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3. Cell Organelles, Membranes, and Transport — Practice Questions 2
This chapter examines the structure and functions of organelles, membrane dynamics, and the various mechanisms of transport used by cells to maintain internal balance.
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(Multiple Choice — Click to Reveal Answer)
1. Which organelle is responsible for producing energy through cellular respiration?
(A) Nucleus
(B) Chloroplast
(C) Mitochondrion
(D) Vacuole
Answer
(C) — Mitochondria convert chemical energy in food into usable ATP energy through cellular respiration.
2. In eukaryotic cells, what surrounds the nucleus and controls the movement of materials in and out?
(A) Cell wall
(B) Plasma membrane
(C) Nuclear envelope
(D) Cytoplasm
Answer
(C) — The nuclear envelope, a double membrane, regulates traffic into and out of the nucleus.
3. Which type of transport moves ions across a membrane without requiring energy?
(A) Endocytosis
(B) Active transport
(C) Facilitated diffusion
(D) Exocytosis
Answer
(C) — Facilitated diffusion allows ions and polar molecules to cross membranes using transport proteins without energy input.
4. In plant cells, which organelle stores water and helps maintain turgor pressure?
(A) Golgi apparatus
(B) Central vacuole
(C) Lysosome
(D) Ribosome
Answer
(B) — The central vacuole stores water and contributes to the structural support of plant cells through turgor pressure.
5. What feature of the phospholipid bilayer makes the plasma membrane selectively permeable?
(A) Embedded ribosomes
(B) Presence of cellulose
(C) Arrangement of hydrophilic heads and hydrophobic tails
(D) Attachment to the cytoskeleton
Answer
(C) — The hydrophilic heads face outward while hydrophobic tails face inward, allowing selective permeability based on molecule polarity and size.
6. Which cell structure is primarily involved in the detoxification of harmful chemicals?
(A) Rough ER
(B) Smooth ER
(C) Ribosome
(D) Lysosome
Answer
(B) — The smooth endoplasmic reticulum (Smooth ER) detoxifies drugs and harmful substances.
7. What type of membrane protein is responsible for sending chemical signals across the plasma membrane?
(A) Structural protein
(B) Receptor protein
(C) Channel protein
(D) Glycoprotein
Answer
(B) — Receptor proteins bind signaling molecules and initiate a cellular response.
8. Which organelle is the site of photosynthesis?
(A) Mitochondrion
(B) Chloroplast
(C) Golgi apparatus
(D) Lysosome
Answer
(B) — Chloroplasts capture sunlight to drive the synthesis of glucose through photosynthesis.
9. The main structural component of the plasma membrane is:
(A) Proteins
(B) Carbohydrates
(C) Phospholipids
(D) Nucleic acids
Answer
(C) — Phospholipids form the bilayer structure that defines the plasma membrane.
10. Which structure helps plant cells remain rigid and upright?
(A) Plasma membrane
(B) Cytoskeleton
(C) Central vacuole
(D) Ribosomes
Answer
(C) — The central vacuole fills with water, creating internal pressure that supports the cell.
11. What is the major difference between prokaryotic and eukaryotic cells?
(A) Presence of a plasma membrane
(B) Presence of ribosomes
(C) Presence of a nucleus
(D) Presence of a cell wall
Answer
(C) — Eukaryotic cells have a true nucleus surrounded by a membrane; prokaryotes do not.
12. Water moves across cell membranes by:
(A) Active transport
(B) Facilitated diffusion
(C) Osmosis
(D) Endocytosis
Answer
(C) — Osmosis is the passive movement of water across a selectively permeable membrane.
13. Which organelle packages materials into vesicles for transport?
(A) Smooth ER
(B) Golgi apparatus
(C) Mitochondrion
(D) Nucleus
Answer
(B) — The Golgi apparatus modifies, sorts, and packages molecules for delivery inside or outside the cell.
14. Which component provides a rigid structure in plant cells but not in animal cells?
(A) Plasma membrane
(B) Cell wall
(C) Nucleus
(D) Central vacuole
Answer
(B) — The plant cell wall, made of cellulose, provides strength and protection.
15. Which of the following organelles is enclosed by a double membrane and contains its own DNA?
(A) Ribosome
(B) Golgi apparatus
(C) Chloroplast
(D) Lysosome
Answer
(C) — Chloroplasts have a double membrane and their own DNA, supporting the endosymbiotic theory.
