Biology HL
Theme C: Interaction and interdependence (HL) — Theme C HL
- 1.
Optional kinetic-model extension, not claimed as prescribed IB HL depth: Explain the difference between reversible competitive inhibition in the standard active-site model and pure noncompetitive enzyme inhibition, referring to substrate binding and catalytic activity.
[4 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “Optional kinetic-model extension, not claimed as prescribed IB HL depth: Explain the difference between reversible competitive inhibition in the standard active-site model and pure noncompetitive enzyme inhibition, referring to substrate binding and catalytic activity.” Their response addresses only this point: “States that in the standard competitive model the inhibitor and substrate bind mutually exclusively at the active site; the inhibitor need not be a close structural copy of the substrate.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 3.
Outline how the rate of an enzyme-catalysed reaction changes with increasing substrate concentration, at a fixed enzyme concentration, and explain why it eventually plateaus.
[3 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Outline how the rate of an enzyme-catalysed reaction changes with increasing substrate concentration, at a fixed enzyme concentration, and explain why it eventually plateaus.” Their response addresses only this point: “States that at low substrate concentration, the rate of reaction increases roughly proportionally with substrate concentration.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 5.
Outline the role of the electron transport chain and chemiosmosis in producing ATP during oxidative phosphorylation.
[4 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “Outline the role of the electron transport chain and chemiosmosis in producing ATP during oxidative phosphorylation.” Their response addresses only this point: “States that electrons from NADH and FADH₂ are passed along a series of protein carriers (the electron transport chain) in the inner mitochondrial membrane.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 7.
Explain why oxygen is essential for aerobic cell respiration to continue, in terms of its role at the end of the electron transport chain.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain why oxygen is essential for aerobic cell respiration to continue, in terms of its role at the end of the electron transport chain.” Their response addresses only this point: “States that oxygen acts as the final electron acceptor at the end of the electron transport chain, combining with electrons and H⁺ ions to form water.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 9.
Outline the light-dependent reactions of photosynthesis, including the roles of water and the products formed.
[4 marks] · no calculator - 10.
Marking analysis: A learner attempts the following task: “Outline the light-dependent reactions of photosynthesis, including the roles of water and the products formed.” Their response addresses only this point: “States that light energy is absorbed by chlorophyll and other pigments in the thylakoid membrane, exciting electrons.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 11.
Outline the light-independent reactions (Calvin cycle) of photosynthesis, including the roles of ATP, NADPH and carbon dioxide.
[3 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Outline the light-independent reactions (Calvin cycle) of photosynthesis, including the roles of ATP, NADPH and carbon dioxide.” Their response addresses only this point: “States that carbon dioxide is fixed by combining with a five-carbon acceptor molecule (ribulose bisphosphate, RuBP), catalysed by the enzyme rubisco.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 13.
Explain the effect of increasing light intensity on the rate of photosynthesis, and why the rate eventually plateaus even as light intensity continues to increase.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Explain the effect of increasing light intensity on the rate of photosynthesis, and why the rate eventually plateaus even as light intensity continues to increase.” Their response addresses only this point: “States that at low light intensity, the rate of photosynthesis increases as light intensity increases, since light is the limiting factor.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 15.
Outline why fermentation in human muscle or yeast yields much less ATP per glucose than aerobic respiration, referring to the electron transport chain.
[3 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Outline why fermentation in human muscle or yeast yields much less ATP per glucose than aerobic respiration, referring to the electron transport chain.” Their response addresses only this point: “States that fermentation regenerates NAD+ by reducing pyruvate or a derivative, allowing glycolysis to continue without using a respiratory electron transport chain.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 17.
Explain why an increase in temperature, up to the optimum, increases both enzyme reaction rate and the rate of respiration.
[3 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Explain why an increase in temperature, up to the optimum, increases both enzyme reaction rate and the rate of respiration.” Their response addresses only this point: “States that increasing temperature increases the kinetic energy of both enzyme and substrate molecules, causing them to move faster.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 19.
Compare the location within the chloroplast of the light-dependent reactions and the light-independent reactions of photosynthesis.
[2 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Compare the location within the chloroplast of the light-dependent reactions and the light-independent reactions of photosynthesis.” Their response addresses only this point: “States that the light-dependent reactions occur on/in the thylakoid membranes.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 marks] · no calculator - 21.
Explain how auxin controls the phototropic response of a shoot growing towards a unidirectional light source.
