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A Level H1 Biology Cells Biomolecules Quiz
Free A Level H1 Biology Cells Biomolecules quiz, Qwen3.6 Exam version, with questions, answers, and A Level-style practice for Singapore students.
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A-Level Biology H1 Quiz - Cells Biomolecules - Answer Key
Total Marks: 40
Section A: Multiple Choice
1. B
- Marking Note: Phosphate head is hydrophilic (water-loving), fatty acid tails are hydrophobic (water-fearing).
2. A
- Marking Note: Peptidoglycan cell wall and lack of membrane-bound organelles are key features of prokaryotes (bacteria).
3. C
- Marking Note: Primary structure is the sequence of amino acids held together by peptide bonds.
4. B
- Marking Note: Polarity allows water to form hydration shells around ions and polar molecules, dissolving them.
5. C
- Marking Note: Thymine is found in DNA; Uracil is found in RNA. Both have phosphate and pentose sugars (deoxyribose vs ribose).
Section B: Structured Response
6. (a)
- Structure: Cholesterol [1]
- Function: Regulates membrane fluidity / stabilises the membrane / prevents packing of phospholipids at low temps or excessive movement at high temps. [1]
(b)
- The hydrophobic fatty acid tails face inwards, away from the aqueous environment. [1]
- This creates a non-polar interior that repels water-soluble (polar/charged) substances, preventing them from passing freely. [1]
7. (a)
- As temperature increases, kinetic energy of enzyme and substrate molecules increases. [1]
- This leads to more frequent collisions between enzyme and substrate. [1]
- More enzyme-substrate complexes are formed per unit time, increasing the rate of reaction. [1]
(b)
- At 70°C, the high temperature breaks the hydrogen bonds and other bonds maintaining the tertiary structure of the enzyme. [1]
- The enzyme is denatured; the active site changes shape and is no longer complementary to the substrate, so no complexes can form. [1]
8. (a)
- Krebs cycle (or Citric Acid Cycle / Link Reaction). [1]
(b)
- Glucose must first be broken down into pyruvate via glycolysis. [1]
- Glycolysis occurs in the cytoplasm, not in the mitochondria. [1]
- Isolated mitochondria lack the enzymes for glycolysis, so they cannot process glucose, but can process pyruvate directly in the Krebs cycle. [1]
9. (a)
- Condensation (or Esterification). [1]
(b)
- A triglyceride has three fatty acids attached to glycerol, whereas a phospholipid has two fatty acids and one phosphate group attached to glycerol. [1]
- Alternative: Phospholipids have a hydrophilic head and hydrophobic tails; triglycerides are entirely hydrophobic.
(c)
- Triglycerides are insoluble in water, so they do not affect the water potential of cells/osmotic balance. [1]
- They have a high energy-to-mass ratio (more C-H bonds than carbohydrates), storing more energy per gram. [1]
10.
- Receives proteins (from RER) in transport vesicles. [1]
- Modifies proteins (e.g., adding carbohydrate groups to form glycoproteins, folding, or packaging). [1]
- Packages proteins into secretory vesicles for transport to the cell membrane for exocytosis. [1]
11. (a)
- High latent heat of vaporisation means a large amount of heat energy is required to evaporate water. [1]
- When sweat evaporates from the skin, it removes a large amount of body heat, cooling the organism without significant loss of water volume. [1]
(b)
- Cohesion allows water molecules to stick together via hydrogen bonds. [1]
- This creates a continuous column of water in the xylem, allowing it to be pulled up the plant under tension (transpiration pull). [1]
12.
- Similarity: Both are polymers of glucose / both contain glycosidic bonds. [1]
- Difference 1: Glycogen contains alpha-glucose; Cellulose contains beta-glucose. [1]
- Difference 2: Glycogen is branched and coiled (compact for storage); Cellulose is unbranched and forms straight chains held by hydrogen bonds (for strength). [1]
- Difference 3: Glycogen has 1,6-glycosidic bonds (branching); Cellulose only has 1,4-glycosidic bonds. [1]
- Award max 4 marks.