16. Which transport method moves materials out of a cell using vesicles?
(A) Endocytosis
(B) Osmosis
(C) Exocytosis
(D) Diffusion
Answer
(C) — Exocytosis uses vesicles that fuse with the membrane to expel materials outside the cell.
17. Which term describes the difference in concentration of a substance across a space?
(A) Equilibrium
(B) Concentration gradient
(C) Osmotic pressure
(D) Active zone
Answer
(B) — A concentration gradient is the difference in the amount of a substance between two regions.
18. Which structure helps maintain the shape of animal cells and facilitates cellular movement?
(A) Central vacuole
(B) Plasma membrane
(C) Cytoskeleton
(D) Ribosomes
Answer
(C) — The cytoskeleton provides structural support and assists in movement.
19. Which molecule primarily composes the hydrophilic head of a phospholipid?
(A) Fatty acid
(B) Glycerol
(C) Phosphate group
(D) Protein
Answer
(C) — The phosphate group forms the hydrophilic (water-attracting) head of a phospholipid.
20. What is the primary function of the rough ER in cells?
(A) Synthesizing DNA
(B) Storing ions
(C) Synthesizing proteins
(D) Digesting old organelles
Answer
(C) — The rough ER, studded with ribosomes, synthesizes and processes proteins.
21. Which of the following best describes passive transport?
(A) Requires ATP
(B) Moves substances against the concentration gradient
(C) Moves substances down the concentration gradient without energy
(D) Uses vesicles
Answer
(C) — Passive transport moves substances down their concentration gradient without energy input.
22. What organelle is responsible for storing calcium ions and detoxifying harmful substances?
(A) Rough ER
(B) Golgi apparatus
(C) Smooth ER
(D) Ribosome
Answer
(C) — The smooth ER stores calcium and detoxifies drugs and poisons.
23. Which membrane protein is mainly responsible for transporting ions like Na⁺ and K⁺ across the membrane actively?
(A) Channel protein
(B) Receptor protein
(C) Pump protein
(D) Structural protein
Answer
(C) — Pump proteins, such as the sodium-potassium pump, actively move ions against concentration gradients using ATP.
24. If a freshwater plant cell is placed in salt water, what will most likely happen?
(A) Water enters the cell and causes it to swell
(B) Water leaves the cell and causes it to shrink
(C) The cell remains unchanged
(D) The plasma membrane becomes rigid
Answer
(B) — In a hypertonic environment (salt water), water leaves the cell, causing it to shrink (plasmolysis).
25. Which part of the plasma membrane provides specific recognition of other cells?
(A) Phospholipid heads
(B) Cholesterol
(C) Glycoproteins
(D) Channel proteins
Answer
(C) — Glycoproteins serve as cellular identification markers on the plasma membrane.
26. Which of the following best explains why membrane proteins are amphipathic?
(A) They consist only of hydrophobic amino acids
(B) They are composed of phospholipids
(C) They have hydrophobic regions that interact with the membrane interior and hydrophilic regions that interact with the aqueous environment
(D) They are embedded only on the cytoplasmic side
Answer
(C) — Membrane proteins have both hydrophilic and hydrophobic regions, allowing them to integrate into the phospholipid bilayer.
27. Which of the following organelles is thought to have arisen first according to the endosymbiotic theory?
(A) Golgi apparatus
(B) Ribosome
(C) Mitochondrion
(D) Nucleus
Answer
(C) — Mitochondria are believed to have evolved from free-living prokaryotes engulfed by ancestral eukaryotic cells.
28. If a mutation prevents the production of transport proteins in a cell, which process would be directly affected?
(A) Passive diffusion of oxygen
(B) Osmosis
(C) Facilitated diffusion of glucose
(D) Simple diffusion of carbon dioxide
Answer
(C) — Facilitated diffusion requires specific transport proteins to move molecules like glucose across membranes.
29. Which component of the plasma membrane helps to maintain its fluidity at lower temperatures?
(A) Phospholipids
(B) Proteins
(C) Cholesterol
(D) Glycoproteins
Answer
(C) — Cholesterol prevents the membrane from becoming too rigid at low temperatures and too fluid at high temperatures.
30. In which of the following situations would a plant cell become plasmolyzed?
(A) It is placed in distilled water
(B) It is placed in a hypertonic solution
(C) It is placed in an isotonic solution
(D) It is exposed to hypotonic conditions
Answer
(B) — In a hypertonic solution, water exits the plant cell, causing the plasma membrane to pull away from the cell wall (plasmolysis).