[4 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Explain how auxin controls the phototropic response of a shoot growing towards a unidirectional light source.” Their response addresses only this point: “States that auxin is produced in the shoot tip and is transported laterally away from the light towards the shaded side.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 23.
Outline the role of gibberellin in breaking seed dormancy and initiating germination in cereal seeds.
[3 marks] · no calculator - 24.
Marking analysis: A learner attempts the following task: “Outline the role of gibberellin in breaking seed dormancy and initiating germination in cereal seeds.” Their response addresses only this point: “States that water uptake by the seed triggers the embryo to release gibberellin.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 25.
Outline how the primary and secondary immune responses differ in speed and magnitude, and explain the biological reason for this difference.
[4 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Outline how the primary and secondary immune responses differ in speed and magnitude, and explain the biological reason for this difference.” Their response addresses only this point: “States that the primary response is slow to develop (taking days) and produces a relatively low concentration of antibody.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 27.
Explain how vaccination can stimulate protective immunity without the person having to experience the corresponding natural disease.
[3 marks] · no calculator - 28.
Marking analysis: A learner attempts the following task: “Explain how vaccination can stimulate protective immunity without the person having to experience the corresponding natural disease.” Their response addresses only this point: “States that a vaccine supplies pathogen antigens, or instructions for making an antigen, in a form designed to stimulate immunity with much lower risk than natural infection.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 29.
Outline the roles of nitrogen-fixing bacteria, nitrifying bacteria, and denitrifying bacteria in the nitrogen cycle.
[3 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Outline the roles of nitrogen-fixing bacteria, nitrifying bacteria, and denitrifying bacteria in the nitrogen cycle.” Their response addresses only this point: “States that nitrogen-fixing bacteria (e.g. Rhizobium, often in root nodules of legumes, or free-living in soil) convert atmospheric nitrogen gas (N₂), which most organisms cannot use directly, into ammonia/ammonium (NH₃/NH₄⁺).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 31.
A population has an intrinsic growth rate (r) of 0.5 per year, a current size (N) of 50 individuals, and the habitat has a carrying capacity (K) of 200 individuals. (a) Using the logistic growth equation dN/dt = rN(1 − N/K), calculate the current rate of population growth. (b) Explain what happens to this growth rate as N approaches K.
[4 marks] - 32.
Marking analysis: A learner attempts the following task: “A population has an intrinsic growth rate (r) of 0.5 per year, a current size (N) of 50 individuals, and the habitat has a carrying capacity (K) of 200 individuals. (a) Using the logistic growth equation dN/dt = rN(1 − N/K), calculate the current rate of population growth. (b) Explain what happens to this growth rate as N approaches K.” Their response addresses only this point: “Substitutes the given values into the logistic growth equation: dN/dt = 0.5 × 50 × (1 − 50/200).” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] - 33.
State the competitive exclusion principle, and explain how niche differentiation allows two similar species to coexist in the same habitat without one driving the other to local extinction.
[3 marks] · no calculator - 34.
Marking analysis: A learner attempts the following task: “State the competitive exclusion principle, and explain how niche differentiation allows two similar species to coexist in the same habitat without one driving the other to local extinction.” Their response addresses only this point: “States the competitive exclusion principle: two species competing for exactly the same limited resource (occupying an identical ecological niche) cannot indefinitely coexist in the same habitat — one will eventually outcompete and exclude the other.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 35.
An enzyme is tested at substrate concentrations of 1, 2, 4 and 8 mmol dm⁻³. Rates without inhibitor are 12, 20, 31 and 40 units; with inhibitor they are 6, 12, 24 and 38 units. (a) Compare the effect of the inhibitor at low and high substrate concentration. (b) Deduce the most likely type of inhibition. (c) Explain the molecular basis for this deduction. (d) Suggest additional data that would strengthen the conclusion.
[5 marks] · no calculator - 36.
Marking analysis: A learner attempts the following task: “An enzyme is tested at substrate concentrations of 1, 2, 4 and 8 mmol dm⁻³. Rates without inhibitor are 12, 20, 31 and 40 units; with inhibitor they are 6, 12, 24 and 38 units. (a) Compare the effect of the inhibitor at low and high substrate concentration. (b) Deduce the most likely type of inhibition. (c) Explain the molecular basis for this deduction. (d) Suggest additional data that would strengthen the conclusion.” Their response addresses only this point: “States that the inhibitor substantially reduces rate at low substrate concentration.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] · no calculator