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O Level Combined Science Life Sciences Quiz

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Questions

O-Level Combined Science Quiz - Life Sciences

Name: _________________________ Class: _________________________ Date: _________________________ Score: _____ / 40

Duration: 45 minutes Total Marks: 40

Instructions:

This quiz contains 20 questions on Life Sciences topics.
Answer ALL questions in the spaces provided.
Show all working where applicable.
Marks are indicated in brackets [ ].

Section A: Cell Biology and Movement of Substances [10 marks]

Answer all questions in this section.

1. The diagram below shows a typical animal cell as seen under a light microscope.

Image pending generation for this question.

(a) Name the structure labelled X that controls all activities of the cell. [1]

X: _________________________

(b) State one function of the structure labelled Y (mitochondrion). [1]

2. A student places a drop of concentrated salt solution on a slide containing red blood cells and observes them under a microscope.

(a) Describe what happens to the red blood cells. [1]

(b) Explain your answer in terms of water potential. [2]

3. The table below shows the concentration of four mineral ions in a root hair cell and in the surrounding soil solution.

Mineral ion	Concentration in root hair cell (arbitrary units)	Concentration in soil solution (arbitrary units)
Potassium	80	20
Nitrate	120	30
Calcium	15	25
Magnesium	10	8

(a) Which mineral ion is absorbed by active transport? Explain your choice. [2]

(b) State one factor that would reduce the rate of active transport of this ion. [1]

4. A plant cell is placed in distilled water. The cell does not burst.

(a) Name the structure that prevents the plant cell from bursting. [1]

(b) State the term used to describe a plant cell that is fully turgid. [1]

5. The diagram below shows an enzyme-catalysed reaction.

Image pending generation for this question.

(a) Name the part of the enzyme labelled Z where the substrate binds. [1]

Z: _________________________

(b) Explain why an enzyme is described as a biological catalyst. [1]

Section B: Human Physiology – Nutrition and Enzymes [10 marks]

Answer all questions in this section.

6. The diagram below shows part of the human digestive system.

Image pending generation for this question.

(a) Name the organ labelled P where most nutrient absorption occurs. [1]

P: _________________________

(b) State two structural adaptations of organ P that increase the rate of absorption. [2]

7. An experiment was carried out to investigate the effect of pH on the activity of enzyme amylase. The results are shown in the table below.

pH	Time taken to digest starch (minutes)
2	No digestion after 30 minutes
4	25
6	10
7	5
8	8
10	No digestion after 30 minutes

(a) State the optimum pH for amylase activity. [1]

(b) Explain why no digestion occurred at pH 2 and pH 10. [2]

8. A person consumes a meal rich in proteins.

(a) Name the enzyme in the stomach that begins protein digestion. [1]

(b) State the pH condition in the stomach and explain why this condition is necessary for the enzyme named in (a). [2]

9. The diagram below shows a villus in the small intestine.

Image pending generation for this question.

(a) Name the vessel labelled Q that absorbs fatty acids and glycerol. [1]

Q: _________________________

(b) Explain how the structure of a villus helps in the absorption of glucose. [1]

10. A student investigates the effect of temperature on the activity of lipase.

(a) State the substrate that lipase acts on. [1]

(b) Predict the effect of boiling the lipase solution before adding the substrate. Explain your answer. [1]

Section C: Transport and Respiration in Humans [10 marks]

Answer all questions in this section.

11. The diagram below shows a section through the human heart.

Image pending generation for this question.

(a) Name the chamber labelled A that pumps blood to the lungs. [1]

A: _________________________

(b) State one difference between the wall of chamber A and the wall of chamber B (left ventricle). Explain the reason for this difference. [2]

12. The table below shows the composition of inhaled air and exhaled air.

Gas	Inhaled air (%)	Exhaled air (%)
Oxygen	21	16
Carbon dioxide	0.04	4
Nitrogen	78	78
Water vapour	Variable	Saturated

(a) Explain why the percentage of oxygen decreases in exhaled air. [1]

(b) State the process by which carbon dioxide is transported from body cells to the lungs. [1]

13. An athlete runs a 100-metre sprint.

(a) State the type of respiration that occurs in the athlete's muscle cells during the sprint. [1]

(b) Name the substance that accumulates in the muscles during this type of respiration. [1]

14. The diagram below shows the human respiratory system.

Image pending generation for this question.

