Cell Structure & Function MCQs set 2 for NUMS MDCAT (Military Medical) Biology — 20 solved questions.
Q1. A botanist observing the structural integrity of hardwood trees notes that the secondary cell wall provides significant strength. Which chemical substance is primarily responsible for this?
Answer: Lignin deposits
Explanation: Lignin provides the primary structural strength in secondary walls. Cellulose is tempting but it is the basic framework, not the specific hardening agent.
Q2. A patient with long-term barbiturate use shows increased drug tolerance due to liver adaptation. Which organelle has likely proliferated to facilitate this detoxification process?
Answer: Smooth Endoplasmic Reticulum
Explanation: Smooth ER contains enzymes for drug detoxification. Rough ER is tempting because it is also ER, but it focuses on protein synthesis instead.
Q3. A child is diagnosed with Tay-Sachs disease, where brain cells become clogged with undigested lipids. This condition results from the failure of which specific organelle?
Answer: Lysosomes
Explanation: Lysosomes lack the enzyme to break down glycolipids in Tay-Sachs. Peroxisomes are tempting because they handle oxidative reactions, but not lipid storage diseases.
Q4. In pancreatic cells, digestive enzymes are synthesized and then modified for export. Which organelle is responsible for the final packaging of these secretory products?
Answer: Golgi Apparatus
Explanation: Golgi bodies process and package cell secretions into vesicles. The ER is tempting as the site of synthesis, but packaging occurs in Golgi.
Q5. A male patient presents with respiratory issues and infertility due to immotile cilia and sperm. This clinical scenario indicates a defect in which cytoskeletal component?
Answer: Microtubules
Explanation: Microtubules form the 9+2 arrangement in cilia and flagella. Microfilaments are tempting as they are also cytoskeletal, but they handle cell crawling.
Q6. During cellular metabolism, toxic hydrogen peroxide is produced. Which organelle protects the cell by using catalase to convert this toxin into water and oxygen?
Answer: Peroxisomes
Explanation: Peroxisomes contain catalase to break down toxic H2O2. Glyoxysomes are tempting but they are specialized for lipid-to-sugar conversion in germinating seeds.
Q7. A histopathologist examines a malignant tumor and observes unusually large and prominent nucleoli. This observation directly correlates with an increased rate of which process?
Answer: Ribosomal RNA synthesis
Explanation: The nucleolus is the site of ribosomal RNA synthesis. Chromatin is tempting as it contains DNA, but the nucleolus specifically handles rRNA.
Q8. A marathon runner experiences a sudden drop in energy levels and muscle weakness. Which organelle is primarily responsible for generating the ATP required for this activity?
Answer: Mitochondria
Explanation: Mitochondria are the primary site of aerobic ATP production. Ribosomes are tempting as they make proteins, but they do not produce energy.
Q9. Plasma B-cells are specialized to produce and secrete massive amounts of antibody proteins. Which organelle would be most extensively developed in these cells?
Answer: Rough Endoplasmic Reticulum
Explanation: RER is the site for synthesizing proteins destined for secretion. SER is tempting but it focuses on lipid synthesis and detoxification instead.
Q10. In organisms living in extremely cold environments, the plasma membrane remains fluid. This adaptation is achieved by increasing the proportion of which membrane component?
Answer: Unsaturated fatty acids
Explanation: Unsaturated fatty acids prevent tight packing, maintaining fluidity at low temperatures. Cholesterol is tempting but it acts as a fluidity buffer, not the primary cold-adaptation.
Q11. During the germination of castor bean seeds, stored fatty acids are converted into carbohydrates. Which organelle provides the enzymes necessary for this metabolic transition?
Answer: Glyoxysomes
Explanation: Glyoxysomes convert stored lipids into carbohydrates via the glyoxylate cycle. Peroxisomes are tempting but they lack the specific enzymes for this conversion.
Q12. A houseplant wilts because it has not been watered for a week. This loss of turgor pressure is primarily due to the shrinking of which structure?
Answer: Central Vacuole
Explanation: The central vacuole maintains turgor pressure in plant cells. The nucleus is tempting but it has no role in maintaining plant cell rigidity.
Q13. A chemotherapy drug inhibits the formation of spindle fibers during mitosis. Which organelle is the drug most likely targeting to prevent cancer cell division?
Answer: Centrioles
Explanation: Centrioles organize the spindle apparatus during animal cell division. Lysosomes are tempting because they are also small organelles, but they handle digestion.
Q14. A researcher discovers a virus that prevents mRNA from leaving the nucleus. Which specific structural component of the nucleus is the virus most likely blocking?
Answer: Nuclear pores
Explanation: Nuclear pores regulate the transport of mRNA to the cytoplasm. The nuclear envelope is tempting but it is the entire double membrane, not the specific channel.
Q15. While observing Elodea leaves under a microscope, a student notices the circular streaming of cytoplasm (cyclosis). This movement is primarily facilitated by which cytoskeletal element?
Answer: Microfilaments
Explanation: Cyclosis is driven by microfilaments (actin). Microtubules are tempting as they also assist transport, but microfilaments specifically drive cytoplasmic streaming.
Q16. White blood cells must undergo rapid changes in shape to squeeze through narrow capillary walls into infected tissues. Which cytoskeletal component enables this amoeboid movement?
Answer: Microfilaments
Explanation: Microfilaments (actin) are responsible for amoeboid movement and shape changes. Intermediate filaments are tempting but they provide static structural support, not movement.
Q17. A genetic defect in keratin proteins leads to skin blistering when even minor pressure is applied. This highlights the role of which cytoskeletal fiber in providing mechanical strength?
Answer: Intermediate filaments
Explanation: Intermediate filaments like keratin provide mechanical strength to skin. Microfilaments are tempting but they are involved in movement, not tensile strength.
Q18. An antibiotic like Streptomycin targets 70S ribosomes to inhibit bacterial protein synthesis. Why does this drug generally not interfere with protein synthesis in human cytoplasm?
Answer: Human cytoplasm contains 80S ribosomes
Explanation: Human cytoplasmic ribosomes are 80S, while bacteria have 70S. Mitochondrial ribosomes are tempting because they are 70S, but the drug's safety depends on cytoplasmic differences.
Q19. A bacterial strain survives exposure to penicillin by producing an enzyme that degrades the drug. This resistance gene is typically located on which structure?
Answer: Plasmids
Explanation: Plasmids carry extra-chromosomal genes like antibiotic resistance. Mesosomes are tempting but they are involved in respiration and DNA replication.
Q20. As a fruit ripens, it becomes soft because the pectin-rich 'cementing' layer between adjacent plant cells dissolves. Which layer of the cell wall is this?
Answer: Middle lamella
Explanation: The middle lamella is the first layer formed and acts as cement. The primary wall is tempting but it is formed after the middle lamella.