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O Level Biology Practice Paper 5

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TuitionGoWhere Practice Paper - Biology O-Level

TuitionGoWhere Practice Paper (AI)
Version: 5 of 5
Subject: Biology (6093)
Level: O-Level
Paper: Theme I Practice – Cells and Biomolecules
Duration: 1 hour 15 minutes
Total Marks: 60

Name: __________________________
Class: __________________________
Date: __________________________

Instructions to Candidates

Write your name, class, and date in the spaces above.
Answer all questions.
Write your answers in the spaces provided in this booklet.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a calculator.

Section A: Multiple Choice and Short Structured Questions

Answer all questions in this section.

1. Which row correctly describes the structures found in a typical plant cell and a typical animal cell? [1]

	Plant Cell	Animal Cell
A	Cell wall present	Cell wall absent
B	Chloroplasts absent	Chloroplasts present
C	Large permanent vacuole	Large permanent vacuole
D	Glycogen storage	Starch storage

2. A student observes a cell under a light microscope. The cell has a nucleus, mitochondria, and a cell membrane, but no cell wall. Which type of cell is this most likely to be? [1]

A. Bacterial cell
B. Palisade mesophyll cell
C. White blood cell
D. Root hair cell

3. The diagram below shows an electron micrograph of a cell organelle.

(Imagine a diagram showing a stack of flattened sacs with vesicles budding off)

Identify the organelle and state its primary function. [2]

Organelle: _________________________________________________________
Function: __________________________________________________________

4. Explain why red blood cells do not contain a nucleus. [2]

5. A potato cylinder was placed in a concentrated sugar solution. After 30 minutes, the cylinder became flaccid.
(a) Name the process responsible for this change. [1]

(b) Explain, in terms of water potential, why the potato cylinder became flaccid. [3]

6. The graph below shows the rate of an enzyme-controlled reaction at different temperatures.

(Imagine a bell-shaped curve peaking at 37°C and dropping to zero at 60°C)

(a) Explain why the rate of reaction increases between 10°C and 37°C. [2]

(b) Explain why the rate of reaction drops to zero at 60°C. [2]

7. Which chemical elements are found in all proteins but not in carbohydrates? [1]

A. Carbon and Hydrogen
B. Nitrogen and Sulphur
C. Oxygen and Nitrogen
D. Phosphorus and Sulphur

8. A food sample was tested with three reagents. The results are shown below.

Reagent	Result
Iodine Solution	Orange-brown (no change)
Benedict’s Solution (heated)	Brick-red precipitate
Biuret Solution	Blue (no change)

Identify the nutrient present in the food sample. [1]

9. Describe the ‘lock and key’ hypothesis of enzyme action. [3]

10. State the monomers that make up the following large biological molecules: [2]
(a) Starch: __________________________
(b) Protein: __________________________

Section B: Structured Response Questions

Answer all questions in this section.

11. The diagram below shows a section through a leaf.

(Imagine a cross-section of a leaf showing upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, and stomata)

(a) Identify the tissue labelled X if it contains many chloroplasts and is arranged in vertical columns. [1]

(b) Explain how the structure of the palisade mesophyll cells is adapted for photosynthesis. [2]

12. Active transport is an important process in living organisms.
(a) Define active transport. [2]

(b) Root hair cells absorb mineral ions from the soil. Explain why active transport is necessary for this process, even when the concentration of ions is higher in the root hair cell than in the soil. [3]

13. Enzymes are used in biological washing powders to remove stains.
(a) Suggest why protease enzymes are included in these washing powders. [2]

(b) A manufacturer claims that their washing powder works best at 40°C. A student tests this by washing stained cloth pieces at 20°C, 40°C, and 60°C.
(i) Predict the results at 60°C compared to 40°C. [1]

(ii) Explain your prediction. [2]

14. The table below compares three types of biological molecules. Complete the table. [6]

Molecule	Elements Present	One Function in Humans
Carbohydrate	C, H, O	(a) __________________________
Fat	(b) __________________________	Insulation and energy storage
Protein	C, H, O, N	(c) __________________________

(d) Describe how you would test a sample of milk for the presence of protein. Include the reagent used and the positive result. [3]

15. Cell specialisation allows multicellular organisms to function efficiently.
Compare the structure of a ciliated epithelial cell and a sperm cell. For each cell, explain how its structure is related to its function. [6]

Ciliated Epithelial Cell:
Structure: ______________________________________________________________
Function Link: ___________________________________________________________

Sperm Cell:
Structure: ______________________________________________________________
Function Link: ___________________________________________________________

Section C: Free Response Questions

Answer all questions in this section.

