Edexcel iGCSE Biology 4BI1 - Paper 2B -Selective breeding- Exam Style Questions- New Syllabus

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

Hair colour in cattle is controlled by one gene with two alleles. The allele for white hair, C^W, is codominant with the allele for red hair, C^R.

Heterozygous cattle are a pale red colour called roan.

(a) State what is meant by the term gene.

(b) (i) Complete the table by giving the genotypes of red cattle, white cattle, and roan cattle.

(ii) Two roan-coloured cattle are mated.

Determine the probability that the calf produced is a male calf with roan-coloured hair.

Include a genetic diagram in your answer.

(c) (i) In a group of cattle, there are cattle with white-, red-, and roan-coloured hair. Height of cattle is also a genetically controlled characteristic. In the same group, there is a greater variation of heights compared with hair colour.

Explain why there is a greater variation in height of the cattle than there is in hair colour.

(ii) Describe how a farmer could use selective breeding to increase the height of cattle.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(b): Inheritance — parts (a), (b)(i), (b)(ii), (c)(i)
• 5(b): Selective breeding — part (c)(ii)

▶️ Answer/Explanation

Solution

(a) A gene is a section or length of DNA that codes for a protein, polypeptide, or chain of amino acids.

Explanation: Genes are the fundamental units of heredity. They are specific sequences of DNA nucleotides that carry the instructions for building proteins. These proteins determine various traits and characteristics in organisms, such as hair color in cattle.

(b)(i)

Cattle hair colour	Genotype
red	C^RC^R
white	C^WC^W
roan	C^WC^R or C^RC^W

Explanation: Since the alleles are codominant, heterozygous cattle (C^WC^R) express both colors, resulting in the roan phenotype. Homozygous C^RC^R results in red, and homozygous C^WC^W results in white.

(b)(ii) Probability = 0.25 / ¼ / 25%

Genetic Diagram:

Parental genotypes: C^WC^R × C^WC^R

Parental gametes: C^W or C^R (from each parent)

Offspring genotypes:

1 C^RC^R : red
2 C^WC^R : roan
1 C^WC^W : white

Probability of a roan calf = 2/4 = ½

Probability of a male calf = ½

Therefore, probability of a male roan calf = ½ × ½ = ¼

Explanation: The genetic cross shows that there is a 50% chance of getting a roan calf. The sex of the calf is determined independently, with a 50% chance of being male. To find the combined probability of both events (roan AND male), we multiply the individual probabilities: ½ × ½ = ¼.

(c)(i) Height shows greater variation because it is a polygenic trait, controlled by multiple genes, whereas hair color is monogenic, controlled by a single gene. Additionally, environmental factors like nutrition can influence height but not hair color.

Explanation: Polygenic traits, such as height, involve many genes, each contributing a small effect. This results in a continuous range of phenotypes (e.g., various heights). In contrast, monogenic traits like hair color (controlled by one gene with two codominant alleles) have only three distinct phenotypes (red, white, roan). Furthermore, height can be affected by external factors like diet, while hair color is purely genetic.

(c)(ii) The farmer should select the tallest cattle and breed them together. From their offspring, select the tallest again and breed them. Repeat this process over several generations.

Explanation: Selective breeding works by consistently choosing individuals with the desired trait (height) and allowing them to reproduce. This increases the frequency of alleles associated with tallness in the population over time. By repeating this process, the farmer can gradually increase the average height of the cattle herd.

Question

The photograph shows a plant called a snapdragon.

Selective breeding has been used to produce snapdragons with brightly coloured flowers.

(a) (i) Describe how selective breeding can produce snapdragon plants with brightly coloured flowers.

(ii) Micropropagation is often used to make copies of a snapdragon plant. Describe the process of micropropagation.

(b) Scientists investigate the effect of exposing snapdragon explants to increasing amounts of ionising radiation.

This is the scientists’ method:

take a snapdragon plant and use micropropagation to produce many explants
expose groups of explants to different amounts of ionising radiation
grow the explants into plants and record the number of differences in their phenotypes compared with the original plant
take samples of each of the plants and measure the number of differences in DNA nucleotides of each plant compared with the original plant

(i) Give the reason why micropropagation is used to produce the plants to be tested.

(ii) What term is given to all the DNA in an organism?

A. gene
B. genome
C. genotype
D. nucleoid

(iii) The graph shows the scientists’ results.

Discuss the effects that increasing the amount of ionising radiation has on the snapdragons.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 5(b): Selective breeding — part (a)(i)
• 5(d): Cloning — parts (a)(ii), (b)(i)
• 3(b): Inheritance — parts (b)(ii), (b)(iii)
• 3(b): Mutation — part (b)(iii)

▶️ Answer/Explanation

Solution

(a)(i) Selective breeding for brightly colored snapdragons involves first selecting parent plants that exhibit the desired bright flower coloration. These selected plants are then cross-pollinated to produce offspring. From these offspring, those that display the brightest flowers are selected again. This process of selection and breeding is repeated over several generations, gradually increasing the frequency of alleles responsible for bright flower coloration in the population, eventually producing a true-breeding variety with consistently bright flowers.

