Organelles & Their Functions
Chapter: Organelles & Their Functions
Level 2 — Recall (Definitions, standard textbook items, short explanations)
Time Limit: 30 minutes Total Marks: 40
Instructions: Answer all questions. Marks for each question are shown in brackets.
Q1. Define the following in one sentence each: (4 marks) (a) Nucleolus (b) Autophagy
Q2. State three structural or functional differences between the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER). (3 marks)
Q3. Describe the structure of the mitochondrion and explain why it is called the "powerhouse of the cell". (5 marks)
Q4. Ribosomes are composed of two subunits. (a) Name the two chemical components that make up a ribosome. (2 marks) (b) State the role of the ribosome in the cell. (1 mark)
Q5. Explain the function of the Golgi apparatus, naming its receiving (cis) and shipping (trans) faces. (4 marks)
Q6. The chloroplast carries out photosynthesis. (a) Name the stacked, disc-like structures that contain chlorophyll. (1 mark) (b) Name the fluid-filled space surrounding these structures. (1 mark) (c) State one function of the chloroplast. (1 mark)
Q7. Cilia and flagella share a characteristic internal arrangement of microtubules. (a) Name this arrangement. (1 mark) (b) Explain what "9+2" means in this arrangement. (3 marks)
Q8. Complete the table describing the three components of the cytoskeleton. (6 marks)
| Component | Main protein | One function |
|---|---|---|
| Microfilaments | (i) | (ii) |
| Microtubules | (iii) | (iv) |
| Intermediate filaments | (v) | (vi) |
Q9. Trace, in the correct order, the pathway of a secreted protein through the endomembrane system, from its synthesis to its release from the cell. (4 marks)
Q10. State the main polysaccharide found in the plant cell wall, and give one function of the cell wall. (2 marks)
END OF PAPER
Answer keyMark scheme & solutions
Q1. (4 marks) (a) Nucleolus: a dense, non-membrane-bound region within the nucleus where ribosomal RNA (rRNA) is synthesised and ribosomal subunits are assembled. (2) (b) Autophagy: the process by which a cell digests its own worn-out organelles or components using enzymes within lysosomes. (2) Why: Definitions must capture location/nature + function. 1 mark for identity, 1 for function.
Q2. (3 marks) Any three (1 mark each):
- RER has ribosomes on its surface; SER lacks ribosomes (smooth).
- RER synthesises/modifies proteins; SER synthesises lipids/steroids.
- SER also detoxifies drugs and stores calcium ions; RER does not.
- RER appears rough/studded; SER appears smooth/tubular. Why: Each valid contrasting pair = 1 mark.
Q3. (5 marks)
- Double-membrane organelle: smooth outer membrane and folded inner membrane. (1)
- Inner membrane folds form cristae, increasing surface area. (1)
- Central fluid-filled region is the matrix (contains enzymes, DNA, ribosomes). (1)
- Site of aerobic respiration, producing ATP (energy). (1)
- Called "powerhouse" because it generates most of the cell's usable energy (ATP). (1)
Q4. (3 marks) (a) Ribosomal RNA (rRNA) and protein. (2) — 1 mark each. (b) Site of protein synthesis / translation (assembling amino acids into polypeptides). (1)
Q5. (4 marks)
- The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the ER. (2)
- The cis face receives vesicles from the ER. (1)
- The trans face ships packaged products in vesicles to their destinations (e.g. secretion). (1)
Q6. (3 marks) (a) Thylakoids (stacks called grana). (1) (b) Stroma. (1) (c) Carries out photosynthesis (converts light energy into chemical energy/glucose). (1)
Q7. (4 marks) (a) The axoneme / "9+2 arrangement". (1) (b) Nine pairs (doublets) of microtubules arranged in a ring around the outside, plus two single (central) microtubules in the centre. (3) — 1 for nine outer, 1 for "pairs/doublets", 1 for two central singlets.
Q8. (6 marks) 1 mark each cell:
| Component | Main protein | Function |
|---|---|---|
| Microfilaments | (i) Actin | (ii) cell movement / muscle contraction / shape |
| Microtubules | (iii) Tubulin | (iv) intracellular transport / chromosome movement in mitosis / structure |
| Intermediate filaments | (v) Keratin (or vimentin/lamins) | (vi) mechanical strength / anchoring organelles |
Q9. (4 marks) Correct order: Rough ER (synthesis) → transport vesicle → Golgi apparatus (cis→trans, modification) → secretory vesicle → plasma membrane → released by exocytosis. (4) Marking: 1 mark RER first, 1 for vesicle→Golgi, 1 for Golgi modification, 1 for exocytosis at membrane. Deduct for wrong order.
Q10. (2 marks)
- Main polysaccharide: cellulose. (1)
- Function (any one): provides structural support / rigidity, protection, or prevents excessive water uptake (osmotic bursting). (1)
[
{"claim": "Q7: total microtubules in a 9+2 axoneme = 9*2 + 2 = 20", "code": "result = (9*2 + 2 == 20)"},
{"claim": "Q8 has 6 cells to fill, each 1 mark = 6 marks", "code": "cells = 3*2; result = (cells == 6)"},
{"claim": "Total paper marks sum to 40", "code": "marks = [4,3,5,3,4,3,4,6,4,2]; result = (sum(marks) == 40)"},
{"claim": "Q9 endomembrane order places RER before Golgi before plasma membrane", "code": "order = ['RER','vesicle','Golgi','vesicle','plasma_membrane']; result = (order.index('RER') < order.index('Golgi') < order.index('plasma_membrane'))"}
]