Free Cell Structure and Function MCQs with Answers

51. Microtubules, the hollow fibres of the cytoskeleton and of cilia, are built from the protein

• A. actin
• B. tubulin
• C. myosin
• D. keratin

Explanation: Tubulin dimers polymerise into hollow tubes that form the cytoskeleton, spindle fibres, cilia and flagella. Actin makes the thinner microfilaments of muscle and cell cortex, and keratin is an intermediate filament protein of hair and skin.

52. The 9 plus 2 arrangement of microtubules is found in

• A. centrioles
• B. bacterial flagella
• C. microvilli of the intestine
• D. cilia and eukaryotic flagella

Explanation: Cilia and eukaryotic flagella contain nine doublet microtubules around a central pair, an arrangement visible only by electron microscopy. Centrioles are 9 plus zero triplets, and bacterial flagella are solid protein filaments with no microtubules at all.

53. Which organelle is unusual in containing its own DNA and its own ribosomes?

• A. Golgi apparatus
• B. Lysosome
• C. Mitochondrion
• D. Peroxisome

Explanation: Mitochondria carry a small circular genome and 70S ribosomes and make some of their own proteins, evidence of their endosymbiotic origin. Golgi, lysosomes and peroxisomes contain no genetic material and depend entirely on nuclear genes.

54. The cristae of the mitochondrion greatly increase the surface area available for

• A. the reactions of glycolysis
• B. the reactions of the electron transport chain
• C. the storage of fat
• D. the synthesis of ribosomal RNA

Explanation: The electron carriers and ATP synthase are embedded in the inner membrane, so its folding into cristae multiplies the space for oxidative phosphorylation. Glycolysis happens outside the mitochondrion in the cytoplasm, a point examiners frequently test.

55. The grana of a chloroplast consist of

• A. stacks of flattened thylakoid sacs
• B. free ribosomes and DNA
• C. grains of stored starch
• D. infoldings of the outer membrane

Explanation: Thylakoids pile into grana, and their membranes carry chlorophyll and the photosynthetic electron chain, while the surrounding stroma carries the enzymes of carbon fixation. Starch grains may be stored nearby but are not what grana are.

56. A chromosome whose centromere lies at or very near one end is described as

• A. metacentric
• B. submetacentric
• C. acrocentric
• D. telocentric

Explanation: Centromere position names the chromosome: metacentric gives equal arms, submetacentric unequal ones, acrocentric a very short arm, and telocentric a terminal centromere. These shapes are read directly from a karyotype photograph.

57. Homologous chromosomes are pairs of chromosomes that

• A. are found only in gametes
• B. consist of a single chromatid each throughout the cell cycle
• C. carry genes for the same characteristics and come one from each parent
• D. are present in prokaryotic cells

Explanation: One member of each homologous pair is maternal and the other paternal, matching in size, centromere position and gene positions though possibly carrying different alleles. Prokaryotes have a single chromosome, so pairing applies only to diploid eukaryotes.

58. Before a cell divides, each chromosome is replicated. The two identical copies remain attached and are called

• A. homologues
• B. sister chromatids
• C. bivalents
• D. telomeres

Explanation: DNA replication produces two identical sister chromatids joined at the centromere, which separate at anaphase into different daughter cells. Homologues are the maternal and paternal members of a pair, not copies of one chromosome.

59. The position of the centromere and the overall size of each chromosome are useful because they

• A. allow chromosomes to be identified in a karyotype
• B. change from one cell division to the next
• C. by themselves determine the sex of the individual
• D. are identical for every chromosome in the cell

Explanation: Since each chromosome type has a characteristic length and centromere position, these features let cytogeneticists arrange a karyotype in standard order and spot missing or extra chromosomes. Sex is determined specifically by the X and Y pair, not by size alone.

60. Human sex chromosomes differ from autosomes mainly in that sex chromosomes

• A. are absent from every gamete
• B. carry no genes at all
• C. determine the sex of the individual
• D. are present in four pairs

Explanation: The 23rd pair, XX in females and XY in males, determines sex, while the 22 pairs of autosomes govern the rest of the body. Gametes carry one sex chromosome each, and the Y chromosome, though gene poor, still carries the male determining SRY gene.