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Secondary 4 Pure Biology Cells Biomolecules Quiz
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Questions
Secondary 4 Pure Biology Quiz - Cells Biomolecules
Name: ________________________
Class: ________________________
Date: ________________________
Score: ______ / 50
Duration: 45 minutes
Total Marks: 50
Instructions:
- This quiz contains 20 questions on the topic of Cells & Biomolecules.
- Answer ALL questions in the spaces provided.
- The marks for each question are indicated in brackets.
- Show your working for calculation questions.
- Use scientific terminology where appropriate.
Section A: Multiple Choice (5 × 1 mark = 5 marks)
Circle the correct answer for each question.
1. Which organelle is responsible for the synthesis of proteins within a cell?
A. Golgi apparatus
B. Mitochondrion
C. Ribosome
D. Chloroplast
[1 mark]
2. A student placed a drop of blood into a solution and observed under the microscope that the red blood cells had shrunk and appeared spiky. Which type of solution was the blood placed in?
A. Isotonic solution
B. Hypotonic solution
C. Hypertonic solution
D. Distilled water
[1 mark]
3. Which of the following correctly pairs a food test with the nutrient it detects?
A. Iodine test – reducing sugar
B. Biuret test – starch
C. Ethanol emulsion test – fat
D. Benedict's test – protein
[1 mark]
4. The diagram below shows the lock-and-key model of enzyme action.
Substrate
↓
[Active site] → [Enzyme-substrate complex] → [Products released]
↑
Enzyme
What happens to the enzyme after the products are released?
A. The enzyme is permanently altered and cannot be reused.
B. The enzyme remains unchanged and can bind to another substrate molecule.
C. The enzyme breaks down into amino acids.
D. The enzyme combines with the products to form a new substrate.
[1 mark]
5. A student investigated the effect of pH on the activity of enzyme X. The results are shown in the table below.
| pH | Rate of reaction (arbitrary units) |
|---|---|
| 2 | 0 |
| 4 | 2 |
| 6 | 8 |
| 7 | 10 |
| 8 | 9 |
| 10 | 1 |
| 12 | 0 |
What is the optimum pH for enzyme X?
A. pH 2
B. pH 6
C. pH 7
D. pH 12
[1 mark]
Section B: Short Answer (10 × 2–3 marks = 25 marks)
Answer all questions in the spaces provided.
6. State two differences between the structure of a typical plant cell and a typical animal cell.
[2 marks]
7. The diagram below shows an electron micrograph of a cell organelle.
(Imagine a diagram showing an organelle with folded inner membranes and a smooth outer membrane.)
(a) Identify the organelle shown.
___________________________________________________________________________ [1 mark]
(b) State the function of this organelle.
___________________________________________________________________________ [1 mark]
8. A student carried out the Benedict's test on an unknown solution and obtained a brick-red precipitate.
(a) What food substance is present in the solution?
___________________________________________________________________________ [1 mark]
(b) Explain why the Benedict's test must be heated in a water bath.
___________________________________________________________________________ [2 marks]
9. Define the term diffusion and state one factor that increases the rate of diffusion.
Definition: ___________________________________________________________________
___________________________________________________________________________ [1 mark]
Factor: ___________________________________________________________________________ [1 mark]
10. Explain why a plant wilts when it is not watered for several days. Use the term turgor pressure in your answer.
___________________________________________________________________________ [3 marks]
11. A student placed identical potato strips into three different sucrose solutions: 0.1 mol/dm³, 0.3 mol/dm³, and 0.5 mol/dm³. After 30 minutes, the strip in 0.1 mol/dm³ had increased in length, the strip in 0.3 mol/dm³ showed no change, and the strip in 0.5 mol/dm³ had decreased in length.
Explain these results in terms of water potential and osmosis.
___________________________________________________________________________ [3 marks]
12. State the chemical elements present in carbohydrates and proteins.
Carbohydrates: ________________________________________________________________ [1 mark]
Proteins: ___________________________________________________________________ [1 mark]
13. Describe the role of the Golgi apparatus in a cell.
___________________________________________________________________________ [2 marks]
14. Explain why enzymes are described as biological catalysts and state why they are specific in their action.
___________________________________________________________________________ [3 marks]
15. A red blood cell was placed in distilled water. Describe and explain what would happen to the cell.
___________________________________________________________________________ [3 marks]
Section C: Data Interpretation and Extended Response (5 × 4–5 marks = 20 marks)
Answer all questions in the spaces provided.
16. Fig. 16.1 shows the effect of substrate concentration on the rate of an enzyme-catalysed reaction.
(Imagine a graph with substrate concentration on the x-axis and rate of reaction on the y-axis. The curve rises steeply at first, then gradually levels off to a plateau.)
(a) Describe the trend shown in the graph.
