Rucete ✏ AP Biology In a Nutshell
3. Cell Organelles, Membranes, and Transport — Practice Questions 3
This chapter explores how cellular structures support life processes, emphasizing the role of membranes, organelles, and transport systems in maintaining internal balance.
(Multiple Choice — Click to Reveal Answer)
1. Which of the following organelles is involved in synthesizing proteins that are secreted from the cell?
(A) Free ribosome
(B) Rough endoplasmic reticulum
(C) Smooth endoplasmic reticulum
(D) Lysosome
Answer
(B) — Ribosomes attached to the rough ER synthesize proteins destined for secretion or membrane integration.
2. What type of molecule would most easily pass through the phospholipid bilayer without assistance?
(A) Large polar molecule
(B) Ion
(C) Small nonpolar molecule
(D) Large hydrophilic molecule
Answer
(C) — Small nonpolar molecules like O₂ and CO₂ easily diffuse through the membrane.
3. Which organelle is primarily responsible for breaking down harmful substances and metabolic waste in a cell?
(A) Mitochondrion
(B) Smooth ER
(C) Peroxisome
(D) Ribosome
Answer
(C) — Peroxisomes detoxify chemicals and break down fatty acids, aiding cell metabolism and defense.
4. Which property of membranes allows endocytosis and exocytosis to occur?
(A) Rigidity
(B) Fluidity
(C) Permeability
(D) Conductivity
Answer
(B) — Membrane fluidity allows vesicles to form and fuse with the plasma membrane during transport processes.
5. Which statement correctly describes the relationship between surface area-to-volume ratio and cell size?
(A) Larger cells have higher surface area-to-volume ratios
(B) Smaller cells have lower surface area-to-volume ratios
(C) A larger surface area-to-volume ratio allows more efficient exchange
(D) Surface area has no effect on material exchange
Answer
(C) — A higher surface area-to-volume ratio enhances material exchange efficiency, favoring smaller cells.
6. Which structure allows materials to move between the nucleus and the cytoplasm?
(A) Nuclear envelope
(B) Nuclear pores
(C) Rough ER
(D) Plasma membrane
Answer
(B) — Nuclear pores allow selective exchange of materials between the nucleus and the cytoplasm.
7. Which process moves molecules across a membrane against their concentration gradient?
(A) Simple diffusion
(B) Facilitated diffusion
(C) Active transport
(D) Osmosis
Answer
(C) — Active transport requires energy (ATP) to move substances against their gradient.
8. In which organelle would you find thylakoid membranes stacked into grana?
(A) Mitochondrion
(B) Chloroplast
(C) Ribosome
(D) Nucleus
Answer
(B) — Thylakoids inside chloroplasts are stacked into grana, where the light reactions of photosynthesis occur.
9. Which type of transport requires the cell to expend energy?
(A) Facilitated diffusion
(B) Active transport
(C) Simple diffusion
(D) Osmosis
Answer
(B) — Active transport moves substances against their gradient using cellular energy (ATP).
10. Which organelle is the site of ATP production in both plant and animal cells?
(A) Chloroplast
(B) Golgi apparatus
(C) Ribosome
(D) Mitochondrion
Answer
(D) — Mitochondria generate ATP through cellular respiration in both plant and animal cells.
11. Which component of the plasma membrane helps cells identify each other?
(A) Cholesterol
(B) Phospholipids
(C) Glycoproteins
(D) Integral proteins
Answer
(C) — Glycoproteins serve as cell recognition markers for communication and immune response.
12. In plant cells, what is the main function of plasmodesmata?
(A) Strengthen the cell wall
(B) Allow transport of materials between adjacent cells
(C) Facilitate photosynthesis
(D) Produce ATP
Answer
(B) — Plasmodesmata are channels that allow cytoplasm and molecules to move between plant cells.
13. What is the main function of smooth endoplasmic reticulum in liver cells?
(A) Protein synthesis
(B) Detoxification of toxins
(C) Energy production
(D) DNA replication
Answer
(B) — Smooth ER detoxifies chemicals and produces lipids, especially in liver cells.
14. Which process describes the movement of water across a selectively permeable membrane?
(A) Active transport
(B) Facilitated diffusion
(C) Osmosis
(D) Exocytosis
Answer
(C) — Osmosis refers to the passive movement of water across a membrane toward a higher solute concentration.
