igcse model questions vol1 2019 biology | Essay

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Question 1 View Details
The diagram shows a typical plant cell with its major structures labelled.
Question Parts
(a)
List the labelled structures shown in the diagram.
(b)
Choose any three of the structures listed in part (a) and describe their main functions in the cell.
(c)
Explain how substances move across the cell membrane, mentioning at least two different transport mechanisms.
(d)
Compare a typical plant cell with a typical animal cell, giving two structural differences and one functional implication of each difference.
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Question 2 View Details
The diagram depicts the sequential stages of mitosis in a eukaryotic cell.
Question Parts
(a)
List the stages of mitosis in the correct order as shown in the diagram.
(b)
For each stage listed in part (a), briefly describe the key cellular events that occur.
(c)
Explain the role of spindle fibres during mitosis.
(d)
Compare mitosis with meiosis, giving two major differences in purpose and outcome.
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Question 3 View Details
The diagram shows the human digestive system with the following labelled parts: A – Mouth, B – Esophagus, C – Stomach, D – Liver, E – Pancreas, F – Small intestine, G – Large intestine.
Question Parts
(a)
Identify three organs shown in the diagram that are directly involved in chemical digestion. For each organ, name the principal enzyme it secretes and briefly describe the role of that enzyme in digestion.
(b)
Explain how the structure of the small intestine (part F) maximises the absorption of nutrients.
(c)
A person lacks the enzyme lactase. Explain the likely symptoms they would experience after drinking milk and the physiological reason for those symptoms.
(d)
The inner surface of the small intestine is covered with approximately 10⁹ villi. Each villus contributes about 0.02 mm² to the absorptive area. (i) Estimate the total additional surface area provided by the villi in square metres. (ii) Discuss why such a large surface area is important for digestion.
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Question 4 View Details
A student records the rates of oxygen consumption (VO₂) and carbon dioxide production (VCO₂) of a volunteer at rest and while exercising on a stationary bike. The data obtained are shown in the table below. | Activity | VO₂ (mL·min⁻¹) | VCO₂ (mL·min⁻¹) | |----------|----------------|-----------------| | Rest | 250 | 200 | | Exercise | 800 | 720 | Assume the measurements are taken under steady‑state conditions.
Question Parts
(a)
Describe the main physiological changes that occur in the respiratory system when a person moves from rest to moderate exercise.
(b)
(i) Calculate the respiratory quotient (RQ) at rest and during exercise. (ii) Explain what the difference in RQ values indicates about the predominant metabolic substrate being used.
(c)
Discuss how the body regulates breathing rate to maintain blood pH within the normal range during and after exercise.
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Question 5 View Details
The circulatory system transports nutrients, gases and waste products throughout the human body.
Question Parts
(a)
Describe the complete pathway of blood from the right side of the heart to the lungs and back to the left side of the heart, mentioning the role of the valves encountered.
(b)
Explain how oxygen is transported in the blood and why haemoglobin is essential for this process.
(c)
A mountaineer ascends to an altitude of 3000 m where the atmospheric pressure is lower. Discuss how this altitude affects the transport of oxygen in the blood and the physiological adjustments that help maintain oxygen delivery to tissues.
(d)
During moderate exercise a student’s heart rate rises from a resting 70 bpm to 110 bpm. (i) Calculate the percentage increase in heart rate. (ii) Explain why the heart rate increases during exercise in terms of transport requirements.
() Calculate the percentage increase in heart rate.
() Explain why the heart rate increases during exercise in terms of transport requirements.
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Question 6 View Details
The labelled diagram shows the major structures of the human excretory system.
Question Parts
(a)
Trace the complete route taken by urine from its formation in the kidney to its exit from the body, naming each structure it passes through.
(b)
For each of the following nephron components – glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct – explain its specific role in the processes of filtration, reabsorption and secretion.
(c)
A patient suffers from a blockage in the left ureter. Discuss the likely physiological consequences of this condition on (i) urine accumulation, (ii) blood pressure regulation, and (iii) overall fluid balance.
(d)
Compare the excretory adaptations of humans with those of freshwater fish, focusing on how each organism conserves water and eliminates nitrogenous waste.
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Question 7 View Details
A 20‑year‑old athlete runs for 30 minutes at a moderate pace. During the exercise his core body temperature rises and his skin becomes moist with sweat.
Question Parts
(a)
Describe the role of the hypothalamus in maintaining body temperature during the exercise.
(b)
Explain how vasodilation of cutaneous blood vessels and sweating together help to reduce the rise in body temperature.
(c)
Predict what would happen if the negative feedback loop controlling temperature were impaired, and suggest two possible health consequences.
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Question 8 View Details
A person reaches out to pick up a glass of water from a table and then brings the glass to his mouth.
Question Parts
(a)
Outline the neural pathway from the sensory receptors in the hand to the motor neurons that cause the hand to close around the glass.
(b)
Compare the roles of the cerebellum and the basal ganglia in coordinating this movement.
(c)
A patient suffers a lesion in the corticospinal tract. Discuss how this would affect the ability to perform the task described, and explain why.
(d)
Suggest one rehabilitation strategy that could help restore coordinated movement in such a patient, and justify its basis.
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Question 9 View Details
A female rabbit (Oryctolagus cuniculus) has been artificially inseminated and is being monitored throughout her pregnancy. The normal gestation period for this species is 31 days.
Question Parts
(a)
Describe the sequence of events from fertilisation to implantation in a typical mammalian pregnancy, stating where fertilisation normally occurs and the key cellular changes that take place.
(b)
Explain the role of progesterone in maintaining pregnancy in rabbits and discuss the likely consequences if progesterone levels were to fall sharply before day 25 of gestation.
(c)
The rabbit in this case gave birth after 28 days instead of the normal 31 days. Discuss at least two plausible biological reasons for this shortened gestation and the possible effects on the newborn kits.
(d)
Evaluate the advantages and disadvantages of viviparous (live‑birth) versus oviparous (egg‑laying) reproduction in mammals, focusing on parental investment, offspring survival and environmental constraints.
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Question 10 View Details
In a small community, a hereditary disorder shows the following pattern over three generations: - Generation I: Affected male (II-1) marries an unaffected female. - Generation II: Their two children, a son (III-1) and a daughter (III-2), are both unaffected. - Generation III: The son (III-1) marries an unaffected female and has two children, both affected. The daughter (III-2) marries an unaffected male and has one child, who is unaffected. No other family members are reported to have the disorder.
Question Parts
(a)
Identify the most likely mode of inheritance for this disorder and justify your answer using the information given.
(b)
Assuming the disorder is autosomal recessive, calculate the probability that two unaffected carriers (both heterozygous) will have a child who is (i) affected, (ii) a carrier, and (iii) completely free of the mutant allele.
(c)
Explain how crossing‑over during meiosis contributes to genetic variation and discuss how it could affect the frequency of this disorder in future generations.
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