Biology — Diversity, Cell Biology, Plant & Animal Physiology — Practice

Question 1

Why are Bryophytes called the 'amphibians of the plant kingdom'?

Accepted Answer

Bryophytes (mosses and liverworts) are called the 'amphibians of the plant kingdom' because they LIVE ON LAND but depend on WATER for reproduction — specifically, water is essential for the male gametes (antherozoids) to swim to the female archegonium for fertilisation. They have no true roots (only rhizoids), no true vascular tissue, and cannot survive without moisture. Just as amphibians need water for reproduction but can live on land, bryophytes are terrestrial but reproductively tied to aquatic environments.

Question 2

Compare mitosis and meiosis under the headings: (a) location in the body, (b) number of divisions, (c) products, (d) genetic outcome.

Accepted Answer

(a) LOCATION: Mitosis occurs in somatic (body) cells throughout the organism. Meiosis occurs only in reproductive organs (gonads — testes and ovaries) in organisms that reproduce sexually. (b) DIVISIONS: Mitosis involves ONE division. Meiosis involves TWO sequential divisions (Meiosis I and Meiosis II). (c) PRODUCTS: Mitosis → 2 diploid (2n) daughter cells. Meiosis → 4 haploid (n) cells (gametes). (d) GENETIC OUTCOME: Mitosis produces cells GENETICALLY IDENTICAL to the parent cell. Meiosis produces cells that are GENETICALLY DIFFERENT from each other and from the parent, due to crossing over in Prophase I and independent assortment.

Question 3

Describe the three processes by which urine is formed in the nephron.

Accepted Answer

Urine formation in the nephron occurs in three stages: (1) GLOMERULAR FILTRATION: Blood flows at high pressure through the glomerulus (a knot of capillaries in the Bowman's capsule). The filtration membrane forces water, glucose, urea, salts, and small molecules into the Bowman's capsule as 'glomerular filtrate.' Proteins and blood cells are too large to pass — they remain in the blood. About 180 litres of filtrate are formed per day. (2) TUBULAR REABSORPTION: As the filtrate passes through the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, ~99% of water, all glucose, and useful salts are ACTIVELY reabsorbed back into the surrounding capillaries. ADH (antidiuretic hormone) from the pituitary regulates water reabsorption in the collecting duct. (3) TUBULAR SECRETION: Some substances (excess H⁺, K⁺, certain drugs) are actively secreted FROM the blood INTO the tubule for excretion. The remaining fluid — concentrated urine (~1.5 L/day) — passes to the pelvis, ureters, bladder, and urethra.

Practice — Biology — Diversity, Cell Biology, Plant & Animal Physiology

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