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Secondary 3 Biology Practice Paper 3

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TuitionGoWhere Practice Paper - Biology Secondary 3

TuitionGoWhere Practice Paper (AI)
Version: 3 of 5
Subject: Biology
Level: Secondary 3 (Express / G3)
Paper: Practice Paper – Cells and Biomolecules
Duration: 1 Hour
Total Marks: 40

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 on this paper.
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 Questions

Answer all questions. For each question, there are four options. Choose the correct one.

1. Which of the following structures is found in a typical plant cell but not in a typical animal cell?
A. Cell membrane
B. Cytoplasm
C. Mitochondrion
D. Cell wall
[1]

2. A student observes a cell under an electron microscope. The cell contains many mitochondria and extensive rough endoplasmic reticulum (RER). What is the most likely function of this cell?
A. Storage of starch
B. Synthesis and secretion of proteins
C. Absorption of water
D. Contraction for movement
[1]

3. Which row correctly identifies the elements present in proteins and carbohydrates?

	Proteins	Carbohydrates
A	C, H, O, N	C, H, O
B	C, H, O	C, H, O, N
C	C, H, O, N, P	C, H, O
D	C, H, O, N	C, H, O, N, P

[1]

4. An enzyme is heated to 80°C and then cooled to its optimum temperature of 37°C. The enzyme no longer catalyses the reaction. Why?
A. The enzyme has been denatured.
B. The substrate has been denatured.
C. The kinetic energy of the molecules is too low.
D. The active site has become more flexible.
[1]

5. Which process requires energy from ATP to move substances across a cell membrane?
A. Diffusion of oxygen into a cell
B. Osmosis of water into a root hair cell
C. Active transport of nitrate ions into a root hair cell
D. Facilitated diffusion of glucose into a liver cell
[1]

Section B: Structured Questions

Answer all questions in the spaces provided.

6. Fig. 6.1 shows a diagram of a liver cell as seen under an electron microscope.

(Imagine a diagram showing a nucleus, mitochondria, RER, Golgi apparatus, and cell membrane)

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

(b) State the function of the mitochondria in this cell.
_________________________________________________________________________ [1]

_________________________________________________________________________ [2]

7. A student investigated the effect of pH on the activity of the enzyme amylase. The results are shown in the table below.

pH	Time taken for starch to disappear (seconds)
3	480
5	120
7	60
9	180
11	>600 (no change)

(a) Describe the effect of increasing pH from 3 to 7 on the time taken for starch to disappear.

_________________________________________________________________________ [2]

(b) Explain the results at pH 11.

_________________________________________________________________________ [3]

(c) Suggest one variable, other than pH and temperature, that must be kept constant in this investigation.
_________________________________________________________________________ [1]

8. Fig. 8.1 shows a red blood cell and a white blood cell.

(a) State one structural difference between a red blood cell and a white blood cell.
_________________________________________________________________________ [1]

(b) Red blood cells are adapted for transporting oxygen. Explain how the biconcave shape of the red blood cell helps in this function.

_________________________________________________________________________ [2]

9. Biological molecules are large molecules made up of smaller basic units.

(a) Complete the table below.

Biological Molecule	Basic Unit (Monomer)	Food Test Reagent	Positive Result Colour
Starch	Glucose	Iodine solution	(i) _______________
Protein	(ii) _______________	Biuret solution	Purple / Violet
Reducing Sugar	Glucose	(iii) _______________	Brick-red precipitate

[3]

(b) Describe how you would carry out the food test for fats (lipids) using ethanol.

_________________________________________________________________________ [3]

10. Fig. 10.1 shows a setup used to demonstrate osmosis using visking tubing (a semi-permeable membrane). The visking tubing contains a concentrated sugar solution and is placed in a beaker of distilled water.

(a) Define osmosis.

_________________________________________________________________________ [3]

(b) After 2 hours, the level of liquid in the thistle funnel rises. Explain why this happens.

_________________________________________________________________________ [3]

Section C: Free Response Questions

Answer all questions.

11. Enzymes are biological catalysts.

(a) Explain the 'lock and key' hypothesis of enzyme action.

_________________________________________________________________________ [4]

(b) Compare and contrast the effects of temperature and substrate concentration on the rate of an enzyme-controlled reaction.

_________________________________________________________________________ [5]

12. Cells are organised into tissues, organs, and systems.

(a) Define the term tissue.
_________________________________________________________________________ [1]

(b) Describe how the structure of a root hair cell is adapted for the absorption of water and mineral ions.

_________________________________________________________________________ [4]

(c) Explain why active transport is necessary for the uptake of mineral ions by root hair cells, whereas water uptake occurs by osmosis.

_________________________________________________________________________ [4]

Answers

TuitionGoWhere Practice Paper - Biology Secondary 3 (Answer Key)

Version: 3 of 5
Subject: Biology
Level: Secondary 3

Section A: Multiple Choice Answers

1. D
Reasoning: Cell walls, chloroplasts, and large permanent vacuoles are found in plant cells but not animal cells. Cell membranes, cytoplasm, and mitochondria are found in both.