15. Which of the following would most likely cross a lipid bilayer without assistance?
(A) Sodium ion
(B) Glucose molecule
(C) Carbon dioxide gas
(D) Protein molecule
Answer
(C) — Small, nonpolar molecules like CO₂ can pass directly through the phospholipid bilayer.
16. What term describes the process by which cells internalize large molecules by engulfing them?
(A) Exocytosis
(B) Osmosis
(C) Endocytosis
(D) Diffusion
Answer
(C) — Endocytosis brings large molecules into the cell by forming vesicles.
17. Which statement about membrane fluidity is correct?
(A) It is reduced by unsaturated fatty acids
(B) It is increased by cholesterol at high temperatures
(C) It is necessary for vesicle formation
(D) It prevents movement of proteins
Answer
(C) — Membrane fluidity allows vesicle formation and fusion during transport processes.
18. In an animal cell, which organelle directly receives vesicles from the rough ER?
(A) Mitochondrion
(B) Nucleus
(C) Golgi apparatus
(D) Ribosome
Answer
(C) — The Golgi apparatus modifies and packages proteins received from the rough ER.
19. Which condition would cause an animal cell to burst?
(A) Placement in an isotonic solution
(B) Placement in a hypertonic solution
(C) Placement in a hypotonic solution
(D) Placement in a concentrated sugar solution
Answer
(C) — In a hypotonic solution, water enters the cell, potentially causing it to swell and burst (lysis).
20. Which type of protein forms a hydrophilic channel across the membrane for molecules to pass?
(A) Glycoprotein
(B) Carrier protein
(C) Channel protein
(D) Peripheral protein
Answer
(C) — Channel proteins allow specific substances to pass freely through the membrane.
21. Which molecule stabilizes membrane fluidity across temperature changes?
(A) Phospholipid
(B) Cholesterol
(C) Glycoprotein
(D) Ribosomal RNA
Answer
(B) — Cholesterol buffers membrane fluidity at both high and low temperatures.
22. In what type of transport are proteins used but no energy required?
(A) Active transport
(B) Facilitated diffusion
(C) Exocytosis
(D) Endocytosis
Answer
(B) — Facilitated diffusion uses transport proteins to move molecules without energy input.
23. Which organelle is mainly responsible for digesting engulfed bacteria in white blood cells?
(A) Mitochondrion
(B) Lysosome
(C) Golgi apparatus
(D) Ribosome
Answer
(B) — Lysosomes digest ingested materials, including bacteria, using hydrolytic enzymes.
24. What happens to plant cells in a hypotonic environment?
(A) They shrink
(B) They burst
(C) They become turgid
(D) They plasmolyze
Answer
(C) — Plant cells become turgid (firm) as water enters and fills the central vacuole.
25. What is the function of integral proteins in the membrane?
(A) Synthesizing ATP
(B) Assisting with molecular transport
(C) Producing ribosomes
(D) Storing genetic information
Answer
(B) — Integral proteins span the membrane and facilitate transport of molecules across it.
26. Which of the following best explains why cell membranes are described as "selectively permeable"?
(A) They allow all molecules to pass freely
(B) They allow only water molecules to pass
(C) They regulate the entry and exit of specific substances
(D) They are completely impermeable to ions
Answer
(C) — Selective permeability means only certain molecules can pass through the membrane based on size, polarity, or the presence of specific transport proteins.
27. A defect in which organelle would most directly affect the synthesis of new membrane phospholipids?
(A) Rough ER
(B) Smooth ER
(C) Ribosome
(D) Golgi apparatus
Answer
(B) — The smooth endoplasmic reticulum is responsible for synthesizing membrane lipids.
28. Which condition would most likely increase the rate of facilitated diffusion?
(A) Increasing the number of transport proteins
(B) Lowering the concentration gradient
(C) Adding ATP
(D) Decreasing membrane fluidity
Answer
(A) — More transport proteins provide more pathways for molecules to move across the membrane, increasing diffusion rate.
29. Which of the following changes would most likely decrease membrane fluidity?
(A) More unsaturated fatty acids in phospholipids
(B) Increased cholesterol at low temperatures
(C) More saturated fatty acids in phospholipids
(D) Higher temperature
Answer
(C) — Saturated fatty acids pack tightly together, reducing membrane fluidity.
30. Which process involves the engulfing of large particles such as bacteria by the plasma membrane?
(A) Pinocytosis
(B) Phagocytosis
(C) Exocytosis
(D) Facilitated diffusion
Answer
(B) — Phagocytosis is the process of engulfing large particles into the cell.