(a) Name the structure labelled R where gaseous exchange occurs. [1]

R: _________________________

(b) State one feature of structure R that makes gaseous exchange efficient. [1]

15. A person has a disease that reduces the number of red blood cells.

(a) Name the substance in red blood cells that transports oxygen. [1]

(b) Explain why this person feels tired easily. [1]

Section D: Molecular Genetics, Inheritance, and Ecology [10 marks]

Answer all questions in this section.

16. The diagram below shows a short section of a DNA molecule.

Image pending generation for this question.

(a) Name the sugar molecule present in DNA. [1]

(b) State the base-pairing rule in DNA. [1]

(c) A DNA molecule contains 30% thymine. Calculate the percentage of guanine in this DNA molecule. Show your working. [2]

17. In pea plants, the allele for tall stem (T) is dominant over the allele for short stem (t). A heterozygous tall pea plant is crossed with a short pea plant.

(a) State the genotype of the heterozygous tall pea plant. [1]

(b) Using a genetic diagram, determine the expected ratio of tall to short offspring. [3]

18. The diagram below shows a simple food web in a freshwater pond.

Image pending generation for this question.

Algae → Water flea → Small fish → Kingfisher Algae → Tadpole → Small fish → Kingfisher

(a) Name the producer in this food web. [1]

(b) State the source of energy for this food web. [1]

(c) If all the small fish are removed from the pond, predict what would happen to the population of water fleas. Explain your answer. [2]

19. The diagram below shows the carbon cycle.

Image pending generation for this question.

(a) Name the process labelled S that removes carbon dioxide from the atmosphere. [1]

S: _________________________

(b) State one human activity that increases the amount of carbon dioxide in the atmosphere. [1]

20. A farmer uses a pesticide to kill insects on his crops.

(a) Explain why some insects survive after repeated use of the same pesticide. [2]

(b) State one disadvantage of using pesticides. [1]

END OF QUIZ

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Answers

O-Level Combined Science Quiz - Life Sciences: Answer Key

Total Marks: 40

Section A: Cell Biology and Movement of Substances [10 marks]

1. (a) Nucleus [1]

(b) Site of aerobic respiration / releases energy (ATP) for cell activities [1]

2. (a) The red blood cells shrink / become crenated [1]

(b) The salt solution has a lower water potential than the cell contents / cytoplasm. Water moves out of the cells by osmosis, from a region of higher water potential to a region of lower water potential, through the partially permeable cell membrane. [2] Award 1 mark for correct water potential comparison; 1 mark for water movement direction and membrane.

3. (a) Potassium and nitrate ions are absorbed by active transport. Their concentration is higher inside the root hair cell than in the soil, so they must be absorbed against the concentration gradient, which requires energy (active transport). [2] Award 1 mark for identifying ions with higher internal concentration; 1 mark for explaining movement against concentration gradient.

(b) Lack of oxygen (which reduces respiration and ATP production) / low temperature (which reduces enzyme activity and respiration rate) / presence of a respiratory inhibitor (e.g., cyanide). [1] Accept any one valid factor.

4. (a) Cell wall [1]

(b) Turgid [1]

5. (a) Active site [1]

(b) An enzyme speeds up a chemical reaction without being chemically changed at the end of the reaction. [1]

Section B: Human Physiology – Nutrition and Enzymes [10 marks]

6. (a) Small intestine / ileum [1]

(b) Any two from:

It is very long, providing a large surface area for absorption.
Its inner wall is folded into villi, further increasing surface area.
The epithelial cells of the villi have microvilli, increasing surface area.
The villi have a dense network of blood capillaries to transport absorbed nutrients away quickly, maintaining a concentration gradient.
The epithelium is one cell thick, providing a short diffusion distance. [2] Award 1 mark for each correct adaptation, maximum 2.

7. (a) pH 7 [1]

(b) At pH 2 and pH 10, the enzyme amylase is denatured. The extreme pH alters the shape of the active site, so the starch substrate can no longer fit, and no enzyme-substrate complex can form. [2] Award 1 mark for denaturation; 1 mark for explanation linking active site shape to loss of function.

