Free Cell Structure and Function MCQs with Answers

71. Which cell junction allows direct cytoplasmic communication between adjacent cells?

• A. Tight junctions
• B. Desmosomes
• C. Gap junctions
• D. Adherens junctions

Explanation: Gap junctions (or plasmodesmata in plants) form channels that allow direct exchange of ions and small molecules between cells.

72. In osmosis, water moves from

• A. High solute concentration to low solute concentration
• B. Low water potential to high water potential
• C. High water potential to low water potential
• D. Hypertonic to hypotonic solution

Explanation: Water moves from high water potential (dilute, hypotonic) to low water potential (concentrated, hypertonic).

73. What is the function of a centromere?

• A. To protect the ends of chromosomes
• B. To hold sister chromatids together
• C. To carry genetic information
• D. To initiate DNA replication

Explanation: The centromere joins the two sister chromatids and carries the kinetochore, the protein plate that the spindle microtubules attach to during division. Protecting the chromosome ends is the job of the telomeres, which is the closest distractor here. Genetic information is carried along the whole length of the DNA rather than at one point, and replication begins at origins distributed across the chromosome.

74. All are the functions of lysosome EXCEPT:

• A. Intra cellular digestion
• B. Removal of the waste
• C. Autophagy
• D. Lipid synthesis

Explanation: Lysosomes contain hydrolytic enzymes and therefore break molecules down, digesting food vacuoles, clearing waste and destroying worn out organelles by autophagy. Building lipids is a synthetic process carried out by the smooth endoplasmic reticulum, which is the opposite kind of activity. Recognising that every genuine lysosomal role is destructive answers the question without recalling a list.

75. A mature duplicated chromosome consists of:

• A. Two identical double helical DNA molecules
• B. Two different double helical DNA molecules
• C. A double helical DNA molecule distributed in both chromatids
• D. Histone chains wrapped around DNA core

Explanation: Replication is semi conservative and highly accurate, so the two sister chromatids each hold a complete double helix and the two are identical copies joined at the centromere. They are not different molecules, which is what distinguishes sister chromatids from homologous chromosomes. Note also that DNA wraps around the histones rather than the other way round, which makes the last option backwards.

76. Identify the most appropriate function of chromosomes

• A. Energy production and storage
• B. Protein synthesis and regulation
• C. Storage of genetic information
• D. Lipid metabolism and transport

Explanation: A chromosome is DNA packaged with histones, and its role is to hold the hereditary information and pass it on accurately when the cell divides. Protein synthesis is the tempting option, since genes direct it, but the synthesis itself happens on ribosomes and the chromosome only stores the instructions. Energy production belongs to mitochondria and lipid handling to the smooth endoplasmic reticulum.

77. __________ arranges the DNA into the chromosomes in a eukaryotic cell.

• A. Hormones
• B. Elastin
• C. Histone
• D. Nucleosome

Explanation: Histones are small positively charged proteins that the negatively charged DNA winds around, condensing roughly two metres of DNA into a nucleus a few micrometres across. A nucleosome is the resulting bead of DNA wrapped around eight histones, so it is the product of the packaging rather than the agent doing it, which makes it the deliberate near miss here. Elastin is a structural protein of connective tissue.

78. The function of nucleolus is to make:

• A. rDNA
• B. Lysosomes
• C. Ribosomes
• D. Chromosomes

Explanation: The nucleolus transcribes ribosomal RNA and assembles it with proteins into the ribosomal subunits, which are then exported through the nuclear pores. Cells that make a great deal of protein have correspondingly prominent nucleoli. Lysosomes are budded off by the Golgi apparatus, and rDNA is the template the nucleolus reads rather than something it makes.

79. Which of the following statements best compares cell division in prokaryotic and eukaryotic cells?

• A. Eukaryotes divide by budding; prokaryotes by mitosis
• B. Eukaryotes use binary fission; prokaryotes by meiosis
• C. Eukaryotes divide by mitosis; prokaryotes by binary fission
• D. Both use mitosis by cell division

Explanation: Mitosis needs a spindle and organised chromosomes, which only eukaryotes possess, while a prokaryote simply replicates its single circular chromosome and splits by binary fission. This is much faster, which is why bacteria can divide every twenty minutes. Meiosis is confined to eukaryotes producing gametes.

80. A student observed a boundary in both plant and animal cells that controls entry and exit of substances. Which of the following structures is likely being observed?

• A. Mitochondria
• B. Golgi apparatus
• C. Plasma membrane
• D. Cell wall

Explanation: The plasma membrane is present in every cell and is partially permeable, so it decides what enters and leaves, which is exactly the function described. The cell wall is the trap: it is a boundary too, but it occurs only in plants and is fully permeable, so it controls nothing. The words both plant and animal are what rule it out.