31. A mutation that disrupts the formation of tight junctions in epithelial tissue would most likely affect:
(A) ATP production
(B) Regulation of material passage between cells
(C) Protein synthesis
(D) Vesicle formation
Answer
(B) — Tight junctions prevent leakage between cells, maintaining controlled material movement across tissues.
32. Which type of cellular transport requires receptor proteins to recognize and bind specific molecules before uptake?
(A) Simple diffusion
(B) Facilitated diffusion
(C) Receptor-mediated endocytosis
(D) Phagocytosis
Answer
(C) — In receptor-mediated endocytosis, specific receptors on the membrane bind target molecules before vesicle formation.
33. Which feature of mitochondrial membranes directly contributes to efficient ATP production?
(A) Presence of thylakoid membranes
(B) Fluid mosaic structure
(C) Highly folded inner membrane (cristae)
(D) Double membrane separating nucleus and cytoplasm
Answer
(C) — The folded cristae greatly increase surface area for the enzymes involved in ATP production.
34. Which situation describes an isotonic environment for a cell?
(A) Water flows equally into and out of the cell
(B) Water flows only into the cell
(C) Water flows only out of the cell
(D) No water movement occurs at all
Answer
(A) — In an isotonic solution, water enters and exits the cell at equal rates, maintaining cell volume.
35. Which part of the plasma membrane acts as a barrier to ions and large polar molecules?
(A) Hydrophilic phosphate heads
(B) Hydrophobic fatty acid tails
(C) Embedded proteins
(D) Attached carbohydrates
Answer
(B) — The hydrophobic fatty acid tails in the membrane core block ions and polar molecules from freely passing through.
36. What is the main role of the rough endoplasmic reticulum in protein production?
Answer
The rough ER modifies and transports proteins synthesized by attached ribosomes, especially those destined for secretion or membranes.
37. Why are lysosomes important for maintaining cellular health?
Answer
Lysosomes contain hydrolytic enzymes that digest waste, damaged organelles, and foreign substances, preventing buildup and promoting recycling inside the cell.
38. How does the structure of the phospholipid bilayer contribute to its selective permeability?
Answer
The hydrophobic core prevents the free passage of polar molecules and ions, while allowing small nonpolar molecules to diffuse through easily.
39. What cellular structure provides mechanical support and maintains cell shape?
Answer
The cytoskeleton, composed of microfilaments, intermediate filaments, and microtubules, supports the cell and facilitates movement.
40. How does membrane fluidity benefit cellular function?
Answer
Fluidity allows for dynamic processes such as vesicle formation, membrane protein movement, and quick responses to environmental changes.
41. What would happen to an animal cell placed in a hypertonic solution?
Answer
The cell would lose water and shrink (crenation) due to osmosis moving water out of the cell.
42. Name one organelle involved in protein modification and export.
Answer
The Golgi apparatus modifies, packages, and ships proteins synthesized in the rough ER.
43. How is facilitated diffusion different from simple diffusion?
Answer
Facilitated diffusion uses specific transport proteins to help polar molecules and ions cross the membrane, while simple diffusion occurs directly through the bilayer.
44. What is the function of cholesterol in the plasma membrane?
Answer
Cholesterol stabilizes membrane fluidity, preventing it from becoming too rigid in cold temperatures or too fluid in high temperatures.
45. During endocytosis, what structure forms to bring materials into the cell?
Answer
A vesicle forms from the plasma membrane, enclosing extracellular materials for transport into the cell.
46. How does ATP provide energy for active transport?
Answer
ATP hydrolysis releases energy by breaking a phosphate bond, powering transport proteins to move molecules against concentration gradients.
47. Why is the surface area-to-volume ratio important for cells?
Answer
A high surface area-to-volume ratio allows efficient exchange of materials between the cell and its environment, supporting metabolism and homeostasis.
48. What organelle contains its own DNA and ribosomes, besides the nucleus?
Answer
Mitochondria (and chloroplasts in plants) have their own DNA and ribosomes, supporting their role in energy production and partial autonomy.
49. How does exocytosis differ from endocytosis?
Answer
Exocytosis expels materials from the cell by vesicle fusion with the plasma membrane, while endocytosis internalizes materials into vesicles.
50. Explain how aquaporins assist in osmosis.
Answer
Aquaporins are channel proteins that facilitate the rapid movement of water molecules across the plasma membrane during osmosis.