igcse model questions vol1 2025 biology | Essay

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Question 1 View Details
The labelled diagram shows a typical animal cell with the parts numbered as follows: 1 = cell membrane, 2 = cytoplasm, 3 = nucleus, 4 = nucleolus, 5 = mitochondrion, 6 = ribosome.
Question Parts
(a)
State the main function of each of the following structures: nucleus, mitochondrion and ribosome.
(b)
Explain how the cell membrane regulates the movement of substances into and out of the cell, making reference to the diagram.
(c)
Compare the structure of the cell membrane with that of a typical plant cell wall and explain why the plant cell wall is important.
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Question 2 View Details
The labelled diagram shows an animal cell at six successive stages of mitosis (panels A–F).
Question Parts
(a)
Identify the stage shown in each panel.
() Panel A shows which stage?
() Panel B shows which stage?
() Panel C shows which stage?
() Panel D shows which stage?
() Panel E shows which stage?
() Panel F shows which stage?
(b)
For the stage identified as metaphase, describe the arrangement of chromosomes and the role of the spindle fibres.
(c)
Explain why cytokinesis results in two daughter cells with identical chromosome numbers. Include reference to the preceding stages of mitosis.
(d)
A researcher uses a drug that disrupts spindle‑fibre formation. Predict the most likely effect on the stages of mitosis and on the final chromosome number in the daughter cells. Justify your answer.
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Question 3 View Details
The diagram shows the main parts of the human digestive system.
Question Parts
(a)
Identify each numbered part in the diagram by writing its correct name.
(b)
For each organ you identified, describe its principal role in the digestion and absorption of nutrients.
(c)
Explain how the structure of the small intestine is adapted to maximise nutrient absorption.
(d)
A person changes from a diet high in carbohydrates to one high in protein. Discuss two physiological changes in the digestive system that would occur to accommodate the new diet.
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Question 4 View Details
The diagram shows the major structures of the human respiratory system.
Question Parts
(a)
Describe, in the correct order, the complete pathway that air follows from the external environment to the site where gas exchange occurs. Name each structure the air passes through.
(b)
Explain the roles of the diaphragm and the external intercostal muscles during (i) inhalation and (ii) exhalation, and state how their actions affect the volume of the thoracic cavity.
(c)
The partial pressure of oxygen (pO₂) in alveolar air is 0.16 atm and in the blood of the pulmonary capillaries it is 0.13 atm. Using these values, explain why oxygen diffuses from the alveoli into the blood, referring to the principles of diffusion.
(d)
A swimmer at sea level (atmospheric pressure 1.0 atm) takes a deep breath and holds it for 5 seconds before diving. Discuss two physiological advantages of this breath‑holding technique for the swimmer.
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Question 5 View Details
In mammals, the transport of oxygen from the external environment to the cells involves several structures and processes.
Question Parts
(a)
Describe the complete pathway that oxygen follows from the moment it is inhaled until it reaches the body cells. Include all major anatomical structures.
(b)
Explain how the structural features of capillary walls enable efficient exchange of oxygen and carbon dioxide between the blood and surrounding tissues.
(c)
A student records a partial pressure of oxygen (pO₂) of 100 kPa in alveolar air but only 95 kPa in systemic arterial blood. Discuss two physiological factors that could account for this difference.
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Question 6 View Details
The human kidney is essential for excretion and the maintenance of internal homeostasis.
Question Parts
(a)
Outline the route taken by blood through the kidney, naming each major structure from the renal artery to the renal vein.
(b)
Explain two key processes that enable the kidney to regulate the volume and composition of urine.
(c)
A patient with a deficiency of antidiuretic hormone (ADH) produces a large volume of dilute urine. Predict two changes that are likely to occur in the composition of the blood plasma and explain the physiological basis for each change.
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Question 7 View Details
The maintenance of internal conditions within narrow limits is essential for normal cellular function.
Question Parts
(a)
Describe the negative feedback mechanism that regulates blood glucose concentration after a meal.
(b)
Explain the role of glucagon in restoring blood glucose when it falls below normal.
(c)
Predict the short‑term and long‑term physiological consequences if insulin secretion is severely reduced.
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Question 8 View Details
Coordination of activities in the human body is achieved through the nervous and endocrine systems.
Question Parts
(a)
Compare the speed and specificity of neural communication with hormonal communication, giving one advantage and one limitation of each system.
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Question 9 View Details
A 22‑year‑old woman reports irregular menstrual cycles over the past six months and seeks advice on managing her reproductive health.
Question Parts
(a)
Explain the hormonal regulation of the normal menstrual cycle, describing the roles of the key hormones in each phase.
(b)
Identify two possible hormonal causes of her irregular cycles and briefly explain how each disrupts the normal pattern.
(c)
Discuss two modern contraceptive methods, outlining their mechanism of action, one major advantage and one disadvantage of each.
(d)
Evaluate how two lifestyle factors can influence her fertility, giving one positive and one negative effect for each factor.
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Question 10 View Details
A plant breeder is developing a new tomato variety that is resistant to a fungal disease. Resistance is controlled by a single recessive allele (r). The breeder crosses a heterozygous resistant plant (Rr) with a homozygous susceptible plant (RR).
Question Parts
(a)
Predict the genotypic and phenotypic ratios expected in the F1 generation.
(b)
Two F1 plants are inter‑crossed. Calculate the probability that a randomly selected F2 seed will be resistant to the disease.
(c)
Occasionally the observed proportion of resistant seedlings deviates from 25 %. The breeder suspects that the resistance gene is linked to a gene controlling fruit size (S) with a recombination frequency of 10 %. Explain how a test cross could be used to confirm linkage and state the expected phenotypic ratios among the progeny if the two genes are linked with 10 % recombination.
(d)
Discuss two ethical considerations that should be taken into account before releasing a genetically modified tomato variety with disease resistance into the market.
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