protein
B) DNA translation → RNA transcription → protein
C) RNA transcription → DNA translation → protein
D) RNA translation → DNA transcription → protein

(b) The table shows different mRNA codons for some amino acids.

Codons	Amino acid
UUU, UUC	W
AUG	X
UGU, UGC	Y

(i) UUU-AUG-UGU is one combination of codons that codes for the sequence of amino acids W-X-Y.

Give the number of other combinations that code for the same amino acid sequence.

(ii) Explain why most genetic mutations have no effect on the phenotype of an organism.

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

(iii) State one factor that can increase the rate of mutation.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 4(b): Inheritance — DNA structure, protein synthesis, mutations — parts (a)(i), (a)(ii), (b)(ii), (b)(iii)
• 4(b): Inheritance — The genetic code — part (b)(i)

▶️ Answer/Explanation

Solution

(a)(i) A (ATG GCA TTA ATA)
B is incorrect because DNA does not contain Uracil (U).
C is incorrect because the base pairing is wrong (A pairs with T, C pairs with G).
D is incorrect because DNA does not contain Uracil (U) and the pairing is wrong.

(a)(ii) A (DNA → transcription → RNA → translation → protein)
B is incorrect because translation is in the wrong place.
C is incorrect because RNA is in the wrong place.
D is incorrect because RNA is in the wrong place.

(b)(i) • 3
Reasoning: The codon for amino acid W (UUU, UUC) offers 2 choices. The codon for amino acid X (AUG) offers 1 choice. The codon for amino acid Y (UGU, UGC) offers 2 choices. Total combinations: \(2 \times 1 \times 2 = 4\). One combination (UUU-AUG-UGU) is given, so other combinations = \(4 – 1 = 3\).

(b)(ii) An explanation that makes reference to three of the following points:
1. Some sequences / codons / different base triplets may code for the same amino acid (e.g., UUU and UUC both code for W) / the genetic code is degenerate. (1)
2. (Same amino acid so) no change in protein structure / no change in enzyme / protein has same function. (1)
3. Mutation may not affect bonding / (3D) shape / active site of enzyme. (1)
4. Mutation / allele may be recessive / not expressed. (1)
5. Mutation may occur in non-coding DNA / introns. (1)

(b)(iii) • (Ionising) radiation / UV light / tar (in tobacco) / mutagen / carcinogen / gamma rays / X-rays / radioactivity. (1)
Do not accept infra-red radiation.
Accept smoking or other correct mutagens.

Question 6

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)
• 6(a): Food production (Fish farming) — parts (b)(i), (b)(ii), (b)(iii), (b)(iv), (b)(v)
• 6(c): Genetic modification (genetic engineering) — parts (b)(i), (b)(iii), (b)(v)
• 5(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)

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