___________________________________________________________________________ [2 marks]
(b) Explain why the rate of reaction levels off at high substrate concentrations.
___________________________________________________________________________ [2 marks]
(c) Suggest one way the maximum rate of reaction could be increased without changing the substrate concentration.
___________________________________________________________________________ [1 mark]
17. A student investigated the effect of temperature on the activity of amylase. The results are shown in Table 17.1.
Table 17.1
| Temperature (°C) | Time taken for starch to be digested (minutes) |
|---|---|
| 10 | 25 |
| 20 | 15 |
| 30 | 8 |
| 40 | 4 |
| 50 | 6 |
| 60 | 20 |
| 70 | No digestion after 30 minutes |
(a) Calculate the rate of reaction at 40°C. Express your answer as 1/time.
___________________________________________________________________________ [1 mark]
(b) Explain why the time taken for starch digestion decreases between 10°C and 40°C.
___________________________________________________________________________ [2 marks]
(c) Explain why no digestion occurred at 70°C.
___________________________________________________________________________ [2 marks]
18. Fig. 18.1 shows two plant cells, P and Q, that have been placed in different solutions.
- Cell P: The cell membrane is pressed tightly against the cell wall.
- Cell Q: The cell membrane has pulled away from the cell wall.
(a) State the type of solution that cell P was placed in. Explain your answer.
___________________________________________________________________________ [2 marks]
(b) Name the process that has occurred in cell Q. Explain why this has happened.
___________________________________________________________________________ [2 marks]
(c) Suggest what would happen if cell Q was transferred to distilled water.
___________________________________________________________________________ [1 mark]
19. Compare the processes of diffusion, osmosis, and active transport in terms of:
(i) Whether energy is required
(ii) The direction of movement relative to the concentration gradient
(iii) The types of substances transported
___________________________________________________________________________ [5 marks]
20. A student stated: "All enzymes are proteins, and all proteins are enzymes."
Discuss whether this statement is correct. In your answer, you should refer to the functions of proteins and the nature of enzymes.
___________________________________________________________________________ [5 marks]
END OF QUIZ
Check your answers carefully before submitting.
Answers
Secondary 4 Pure Biology Quiz - Cells Biomolecules
Answer Key and Marking Scheme
Total Marks: 50
Section A: Multiple Choice (5 × 1 mark = 5 marks)
1. C. Ribosome
Ribosomes are the sites of protein synthesis in cells. The Golgi apparatus modifies and packages proteins; mitochondria produce ATP; chloroplasts carry out photosynthesis.
2. C. Hypertonic solution
A hypertonic solution has a lower water potential than the cell contents. Water moves out of the red blood cells by osmosis, causing them to shrink and become crenated (spiky appearance).
3. C. Ethanol emulsion test – fat
The ethanol emulsion test detects fats (a cloudy white emulsion forms). Iodine tests for starch (blue-black); Biuret tests for protein (purple); Benedict's tests for reducing sugars (brick-red precipitate on heating).
4. B. The enzyme remains unchanged and can bind to another substrate molecule.
Enzymes are not used up or permanently changed in reactions. After products are released, the active site is free to bind another substrate molecule.
5. C. pH 7
The optimum pH is the pH at which the rate of reaction is highest. The highest rate (10 arbitrary units) occurs at pH 7.
Section B: Short Answer (10 × 2–3 marks = 25 marks)
6. State two differences between the structure of a typical plant cell and a typical animal cell. [2 marks]
Answer: Any two from:
- Plant cells have a cellulose cell wall; animal cells do not.
- Plant cells have chloroplasts; animal cells do not.
- Plant cells have a large central vacuole; animal cells have small, temporary vacuoles (if present).
- Plant cells have a regular/fixed shape; animal cells have an irregular shape.
Marking: 1 mark for each correct difference. Accept other valid structural differences.
7. (a) Identify the organelle shown. [1 mark]
Answer: Mitochondrion / Mitochondria
(b) State the function of this organelle. [1 mark]
Answer: Site of aerobic respiration / Produces ATP (energy) for the cell.
Marking: Accept "powerhouse of the cell" or "releases energy from glucose."
8. (a) What food substance is present in the solution? [1 mark]
Answer: Reducing sugar / Glucose (or any named reducing sugar)
(b) Explain why the Benedict's test must be heated in a water bath. [2 marks]
Answer: Heating provides activation energy for the reaction between reducing sugars and copper(II) sulfate in Benedict's solution. Without heating, the reaction would be too slow for the colour change (brick-red precipitate) to occur within a reasonable time.
Marking: 1 mark for mentioning activation energy or speeding up the reaction; 1 mark for linking to the reaction between reducing sugar and Benedict's solution.
