Secondary 3 Combined Science Physical Sciences Quiz

Secondary 3 Combined Science Quiz - Physical Sciences (Answers)

Section A: Short Answer Questions [10 marks]

1. State the Principle of Conservation of Energy. [2]

• Energy cannot be created or destroyed [1]
• Energy can only be converted from one form to another [1]

2. State one function and one adaptation of xylem tissue. [2] Function: Transport water and mineral salts from roots to other parts of plant [1] Adaptation: Lignified walls for strength / Hollow lumen for water transport / No cross-walls (continuous tubes) [1]

3. Name the main force responsible for the rise of water in plant stems during transpiration. [1]

• Transpiration pull [1]

4. State the purpose of using a glass heat shield in a photosynthesis experiment. [1]

• To make sure temperature is constant / To prevent overheating of the plant [1]

5. Write the ionic equation for the reaction between solid zinc carbonate and dilute hydrochloric acid. [2]

• ZnCO₃(s) + 2H⁺(aq) → Zn²⁺(aq) + CO₂(g) + H₂O(l) [2]
• [1 mark for correct reactants and products, 1 mark for correct balancing and state symbols]

6. Suggest one way that light intensity can be varied in a photosynthesis experiment. [1]

• Change the number of light bulbs / Change the power of light bulbs / Change the distance of the light bulb to the apparatus [1]

7. Describe the state of a plant cell that has been placed in a concentrated salt solution for 30 minutes. [1]

• Plasmolysed / Cell membrane or cytoplasm shrinks away from cell wall [1]

Section B: Structured Response Questions [20 marks]

8.(a) Describe the pathway of water through the plant from the soil to leaving the leaves. [5]

• Water absorbed by root hair cells from soil [1]
• Moves through cortex and endodermis [1]
• Enters xylem in root [1]
• Transported up stem via xylem [1]
• Reaches leaves and exits via stomata through transpiration [1]

8.(b) Explain why the plastic rod in a potato osmosis experiment bends down after two hours when the potato cube is placed in distilled water. [3]

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

9.(a) Explain why the amount of amino acids increases from the stomach to the beginning of the small intestine. [2]

• Polypeptides/proteins are digested by protease [1]
• Into amino acids [1]

9.(b) Explain why the amount of amino acids decreases from the beginning to the middle of the small intestine. [2]

• Amino acids are absorbed [1]
• Into blood through small intestine wall [1]

10.(a) Calculate the rate of oxygen production in cm³/min. [1] Working: 15 cm³ ÷ 10 minutes = 1.5 cm³/min Answer: 1.5 cm³/min [1]

10.(b) State two variables that must be kept constant during this experiment. [2]

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

10.(c) Explain why oxygen production increases with light intensity up to a certain point, then levels off. [2]

• Light intensity is the limiting factor initially, so increasing it increases photosynthesis rate [1]
• At high light intensity, another factor becomes limiting (temperature/CO₂ concentration), so rate levels off [1]