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Secondary 4 Pure Biology Plant Biology Quiz
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Secondary 4 Pure Biology Quiz - Plant Biology (Answer Key)
Total Marks: 45
Section A: Multiple Choice Answers
- B [1]
Water moves by osmosis (high to low water potential). Mineral ions often move against concentration gradient via active transport. - C [1]
CO2 concentration, temperature, and plant health must be controlled. Distance is the independent variable; bubbles are the dependent variable. - B [1]
Palisade mesophyll cells are packed with chloroplasts and located at the top of the leaf to capture maximum light. - B [1]
Translocation is the transport of organic nutrients (sucrose/amino acids) in phloem. - D [1]
In hot/dry/windy conditions, water loss exceeds uptake. Guard cells lose turgor (become flaccid), causing stomata to close to prevent wilting.
Section B: Structured Answers
6.
(a) Long hair-like projection / root hair. [1]
(b) Root hair cells are located underground / in the soil [1]. They do not receive light, so they cannot perform photosynthesis / do not need chloroplasts. [1]
(c) Process: Active Transport [1]. Energy Source: Respiration (ATP) / Mitochondria. [1]
7.
(a) Glucose. [1]
(b) Chlorophyll absorbs light energy [1]. This energy is used to split water molecules / convert light energy to chemical energy. [1]
(c) To destarch the plant / remove existing starch [1]. This ensures that any starch detected after the experiment was produced during the experiment, not stored previously. [1]
8.
(a) Light intensity. [1]
(b) Photosynthesis involves enzymes [1]. At 30°C, enzymes have more kinetic energy / collide more frequently with substrates than at 20°C [1]. The rate of reaction is higher until another factor becomes limiting. [1]
(c) High temperature denatures the enzymes [1]. The active site changes shape, and the substrate no longer fits / enzyme-substrate complexes cannot form. [1]
9.
(a) Xylem. [1]
(b) Water molecules are cohesive (stick together) due to hydrogen bonding [1]. As water evaporates from leaves (transpiration pull), it pulls the continuous column of water up the xylem [1]. This creates tension in the xylem vessels. [1]
(c) Some water is used for photosynthesis / maintaining turgor pressure / cell growth [1]. Therefore, not all water taken up is lost via transpiration. [1]
10.
(a) Transport of organic nutrients (sucrose/amino acids) from source to sink. [1]
(b) Xylem vessels are dead, hollow tubes with lignified walls [1]. Phloem sieve tubes are living cells with sieve plates and companion cells [1]. Xylem transports water/minerals; Phloem transports food. [1]
11.
(a) Nitrates are needed to make amino acids / proteins / chlorophyll. [1]
(b) Waterlogged soil has no air spaces / lacks oxygen [1]. Root cells cannot perform aerobic respiration [1]. They switch to anaerobic respiration which produces less energy / toxic ethanol, leading to cell death. [1]
12.
(a) Spongy mesophyll. [1]
(b) Large air spaces allow for rapid diffusion of gases (CO2 and O2) [1]. This ensures a constant supply of CO2 to the palisade cells for photosynthesis. [1]
13.
(a) Rate of transpiration increases. [1]
(b) Wind blows away water vapor accumulating near the leaf surface [1]. This maintains a steep concentration gradient of water vapor between the inside of the leaf and the outside air [1]. Faster diffusion of water vapor out of the stomata occurs. [1]
14.
| Feature | Cuticle | Stomata |
|---|---|---|
| Main Function | Reduce water loss / Protection | Gas exchange / Transpiration |
| Permeability to Water | Impermeable | Permeable (when open) |
[1] for each correct cell. Total [4].
15.
Photosynthesis produces glucose/organic food [1]. Heterotrophs (animals/fungi) eat plants or other animals to obtain this energy [1]. Photosynthesis also releases oxygen [1], which is required for aerobic respiration in most living organisms. [1] (Any 3 points)
Section C: Free Response Answers
16.
Water enters the root hair cell by osmosis because the cell sap has a lower water potential than the soil water [1]. Water moves across the cortex cells via the symplast pathway (through cytoplasm/plasmodesmata) or apoplast pathway (cell walls) [1]. At the endodermis, the Casparian strip forces water into the symplast to control entry [1]. Water enters the xylem vessels by osmosis/active transport of ions, creating a water potential gradient. [1]
17.
In light, potassium ions () are actively pumped into the guard cells from surrounding epidermal cells [1]. This lowers the water potential inside the guard cells [1]. Water enters the guard cells by osmosis [1]. The guard cells become turgid. Because the inner cell wall is thicker than the outer wall, they curve outward, opening the stomatal pore. [1]
18.
(a) The plant cells will lose water and become plasmolyzed [1]. The cytoplasm pulls away from the cell wall. [1]
(b) The salt solution has a lower water potential than the cell sap [1]. Water moves out of the cell by osmosis [1], down the water potential gradient, across the partially permeable cell membrane. [1]
19.
Benefit 1: Cools the plant / prevents overheating via evaporation. [1]
Benefit 2: Creates transpiration pull to transport water and mineral ions from roots to leaves. [1]
Disadvantage: Can lead to wilting / water deficit if water loss exceeds uptake, potentially killing the plant. [1]
(Explanation of any point for 4th mark) [1]
20.
- Thin/Transparent Upper Epidermis: Allows maximum light penetration to palisade cells. [1]
- Palisade Mesophyll: Packed with chloroplasts and arranged vertically to absorb maximum light. [1]
- Spongy Mesophyll: Air spaces facilitate rapid diffusion of CO2 to photosynthetic cells. [1]
- Stomata: Allow entry of CO2 and exit of O2. [1]
- Vascular Bundles (Xylem): Bring water to the leaf cells for photosynthesis. [1]
(Any 5 distinct adaptations with explanations)