Free Cell Structure and Function MCQs with Answers

31. A karyotype is

• A. the complete set of genes in a gamete
• B. the sequence of bases in one chromosome
• C. a display of all the chromosomes of a cell arranged in pairs by size and shape
• D. the number of chromatids in a chromosome

Explanation: Chromosomes are photographed at metaphase, when they are most condensed, then cut out and arranged in numbered pairs, which makes an abnormal number or a structural change immediately visible. This is how Down syndrome is confirmed as an extra copy of chromosome 21. It shows chromosome number and shape only, not the base sequence or the individual genes.

32. Of the 23 pairs of chromosomes in a human somatic cell, the number of pairs of autosomes is

• A. 22
• B. 23
• C. 21
• D. 44

Explanation: Twenty two pairs are autosomes, which carry the genes for body characters and are identical in appearance in both sexes, and the remaining pair are the sex chromosomes, XX in a female and XY in a male. The figure 44 is the total number of individual autosomes rather than the number of pairs, which is the usual careless error. A gamete carries 22 autosomes plus one sex chromosome.

33. Peroxisomes protect the cell because they contain the enzyme catalase, which

• A. digests worn out organelles
• B. synthesises hydrogen peroxide for defence
• C. adds sugar groups to newly made proteins
• D. breaks down toxic hydrogen peroxide into water and oxygen

Explanation: Hydrogen peroxide is a damaging by product of several oxidation reactions, and catalase destroys it almost as fast as it forms, making it one of the fastest enzymes known. Peroxisomes are also active in the oxidation of fatty acids and, in liver cells, in detoxifying alcohol. Digestion of worn out organelles is the work of lysosomes, which is the usual confusion.

34. The primary cell wall of a plant cell is composed mainly of

• A. cellulose
• B. chitin
• C. peptidoglycan
• D. lignin

Explanation: Cellulose microfibrils, polymers of beta glucose, give the plant wall its strength, while chitin builds fungal walls and peptidoglycan bacterial ones. Lignin is a secondary strengthening chemical laid down later in woody tissue, not the primary wall material.

35. The middle lamella, which cements neighbouring plant cells together, is composed mainly of

• A. cellulose
• B. pectin
• C. lignin
• D. suberin

Explanation: The middle lamella is a shared pectin-rich layer formed first during cell division, gluing adjacent walls together. Cellulose makes up the wall itself on each side of it, and suberin is the waterproofing of cork, not the cementing layer.

36. As a cell grows larger, its surface area to volume ratio

• A. increases steadily
• B. remains constant
• C. decreases
• D. first falls and then rises again

Explanation: Volume grows with the cube of the radius while surface area grows only with the square, so a larger cell has proportionally less membrane through which to feed its cytoplasm. This falling ratio is one of the main reasons cells divide instead of growing indefinitely.

37. The engulfing of solid food particles by a cell through infolding of its membrane is called

• A. pinocytosis
• B. osmosis
• C. facilitated diffusion
• D. phagocytosis

Explanation: Phagocytosis, literally cell eating, wraps the membrane around a particle to form a vacuole, as white blood cells do to bacteria. Pinocytosis is the drinking of fluid droplets, and both are forms of endocytosis that need membrane, unlike diffusion.

38. Pinocytosis differs from phagocytosis in that pinocytosis

• A. engulfs large solid particles
• B. occurs without any membrane
• C. takes in dissolved substances in tiny droplets of fluid
• D. occurs only in plant cells

Explanation: Pinocytosis brings in small vesicles of extracellular fluid with dissolved solutes, while phagocytosis handles solid particles. Both require the plasma membrane to fold inward, and both occur in animal cells, so neither of those features separates them.

39. Exocytosis is the process by which a cell

• A. releases materials in vesicles that fuse with the plasma membrane
• B. takes in fluid droplets from its surroundings
• C. pumps ions against their concentration gradient
• D. divides its cytoplasm during cell division

Explanation: Secretory vesicles from the Golgi move to the surface and merge with the membrane, discharging their contents outside, which is how enzymes, hormones and neurotransmitters leave the cell. The reverse process is endocytosis, and ion pumping is active transport.

40. A solution in which a red blood cell shrinks and becomes wrinkled is described as

• A. isotonic
• B. hypotonic
• C. pure water
• D. hypertonic

Explanation: In a hypertonic solution the external solute concentration is higher, so water leaves the cell by osmosis and it crenates. In a hypotonic solution the same cell would swell and burst, while isotonic saline keeps it unchanged.