Free Cell Structure and Function MCQs with Answers

61. The DNA of a eukaryotic chromosome is first coiled around histone proteins to form repeating units called

• A. centromeres
• B. kinetochores
• C. chromatids
• D. nucleosomes

Explanation: Each nucleosome is DNA wrapped around a core of eight histones, like beads on a string, and these coil further to condense the chromosome. The centromere is a region of the chromosome and the kinetochore the spindle attachment on it, neither of which packages DNA.

62. The tips of eukaryotic chromosomes, made of repeated non coding sequences that protect the ends from loss during replication, are called

• A. centromeres
• B. kinetochores
• C. telomeres
• D. nucleosomes

Explanation: Telomeres shorten a little with every division and act like the plastic tips of shoelaces, preventing the loss of essential genes and stopping chromosome ends from sticking together. Cells with active telomerase, such as germ cells and many cancer cells, maintain them.

63. Which of the following is NOT a characteristic of prokaryotic cells?

• A. Absence of membrane-bound nucleus
• B. Presence of 70S ribosomes
• C. Presence of histone proteins
• D. Circular DNA

Explanation: Prokaryotes lack histone proteins. Their DNA is not organized into nucleosomes with histones, unlike eukaryotes.

64. The fluid mosaic model of cell membrane was proposed by

• A. Robertson
• B. Singer and Nicolson
• C. Gorter and Grendel
• D. Danielli and Davson

Explanation: Singer and Nicolson proposed the fluid mosaic model in 1972, describing the membrane as a fluid lipid bilayer with embedded proteins.

65. Which organelle is responsible for the synthesis of proteins destined for secretion?

• A. Smooth ER
• B. Golgi apparatus
• C. Rough ER
• D. Lysosomes

Explanation: Rough ER has ribosomes on its surface and synthesizes proteins that are either secreted or inserted into membranes.

66. The powerhouse of the cell is

• A. Nucleus
• B. Mitochondria
• C. Chloroplast
• D. Ribosome

Explanation: Mitochondria are called the powerhouse because they produce ATP through oxidative phosphorylation.

67. Which of the following is TRUE about the Na+/K+ pump?

• A. It moves 2 Na+ out and 3 K+ in
• B. It moves 3 Na+ out and 2 K+ in
• C. It is a passive transport mechanism
• D. It does not require ATP

Explanation: The Na+/K+ ATPase pump moves 3 Na+ out and 2 K+ in against their concentration gradients, using ATP.

68. Lysosomes are called 'suicide bags' because

• A. They contain digestive enzymes
• B. They can digest the cell itself when ruptured
• C. They kill bacteria
• D. They produce toxic substances

Explanation: When lysosomes rupture, their hydrolytic enzymes can digest the cell's own components, causing autolysis.

69. Which of the following has its own DNA and 70S ribosomes?

• A. Nucleus
• B. Mitochondria
• C. Golgi apparatus
• D. Peroxisomes

Explanation: Mitochondria (and chloroplasts) have their own circular DNA and 70S ribosomes, supporting the endosymbiotic theory.

70. The site of photosynthesis in eukaryotic cells is

• A. Mitochondria
• B. Chloroplast
• C. Ribosome
• D. Nucleus

Explanation: Chloroplasts contain chlorophyll and are the site of photosynthesis in plant cells and algae.