igcse model questions vol1 2021 biology | Essay

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Question 1 View Details
The diagram shows a typical animal cell with several organelles labelled 1–6.
Question Parts
(a)
Identify the organelle represented by each label (1‑6).
(b)
Explain the main function of the mitochondrion and the ribosome.
(c)
Compare an animal cell with a typical plant cell in terms of structures that are present in the plant cell but absent in the animal cell shown in the diagram.
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Question 2 View Details
The labelled diagram depicts the successive stages of mitosis in a eukaryotic cell, labelled A–D.
Question Parts
(a)
Identify the mitotic stage represented by each label (A, B, C, D).
(b)
For each stage, briefly describe the key events that occur.
(c)
Explain why accurate segregation of chromosomes during mitosis is essential for the organism, and state one possible consequence of an error in this process.
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Question 3 View Details
The diagram shows a labelled human digestive system highlighting the mouth, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, liver, pancreas and gallbladder.
Question Parts
(a)
For each organ shown, briefly describe its principal function in the digestion and absorption of nutrients.
(b)
State where the majority of carbohydrate, protein and lipid digestion occurs and give a brief justification for each.
(c)
A diet supplies 2500 kJ from carbohydrates, 1500 kJ from proteins and 2000 kJ from fats. (i) Calculate the mass in grams of each macronutrient consumed. (ii) The recommended energy distribution is 55 % carbohydrate, 15 % protein and 30 % fat. Comment on whether the diet meets these recommendations.
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Question 4 View Details
The labelled diagram shows the main structures of the human respiratory system.
Question Parts
(a)
Describe the complete pathway that air follows from the external environment to the alveoli, naming each structure it passes through.
(b)
Explain how the diaphragm and the external intercostal muscles cooperate during inhalation and how they behave during normal (quiet) exhalation.
(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 the direction of diffusion of oxygen and why this diffusion is essential for cellular respiration.
(d)
A person suffers a blockage in the right main bronchus. Discuss two physiological consequences of this condition on gas exchange.
(e)
Tidal volume and minute ventilation:
() Define tidal volume.
() If a person’s tidal volume is 500 mL and they breathe 12 times per minute, calculate the minute ventilation. Show your working.
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Question 5 View Details
Explain how water is transported through a plant and the factors that influence the rate of transport.
Question Parts
(a)
Describe the complete pathway that water follows from the soil to the mesophyll cells of a leaf, naming the structures involved.
(b)
A 2.5 m‑tall tree has a total leaf area of 0.05 m². Its average transpiration rate is 0.8 mm h⁻¹. Estimate the volume of water lost from the tree in a 24‑hour period. Show the reasoning you use.
(c)
Discuss two structural or physiological adaptations that desert plants possess to reduce water loss, explaining how each adaptation works.
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Question 6 View Details
Describe the processes involved in human excretion and the factors that regulate urine formation.
Question Parts
(a)
Outline the three main processes that produce urine in the kidney, stating where each process occurs.
(b)
A person drinks 2 L of water per day. Their kidneys filter 180 L of plasma each day. If 99 % of the filtrate is re‑absorbed, calculate the volume of urine produced in a day.
(c)
Explain how the hormone antidiuretic hormone (ADH) influences the concentration of urine and give one physiological situation in which ADH secretion is increased.
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Question 7 View Details
The maintenance of internal stability (homeostasis) is essential for the proper functioning of the human body.
Question Parts
(a)
Explain how the pancreas contributes to the regulation of blood glucose concentration, describing the hormones involved and the feedback mechanism.
(b)
A person with type 1 diabetes is unable to produce insulin. Predict the immediate effect on blood glucose concentration and describe two physiological consequences of prolonged hyperglycaemia.
(c)
Suggest two lifestyle measures that can help a person with diabetes maintain glucose homeostasis and justify how each measure contributes to regulation.
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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)
Describe the complete pathway of a stretch reflex, naming all structures involved from the sensory receptor to the effector muscle.
(b)
Explain how calcium ions facilitate neurotransmitter release at a chemical synapse and how the signal is terminated.
(c)
Compare the speed of nerve impulse transmission in myelinated and unmyelinated nerve fibres and explain why the difference occurs.
(d)
Multiple sclerosis involves loss of myelin in the central nervous system. Predict two effects this demyelination can have on a person’s coordination and propose one therapeutic approach for each effect.
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Question 9 View Details
Human reproduction involves a complex interplay of anatomical structures, hormones and cellular events. Answer the following questions in detail.
Question Parts
(a)
Describe the hormonal regulation of the menstrual cycle, giving particular attention to the feedback mechanisms that operate during the follicular phase, the mid‑cycle LH surge and the luteal phase.
(b)
Explain the sequence of events that occur from the moment a sperm reaches the ovum to the formation of the zygote, and describe the changes that prevent polyspermy.
(c)
Two widely used contraceptive methods are the combined oral contraceptive pill (COCP) and the intra‑uterine device (IUD). Evaluate both methods in terms of effectiveness, side‑effects and suitability for different groups of women.
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Question 10 View Details
Genetics explores how traits are transmitted and how modern techniques can detect genetic variation. Answer the following questions.
Question Parts
(a)
Two genes, A and B, are located on the same chromosome with a recombination frequency of 20 %. An individual heterozygous for both genes (genotype AaBb) is in coupling phase (chromosome 1 carries AB, chromosome 2 carries ab). This individual is crossed with a homozygous recessive aabb. Calculate the expected phenotypic ratio of the offspring, assuming A and B are each dominant over a and b respectively.
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