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Secondary 4 Pure Biology Practice Paper 4

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Questions

Secondary 4 Pure Biology Quiz - Cells Biomolecules

Name: __________________________ Class: __________ Date: __________
Score: ________ / 40 Duration: 45 minutes

Instructions:

Answer all questions.
Write your answers in the spaces provided.
The number of marks is indicated in brackets [ ] at the end of each question or part question.
This quiz covers Topic 1 (Cell Structure), Topic 2 (Movement of Substances), and Topic 3 (Biological Molecules).

Section A: Cell Structure and Organisation (Questions 1–5)

1. Fig. 1.1 shows an electron micrograph of a pancreatic cell, which synthesises and secretes digestive enzymes.

(Imagine Fig 1.1 showing a cell with prominent Rough Endoplasmic Reticulum, Golgi apparatus, and many mitochondria)

(a) Identify the organelle labelled X which appears as a stack of flattened sacs. [1]

(b) Explain why this cell contains a large number of mitochondria. [2]

2. Complete the table below by stating the function of the following cell structures. [3]

Structure	Function
Cell Membrane	__________________________________________________
Nucleus	__________________________________________________
Ribosome	__________________________________________________

3. A student observes a plant cell under a light microscope. The cell is turgid. (a) Which structure prevents the plant cell from bursting when water enters by osmosis? [1]

(b) State one structural difference between this plant cell and a typical human red blood cell. [1]

4. Root hair cells are specialised for absorption. (a) State the specific substance absorbed by root hair cells from the soil. [1]

(b) Explain how the shape of a root hair cell increases the efficiency of absorption. [2]

5. Which of the following structures is found in a prokaryotic cell (e.g., bacteria) but NOT in a human liver cell? [1] A. Cell membrane B. Cytoplasm C. DNA D. Cell wall

Answer: _______

Section B: Movement of Substances (Questions 6–12)

6. Define the term active transport. [2]

7. Fig. 7.1 shows three test tubes containing dialysis tubing bags filled with starch solution, placed in different external solutions.

Tube A: Bag in distilled water.
Tube B: Bag in concentrated sugar solution.
Tube C: Bag in dilute iodine solution.

(a) In Tube A, describe the movement of water molecules. [2]

(b) In Tube C, the solution inside the bag turns blue-black after 10 minutes, but the solution outside remains yellow-brown. Explain these observations. [3]

8. A patient with kidney failure undergoes dialysis. The dialysis fluid contains no urea. Explain why urea moves from the patient’s blood into the dialysis fluid. [2]

9. Which process requires energy from ATP? [1] A. Diffusion of oxygen into alveoli B. Osmosis of water into root hair cells C. Active transport of glucose into villi D. Diffusion of carbon dioxide out of leaves

Answer: _______

10. Potato strips were placed in sucrose solutions of varying concentrations. The change in mass was recorded.

In 0.0 mol/dm³ sucrose, mass increased by 10%.
In 0.5 mol/dm³ sucrose, mass decreased by 5%.

(a) Explain why the mass increased in the 0.0 mol/dm³ solution. [2]

(b) Estimate the concentration of sucrose solution that is isotonic to the potato cell sap. [1]

11. State two factors that affect the rate of diffusion. [2]

12. Red blood cells are placed in a hypotonic solution. (a) Describe what happens to the red blood cells. [1]

(b) Explain why plant cells do not burst in the same solution. [2]

Section C: Biological Molecules and Enzymes (Questions 13–20)

13. State the chemical elements present in: [2] (a) Carbohydrates: __________________________________________________ (b) Proteins: _______________________________________________________

14. A student performs food tests on an unknown solution.

Biuret test: Turns purple.
Benedict’s test: Remains blue after heating.
Iodine test: Remains brown.

(a) Which nutrient is present in the solution? [1]

(b) Describe how you would test for the presence of fats (lipids) in a sample. [2]

15. Enzymes are biological catalysts. (a) Define the term catalyst. [1]

(b) Explain the "lock and key" hypothesis of enzyme action. [3]

16. Fig. 16.1 shows the effect of temperature on the activity of enzyme X.

Image pending generation for this question.

