A-Level Biology — Questions and Answers
Question 1: What is the role of ATP in cellular processes as studied in Singapore A-Level Biology?
- It stores genetic information
- It is the universal energy currency of cells, providing immediate energy for cellular activities (Correct answer)
- It transports oxygen in the blood
- It forms the cell membrane
Correct answer: It is the universal energy currency of cells, providing immediate energy for cellular activities
ATP (adenosine triphosphate) is the immediate energy source for cellular processes. It releases energy when the terminal phosphate bond is hydrolysed to form ADP and inorganic phosphate.
Question 2: What is the structure of DNA according to the Watson-Crick model?
- A single-stranded helix
- A double helix with antiparallel strands connected by complementary base pairing (A-T, G-C) through hydrogen bonds (Correct answer)
- A triple-stranded structure
- A circular ring structure
Correct answer: A double helix with antiparallel strands connected by complementary base pairing (A-T, G-C) through hydrogen bonds
DNA is a double helix with two antiparallel polynucleotide strands. Adenine pairs with thymine (2 hydrogen bonds) and guanine pairs with cytosine (3 hydrogen bonds). The sugar-phosphate backbone is on the outside.
Question 3: What is the difference between mitosis and meiosis?
- Mitosis produces 4 cells; meiosis produces 2 cells
- Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically different haploid cells (Correct answer)
- They are the same process
- Mitosis only occurs in plants
Correct answer: Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically different haploid cells
Mitosis produces two genetically identical diploid daughter cells (for growth and repair). Meiosis produces four genetically different haploid cells (gametes) through two divisions and introduces genetic variation.
Question 4: What is the lock-and-key model of enzyme action?
- Enzymes break apart like keys
- The substrate fits precisely into the enzyme's active site, like a key fitting a lock, forming an enzyme-substrate complex (Correct answer)
- Enzymes are made of metal like locks
- The enzyme changes shape to fit the substrate
Correct answer: The substrate fits precisely into the enzyme's active site, like a key fitting a lock, forming an enzyme-substrate complex
In the lock-and-key model, the enzyme's active site has a fixed complementary shape to the substrate. The substrate fits precisely, forming an enzyme-substrate complex for the reaction to occur.
Question 5: What is natural selection as described in the Singapore A-Level Biology syllabus?
- Organisms choosing their mates
- The process by which organisms with favourable inherited traits are more likely to survive and reproduce, passing those traits to offspring (Correct answer)
- Farmers selecting the best crops
- A random process with no direction
Correct answer: The process by which organisms with favourable inherited traits are more likely to survive and reproduce, passing those traits to offspring
Natural selection is the mechanism of evolution where environmental pressures favour organisms with advantageous traits. These organisms are more likely to survive, reproduce, and pass on their beneficial alleles.
Question 6: What is the Calvin cycle in photosynthesis?
- The light-dependent reaction
- The light-independent reaction where CO₂ is fixed and reduced to form glucose using ATP and NADPH from the light reactions (Correct answer)
- The process of water splitting
- The electron transport chain in chloroplasts
Correct answer: The light-independent reaction where CO₂ is fixed and reduced to form glucose using ATP and NADPH from the light reactions
The Calvin cycle (light-independent reactions) occurs in the stroma of chloroplasts. CO₂ is fixed by RuBisCO, then reduced using ATP and NADPH to eventually produce glucose.
A-Level Biology
What is the role of ATP in cellular processes as studied in Singapore A-Level Biology?