A-Level Biology Key Concepts 2 — Questions and Answers
Question 1: What is the role of the enzyme rubisco in the Calvin cycle?
- It catalyses the fixation of CO₂ by combining it with ribulose bisphosphate (RuBP) (Correct answer)
- It reduces GP to G3P using ATP and NADPH
- It regenerates RuBP from G3P molecules
- It splits water molecules during the light-dependent stage
Correct answer: It catalyses the fixation of CO₂ by combining it with ribulose bisphosphate (RuBP)
Rubisco (ribulose bisphosphate carboxylase/oxygenase) catalyses the carboxylation of RuBP, combining it with CO₂ to form two molecules of glycerate-3-phosphate (GP). It is the most abundant enzyme on Earth.
Question 2: Which type of immunity is provided by vaccination?
- Artificial active immunity (Correct answer)
- Natural active immunity
- Artificial passive immunity
- Natural passive immunity
Correct answer: Artificial active immunity
Vaccination introduces antigens (weakened/dead pathogens or their fragments) to stimulate the immune system to produce memory cells and antibodies. It is 'artificial' because it involves deliberate exposure, and 'active' because the body mounts its own immune response.
Question 3: During meiosis, when does crossing over occur?
- Prophase I (Correct answer)
- Metaphase I
- Anaphase II
- Telophase I
Correct answer: Prophase I
Crossing over occurs during prophase I when homologous chromosomes pair up (synapsis) and form bivalents. Sections of non-sister chromatids exchange, producing recombinant chromosomes and increasing genetic variation.
Question 4: What is the net gain of ATP from one molecule of glucose during glycolysis?
- 2 ATP (Correct answer)
- 4 ATP
- 36 ATP
- 38 ATP
Correct answer: 2 ATP
Glycolysis produces 4 ATP in total but uses 2 ATP in the phosphorylation of glucose and fructose-6-phosphate, giving a net gain of 2 ATP per glucose molecule.
Question 5: In the Hardy-Weinberg equation p² + 2pq + q² = 1, what does 2pq represent?
- The frequency of heterozygous individuals in the population (Correct answer)
- The frequency of the dominant allele
- The frequency of homozygous dominant individuals
- The frequency of homozygous recessive individuals
Correct answer: The frequency of heterozygous individuals in the population
In Hardy-Weinberg equilibrium, p² represents homozygous dominant frequency, q² represents homozygous recessive frequency, and 2pq represents heterozygous frequency. The equation models allele frequencies in a non-evolving population.
Question 6: Which cells in the immune system are responsible for producing antibodies?
- Plasma cells (differentiated B lymphocytes) (Correct answer)
- T helper cells
- Macrophages
- Natural killer cells
Correct answer: Plasma cells (differentiated B lymphocytes)
Plasma cells are fully differentiated B lymphocytes that secrete large quantities of specific antibodies. After antigen presentation and T helper cell activation, B cells clonally expand and differentiate into plasma cells and memory B cells.
A-Level Biology Key Concepts 2
What is the role of the enzyme rubisco in the Calvin cycle?