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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.

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):

• 5(d): Human influences on the environment — parts (c), (e)
• 6(a): Food production (Fish farming) — parts (a), (b), (d)(i), (d)(ii), (f), (g), (h)
• 6(b): Selective breeding — part (d)(i)
• 6(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 2

Mammals, such as humans, need to regulate their internal environment.

(a) What is the process that maintains a constant internal environment?

A) absorption
B) diffusion
C) egestion
D) homeostasis

(b) Table 1 shows the water input and output per day for a person in normal temperature conditions.

Water input (intake)		Water output (losses)
source	volume in litres	source	volume in litres
drinking	1.5	urine	1.5
food	0.5	gas exchange	0.4
metabolism	0.5	sweating	0.5
		faeces	0.1

The water loss from gas exchange plus the loss from sweating are referred to as the insensible water loss. This water loss is called insensible because it cannot be measured directly.

(i) Calculate the percentage of the water loss that is classified as insensible.

(ii) This data comes from a person who has a mass of 70 kg. Assuming the same proportions, calculate the water input from food for a person who has a mass of 110 kg.

(iii) Water loss in faeces is usually relatively low. Illness such as food poisoning can produce symptoms including vomiting, diarrhoea and a high temperature. These symptoms can change water balance in the body. Explain how the symptoms of food poisoning can change water balance in the body.

(c) The photograph shows a mammal called a degu.

A degu is a rodent that lives in a very dry environment in South America. The degu gets its water input by feeding on plants. The water intake of the degu changes during the winter and summer months.

Table 2 shows the body mass, water intake and urine concentration of the degu in the winter and in the summer. It also shows the total rainfall in winter and in summer.

Measurement	Winter	Summer
total rainfall in mm	245	12
body mass in g	119.7	124.8
water intake in one day in cm\(^3\)	40.4	10.3
urine concentration in arbitrary units	1123	3137

Comment on the differences in body mass, water intake and urine concentration in winter and summer. Use the data in the table and your own knowledge in your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(j) / 3.31: Homeostasis — part (a)
• Appendix 3: Mathematical skills — parts (b)(i), (b)(ii)
• 3(i) / 3.28B: Excretion, osmoregulation, ADH — parts (b)(iii), (c)
• 3(i) / 3.22B–3.29B: Kidney function and water balance — part (b)(iii)
• 5(a) / 5.5: Abiotic factors and organisms — part (c)

▶️ Answer/Explanation

Solution

(a) D (homeostasis)
A is not correct as it is not absorption
B is not correct as it is not diffusion
C is not correct as it is not egestion

(b)(i) Calculation method:
Insensible loss = gas exchange + sweating = \(0.4 + 0.5 = 0.9\) litres
Total water loss = urine + gas exchange + sweating + faeces = \(1.5 + 0.4 + 0.5 + 0.1 = 2.5\) litres
Percentage insensible loss = \(\frac{0.9}{2.5} \times 100 = 36\%\)

(b)(ii) Calculation method:
Water input from food for 70 kg person = 0.5 litres
Water input per kg = \(\frac{0.5}{70} = 0.007142857\) litres/kg
For 110 kg person: \(0.007142857 \times 110 = 0.7857\) litres ≈ \(0.79\) litres (accept \(0.77–0.80\))

(b)(iii) An explanation that makes reference to four of the following points:
1. more water lost / less water in body /eq (1)
2. water / liquid lost in vomiting / faeces / diarrhoea / eq (1)
3. (more) sweating / eq (1)
4. concentration of blood increases / water potential lowered / eq (1)
5. (more) ADH produced / secreted / eq (1)
6. by hypothalamus / pituitary (1)
7. permeability of collecting duct increases / eq (1)
8. more water reabsorbed / less water lost in urine / more concentrated urine / less urine / eq (1)

(c) An answer that makes reference to four of the following points:
In winter:
1. body mass lower / eq (1)
2. as fewer plants available / less food / hibernating / eq (1)
3. less sunlight / lower temp / less photosynthesis / eq (1)
4. (much) more water intake / eq (1)
5. as more rainfall/ eq (1)
6. less concentrated urine in winter / more urine / eq (1)
7. (so) more water lost in urine / eq (1)
8. Ref to data for urine 3× less concentrated in winter / water input 4 × higher in winter / eq (1)
In summer: converse of above points applies.

Question 3

The diagram shows a section of human skin with some structures labelled.

(a) (i) Which structure is a pore of a sweat gland?

A) Q
B) R
C) S
D) T

(ii) Which structure carries blood?

A) P
B) R
C) S
D) T

(iii) The skin responds to changes in temperature.

Describe how the skin responds when a person enters a cold environment.

(b) Scientists investigate the effect of heat strain on two groups of men. Heat strain is caused by increasing the external temperature. The scientists measure the skin temperature with no heat strain, low heat strain and moderate heat strain. They also measure the rate of sweating with low and moderate heat strain.

The table shows the scientists’ results.