(a)(ii) Micropropagation is a tissue culture technique used to rapidly produce large numbers of genetically identical plants (clones). The process begins with taking small tissue samples (explants) from the parent plant, often from meristematic tissue. These explants are sterilized using ethanol or other disinfectants to remove any microorganisms. The sterile explants are then placed on a nutrient-rich agar medium containing essential minerals, sugars, amino acids, and plant growth regulators (such as auxins and cytokinins). Under controlled environmental conditions, the explants develop into small plantlets. These plantlets are eventually transferred to soil where they grow into mature plants genetically identical to the original parent plant.

(b)(i) Micropropagation is used to produce the plants for testing because it generates genetically identical clones. This ensures that any differences observed in phenotypes or DNA after radiation exposure are due to the radiation treatment itself rather than genetic variation between individual plants. Using clones controls for genetic variables, making the experiment more reliable and the results more valid.

(b)(ii) Answer: B (genome)
Explanation: The genome refers to the complete set of DNA in an organism, including all of its genes. A gene is a specific segment of DNA that codes for a particular protein or functional RNA. Genotype refers to the genetic makeup of an individual organism for specific traits. Nucleoid is the region in prokaryotic cells where DNA is located, but not the term for all DNA in an organism.

(b)(iii) Increasing ionising radiation has several effects on snapdragons. Firstly, it causes an increase in DNA mutations, as shown by the rising number of changes in DNA nucleotides. This occurs because radiation damages DNA by breaking strands or altering bases. Secondly, it increases phenotypic variation, as more different phenotypes appear with higher radiation doses. However, the relationship isn’t perfectly proportional – DNA changes increase more rapidly than phenotypic variations. This is because many mutations are silent (don’t change amino acid sequences), occur in non-coding regions, or are recessive and don’t affect the phenotype when heterozygous. Additionally, some mutations may be lethal and not represented in the phenotypic data. At very high radiation levels, the mutation rate may become detrimental to plant survival and reproduction.

Question

Fish farming is often used to produce protein rich food.

(a) Selective breeding is often used to produce fish that grow rapidly and do not waste much food.

Explain how selective breeding can be used to produce fish that grow rapidly.

(b) Fish farming systems can often release ammonia into the water. The ammonia is converted into nitrates.

Describe how ammonia is converted into nitrates.

(c) Multi-trophic level aquaculture is a method of fish farming that has been developed to reduce environmental pollution and increase profits.

The diagram shows a multi-trophic level aquaculture system.

Explain how the multi-trophic level aquaculture system reduces environmental pollution, and increases the profits of fish farming.

Use information from the diagram and your own knowledge to support your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 5(a): Food production — part (a), (c) (fish farming context)
• 5(b): Selective breeding — part (a) (selective breeding in animals)
• 4(c): Cycles within ecosystems — part (b) (nitrogen cycle processes)
• 4(d): Human influences on the environment — part (c) (pollution reduction, sustainable practices)

▶️ Answer/Explanation

Solution

(a)

Explanation: Selective breeding involves a deliberate process to enhance desirable traits. To produce fish that grow rapidly, fish farmers would first identify and select parent fish that already exhibit fast growth rates. These selected fish are then bred together. From their offspring, the fastest-growing individuals are again selected to be the parents for the next generation. By repeating this process over many generations, the alleles (gene variants) responsible for rapid growth become more common in the population, leading to a stock of fish that consistently grows quickly.

(b)

Explanation: The conversion of ammonia to nitrates is a natural biological process called nitrification. This process is carried out by specific types of bacteria known as nitrifying bacteria. These bacteria are autotrophs that obtain energy by oxidizing nitrogen compounds. The process occurs in two main stages. First, bacteria such as Nitrosomonas convert ammonia (NH₃) into nitrites (NO₂⁻). Then, other bacteria, like Nitrobacter, convert these nitrites into nitrates (NO₃⁻). Nitrates are a form of nitrogen that can be more easily utilized by plants and algae.

(c)

Explanation: The multi-trophic level aquaculture system is designed to create a more balanced and efficient ecosystem, which directly addresses pollution and profitability.

Reducing Pollution:

The system significantly reduces solid waste pollution because lobsters and crabs consume the waste food and faeces produced by the main fish stock. This means less organic matter accumulates on the seabed.
With less waste material available, there is a reduction in the population of decomposing bacteria. This is beneficial because these bacteria consume large amounts of oxygen during respiration; therefore, lower bacterial numbers help to maintain higher oxygen levels in the water, preventing oxygen depletion that can kill aquatic life.
Furthermore, the seaweed plays a crucial role in reducing dissolved nutrient pollution. It absorbs nitrates, phosphates, and other minerals from the water that would otherwise act as fertilizers, potentially causing excessive algal growth (algal blooms) and eutrophication. The seaweed also releases oxygen through photosynthesis, further improving water quality.