31. A transport vesicle fuses with the plasma membrane and releases its contents outside the cell. What process is this?
(A) Endocytosis
(B) Osmosis
(C) Exocytosis
(D) Active diffusion
Answer
(C) — Exocytosis is the process by which cells export substances using vesicles that fuse with the plasma membrane.
32. Which of the following best describes pinocytosis?
(A) The cell engulfs large particles
(B) The cell engulfs liquids into small vesicles
(C) The diffusion of ions through channels
(D) The active transport of glucose
Answer
(B) — Pinocytosis is the "cell drinking" process where cells internalize extracellular fluids into vesicles.
33. Which property of the plasma membrane is essential for the formation of vesicles during endocytosis and exocytosis?
(A) Rigidity
(B) Fluidity
(C) Polarity
(D) Hydrophobicity
Answer
(B) — The fluid nature of the membrane allows it to bend and form vesicles for endocytosis and exocytosis.
34. During osmosis, water moves toward the side with:
(A) Lower solute concentration
(B) Higher solute concentration
(C) Higher pressure
(D) More hydrophobic molecules
Answer
(B) — Water moves toward the region with higher solute concentration to balance solute levels across the membrane.
35. Which membrane structure enables cells to recognize each other and communicate?
(A) Cholesterol
(B) Phospholipids
(C) Glycoproteins
(D) Peripheral proteins
Answer
(C) — Glycoproteins on the cell surface function in cell recognition and communication.
36. Explain why oxygen can diffuse freely across the plasma membrane but glucose cannot.
Answer
Oxygen is small and nonpolar, allowing it to pass easily through the hydrophobic core of the membrane, while glucose is large and polar, requiring transport proteins.
37. Describe the role of vesicles in intracellular transport.
Answer
Vesicles transport materials between organelles and to and from the plasma membrane, ensuring proper distribution and secretion of molecules.
38. Why are phospholipids arranged in a bilayer in biological membranes?
Answer
The hydrophilic heads face the aqueous environment, while the hydrophobic tails point inward, away from water, forming a stable bilayer.
39. Identify one structural feature shared by mitochondria and chloroplasts that supports the endosymbiotic theory.
Answer
Both mitochondria and chloroplasts have a double membrane, their own DNA, and ribosomes, similar to free-living prokaryotes.
40. How does the cytoskeleton assist in endocytosis?
Answer
The cytoskeleton helps reshape the plasma membrane, enabling the formation of vesicles during endocytosis.
41. What would happen to a red blood cell placed in a hypotonic solution?
Answer
Water would enter the cell, causing it to swell and potentially burst (lyse).
42. How do carrier proteins differ from channel proteins?
Answer
Carrier proteins bind to specific molecules and undergo shape changes to transport them across membranes, while channel proteins create pores for passive movement.
43. Describe how active transport differs from passive transport in terms of energy usage.
Answer
Active transport requires ATP energy to move substances against their concentration gradient, while passive transport does not use energy.
44. What is the function of the nucleolus inside the nucleus?
Answer
The nucleolus synthesizes ribosomal RNA (rRNA) and assembles ribosome subunits.
45. Why is membrane fluidity essential for the survival of cells?
Answer
Membrane fluidity allows for membrane proteins to move, vesicles to form, and cells to respond dynamically to environmental changes.
46. What happens during receptor-mediated endocytosis?
Answer
Specific molecules bind to receptors on the plasma membrane, triggering vesicle formation to internalize the bound molecules.
47. How does the sodium-potassium pump maintain cellular homeostasis?
Answer
The pump moves 3 Na⁺ ions out and 2 K⁺ ions into the cell against their concentration gradients, helping regulate ion balance and membrane potential.
48. Which organelle works closely with the rough ER to modify and package proteins?
Answer
The Golgi apparatus modifies and packages proteins received from the rough ER for delivery inside or outside the cell.
49. Why is cholesterol important in animal cell membranes but not typically found in plant cell membranes?
Answer
Cholesterol stabilizes membrane fluidity in animal cells; plants rely more on their rigid cell walls for structural stability.
50. How does the central vacuole contribute to a plant cell’s size and shape?
Answer
The central vacuole stores water, generating turgor pressure that pushes the plasma membrane against the cell wall, maintaining cell structure.