Group	Number in group	Mean age in years	Mean skin temperature in °C			Mean sweating rate per cm² of skin in mg per min
Group	Number in group	Mean age in years	no heat strain	low heat strain	moderate heat strain	low heat strain	moderate heat strain
young	14	24	34.9	37.6	38.1	1.0	1.2
old	16	69	34.0	37.3	37.7	0.2	0.8

Discuss the relationship between age and the effect of heat strain on the mean skin temperature and the mean rate of sweating. Use information from the table and your own knowledge in your answer. (5)

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(j): Co-ordination and response — parts (a)(iii), (b)
• 3(j): Homeostasis — parts (a)(iii), (b)
• 2(b): Cell structure and function — parts (a)(i), (a)(ii)
• 3(h): Transport in humans — part (a)(ii)

▶️ Answer/Explanation

Solution

(a)(i) D (T)
A is not correct as Q is not the pore of a sweat gland
B is not correct as R is not the pore of a sweat gland
C is not correct as S is not the pore of a sweat gland

(a)(ii) B (R)
A is not correct as P is not the structure that carries blood
C is not correct as S is not the structure that carries blood
D is not correct as T is not the structure that carries blood

(a)(iii) A description that makes reference to four of the following points:
1. vasoconstriction (1)
2. arterioles supplying capillaries near skin surface constrict / blood vessels supplying skin narrow (1)
3. less blood flows to skin surface (1)
4. hair erector muscle contracts / hair stands up (1)
5. traps air / insulates (1)
6. less heat loss by radiation / convection / evaporation (of sweat) (1)
7. less sweating (1)

(b) An answer that makes reference to five of the following points:
1. (mean) skin temperature is higher in young (1)
2. (mean) skin temperature is higher with heat strain (1)
3. mean sweating rate higher in young (1)
4. mean sweating rate higher in moderate/higher heat strain (1)
5. smaller difference in sweating rate between low and moderate strain in young (1)
6. no information on sweat rate with no heat strain / at rest (1)
7. more sweat glands in young / each gland produces more sweat in young (1)
8. young can reduce (core) body temperature faster / young less likely to overheat (1)
9. numbers very small / not repeated / unreliable / no information on age (1)
10. no information on BMI / fat layers / health / diet (1)

Question 4

A teacher investigates gas exchange in different conditions.

They use orange hydrogen-carbonate indicator solution, which changes colour depending upon the concentration of carbon dioxide in the tube.

This is their method.

Step 1:   put \(5\ cm^{3}\) of hydrogen-carbonate indicator solution into each of five test tubes A, B, C, D and E
Step 2:   place a wire mesh and two green leaves in test tube A
Step 3:   set up tubes A to D so that they contain leaves or maggots as shown in the diagrams
Step 4:   set up tube E without leaves or maggots
Step 5:   place test tubes A, C and E in bright light for two hours
Step 6:   place test tubes B and D in the dark for two hours
Step 7:   observe the colour of the indicator in each test tube

(a) (i) State the dependent variable in this investigation.
(ii) Give the function of the wire mesh in the test tubes.
(iii) State one variable that the teacher has controlled in their investigation.

(b) The table shows the results of this investigation.

Tube	Contents of test tube	Light condition	Colour of indicator after two hours
A	leaves	light	dark red
B	leaves	dark	yellow
C	maggots	light	yellow
D	maggots	dark	yellow
E	empty	light	orange

Explain the relationship between the test tube contents, the light condition and the colour of the indicator after two hours.

(c) The teacher sets up another test tube that contains leaves and maggots. They put the test tube in the light for two hours.

The colour of the indicator after two hours remains orange.

Explain why the indicator remains orange.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(g): Gas exchange — Flowering plants (2.44B, 2.45B) — parts (a), (b), (c)
• 2(f): Respiration — (2.36, 2.39) — part (b)
• 3: Experimental skills and analysis — parts (a)(i), (a)(ii), (a)(iii)

▶️ Answer/Explanation

Solution

(a)(i) • colour of indicator / carbon dioxide concentration / eq (1)

(a)(ii) • stops leaves / maggots falling in indicator / hold organisms in place / separates organism from solution/ eq (1)

(a)(iii) • volume of indicator / volume of solution / time in tube / size of tube / eq (1)

(b) An explanation that makes reference to four of the following points:
1. tube C / tube D / maggots produce \(CO_{2}\) / \(CO_{2}\) increases (light and dark) / eq (1)
2. by respiration / eq (1)
3. tube B / leaves produce \(CO_{2}\) in dark / \(CO_{2}\) increases / eq (1)
4. tube A / leaves absorb \(CO_{2}\) in the light / \(CO_{2}\) decreases/ eq (1)
5. for photosynthesis /eq (1)
6. tube E no change in \(CO_{2}\) / no gain or loss of \(CO_{2}\) / eq (1)

(c) An explanation that makes reference to two of the following points:
1. carbon dioxide concentration is unchanged / \(CO_{2}\) released and \(CO_{2}\) absorbed / eq (1)
2. respiration and photosynthesis / eq (1)
3. reaction rate is reduced / \(CO_{2}\) increased / eq (1)

Question 5

Loss of trees is known as deforestation.