9. Define the term diffusion and state one factor that increases the rate of diffusion. [2 marks]
Answer:
- Definition: Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. [1 mark]
- Factor (any one): Increased temperature / Steeper concentration gradient / Shorter diffusion distance / Larger surface area / Smaller particle size. [1 mark]
Marking: Accept "movement of particles down a concentration gradient" for the definition. The factor must be stated clearly.
10. Explain why a plant wilts when it is not watered for several days. Use the term turgor pressure in your answer. [3 marks]
Answer: When a plant is not watered, the water potential of the soil decreases (becomes more negative). Water moves out of the root hair cells and then out of the leaf cells by osmosis. The cells lose water, and the vacuoles shrink. The cell membrane pulls away from the cell wall, and turgor pressure decreases. Without sufficient turgor pressure, the cells become flaccid, and the plant wilts.
Marking: 1 mark for water moving out of cells by osmosis; 1 mark for decrease in turgor pressure; 1 mark for linking loss of turgor pressure to wilting/flaccidity.
11. Explain the results of the potato strip experiment in terms of water potential and osmosis. [3 marks]
Answer:
- In 0.1 mol/dm³ sucrose: The solution has a higher water potential than the potato cell sap. Water enters the cells by osmosis, down the water potential gradient. The cells become turgid, and the strip increases in length.
- In 0.3 mol/dm³ sucrose: The solution has the same water potential as the cell sap (isotonic). There is no net movement of water, so the length remains unchanged.
- In 0.5 mol/dm³ sucrose: The solution has a lower water potential than the cell sap. Water leaves the cells by osmosis. The cells become flaccid/plasmolysed, and the strip decreases in length.
Marking: 1 mark for each correct explanation of one concentration. Must mention water potential and osmosis.
12. State the chemical elements present in carbohydrates and proteins. [2 marks]
Answer:
- Carbohydrates: Carbon, hydrogen, oxygen (C, H, O) [1 mark]
- Proteins: Carbon, hydrogen, oxygen, nitrogen (C, H, O, N) — some also contain sulfur [1 mark]
Marking: All three elements required for carbohydrates; all four required for proteins (accept "and sometimes sulfur").
13. Describe the role of the Golgi apparatus in a cell. [2 marks]
Answer: The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum. It packages these substances into vesicles for transport within the cell or for secretion out of the cell (exocytosis).
Marking: 1 mark for modifying/sorting/packaging; 1 mark for vesicle formation/transport/secretion.
14. Explain why enzymes are described as biological catalysts and state why they are specific in their action. [3 marks]
Answer:
- Enzymes are biological catalysts because they speed up chemical reactions in living organisms without being used up or permanently changed in the process. They lower the activation energy required for reactions to occur. [2 marks]
- Enzymes are specific because each enzyme has an active site with a specific three-dimensional shape that is complementary to only one type of substrate (or a small group of closely related substrates). Only the specific substrate can bind to the active site to form an enzyme-substrate complex. [1 mark]
Marking: 1 mark for "speed up reactions"; 1 mark for "not used up/lowers activation energy"; 1 mark for active site shape complementary to substrate.
15. A red blood cell was placed in distilled water. Describe and explain what would happen to the cell. [3 marks]
Answer: Distilled water has a higher water potential than the cytoplasm of the red blood cell. Water enters the cell by osmosis, down the water potential gradient. The cell swells and eventually bursts (haemolyses/lyses) because animal cells do not have a cell wall to resist the inward pressure.
Marking: 1 mark for water entering by osmosis; 1 mark for cell swelling; 1 mark for bursting/haemolysis and reference to lack of cell wall.
Section C: Data Interpretation and Extended Response (5 × 4–5 marks = 20 marks)
16. Enzyme activity and substrate concentration. [5 marks]
(a) Describe the trend shown in the graph. [2 marks]
Answer: As substrate concentration increases, the rate of reaction increases rapidly at first. Then the rate of increase slows down, and eventually the rate of reaction reaches a maximum and levels off (plateaus).
Marking: 1 mark for initial rapid increase; 1 mark for levelling off/plateau.
(b) Explain why the rate of reaction levels off at high substrate concentrations. [2 marks]
Answer: At high substrate concentrations, all the active sites of the enzyme molecules are occupied by substrate molecules at any given time. The enzyme concentration becomes the limiting factor. Adding more substrate cannot increase the rate because there are no free active sites available. The enzyme is saturated.
Marking: 1 mark for all active sites occupied/saturated; 1 mark for enzyme concentration being the limiting factor.
(c) Suggest one way the maximum rate of reaction could be increased without changing the substrate concentration. [1 mark]
Answer: Increase the enzyme concentration / Increase the temperature (up to the optimum) / Adjust pH to the optimum.
Marking: Accept any valid method that increases the number of available active sites or increases the turnover rate of existing enzymes.
