Secondary 3 Combined Science Semestral Assessment 2 (End of Year) Paper 1

TuitionGoWhere Practice Paper - Combined Science Secondary 3

TuitionGoWhere Secondary School (AI)

Subject: Combined Science
Level: Secondary 3
Paper: SA2
Duration: 1 hour 30 minutes
Total Marks: 65

Name: _________________ Class: _________ Date: _____________

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Instructions:

• Answer all questions in the spaces provided
• Show all working for calculations
• Use appropriate scientific terminology
• Diagrams should be clearly labelled

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Section A: Multiple Choice Questions [8 marks]

For each question, choose the best answer and write the letter in the box provided.

1. Which statement best describes the Principle of Conservation of Energy? A. Energy can be created but not destroyed B. Energy cannot be created or destroyed, only converted C. Energy is always lost as heat D. Energy increases in all reactions

Answer: [ ]

2. In which part of the alimentary canal does most absorption of amino acids occur? A. Stomach B. Small intestine C. Large intestine D. Liver

Answer: [ ]

3. What is the main force responsible for water movement up a plant stem? A. Root pressure B. Capillarity C. Transpiration pull D. Osmotic pressure

Answer: [ ]

4. Which equation represents aerobic respiration? A. Glucose → Lactic acid + Energy B. Glucose + Oxygen → Carbon dioxide + Water + Energy C. Carbon dioxide + Water → Glucose + Oxygen + Energy D. Glucose → Ethanol + Carbon dioxide + Energy

Answer: [ ]

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Section B: Structured Response Questions [57 marks]

5. Fig. 1 shows an experiment to investigate osmosis in potato cells.

[THIS IS FIGURE: Diagram showing a potato cube with a plastic rod inserted, placed in a beaker of water]

(a) After 2 hours, the plastic rod bends downward. Explain why this happens. [3]

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(b) Predict what would happen to the rod if the potato cube was placed in concentrated sugar solution instead of water. Give a reason for your answer. [2]

Prediction: __________________________________________________

Reason: ____________________________________________________

(c) State the name of the process responsible for water movement in this experiment. [1]

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6. Table 1 shows the results of a chromatography experiment used to test urine samples from three athletes (X, Y, Z) for banned substances (B1, B2, B3).

Sample	Distance travelled by substance (cm)	Distance travelled by solvent front (cm)
B1	3.0	6.0
B2	4.5	6.0
B3	1.5	6.0
X	3.0, 4.5	6.0
Y	1.5	6.0
Z	4.5	6.0

(a) Calculate the Rf value for substance B2. [2]

Working: ___________________________________________________

Answer: ____________________________________________________

(b) Which banned substances are present in athlete X's urine sample? [1]

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(c) State one advantage of using chromatography to test for banned substances. [1]

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7. Fig. 2 shows the extraction of zinc from zinc sulfide ore.

(a) Write balanced chemical equations for the two main steps in zinc extraction. Include state symbols. [4]

Step 1 (Roasting): __________________________________________

Step 2 (Reduction): ________________________________________

(b) Calculate the volume of carbon dioxide gas produced when 32.6 g of zinc carbonate reacts completely with excess hydrochloric acid. [Molar volume of gas = 24 dm³/mol; Mr of ZnCO₃ = 125] [3]

Working: ___________________________________________________

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Answer: ____________________________________________________

8. A student investigated the effect of light intensity on photosynthesis using aquatic plants.

(a) Table 2 shows the results obtained.

Light intensity (arbitrary units)	Volume of oxygen collected in 10 minutes (cm³)
0	0
20	8
40	15
60	20
80	20

Draw a graph of these results on the grid below. [3]

[THIS IS FIGURE: Grid for plotting graph with x-axis: Light intensity (arbitrary units) 0-100, y-axis: Volume of oxygen (cm³) 0-25]

(b) Describe the relationship between light intensity and oxygen production shown by your graph. [2]

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(c) Suggest two variables that must be controlled in this experiment. [2]

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2. ---

(d) Explain why oxygen production levels off at high light intensities. [2]

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9. Fig. 3 shows blood circulation through the heart.

(a) Describe how oxygenated blood from the lungs is pumped to the rest of the body. [4]

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(b) Explain why the left ventricle has thicker muscular walls than the right ventricle. [2]

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10. With reference to aerobic and anaerobic respiration in humans, explain the differences between these two processes using word equations. [6]

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11. Fig. 4 shows a cell from the pancreas observed under an electron microscope.

(a) Structure P is found in large quantities in this cell. Name structure P and explain why it is present in large quantities. [2]

Name: ______________________________________________________

Explanation: ________________________________________________

(b) State two other organelles that would be found in large quantities in pancreatic cells and explain why. [4]

Organelle 1: ________________________________________________

Explanation: ________________________________________________

Organelle 2: ________________________________________________

Explanation: ________________________________________________

12. Describe the pathway of water through a flowering plant from absorption by the roots to loss from the leaves. Include the tissues involved and the forces responsible for water movement. [6]

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END OF PAPER

TuitionGoWhere Practice Paper - Combined Science Secondary 3 (Marking Scheme)

Section A: Multiple Choice Questions [8 marks]

