Questions & explanations
1. Which of the following plastids is correctly matched with its function?
- A. Chloroplasts – storage of starch
- B. Chromoplasts – photosynthesis
- C. Leucoplasts – storage of nutrients
- D. Chloroplasts – synthesis of coloured pigments
Answer: C. Leucoplasts – storage of nutrients
Leucoplasts are colourless plastids involved in storage of starch (amyloplasts), oils (elaioplasts), or proteins (aleuroplasts). Option A is incorrect because chloroplasts are for photosynthesis, not starch storage. Option B is incorrect because chromoplasts contain coloured pigments but do not perform photosynthesis. Option D is incorrect because chloroplasts are green and perform photosynthesis, not synthesis of coloured pigments.
2. Which of the following features supports the semi-autonomous nature of mitochondria?
- A. Presence of a single membrane and 80S ribosomes
- B. Presence of own DNA and 70S ribosomes
- C. Ability to synthesize all proteins independently
- D. Dependence on nuclear DNA for all functions
Answer: B. Presence of own DNA and 70S ribosomes
Mitochondria contain their own circular DNA and 70S ribosomes, which allow them to synthesize some of their own proteins, making them semi-autonomous. Option A is incorrect because mitochondria have a double membrane and 70S ribosomes. Option C is incorrect because they cannot synthesize all proteins; many are nuclear-encoded. Option D contradicts semi-autonomy.
3. The endosymbiotic theory proposes that mitochondria and plastids originated from:
- A. Invaginations of the plasma membrane
- B. Free-living prokaryotes that were engulfed by a host cell
- C. Fragments of the nucleus
- D. Viruses that integrated into the host genome
Answer: B. Free-living prokaryotes that were engulfed by a host cell
The endosymbiotic theory suggests that mitochondria and plastids were once free-living prokaryotes (likely aerobic bacteria and cyanobacteria, respectively) that were engulfed by a primitive eukaryotic cell and evolved into organelles. Option A describes the origin of the endoplasmic reticulum and nuclear envelope. Option C and D are not supported by evidence.
4. Which of the following correctly describes the structure and function of mitochondria?
- A. Single membrane-bound organelle involved in protein synthesis
- B. Double membrane-bound organelle with cristae and matrix; site of aerobic respiration and ATP synthesis
- C. Double membrane-bound organelle with thylakoids; site of photosynthesis
- D. Single membrane-bound organelle containing hydrolytic enzymes
Answer: B. Double membrane-bound organelle with cristae and matrix; site of aerobic respiration and ATP synthesis
Mitochondria have a double membrane: the outer membrane and the inner membrane folded into cristae, enclosing the matrix. They are the primary site of aerobic respiration and ATP synthesis. Option A is incorrect because mitochondria are double-membraned and not primarily for protein synthesis. Option C describes chloroplasts. Option D describes lysosomes.
5. Which of the following plastids is responsible for the red, yellow, and orange colours in fruits and flowers?
- A. Chloroplasts
- B. Chromoplasts
- C. Leucoplasts
- D. Amyloplasts
Answer: B. Chromoplasts
Chromoplasts contain coloured pigments such as carotenoids (red, yellow, orange) and are responsible for the colours in many fruits and flowers. Option A is incorrect because chloroplasts are green due to chlorophyll. Option C is incorrect because leucoplasts are colourless. Option D is a type of leucoplast that stores starch, not pigments.
6. Which of the following is evidence for the semi-autonomous nature of chloroplasts?
- A. Presence of a single membrane and 80S ribosomes
- B. Presence of own DNA and 70S ribosomes
- C. Complete dependence on nuclear genes for all proteins
- D. Absence of ribosomes
Answer: B. Presence of own DNA and 70S ribosomes
Chloroplasts contain their own circular DNA and 70S ribosomes, enabling them to synthesize some proteins independently, which supports their semi-autonomous nature. Option A is incorrect because chloroplasts have a double membrane and 70S ribosomes. Option C is incorrect because they can synthesize some proteins. Option D is false.
7. Which of the following correctly describes the structure of a chloroplast?
- A. Single membrane enclosing a fluid called stroma
- B. Double membrane with inner membrane folded into cristae
- C. Double membrane with stroma and grana (thylakoids); site of photosynthesis
- D. Double membrane containing 70S ribosomes but no DNA
Answer: C. Double membrane with stroma and grana (thylakoids); site of photosynthesis
Chloroplasts have a double membrane, an internal fluid stroma, and a system of thylakoids stacked into grana. They are the site of photosynthesis. Option A is incorrect because chloroplasts have a double membrane. Option B describes mitochondria. Option D is incorrect because chloroplasts contain both DNA and 70S ribosomes.
8. Which of the following scientists is credited with the extension of the cell theory by stating that all cells arise from pre-existing cells?
- A) Matthias Schleiden
- B) Theodor Schwann
- C) Rudolf Virchow
- D) Robert Hooke
Answer: C) Rudolf Virchow
Rudolf Virchow (1855) famously stated 'Omnis cellula e cellula' (all cells arise from pre-existing cells), completing the cell theory. Schleiden and Schwann proposed that plants and animals are made of cells, but Virchow added the principle of cell division.
9. During cell division in plant cells, the Golgi apparatus is involved in the formation of the:
- Spindle fibers
- Cell plate
- Cleavage furrow
- Nuclear envelope
Answer: Cell plate
In plant cells, the Golgi apparatus produces vesicles that fuse to form the cell plate, which develops into the new cell wall. Spindle fibers are formed by centrosomes, cleavage furrow is in animal cells, and the nuclear envelope reforms from ER fragments.
10. Which of the following is a correct difference between prokaryotic and eukaryotic cells?
- A) Prokaryotes have a nucleus, eukaryotes do not
- B) Prokaryotes have membrane-bound organelles, eukaryotes lack them
- C) Prokaryotes have 70S ribosomes, eukaryotes have 80S ribosomes
- D) Eukaryotes have circular DNA, prokaryotes have linear DNA
Answer: C) Prokaryotes have 70S ribosomes, eukaryotes have 80S ribosomes
Prokaryotic cells contain 70S ribosomes, while eukaryotic cells have larger 80S ribosomes. Other differences: prokaryotes lack a nucleus and membrane-bound organelles, and their DNA is circular, whereas eukaryotes have a true nucleus and linear DNA.
11. Why is the cell considered the structural and functional unit of life?
- A) All cells are identical in structure and function
- B) Cells are the smallest entities that can perform all life processes independently
- C) Cells can only function as part of a multicellular organism
- D) Cells do not require energy to carry out functions
Answer: B) Cells are the smallest entities that can perform all life processes independently
A cell is the smallest unit capable of carrying out all essential life processes such as metabolism, growth, reproduction, and response to stimuli. While cells in multicellular organisms are specialized, each cell is a self-contained living unit.
12. Which of the following correctly describes the coordination of the endomembrane system?
- Proteins are synthesized in the Golgi apparatus and transported to the ER for modification.
- Lysosomal enzymes are synthesized in the rough ER, modified in the Golgi, and packaged into lysosomes.
- Vacuoles receive lipids directly from the smooth ER without Golgi involvement.
- The nuclear envelope is not part of the endomembrane system.
Answer: Lysosomal enzymes are synthesized in the rough ER, modified in the Golgi, and packaged into lysosomes.
Lysosomal enzymes are synthesized by ribosomes on the rough ER, then transported to the Golgi for modification and sorting, and finally packaged into lysosomes. This illustrates the coordinated function of the endomembrane system.