17. Effect of temperature on amylase activity. [5 marks]
(a) Calculate the rate of reaction at 40°C. Express your answer as 1/time. [1 mark]
Answer: Rate = 1/4 = 0.25 min⁻¹ (or 0.25 per minute)
Marking: Accept 0.25 with correct units.
(b) Explain why the time taken for starch digestion decreases between 10°C and 40°C. [2 marks]
Answer: As temperature increases, the kinetic energy of the enzyme and substrate molecules increases. They move faster and collide more frequently. More enzyme-substrate complexes are formed per unit time, so the rate of reaction increases and the time taken for digestion decreases.
Marking: 1 mark for increased kinetic energy/more collisions; 1 mark for more enzyme-substrate complexes formed.
(c) Explain why no digestion occurred at 70°C. [2 marks]
Answer: At 70°C, the high temperature causes the enzyme to denature. The hydrogen bonds maintaining the enzyme's specific three-dimensional shape (tertiary structure) are broken. The active site loses its complementary shape, so the substrate can no longer bind. No enzyme-substrate complexes can form, so no reaction occurs.
Marking: 1 mark for denaturation; 1 mark for active site shape change and inability to bind substrate.
18. Plant cells in different solutions. [5 marks]
(a) State the type of solution that cell P was placed in. Explain your answer. [2 marks]
Answer: Cell P was placed in a hypotonic solution (or distilled water). The cell membrane is pressed against the cell wall because water has entered the cell by osmosis, causing the vacuole to swell and push the cytoplasm against the cell wall. The cell is turgid.
Marking: 1 mark for hypotonic solution; 1 mark for explanation linking water entry and turgidity.
(b) Name the process that has occurred in cell Q. Explain why this has happened. [2 marks]
Answer: Plasmolysis has occurred. Cell Q was placed in a hypertonic solution (solution with lower water potential than the cell sap). Water moved out of the cell by osmosis. The vacuole shrank, and the cell membrane pulled away from the cell wall.
Marking: 1 mark for plasmolysis; 1 mark for explanation (water loss by osmosis in hypertonic solution).
(c) Suggest what would happen if cell Q was transferred to distilled water. [1 mark]
Answer: Water would enter the cell by osmosis. The cell would become turgid again (deplasmolysis), and the cell membrane would press against the cell wall.
Marking: Accept "becomes turgid" or "recovers" or "deplasmolysis occurs."
19. Compare diffusion, osmosis, and active transport. [5 marks]
Answer:
| Feature | Diffusion | Osmosis | Active Transport |
|---|---|---|---|
| Energy required? | No (passive) | No (passive) | Yes (requires ATP) |
| Direction relative to concentration gradient | Down the concentration gradient (high to low) | Down the water potential gradient (high to low water potential) | Against the concentration gradient (low to high) |
| Substances transported | Any small, dissolved particles (e.g., oxygen, carbon dioxide, glucose) | Water molecules only (across a partially permeable membrane) | Ions, glucose, amino acids (specific substances) |
Marking:
- Energy requirement: 1 mark for correctly identifying passive for diffusion and osmosis, and active for active transport.
- Direction: 1 mark for down gradient for diffusion/osmosis; 1 mark for against gradient for active transport.
- Substances: 1 mark for water only for osmosis; 1 mark for examples for diffusion and active transport.
- Award marks for clear comparison in any format (table, bullet points, or prose).
20. Discuss the statement: "All enzymes are proteins, and all proteins are enzymes." [5 marks]
Answer: The statement is partially correct but mostly incorrect.
-
"All enzymes are proteins" is correct. Enzymes are globular proteins with a specific three-dimensional shape. The active site of an enzyme is formed by the folding of the polypeptide chain(s), and this specific shape is essential for enzyme function. Denaturation of the protein structure destroys enzyme activity.
-
"All proteins are enzymes" is incorrect. Proteins have many other functions in living organisms besides acting as enzymes. Examples include:
- Structural proteins (e.g., collagen in skin and bones, keratin in hair and nails)
- Transport proteins (e.g., haemoglobin for oxygen transport)
- Hormonal proteins (e.g., insulin for blood glucose regulation)
- Contractile proteins (e.g., actin and myosin in muscles)
- Antibodies (immunoglobulins) for immune defence
- Membrane proteins (e.g., channel proteins, carrier proteins)
Therefore, while all enzymes are proteins, proteins serve a wide variety of functions, and only some proteins are enzymes.
Marking:
- 1 mark for stating that "all enzymes are proteins" is correct.
- 1 mark for explaining that enzyme function depends on protein structure (active site shape).
- 1 mark for stating that "all proteins are enzymes" is incorrect.
- 2 marks for providing at least two examples of non-enzyme protein functions (1 mark each).
- Accept any valid examples of non-enzyme protein functions.
END OF ANSWER KEY