16. (a) Describe the structure of a typical plant cell as seen under a light microscope. Include the function of each structure mentioned. [5]

(b) Explain how the cell wall of a plant cell differs from the cell membrane in terms of permeability and composition. [3]

17. Osmosis is a special case of diffusion.
(a) Define osmosis. [2]

(b) A student places red blood cells in three different solutions:

Solution A: Distilled water
Solution B: 0.9% salt solution (isotonic to blood)
Solution C: 5.0% salt solution

Describe and explain what happens to the red blood cells in Solution A and Solution C. [6]

Solution A:
Description: ____________________________________________________________
Explanation: ____________________________________________________________

Solution C:
Description: ____________________________________________________________
Explanation: ____________________________________________________________

18. Enzymes are biological catalysts.
(a) Explain what is meant by the term ‘biological catalyst’. [2]

(b) Investigate the effect of pH on the activity of the enzyme amylase.
Describe how you would set up an experiment to determine the optimum pH for amylase activity. Include the variables you would control and how you would measure the rate of reaction. [6]

19. Biological molecules are essential for life.
(a) Describe the test for reducing sugars using Benedict’s solution. [3]

(b) Explain why glucose is a suitable molecule for transport in the blood, whereas starch is suitable for storage in plants. [4]

20. The diagram below shows a model of a cell membrane.

(Imagine a fluid mosaic model diagram with phospholipid bilayer and protein channels)

(a) Label the following parts on the diagram (assume labels A, B, C are pointing to specific parts):
(i) Phospholipid bilayer: ______
(ii) Protein channel: ______
(iii) Glycoprotein: ______
[3]

(b) Explain how the structure of the cell membrane allows it to control the movement of substances in and out of the cell. [4]

End of Paper

Answers

TuitionGoWhere Practice Paper - Biology O-Level (Answer Key)

Version: 5 of 5
Subject: Biology (6093)
Topic: Cells and Biomolecules

Section A: Multiple Choice and Short Structured Questions

1. A [1]
Reasoning: Plant cells have cell walls; animal cells do not. B is incorrect because animal cells lack chloroplasts. C is incorrect because animal cells have small/temporary vacuoles. D is incorrect because plants store starch, animals store glycogen.

2. C [1]
Reasoning: White blood cells are animal cells (no cell wall, have nucleus/mitochondria). Bacterial cells have no nucleus. Palisade and root hair cells are plant cells (have cell walls).

3. [2]
Organelle: Golgi apparatus (or Golgi body) [1]
Function: Modifies, sorts, and packages proteins/lipids for secretion or transport within the cell. [1]

4. [2]

To provide more space for haemoglobin. [1]
This maximises the oxygen-carrying capacity of the cell. [1]
(Accept: Biconcave shape increases surface area, but the question asks about the nucleus specifically).

5. [4]
(a) Osmosis [1]
(b)

The sugar solution has a lower water potential (higher solute concentration) than the potato cell sap. [1]
Water moves out of the potato cells by osmosis. [1]
Water moves from a region of higher water potential (inside cell) to lower water potential (outside) across the partially permeable membrane. [1]
(Note: Do not accept "sugar moves into potato").

6. [4]
(a)

As temperature increases, the kinetic energy of enzyme and substrate molecules increases. [1]
This leads to more frequent successful collisions between enzyme and substrate, forming more enzyme-substrate complexes. [1]
(b)
High temperature breaks the hydrogen bonds holding the enzyme's tertiary structure. [1]
The active site changes shape (denaturation), so the substrate no longer fits/complementary shape is lost. [1]

7. B [1]
Reasoning: Proteins contain Nitrogen (always) and often Sulphur. Carbohydrates only contain C, H, O.

8. Reducing Sugar (e.g., Glucose/Maltose) [1]
Reasoning: Benedict's positive = reducing sugar. Iodine negative = no starch. Biuret negative = no protein.

9. [3]

The enzyme has a specific active site with a unique shape. [1]
The substrate has a complementary shape that fits into the active site. [1]
They bind to form an enzyme-substrate complex, lowering the activation energy for the reaction. [1]

10. [2]
(a) Glucose [1]
(b) Amino acids [1]

Section B: Structured Response Questions

11. [6]
(a) Palisade mesophyll [1]
(b)

Contains many chloroplasts to maximise light absorption for photosynthesis. [1]
Arranged in vertical columns/packed tightly to absorb maximum light near the upper surface. [1]
(c)
Guard cells take up water by osmosis. [1]
They become turgid/swollen. [1]
The inner wall is thicker than the outer wall, causing the cells to curve apart, opening the stoma. [1]

12. [6]
(a) The movement of substances/ions against a concentration gradient (from low to high concentration). [1]
Requires energy (ATP). [1]
(b)

The concentration of ions is higher in the root hair cell than in the soil. [1]
Diffusion would cause ions to move out of the cell. [1]
Active transport allows the plant to absorb ions from the dilute soil solution against the gradient to ensure sufficient mineral uptake. [1]
(c) ATP (from respiration) [1]

13. [7]
(a)

Stains often contain proteins (e.g., blood, egg). [1]
Protease breaks down proteins into amino acids/peptides which are soluble and can be washed away. [1]
(b)
(i) The rate of cleaning/stain removal will be slower or zero. [1]
(ii)
At 60°C, the protease enzyme may be denatured. [1]
The active site changes shape, so it cannot bind to the protein stain. [1]
(Note: If the enzyme is thermostable, the rate might just decrease due to other factors, but standard O-Level assumption is denaturation at high temps unless specified).