From 2001 to 2021, Russia, Brazil and Canada had the most deforestation.

Russia lost 76.0 Mha of tree cover. This loss was 10% of forests in Russia. The loss accounted for 17% of the total tree cover lost in the entire world.
Brazil lost 62.8 Mha of tree cover. This loss was 12% of forests in Brazil. The loss accounted for 14% of the total tree cover loss in the entire world.
Canada lost 49.3 Mha of tree cover. This loss was 11% of forests in Canada. This loss accounted for 11% of the total tree cover loss in the entire world.

(a) (i) Use this data to determine the total tree cover loss by countries other than Russia, Brazil and Canada from 2001 to 2021.
(ii) Calculate the loss of tree cover in Brazil per month from 2001 to 2021. Give your answer in standard form.
(iii) Explain why Russia contributed 17% of the total tree cover loss in the entire world even though the loss of tree cover in Russia was only 10%.

(b) Describe the effects of deforestation on an ecosystem.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• Appendix 3: Mathematical skills — parts (a)(i), (a)(ii)
• 5(d): Human influences on the environment — part (a)(iii), (b)
• 5(b): Feeding relationships — part (b)
• 5(c): Cycles within ecosystems — part (b)

▶️ Answer/Explanation

Solution

(a) (i)
Global loss from Russia, Brazil and Canada = \(76.0 + 62.8 + 49.3 = 188.1\) Mha.
Their combined percentage of global loss = \(17\% + 14\% + 11\% = 42\%\).
Therefore, \(42\% = 188.1\) Mha.
\(1\% = \frac{188.1}{42} \approx 4.4786\) Mha.
Total global loss (\(100\%\)) = \(4.4786 \times 100 \approx 447.86\) Mha.
Loss by other countries = Total global loss − Loss by Russia, Brazil, Canada = \(447.86 – 188.1 \approx 259.8\) Mha.
Allow answer in range 258 to 260 Mha.

(a) (ii)
Loss in Brazil from 2001 to 2021 = 62.8 Mha.
Number of months = \(20 \text{ years} \times 12 = 240\) months.
Loss per month = \(\frac{62.8}{240} \approx 0.2617\) Mha.
In standard form = \(2.617 \times 10^{-1}\) Mha per month.
Allow \(2.6 \times 10^{-1}\) or \(2.62 \times 10^{-1}\).

(a) (iii)
An explanation that makes reference to two of the following:
• Russia has the most forest / larger area / bigger country / most tree cover / eq (1)
• Russia makes up a large % of the world’s total tree cover / has a high proportion of the world’s trees / eq (1)
• so even a low percentage change (10%) represents a large absolute amount / eq (1)

(b)
A description that makes reference to four of the following points:
1. reduces biodiversity / loss of species / habitat loss / eq (1)
2. increases CO\(_2\) (in atmosphere) / less CO\(_2\) absorbed / eq (1)
3. less photosynthesis / eq (1)
4. reduced soil quality / less minerals returned to soil / less fertile / leaching / eq (1)
5. soil erosion / soil washed away / eq (1)
6. flooding / eq (1)
7. disturbs water cycle / less transpiration / less rainfall / eq (1)

Question 6

Cells use genetic information when carrying out protein synthesis.

(a) Give the difference between a gene and a genome.

(b) Describe the process of transcription.

(c) Explain why a change in the sequence of bases in the DNA does not always result in a change in enzyme function.

(d) Some characteristics are determined only by the genes, and some are determined by a combination of the genes and the environment. Give an example of each type of characteristic in humans.

determined only by the genes
determined by the genes and the environment

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 4(b): Inheritance — parts (a), (c), (d) [genes, DNA, variation, mutations]
• 4(b): Protein synthesis — part (b) [transcription]
• 2(c): Biological molecules (Enzymes) — part (c) [effect on enzyme function]
• 4(a): Reproduction and inheritance — implicit link to genetic determination of characteristics

▶️ Answer/Explanation

Solution

(a) A gene is a section of DNA that codes for a single polypeptide/protein, whereas a genome includes all of the DNA/all of the genes in an organism. (Requires both parts for the mark.)

(b) A description that makes reference to four of the following points (1 mark each):

DNA unzips/unwinds.
Involves mRNA (messenger RNA).
mRNA copies the code/sequence of the DNA strand (DNA acts as a template).
Process occurs in the nucleus / mRNA leaves the nucleus.
mRNA goes to a ribosome.

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

Some different base sequences/codons may code for the same amino acid (degeneracy of genetic code).
No change in the protein/enzyme is produced.
The mutation may not affect the bonding/3D shape/active site of the enzyme.
The allele may be recessive and therefore not expressed.
The change may be in non-coding DNA.

(d) An answer that makes reference to the following (1 mark each):

Determined only by genes: Blood group, eye colour, iris colour. (Examples of single-gene traits.)
Determined by genes and environment: Mass, height, skin colour, body shape, hair colour, behavioural traits.

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