(a) Explain why the rate of reaction increases between 10°C and 40°C. [2]

(b) Explain why the rate of reaction is zero at 60°C. [3]

17. Pepsin is an enzyme found in the stomach. (a) State the optimum pH for pepsin. [1]

(b) Why does pepsin not function effectively in the small intestine? [2]

18. Which molecule is the monomer (building block) of proteins? [1] A. Glucose B. Amino acid C. Fatty acid D. Glycerol

Answer: _______

19. Starch and glycogen are both polysaccharides. (a) State one similarity in their chemical structure. [1]

(b) State one difference in their location in living organisms. [1]

20. A student investigates the effect of pH on catalase activity using hydrogen peroxide. Identify the independent variable and the dependent variable in this experiment. [2] Independent variable: __________________________________________________ Dependent variable: ___________________________________________________

End of Quiz

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Answers

Answer Key: Secondary 4 Pure Biology Quiz - Cells Biomolecules

Total Marks: 40

Section A: Cell Structure and Organisation

1. (a) Golgi apparatus / Golgi body [1] (b) Mitochondria are the site of aerobic respiration [1]. They release energy (ATP) [1] required for the synthesis and secretion of enzymes (protein synthesis/active transport/exocytosis). [1] (Max 2 marks)

Cell Membrane: Controls the movement of substances in and out of the cell / Partially permeable. [1]
Nucleus: Contains genetic material (DNA) / Controls cell activities. [1]
Ribosome: Site of protein synthesis. [1]

3. (a) Cell wall [1] (b) Plant cell has a cell wall / large vacuole / chloroplasts; Red blood cell has no nucleus / biconcave shape. (Any valid structural difference) [1]

4. (a) Water (and mineral ions) [1] (b) Root hair cells have a long projection/hair-like extension [1]. This increases the surface area to volume ratio [1], allowing for faster absorption of water/minerals.

5. D. Cell wall [1] (Prokaryotes have cell walls; animal cells do not. Note: Some prokaryotes have capsules, but cell wall is the standard distinction here vs animal cells.)

Section B: Movement of Substances

6. The movement of substances/ions [1] from a region of lower concentration to a region of higher concentration (against the concentration gradient) [1], using energy (ATP).

7. (a) Water moves from the distilled water (higher water potential) into the dialysis bag (lower water potential) [1] by osmosis [1]. (b) Iodine molecules are small [1] and can diffuse through the pores of the dialysis tubing into the bag [1]. Starch molecules are large [1] and cannot diffuse out of the bag [1]. Iodine reacts with starch to form a blue-black complex [1]. (Max 3 marks)

8. There is a higher concentration of urea in the blood than in the dialysis fluid [1]. Urea moves down the concentration gradient [1] by diffusion.

9. C. Active transport of glucose into villi [1]

10. (a) The water potential of the distilled water is higher than that of the potato cell sap [1]. Water enters the potato cells by osmosis [1], causing an increase in mass. (b) Between 0.0 and 0.5 mol/dm³ (approx 0.2 - 0.3 mol/dm³) [1]. (Accept any value where net change is zero).

11. Any two of:

Temperature [1]
Concentration gradient / Difference in concentration [1]
Surface area [1]
Diffusion distance / Thickness of membrane [1]

12. (a) They swell and burst (haemolysis) [1]. (b) Plant cells have a rigid cell wall [1] which withstands the increased turgor pressure and prevents bursting [1].

Section C: Biological Molecules and Enzymes

13. (a) Carbon, Hydrogen, Oxygen (C, H, O) [1] (b) Carbon, Hydrogen, Oxygen, Nitrogen (C, H, O, N) [1] (Sulfur is also acceptable)

14. (a) Protein [1] (b) Add ethanol/alcohol to the sample and shake [1]. Add water to the mixture [1]. A cloudy white emulsion indicates the presence of fat. [1] (Max 2 marks)

15. (a) A substance that speeds up the rate of a chemical reaction [1] without being used up/changed itself. (b) The substrate has a specific shape [1] that fits into the active site of the enzyme [1]. This forms an enzyme-substrate complex [1].

16. (a) As temperature increases, kinetic energy of enzyme and substrate molecules increases [1]. This leads to more frequent collisions [1] and more enzyme-substrate complexes formed. (b) At 60°C, the high temperature breaks the bonds holding the enzyme structure [1]. The enzyme denatures [1]. The shape of the active site changes [1] so the substrate no longer fits.

17. (a) pH 2 (or acidic pH / pH 1-3) [1] (b) The small intestine has an alkaline pH (due to bile/pancreatic juice) [1]. Pepsin denatures/is inactive at alkaline pH [1].

18. B. Amino acid [1]

19. (a) Both are polymers of glucose / Both are polysaccharides [1]. (b) Starch is found in plants; Glycogen is found in animals/fungi [1].

20. Independent variable: pH [1] Dependent variable: Rate of reaction / Volume of oxygen produced / Time taken for reaction [1]