14. [9]
(a) Immediate energy source / Energy storage (glycogen) [1]
(b) C, H, O [1] (Note: Fats do not contain N or P typically in simple triglycerides)
(c) Growth and repair / Enzymes / Hormones / Antibodies [1]
(d)

Add Biuret solution (or Sodium Hydroxide and Copper Sulphate) to the milk sample. [1]
Shake/mix gently. [1]
A purple/violet colour indicates the presence of protein. [1]

15. [6]
Ciliated Epithelial Cell:

Structure: Has cilia (hair-like projections) on the surface. [1]
Function Link: Cilia beat in a coordinated way to move mucus/dust/trapped particles out of the airways. [1]

Sperm Cell:

Structure: Has a long tail (flagellum) and many mitochondria. [1]
Function Link: Tail allows it to swim to the egg; mitochondria provide energy for movement. [1]
(Award marks for clear structure-function links for both. Max 3 marks per cell type).

Section C: Free Response Questions

16. [8]
(a) Any 5 structures with functions:

Cell Wall: Made of cellulose; provides support and maintains shape. [1]
Cell Membrane: Controls movement of substances in/out. [1]
Cytoplasm: Site of chemical reactions. [1]
Nucleus: Contains genetic material/DNA; controls cell activities. [1]
Vacuole: Contains cell sap; maintains turgor pressure. [1]
Chloroplasts: Contains chlorophyll; site of photosynthesis. [1]
(Max 5 marks).
(b)

Permeability: Cell wall is fully permeable; Cell membrane is partially permeable. [1]
Composition: Cell wall is made of cellulose; Cell membrane is made of phospholipids and proteins. [1]
Function: Cell wall provides structural support; Cell membrane controls transport. [1]

17. [8]
(a) The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane. [2]
(b)
Solution A (Distilled Water):

Description: The red blood cells will swell and burst (haemolysis). [1]
Explanation: Distilled water has a higher water potential than the cytoplasm. Water enters the cells by osmosis. Animal cells lack a cell wall to withstand the pressure. [2]

Solution C (5.0% Salt):

Description: The red blood cells will shrink/shrivel (crenation). [1]
Explanation: The salt solution has a lower water potential than the cytoplasm. Water leaves the cells by osmosis. [2]

18. [8]
(a)

A substance produced by living organisms. [1]
It speeds up the rate of chemical reactions without being used up/changed itself. [1]
(b) Experimental Design:
Independent Variable: pH of the solution (use buffer solutions of different pH). [1]
Dependent Variable: Rate of reaction (measured by time taken for starch to disappear or amount of maltose produced). [1]
Control Variables: Temperature (keep constant at optimum, e.g., 37°C), concentration of enzyme, concentration of substrate. [1]
Method: Mix amylase and starch at specific pH. Sample at intervals. Test with iodine. [1]
Measurement: Record time taken for iodine to remain orange-brown (starch gone). [1]
Conclusion: The pH with the shortest time/highest rate is the optimum. [1]

19. [7]
(a)

Add Benedict’s solution to the food sample. [1]
Heat the mixture in a water bath (boil) for a few minutes. [1]
A colour change from blue to green/yellow/orange/brick-red indicates the presence of reducing sugar. [1]
(b)
Glucose: Small, soluble molecule. [1]
Can be easily transported in blood plasma to cells for respiration. [1]
Starch: Large, insoluble molecule. [1]
Does not affect the water potential of the cell (osmotic balance) and is compact for storage. [1]

20. [7]
(a)
(i) Phospholipid bilayer: (Label pointing to the double layer of lipids) [1]
(ii) Protein channel: (Label pointing to the transmembrane protein) [1]
(iii) Glycoprotein: (Label pointing to protein with carbohydrate chain) [1]
(b)

The phospholipid bilayer is hydrophobic in the middle, preventing water-soluble substances/ions from passing through freely. [1]
Protein channels/carriers allow specific ions/large molecules to pass through (facilitated diffusion/active transport). [1]
The membrane is selectively/partially permeable, controlling what enters/exits. [1]
Fluid nature allows flexibility and self-sealing. [1]

End of Marking Scheme