2. B
Reasoning: Rough Endoplasmic Reticulum (RER) is involved in protein synthesis (due to ribosomes), and mitochondria provide the energy (ATP) required for synthesis and secretion. This suggests a secretory cell (e.g., pancreatic or glandular).

3. A
Reasoning: Proteins contain Carbon, Hydrogen, Oxygen, and Nitrogen (C, H, O, N). Some also contain Sulphur. Carbohydrates contain only Carbon, Hydrogen, and Oxygen (C, H, O).

4. A
Reasoning: High temperatures break the bonds holding the enzyme's tertiary structure, changing the shape of the active site. This is called denaturation. It is irreversible; cooling does not restore the shape.

5. C
Reasoning: Active transport moves substances against a concentration gradient and requires energy (ATP). Diffusion and osmosis are passive processes.

Section B: Structured Answers

6.
(a) Golgi apparatus [1]
(b) To release energy (ATP) through aerobic respiration for cellular activities. [1]
(c) Chloroplasts are required for photosynthesis, which needs light. Liver cells are internal organs and do not receive light; they do not perform photosynthesis. [2]
(1 mark for mentioning photosynthesis/light, 1 mark for liver function/location)

7.
(a) As pH increases from 3 to 7, the time taken for starch to disappear decreases. This indicates that the rate of reaction increases. [2]
(1 mark for describing time decrease, 1 mark for linking to rate increase)
(b) At pH 11, the enzyme is denatured. The high pH alters the shape of the active site. The substrate (starch) can no longer fit into the active site, so no enzyme-substrate complexes are formed. [3]
(1 mark for denatured, 1 mark for active site shape change, 1 mark for no complex formation)
(c) Temperature / Concentration of amylase / Concentration of starch / Volume of solution. [1]

8.
(a) Red blood cells have no nucleus (or are biconcave); White blood cells have a nucleus (or are irregular/amoeboid). [1]
(b) The biconcave shape increases the surface area to volume ratio. This allows for a faster rate of diffusion of oxygen into and out of the cell. [2]
(1 mark for surface area, 1 mark for diffusion rate)
(c) It provides more space for haemoglobin. This allows the cell to carry a maximum amount of oxygen. [2]
(1 mark for space/haemoglobin, 1 mark for oxygen capacity)

9.
(a)
(i) Blue-black / Black [1]
(ii) Amino acids [1]
(iii) Benedict’s solution [1]
(b)

Crush the food sample and mix with ethanol. [1]
Shake well to dissolve any fats. [1]
Pour the solution into water. A cloudy white emulsion indicates the presence of fat. [1]

10.
(a) Osmosis is the net movement of water molecules [1] from a region of higher water potential (dilute solution) [1] to a region of lower water potential (concentrated solution) [1] through a partially permeable membrane. [1]
(Max 3 marks. Must mention water, water potential gradient, and membrane)
(b) The distilled water has a higher water potential than the sugar solution inside the tubing. Water molecules move by osmosis from the beaker into the visking tubing. This increases the volume of liquid inside the tubing, causing the level in the funnel to rise. [3]
(1 mark for water potential gradient, 1 mark for direction of flow, 1 mark for volume/level increase)

Section C: Free Response Answers

11.
(a)

The enzyme has a specific active site with a unique shape. [1]
The substrate has a complementary shape to the active site. [1]
The substrate fits into the active site like a key fits into a lock, forming an enzyme-substrate complex. [1]
The reaction occurs, and products are released, leaving the enzyme unchanged and ready to be reused. [1]

(b)
Temperature:

As temperature increases, kinetic energy increases, leading to more frequent collisions between enzyme and substrate, increasing the rate. [1]
At the optimum temperature, the rate is maximum. [1]
Above the optimum, the enzyme denatures (active site changes shape), and the rate drops rapidly to zero. [1]

Substrate Concentration:

As substrate concentration increases, the rate of reaction increases because there are more substrate molecules to collide with enzyme active sites. [1]
Eventually, the rate levels off (plateaus) because all enzyme active sites are saturated (occupied). Adding more substrate does not increase the rate further. [1]

(Comparison: Temperature causes a drop after optimum due to denaturation; Substrate concentration plateaus due to saturation.) [5 marks total allocated for depth of explanation]

12.
(a) A tissue is a group of similar cells [1] that work together to perform a specific function. [1]
(Note: Question asks for definition, usually 1-2 marks. "Group of similar cells" is key.) [1]

(b)

Root hair cells have a long, hair-like projection. This increases the surface area for absorption of water and minerals. [1]
They have a thin cell wall (and cell membrane), providing a short diffusion distance for water and ions. [1]
They contain many mitochondria to provide energy (ATP) for active transport of mineral ions. [1]
They have a large vacuole containing cell sap with a lower water potential than soil water, facilitating water uptake by osmosis. [1]

(c)

Mineral ions are often present in lower concentration in the soil than inside the root hair cell. [1]
Therefore, they must be moved against the concentration gradient. [1]
This requires energy (ATP) from respiration, which is provided by active transport. [1]
Water moves from the soil (higher water potential) into the root hair (lower water potential) down the water potential gradient. [1]
This process is passive and does not require energy, so it occurs by osmosis. [1]
(Max 4 marks)