8. (a) Pepsin [1]

(b) The stomach has a pH of about 2 (acidic). Pepsin works optimally at this low pH; the acidic condition also helps to kill bacteria in food and provides the right environment for pepsin to function. [2] Award 1 mark for stating acidic pH; 1 mark for linking to pepsin function or bacterial killing.

9. (a) Lacteal [1]

(b) The villus has a thin epithelium (one cell thick) which provides a short diffusion distance for glucose absorption. [1] Accept any other valid structural adaptation linked to glucose absorption.

10. (a) Lipids / fats / oils [1]

(b) No digestion would occur. Boiling denatures the lipase enzyme; the shape of the active site is permanently changed, so the substrate can no longer bind to it. [1]

Section C: Transport and Respiration in Humans [10 marks]

11. (a) Right ventricle [1]

(b) The wall of chamber B (left ventricle) is thicker than the wall of chamber A (right ventricle). The left ventricle pumps blood to the whole body (systemic circulation), requiring greater pressure to overcome the resistance of a longer pathway. The right ventricle only pumps blood to the nearby lungs (pulmonary circulation). [2] Award 1 mark for stating the difference; 1 mark for correct explanation.

12. (a) Oxygen is used by body cells for aerobic respiration, so less oxygen remains in exhaled air. [1]

(b) Carbon dioxide is transported dissolved in blood plasma / as hydrogen carbonate ions in plasma / bound to haemoglobin in red blood cells. [1] Accept any one correct method.

(c) Bubble the gas through limewater (calcium hydroxide solution). Carbon dioxide turns limewater milky / cloudy. [2] Award 1 mark for test; 1 mark for observation.

13. (a) Anaerobic respiration [1]

(b) Lactic acid [1]

(c) The athlete breathes heavily to take in extra oxygen to repay the oxygen debt. The oxygen is needed to oxidise / break down the accumulated lactic acid into carbon dioxide and water, or convert it back to glucose in the liver. [1]

14. (a) Alveolus / alveoli [1]

(b) Any one from:

Thin walls (one cell thick) for short diffusion distance.
Dense network of blood capillaries to maintain concentration gradient.
Moist surface to allow gases to dissolve. [1]

15. (a) Haemoglobin [1]

(b) Less haemoglobin means less oxygen can be transported to body cells. Less aerobic respiration occurs, so less energy is released, causing tiredness. [1]

Section D: Molecular Genetics, Inheritance, and Ecology [10 marks]

16. (a) Deoxyribose [1]

(b) Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G). [1] Accept: A-T and C-G base pairing.

(c) If thymine = 30%, then adenine = 30% (base pairing). Total A + T = 60%. Remaining 40% is C + G. Therefore, guanine = 40% ÷ 2 = 20%. [2] Award 1 mark for correct reasoning; 1 mark for correct answer with working.

17. (a) Tt [1]

(b) Parental genotypes: Tt × tt Gametes: T, t and t, t

	T	t
t	Tt	tt
t	Tt	tt

Offspring genotypes: 2 Tt (tall) : 2 tt (short) Phenotypic ratio: 1 tall : 1 short [3] Award 1 mark for correct gametes; 1 mark for correct Punnett square or equivalent; 1 mark for correct ratio.

18. (a) Algae [1]

(b) Light energy from the Sun [1]

(c) The population of water fleas would increase. With the removal of small fish, there is less predation on water fleas. More water fleas survive and reproduce, leading to population growth. [2] Award 1 mark for prediction; 1 mark for explanation linking reduced predation to population increase.

19. (a) Photosynthesis [1]

(b) Burning of fossil fuels / deforestation / combustion. [1] Accept any one valid human activity.

20. (a) Some insects have a natural genetic variation that makes them resistant to the pesticide. These resistant insects survive and reproduce, passing on the resistant allele to their offspring. Over time, the population of resistant insects increases. [2] Award 1 mark for idea of natural variation/resistance; 1 mark for survival and reproduction passing on resistance.

(b) Any one from:

Pesticides may kill non-target / beneficial organisms (e.g., pollinators).
Pesticides may remain in the environment and accumulate in food chains (bioaccumulation).
Pests may develop resistance over time. [1]

END OF ANSWER KEY