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Secondary 3 Biology Cells Biomolecules Quiz
Free Sec 3 Biology Cells Biomolecules quiz, Qwen3.6 Exam version, with questions, answers, and O Level-style practice for Singapore students.
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Secondary 3 Biology Quiz - Cells Biomolecules: Answer Key
Section A: Multiple Choice Questions
1. C
Reasoning: Animal cells (like white blood cells) have a nucleus and mitochondria but no cell wall or chloroplasts. Yeast is a fungus (has cell wall). Palisade and root hair cells are plant cells (have cell wall).
2. B
Reasoning: Mitochondria are the site of aerobic respiration. Golgi modifies/packages proteins. Ribosomes synthesize proteins. Nucleus controls cell activities.
3. B
Reasoning: Amino acids are building blocks for proteins. Synthesis starts at ribosomes (on Rough ER), moves to Golgi for modification/packaging, then to vesicles for secretion.
4. C
Reasoning: The absence of a nucleus creates more space for haemoglobin, maximizing oxygen-carrying capacity.
5. C
Reasoning: Enzymes are catalysts and are not destroyed or used up in the reaction; they can be reused.
Section B: Structured Questions
6.
(a) Absorbs light energy for photosynthesis. [1]
(b) The vacuole contains cell sap which exerts turgor pressure against the cell wall. This pressure keeps the cell rigid and maintains the plant's upright shape. [2]
7.
(a) As temperature increases from 20°C to 40°C, the time taken for starch to disappear decreases, indicating that the rate of enzyme activity increases. [2]
(b) At 60°C, the high temperature causes the enzyme (amylase) to denature. The shape of the active site changes, so the substrate (starch) can no longer fit into the active site. No enzyme-substrate complexes are formed, so no digestion occurs. [3]
8.
(a) Absent [1]
(b) Small, temporary vacuoles (or Absent) [1]
(c) Irregular / Round [1]
9.
(a) Mitochondria [1]
(b) Mitochondria are the site of aerobic respiration, which releases energy (ATP). Muscle cells need large amounts of ATP for contraction. [2]
10.
(a) The active site is a specific region on the enzyme surface where the substrate binds. [1]
(b) The enzyme releases the products and remains unchanged, ready to bind with another substrate molecule. [2]
11.
(a) Long hair-like projection (increases surface area). [1]
(b) The large surface area allows for a faster rate of water uptake by osmosis from the soil solution into the cell. [2]
12.
(a) Blue-black [1]
(b) Benedict’s Solution [1]
(c) Purple / Violet [1]
13.
(a) The potato strip will become shorter / flaccid. [1]
(b) The concentrated sugar solution has a lower water potential than the potato cells. Water moves out of the potato cells by osmosis, down the water potential gradient, through the partially permeable cell membrane. Loss of water causes the cells to become flaccid/plasmolysed. [3]
14.
(a) Biological powders contain enzymes that catalyse the breakdown of stains (proteins/fats) at lower temperatures, saving energy compared to heating water to high temperatures for non-biological powders. [2]
(b) High temperatures (above 60°C) will denature the enzymes, changing the shape of their active sites so they can no longer catalyse the reaction. [2]
15.
(a) A group of similar cells working together to perform a specific function. [1]
(b) Epithelial tissue / Muscle tissue / Glandular tissue. [1]
Section C: Free Response Questions
16.
- Proteins are made of long chains of amino acids folded into specific 3D shapes. [1]
- The specific shape of the enzyme, particularly the active site, determines its specificity. [1]
- Only a substrate with a complementary shape can fit into the active site (lock-and-key). [1]
- If the shape changes (denaturation), the enzyme loses its function. [1]
17.
- Human enzymes have an optimum temperature of around 37°C. [1]
- At this temperature, the kinetic energy of molecules is high enough for frequent collisions between enzyme and substrate, maximizing the reaction rate. [1]
- If temperature deviates significantly (too high), enzymes denature; if too low, reaction rates become too slow to sustain life processes. [1]
18.
- The statement is incorrect. [1]
- Evidence: Root hair cells and epidermal cells in roots do not contain chloroplasts because they are underground and do not receive light. [1]
- Chloroplasts are only found in photosynthetic tissues (e.g., palisade mesophyll) exposed to light. [1]
19.
- Nucleus: Contains DNA which codes for the specific protein sequence. mRNA carries this code to the ribosomes. [1]
- Rough Endoplasmic Reticulum (RER): Ribosomes on the RER synthesize the protein using amino acids. The protein enters the lumen of the RER for initial folding/transport. [2]
- Golgi Apparatus: Receives proteins from the RER. Modifies them (e.g., adding carbohydrates), packages them into vesicles, and sorts them for secretion. [2]
20.
- Enzymes have an optimum pH (e.g., pepsin pH 2, amylase pH 7) where they are most active. [1]
- At optimum pH, the charge distribution on the active site allows optimal binding with the substrate. [1]
- At extreme pH levels (too acidic or too alkaline), the bonds holding the enzyme's 3D structure are broken. [1]
- This causes the enzyme to denature, changing the shape of the active site. [1]
- The substrate can no longer fit, and the rate of reaction drops to zero. [1]