Mitochondria, Plastids and Ribosomes Quiz
This quiz follows Lesson 9: Mitochondria, Plastids and Ribosomes from the course CELL: THE UNIT OF LIFE. It tests the structural details that explain how three remarkable organelles perform their tasks.
- Mitochondria — sausage-shaped double-membrane power houses with cristae, matrix, circular DNA and 70S ribosomes.
- Plastids — chloroplasts, chromoplasts and leucoplasts, with stroma, thylakoids, grana and stroma lamellae.
- Ribosomes — membrane-less granules first seen by George Palade, built from 80S or 70S subunits measured in Svedberg units.
Expect questions on dimensions, membrane arrangements and sedimentation values. Read each option carefully — the distractors are close.
Q1. What is the typical shape and average diameter of a mitochondrion as described in the lesson?
The typical mitochondrion is sausage-shaped or cylindrical with a diameter of 0.2–1.0 μm (average 0.5 μm) and a length of 1.0–4.1 μm.
Q2. The inner membrane of a mitochondrion folds inward to form cristae. What is the main consequence of this folding?
Cristae project towards the matrix and increase the surface area, accommodating more enzyme complexes of respiration. The DNA lies in the matrix, not in the folds.
Q3. Which set of components is found in the mitochondrial matrix?
The matrix possesses a single circular DNA molecule, a few RNA molecules, 70S ribosomes and the components required for protein synthesis.
Q4. Why are mitochondria called the 'power houses' of the cell?
Mitochondria are the sites of aerobic respiration and produce cellular energy as ATP, which earns them the name 'power houses'.
Q5. How do mitochondria increase their number within a cell?
The lesson states that mitochondria divide by fission.
Q6. Which statement about the two mitochondrial membranes is correct?
The two membranes have their own specific enzymes associated with mitochondrial function, making the boundary an enzymatically active interface.
Q7. Which plastid contains fat-soluble carotenoid pigments such as carotene and xanthophylls, giving plant parts a yellow, orange or red colour?
Chromoplasts contain fat-soluble carotenoid pigments like carotene and xanthophylls, which give yellow, orange or red colours.
Q8. An amyloplast, an elaioplast and an aleuroplast are all examples of leucoplasts. What do they store, respectively?
Amyloplasts store carbohydrates (starch), elaioplasts store oils and fats, and aleuroplasts store proteins.
Q9. What is the space limited by the inner membrane of a chloroplast called?
The space limited by the inner chloroplast membrane is called the stroma. The lumen is the space inside a thylakoid.
Q10. Stacks of thylakoids arranged like piles of coins are called grana. What connects the thylakoids of different grana?
Flat membranous tubules called stroma lamellae connect the thylakoids of different grana.
Q11. Where are chlorophyll pigments located in a chloroplast, and what is the size of chloroplast ribosomes compared with cytoplasmic ribosomes?
Chlorophyll pigments are present in the thylakoids, and chloroplast ribosomes are 70S, smaller than the cytoplasmic 80S ribosomes.
Q12. Who first observed ribosomes under the electron microscope as dense particles, and in which year?
Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade in 1953.
Q13. What are the two subunits of an 80S eukaryotic ribosome?
The two subunits of 80S ribosomes are 60S and 40S, while those of 70S ribosomes are 50S and 30S.
Q14. In the abbreviation 'S' of Svedberg's Unit, what does the value actually measure?
'S' stands for the sedimentation coefficient, which is indirectly a measure of density and size.
Q15. Which statement about ribosomes is correct according to the lesson?
Ribosomes are composed of ribonucleic acid (RNA) and proteins and are not surrounded by any membrane.