Increasing Profits:

This system creates additional saleable products. The farmer can now harvest and sell not only the main fish but also the lobsters, crabs, and seaweed, diversifying their income streams.
It also reduces costs. There is no need to purchase extra feed for the lobsters and crabs, as they consume the waste from the fish. Similarly, the seaweed obtains its minerals naturally from the water, eliminating the need for artificial fertilizers.
Healthier fish, resulting from the improved water quality (higher oxygen, lower disease risk), are likely to grow better and have lower mortality rates, leading to higher yields and reduced losses.

Question

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

Toystory

Toystory is a bull who was born in 2001. The photograph shows Toystory.

In the world of dairy farming Toystory is a famous bull. He fathered 500 000 offspring but did not mate with any cows. He was able to father so many offspring because his semen was collected and then used to fertilise cows using artificial insemination.

Toystory’s mother was a high milk producer and his father was a popular bull. He was sold for $4 000 by his owner to a specialist breeding company called Genex.

Genex started to collect semen from Toystory when he was four years old. The semen is carefully collected, using a teaser animal and an artificial rubber vagina.

The semen is divided into many separate samples. These samples are put in small straws and frozen in liquid nitrogen. The straws can then be sold and sent to dairy farmers around the world to inseminate their cows. A total of 2.4 million samples of semen from Toystory was sold in more than 50 countries around the world.

Toystory’s reputation grew as the offspring he fathered went on to be high milk producers. His semen straws sold for over $60 each. Bull semen can now be sold as sexed or unsexed samples, with sexed samples being more expensive to purchase.

Toystory was highly valued because his offspring produced large quantities of milk of a desired composition. His semen was effective at getting cows pregnant, his daughters gave birth easily and were strong. He had a rare mix of fertility, genetics and appearance.

One of his daughters sold for $300 000 in 2009. His record number of offspring is unlikely to be beaten. This is because bulls are often retired earlier as new genetic advances are discovered.

(a) Suggest why Genex waited until Toystory was four years old before beginning to collect his semen (line 9).

(b) Explain how the semen from the bull is used to fertilise cows using artificial insemination.

(c) (i) Suggest why the semen is stored in liquid nitrogen (line 13).
(ii) Sexed semen is guaranteed to produce offspring of one sex. Suggest why dairy farmers would prefer to used sexed semen (line 19).

(d) Determine the percentage success of Toystory’s semen samples in producing offspring (line 2 and line 15).

(e) Describe how scientists could investigate which of two bulls is the best to use as a father in dairy farming.

(f) Explain why the composition of milk is important to consumers (line 22).

(g) (i) Scientists are now using cloning to produce animals. Describe the stages that are required to clone a bull.
(ii) Give two advantages of using cloning rather than selective breeding to produce offspring.

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

• 3(a): Reproduction — parts (a), (b), (c)(ii)
• 5(a): Food production — parts (e), (f)
• 5(b): Selective breeding — part (e)
• 5(d): Cloning — parts (g)(i), (g)(ii)
• 2(d): Movement of substances into and out of cells / Practical application — part (c)(i)
• Appendix 3: Mathematical skills — part (d)

▶️ Answer/Explanation

Solution

(a)
• so semen contained sperm / (bull is) (sexually) mature / sperm in semen / gone through puberty / fully developed.

(b)
An explanation that includes two of the following points:
• collect semen / sperm from penis of bull (1)
• insert straw into / inject semen (into cow) (1)
• put (it / semen / sperm) in vagina / uterus / womb / cervix (1)

(c)(i)
• preserve (sperm) / keep (sperm) alive / viable / prevent growth of microorganisms / slow down metabolism.

(c)(ii)
• provide females (produce milk) / will produce cows.

(d)
$ 500\,000 \div 2.4 \text{ million} = 0.2083 $
Percentage = $ 0.2083 \times 100 = 20.83\% $ (allow 1 mark for ÷ 2.4 million).

(e)
A description that makes reference to three of the following points:
• use semen (from each bull) to fertilise (many / similar) cows (1)
• collect / measure milk yields (1)
• from each daughter / offspring of these cows / mother of bull (1)
• select bull with highest (average) milk yield (across all daughters) (1)

(f)
An explanation that makes reference to two of the following points:
• (milk that contains) (most) fat (1)
• (most) protein (1)
• (most) vitamins (1)
• (milk that contains) (most) calcium (1)

(g)(i)
A description that makes reference to four of the following points:
• nucleus from (body) cell of bull (1)
• insert this nucleus into enucleated egg cell (1)
• electric shock (1)
• mitosis / cell division (1)
• embryo into uterus / womb (1)
• surrogate mother (1)

(g)(ii)
An explanation that makes reference to two of the following points:
• genetically identical / no genetic variation / same (combination of) alleles (1)
• quicker process (1)

Edexcel iGCSE Biology 4BI1 - Paper 2B -Selective breeding- Exam Style Questions- New Syllabus

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