13. (a)
- The shrivelled (crenated) cell. [1]
(b)
- The solution had a lower water potential than the cell cytoplasm. [1]
- Water left the cell by osmosis, causing the cell to shrink/shrivel. [1]
14. (a)
- DNA contains deoxyribose sugar; RNA contains ribose sugar. [1]
- DNA contains Thymine; RNA contains Uracil. [1]
- Alternative: DNA is double-stranded; RNA is usually single-stranded.
(b)
- Complementary base pairing ensures accurate replication of DNA. [1]
- Each strand serves as a template for the synthesis of a new complementary strand, preserving the genetic code. [1]
15. (a)
- The movement of molecules/ions [1]
- From a region of lower concentration to higher concentration (against the concentration gradient), using energy (ATP) and carrier proteins. [1]
(b)
- Absorption of glucose/amino acids in the small intestine. [1]
- Alternative: Reabsorption of glucose in the kidney nephron.
- Alternative: Sodium-Potassium pump in nerve cells.
Section C: Data Interpretation and Extended Response
16. (a)
- Protein. [1] (Biuret turns purple in presence of protein; Benedict's remains blue indicating no reducing sugar).
(b)
- Reducing Sugar. [1] (Benedict's turns brick-red; Biuret remains blue indicating no protein).
(c)
- Test: Emulsion test (Ethanol test). [1]
- Positive Result: Formation of a cloudy white emulsion. [1]
17. (a)
- The phospholipids and proteins are not static; they can move laterally within the layer. [1]
- This movement gives the membrane flexibility and allows for processes like endocytosis/exocytosis. [1]
(b)
- The membrane contains a variety of different proteins (channel, carrier, receptor, enzymatic) scattered throughout the lipid bilayer. [1]
- These proteins create a "mosaic" pattern when viewed from above. [1]
18. (a)
- The enzyme has an active site with a specific shape. [1]
- The substrate has a complementary shape to the active site. [1]
- The substrate fits into the active site like a key into a lock, forming an enzyme-substrate complex. [1]
(b)
- A non-competitive inhibitor binds to an allosteric site (a site other than the active site) on the enzyme. [1]
- This binding changes the shape of the enzyme, including the active site. [1]
- The active site is no longer complementary to the substrate, so the substrate cannot bind, reducing the rate of reaction. [1]
19. (a)
- DNA replication occurs. [1]
- The amount of DNA in the cell doubles (from 2n to 4n content, though chromosome number remains 2n until division). [1]
(b)
- Semi-conservative replication means each new DNA molecule contains one original (parental) strand and one new strand. [1]
- This ensures that the genetic information is conserved and passed on accurately to daughter cells, maintaining genetic stability. [1]
20. Marking Guide for Extended Response (6 Marks):
- Level 3 (5-6 marks): Detailed explanation of at least three properties with clear biological examples. Logical structure.
- Level 2 (3-4 marks): Explanation of two or three properties, but examples may be generic or less detailed.
- Level 1 (1-2 marks): Mentions properties but lacks explanation or biological context.
Indicative Content:
- Solvent Property:
- Water is polar, dissolving ions and polar molecules (e.g., glucose, amino acids, salts).
- Significance: Allows metabolic reactions to occur in solution; transports nutrients and waste in blood/plasma.
- High Specific Heat Capacity:
- Water requires a lot of energy to change temperature due to hydrogen bonding.
- Significance: Buffers temperature changes in organisms and aquatic environments, maintaining stable conditions for enzyme activity.
- High Latent Heat of Vaporisation:
- Much energy is needed to break hydrogen bonds to turn water into gas.
- Significance: Effective cooling mechanism via sweating/panting in mammals; transpiration cooling in plants.
- Cohesion/Adhesion:
- Water molecules stick to each other (cohesion) and to other surfaces (adhesion).
- Significance: Enables transpiration stream in plants (water column in xylem); surface tension supports small organisms (e.g., water striders).
- Metabolite:
- Water is a reactant in hydrolysis and photosynthesis.
- Significance: Essential for digestion of macromolecules and production of glucose in plants.
Award 1 mark for each property identified and explained with biological significance, up to a maximum of 6 marks.