7 (a) Explain the role of the nucleus and cell division in the inheritance of characteristics from parents to offspring. … … … … … … … … [6] (b) If people are exposed to ionising radiation, this may affect the inheritance of characteristics by their children. Suggest how this exposure to radiation may affect inheritance of characteristics. … … … … … … [4] [Total: 10]

7(a) any six from: chromosomes ; DNA / genetic material ; genes / alleles ; code AW + for proteins ; proteins determine characteristics ; meiosis / meiotic division ; reduction division / produces haploid cells / produces gametes AW ; fertilisation / fertilisation described ; combination/mix + of genetic material / genes / chromosomes / DNA / characteristics ; 6 7(b) any four from: increases the chance / probability of; mutation ; change in chromosome number ; change in gene structure / sequence ; codes for new/different/incorrect protein ; may result in new beneficial variation ; may result in genetic disease / example of genetic condition ; 4

2 In 1931 a scientist was pouring the powdered form of a chemical called PTC into a bottle. A small amount of the powder accidentally blew into the air. A short time later another scientist working in the same room said that she had a bitter taste in her mouth from the powder in the air. (a) Describe, with reference to named components of the nervous system, the nervous pathway that led to the scientist detecting that the powder tasted bitter. … … … … … … … … [4] (b) The scientist pouring the powder did not detect any bitter taste. It was later found that inheritance of two forms of the same gene determine if a person is able to detect a bitter taste from PTC or not. (i) State the term used for different forms of the same gene. … [1] (ii) Several years afterwards, it was found that environmental factors cause people to detect a range of different strengths of bitter taste from PTC. State the type of variation now known to be shown by this characteristic. … [1] (c) Chemicals similar to PTC with a bitter taste are produced by some plants to prevent them from being eaten. Animals that eat only plants have fewer genes that enable them to detect chemicals that taste bitter than animals that eat both plants and animals. (i) State the trophic level of plants in a food web. … [1] (ii) State the term used for animals that eat only plants. … [1] (iii) Suggest why animals that eat only plants have fewer genes that enable them to detect chemicals that taste bitter than animals that eat both plants and animals. … … … … [2] [Total: 10]

2(a) 1 impulse ; 2 receptor / taste bud / tongue / sensor / nerve endings / sensory endings ; 3 sensory + neurone / nerve ; 4 brain / CNS ; 4 2(b)(i) alleles ; 1 2(b)(ii) continuous ; 1 2(c)(i) producer / one / first ; 1 2(c)(ii) herbivores ; 1 2(c)(iii) 1 all energy / all nutrients or named + from plants ; 2 food / plants + taste less bitter ; 3 more food / eat more / more variety of food ; 4 mutation / natural selection / evolution / survival of the fittest ; 2 (a) To earn these marks, you need to describe the pathway starting with an impulse, identifying the receptor (e.g., taste bud/tongue), then the sensory neurone/nerve, and finally the brain/CNS. (b)(i) To earn this mark, you must state 'alleles'. (b)(ii) To earn this mark, you must state 'continuous'. (c)(i) To earn this mark, you must state 'producer' or 'first'. (c)(ii) To earn this mark, you must state 'herbivores'. (c)(iii) To earn these marks, you need to explain that all energy/nutrients come from plants, that the food/plants taste less bitter, leading to more food consumption/variety, and mention mutation/natural selection/evolution/survival of the fittest.

5 (a) The passage describes the nucleus of a cell with missing words replaced by the letters J, K, L and M. Read the passage, then select words from the list below the passage to replace letters J, K, L and M. In the nucleus of a body cell from a person with Down’s syndrome, there are J thread- like structures called K. These are made up of many units called L that instruct the cell to produce a particular M. carbohydrate chromosomes DNA fat forty-seven genes protein twenty-four twenty-three J … K … L … M … [4] (b) When suddenly exposed to bright light, some people automatically sneeze. This is known as the photic sneeze reflex. The photic sneeze reflex is the result of the possession of a dominant allele A. Use a genetic diagram to show how parents, both with the photic sneeze reflex, can have a child who is not affected by the photic sneeze reflex. [3] [Total: 7]

5(a) J 47 ; K chromosomes ; L genes ; M protein ; 4 5(b) Aa x Aa ; aa correctly derived and identified ; correct use of the words parents + gametes / genotype + phenotype ; 3 To earn marks, correctly fill in the blanks: J is 'forty-seven', K is 'chromosomes', L is 'genes', and M is 'protein'. For the genetic diagram, show the parents' genotypes as 'Aa x Aa', correctly derive and identify 'aa' as the genotype for the unaffected child, and use genetic terminology like 'parents', 'gametes', 'genotype', and 'phenotype' correctly.

6 The diagram shows a magnified image of the chromosomes from one skin cell of a person. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 19 20 21 22 X Y 16 17 18 (a) State two conclusions that can be made about this person using only information in the diagram and explain each conclusion. 1 … … … … … 2 … … … … … [5] (b) Name the type of gamete produced by a human male. … Outline the process for producing this type of gamete. … … … … … … … [5] [Total: 10]

6(a) male ; X + Y / non-matching sex chromosomes ; Down's syndrome ; 47 + not 46 (chromosomes) ; three / extra + (chromosome) 21 ; 5 6(b) type of gamete: sperm ; process: testes ; meiosis / reduction division ; chromosome number halved ; haploid ; 5 To earn marks, you must state two conclusions and explain each, such as identifying the person as male due to the presence of X and Y chromosomes, and identifying Down's syndrome due to 47 chromosomes or an extra chromosome 21. To earn marks, you must state that the type of gamete is sperm, the process occurs in the testes, it is meiosis (reduction division), and that the chromosome number is halved, resulting in haploid cells.

Cambridge O Level Biology · 5090

O-Level Biology (5090) Inheritance past paper questions

Revise O-Level Biology (5090) — Inheritance with real Cambridge past-paper questions grouped by topic, each shown with its marking scheme. Working one topic at a time targets exactly the skill each question tests.

90 free questions from 2017–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Inheritance in O-Level Biology 5090 exams, 2020–2025

Across 2020–2025, Inheritance accounted for 100 questions worth 400 marks in Cambridge O Level Biology (5090) papers.

By year
Year	Questions	Marks
2020	20	62
2021	13	22
2022	14	60
2023	17	102
2024	17	58
2025	19	96

Most-tested subtopics

17.3 Inheritance157 marks
17.2 DNA132 marks
17.4 Selection105 marks

Appears in

Paper 1 · 70 qs
Paper 2 · 30 qs

All most-tested Biology topics

2021 Oct/Nov · Paper 2 · Q7 · 10 marks
Marking scheme
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2020 Oct/Nov · Paper 2 · Q2 · 10 marks
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2020 May/Jun · Paper 2 · Q5 · 7 marks
Marking scheme
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2020 May/Jun · Paper 2 · Q6 · 10 marks
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2021 May/Jun · Paper 1 · Q37 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q37
Answer: A
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