1. B - Energy cannot be created or destroyed, only converted [1]

2. B - Small intestine [1]

3. C - Transpiration pull [1]

4. B - Glucose + Oxygen → Carbon dioxide + Water + Energy [1]

Section B: Structured Response Questions [57 marks]

5.(a) After 2 hours, the plastic rod bends downward. Explain why this happens. [3]

• Higher water potential in water than in potato cube [1]
• Water enters potato cube by osmosis [1]
• Potato becomes turgid, exerting upward pressure on rod, causing it to bend down [1]

5.(b) Predict what would happen to the rod if the potato cube was placed in concentrated sugar solution instead of water. Give a reason for your answer. [2] Prediction: Rod would bend upward / Rod would not bend down [1] Reason: Water would leave potato cube, making it flaccid/plasmolysed, reducing pressure on rod [1]

5.(c) State the name of the process responsible for water movement in this experiment. [1]

• Osmosis [1]

6.(a) Calculate the Rf value for substance B2. [2] Working: Rf = distance travelled by substance ÷ distance travelled by solvent front = 4.5 ÷ 6.0 [1] Answer: 0.75 [1]

6.(b) Which banned substances are present in athlete X's urine sample? [1]

• B1 and B2 [1]

6.(c) State one advantage of using chromatography to test for banned substances. [1]

• Can separate and identify multiple substances in one test / Quick and reliable / Can detect small amounts [1]

7.(a) Write balanced chemical equations for the two main steps in zinc extraction. Include state symbols. [4] Step 1 (Roasting): 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g) [2] Step 2 (Reduction): ZnO(s) + C(s) → Zn(s) + CO(g) [2] [1 mark each for correct equation, 1 mark each for correct state symbols and balancing]

7.(b) Calculate the volume of carbon dioxide gas produced when 32.6 g of zinc carbonate reacts completely with excess hydrochloric acid. [3] Working: ZnCO₃ + 2HCl → ZnCl₂ + CO₂ + H₂O Moles of ZnCO₃ = 32.6 ÷ 125 = 0.261 mol [1] Moles of CO₂ = 0.261 mol (1:1 ratio) [1] Volume of CO₂ = 0.261 × 24 = 6.26 dm³ [1]

8.(a) Draw a graph of these results on the grid below. [3]

• Correct plotting of all points [1]
• Appropriate smooth curve showing initial increase then leveling off [1]
• Correctly labeled axes with units [1]

8.(b) Describe the relationship between light intensity and oxygen production shown by your graph. [2]

• Oxygen production increases with light intensity initially [1]
• Then levels off/remains constant at higher light intensities [1]

8.(c) Suggest two variables that must be controlled in this experiment. [2]

1. Temperature [1]
2. Carbon dioxide concentration / pH / Type of plant / Volume of water [1]

8.(d) Explain why oxygen production levels off at high light intensities. [2]

• Light intensity is no longer the limiting factor [1]
• Another factor becomes limiting (temperature/CO₂ concentration/chlorophyll concentration) [1]

9.(a) Describe how oxygenated blood from the lungs is pumped to the rest of the body. [4]

• Oxygenated blood returns from lungs via pulmonary veins to left atrium [1]
• Left atrium contracts, pushing blood into left ventricle [1]
• Left ventricle contracts with great force [1]
• Blood is forced through aortic valve into aorta and to the rest of the body [1]

9.(b) Explain why the left ventricle has thicker muscular walls than the right ventricle. [2]

• Left ventricle needs to pump blood to the whole body [1]
• Requires greater pressure/force than right ventricle which only pumps to lungs [1]

10. With reference to aerobic and anaerobic respiration in humans, explain the differences between these two processes using word equations. [6] Aerobic respiration:

• Glucose + Oxygen → Carbon dioxide + Water + Energy [2]
• Requires oxygen / Occurs in mitochondria [1]

Anaerobic respiration:

• Glucose → Lactic acid + Energy [2]
• Does not require oxygen / Occurs in cytoplasm [1]
• Releases less energy than aerobic respiration [1]

11.(a) Structure P is found in large quantities in this cell. Name structure P and explain why it is present in large quantities. [2] Name: Mitochondria [1] Explanation: To provide energy for enzyme production/secretion of digestive enzymes [1]

11.(b) State two other organelles that would be found in large quantities in pancreatic cells and explain why. [4] Organelle 1: Ribosomes/Rough endoplasmic reticulum [1] Explanation: To synthesize digestive enzymes/proteins [1] Organelle 2: Golgi apparatus [1] Explanation: To package and modify enzymes for secretion [1]

12. Describe the pathway of water through a flowering plant from absorption by the roots to loss from the leaves. Include the tissues involved and the forces responsible for water movement. [6]

• Water absorbed by root hair cells from soil [1]
• Moves through cortex and endodermis in root [1]
• Enters xylem vessels in root [1]
• Transported up stem through xylem tissue [1]
• Reaches leaves and moves to mesophyll cells [1]
• Lost through stomata by transpiration / Transpiration pull creates the force for upward movement [1]

Total: 65 marks

Grade Boundaries:

• A: 52-65 marks (80%+)
• B: 46-51 marks (70-79%)
• C: 39-45 marks (60-69%)
• D: 33-38 marks (50-59%)
• E: 26-32 marks (40-49%)
• F: Below 26 marks