ijmb model questions vol1 2020 biology | Essay

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Question 1 View Details
The diagram shows a typical animal cell with eight numbered structures (1‑8).
Question Parts
(a)
Identify the organelle represented by each number (1‑8).
(b)
State the principal function of each organelle, giving particular attention to (i) protein synthesis and (ii) cellular energy metabolism where relevant.
(c)
Discuss how the plasma membrane contributes to cellular homeostasis, citing the role of its phospholipid bilayer and transport proteins.
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Question 2 View Details
The illustration shows an animal cell at successive stages of mitosis. The four stages are labelled I, II, III and IV. Six cellular structures are labelled as follows: A – condensed chromosome, B – spindle fibre, C – centriole pair, D – nuclear envelope, E – separated sister chromatids, F – cytokinetic furrow.
Question Parts
(a)
Identify the stage represented by each of I, II, III and IV (e.g., prophase, metaphase, anaphase, telophase).
(b)
For each stage (I–IV) describe two key events that occur, making reference to the labelled structures (A–F).
(c)
If a complete mitotic division in this cell type takes 60 minutes and the relative durations are: prophase 30 %, metaphase 20 %, anaphase 15 % and telophase 35 %, calculate the time (in minutes) spent in each stage.
(d)
Briefly compare mitosis with meiosis I in terms of (i) chromosome number in the daughter cells and (ii) the generation of genetic variation.
(e)
Answer the following about the structures shown:
() Explain why the presence of centrioles (C) is essential for spindle formation.
() Discuss the possible cellular consequence if spindle fibres (B) fail to attach correctly to chromosomes.
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Question 3 View Details
The labelled diagram shows the major organs of the human digestive system involved in the processing of food.
Question Parts
(a)
Describe, in the correct sequential order, the pathway that a carbohydrate‑rich food follows from ingestion to absorption. For each organ, name the principal enzyme(s) that act on the carbohydrate and the specific chemical change that occurs.
(b)
A meal contains 120 g of carbohydrate, 45 g of protein and 30 g of fat. Calculate the total caloric value of the meal using the Atwater factors (carbohydrate = 4 kcal g⁻¹, protein = 4 kcal g⁻¹, fat = 9 kcal g⁻¹). Then, briefly explain how each macronutrient is processed by the digestive system before absorption.
(c)
If the absorptive surface area of the small intestine were reduced by 30 % (e.g., due to villous atrophy), identify two nutrient deficiencies that are most likely to develop and explain the physiological consequences of each deficiency.
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Question 4 View Details
The diagram shows the human respiratory system with the structures labelled A–I.
Question Parts
(a)
Write the correct anatomical name for each labelled structure (A–I).
(b)
Describe, in order, the pathway that air follows from entry into the body to the site of gas exchange.
(c)
Explain the mechanism of gas exchange at the alveolar–capillary interface, mentioning the roles of partial pressure gradients and diffusion.
(d)
Discuss how the respiratory centre in the medulla adjusts the rate and depth of breathing during moderate exercise, linking your answer to the structures shown in the diagram.
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Question 5 View Details
A capillary of radius 5 µm runs for a length of 1 mm through a well‑perfused skeletal muscle. The oxygen tension in the arterial blood entering the capillary is 100 mmHg, while the tissue oxygen tension surrounding the capillary is 40 mmHg. The diffusion coefficient of oxygen in plasma is 2.1 × 10⁻⁵ cm²·s⁻¹ and the capillary wall thickness is 1 µm.
Question Parts
(a)
Calculate the rate of oxygen diffusion from the blood into the tissue across this capillary segment using Fick’s first law. Show all steps and give your answer in cm³·mmHg·s⁻¹.
(b)
Explain qualitatively how an increase in the capillary wall thickness to 2 µm would affect the diffusion rate, citing the relevant principle.
(c)
A person suffers from anaemia, reducing the haemoglobin concentration by 30 %. Discuss how this change would influence overall oxygen delivery to the muscle, considering both diffusion and transport aspects.
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Question 6 View Details
In a healthy adult the following pressures are recorded in the glomerular capillaries and Bowman's capsule: glomerular hydrostatic pressure (P_gc) = 45 mmHg, Bowman's capsule hydrostatic pressure (P_bc) = 15 mmHg, plasma oncotic pressure (π_gc) = 25 mmHg, and Bowman's capsule oncotic pressure (π_bc) is negligible. The measured glomerular filtration rate (GFR) is 120 mL·min⁻¹.
Question Parts
(a)
Calculate the net filtration pressure (NFP) across the glomerular wall.
(b)
Determine the ultrafiltration coefficient (K_f) of the kidney using the measured GFR and the NFP obtained in part (a). Express K_f in mL·min⁻¹·mmHg⁻¹.
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Question 7 View Details
The human body maintains internal stability through homeostatic mechanisms.
Question Parts
(a)
Describe the negative feedback control of blood glucose concentration, naming the key organs, hormones and the sequence of events when blood glucose rises after a meal.
(b)
Explain how the same feedback principle operates to regulate core body temperature when ambient temperature falls below normal.
(c)
A patient suffers from a tumour that secretes excess insulin irrespective of blood glucose level. Predict the likely physiological disturbances and outline two possible clinical manifestations.
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Question 8 View Details
Coordination of movement in humans involves the integration of the nervous and muscular systems.
Question Parts
(a)
Outline the pathway of a voluntary skeletal muscle contraction from the motor cortex to the muscle fibre, naming all major neuronal structures involved.
(b)
Discuss how the speed of this signal transmission is modified by the presence of myelination and fibre diameter, and explain the physiological advantage of these modifications for rapid movements.
(c)
Compare and contrast a monosynaptic stretch reflex with a polysynaptic withdrawal reflex in terms of (i) sensory input, (ii) number of synapses, (iii) functional significance.
(d)
Design a simple experimental protocol to investigate the effect of fatigue on the latency of the patellar tendon reflex in healthy adults. Include the variables to be measured, control measures, and how data would be interpreted.
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Question 9 View Details
A 28‑year‑old male presents with reduced fertility. Investigations reveal a pituitary macroadenoma that secretes excess prolactin (hyperprolactinaemia).
Question Parts
(a)
Explain the normal hormonal regulation of spermatogenesis, naming the hypothalamic, pituitary and testicular hormones involved and their feedback relationships.
(b)
Describe how excess prolactin from the adenoma disrupts this regulation and leads to the observed infertility. Include the effect on gonadotropin release and downstream testicular function.
(c)
Outline two management strategies (pharmacological and surgical) for restoring fertility in this patient, indicating the rationale for each.
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Question 10 View Details
In a certain plant species, flower colour (P = purple, p = white) and seed shape (R = round, r = wrinkled) are controlled by two genes that are linked on the same chromosome. In a testcross, the following progeny were obtained from a heterozygous plant (PpRr) crossed with a homozygous recessive (pprr):\n\n400 purple‑round, 100 purple‑wrinkled, 90 white‑round, 410 white‑wrinkled.
Question Parts
(a)
Calculate the recombination frequency between the two genes and estimate their map distance in centiMorgans (cM).
(b)
Using the data, determine the most likely parental (non‑recombinant) gamete types produced by the heterozygous parent.
(c)
A couple, both carriers of an autosomal recessive disorder (genotype Aa), seek genetic counselling. Explain the probability that their first child will be affected, will be a carrier, and will be completely free of the mutant allele. Also discuss one prenatal diagnostic option.
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