Biology SL
Theme C: Interaction and interdependence — Theme C
- 1.
Explain how enzymes lower the activation energy of a reaction, using the concept of the enzyme-substrate complex.
[3 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “Explain how enzymes lower the activation energy of a reaction, using the concept of the enzyme-substrate complex.” Their response addresses only this point: “States that the substrate binds to the enzyme's active site, forming an enzyme-substrate complex.” 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 - 3.
Explain the effect of increasing temperature above the optimum on the rate of an enzyme-catalysed reaction.
[3 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Explain the effect of increasing temperature above the optimum on the rate of an enzyme-catalysed reaction.” Their response addresses only this point: “States that above the optimum temperature, the rate of reaction decreases sharply.” 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.
Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the difference between anaerobic cell respiration in yeast (alcoholic fermentation) and in human muscle cells (lactic acid fermentation).
[3 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the difference between anaerobic cell respiration in yeast (alcoholic fermentation) and in human muscle cells (lactic acid fermentation).” Their response addresses only this point: “States that both processes begin with glycolysis, producing pyruvate and a small yield of ATP, without requiring oxygen.” 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 - 7.
Extension practice (includes HL content beyond the prescribed SL syllabus): Compare the net ATP yield per glucose molecule of fermentation in yeast or human muscle with aerobic cell respiration, and explain the reason for the difference.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Compare the net ATP yield per glucose molecule of fermentation in yeast or human muscle with aerobic cell respiration, and explain the reason for the difference.” Their response addresses only this point: “States that anaerobic fermentation yields a small net amount of ATP (glycolysis only, approximately 2 ATP per glucose).” 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.
Annual net production is 48 000 kJ m^-2 yr^-1 for producers and 7200 kJ m^-2 yr^-1 for primary consumers. Calculate the percentage energy transfer and explain three causes of energy loss between these trophic levels.
[5 marks] - 10.
Marking analysis: A learner attempts the following task: “Annual net production is 48 000 kJ m^-2 yr^-1 for producers and 7200 kJ m^-2 yr^-1 for primary consumers. Calculate the percentage energy transfer and explain three causes of energy loss between these trophic levels.” Their response addresses only this point: “Uses percentage transfer = 7200/48 000 × 100.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] - 11.
Distinguish between a population, a community and an ecosystem.
[3 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Distinguish between a population, a community and an ecosystem.” Their response addresses only this point: “Defines a population as organisms of the same species living in the same area at the same time.” 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 role of decomposers in recycling nutrients within an ecosystem.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Explain the role of decomposers in recycling nutrients within an ecosystem.” Their response addresses only this point: “States that decomposers (e.g. bacteria and fungi) break down dead organic matter and waste products.” 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 the processes by which carbon enters and leaves the atmosphere as part of the carbon cycle.
[4 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Outline the processes by which carbon enters and leaves the atmosphere as part of the carbon cycle.” Their response addresses only this point: “States that photosynthesis removes carbon dioxide from the atmosphere, fixing carbon into organic compounds in producers.” 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 - 17.
A food chain is: grass → grasshopper → frog → snake. Identify the trophic level of the frog and explain why food chains rarely extend beyond four or five trophic levels.
[3 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “A food chain is: grass → grasshopper → frog → snake. Identify the trophic level of the frog and explain why food chains rarely extend beyond four or five trophic levels.” Their response addresses only this point: “Identifies the frog as a secondary consumer (third trophic level).” 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.
Outline how a pyramid of energy differs from a pyramid of numbers, and state one advantage of using a pyramid of energy.
[2 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Outline how a pyramid of energy differs from a pyramid of numbers, and state one advantage of using a pyramid of energy.” Their response addresses only this point: “States that a pyramid of numbers represents the number of individual organisms at each trophic level, while a pyramid of energy represents the rate of energy flow (e.g. kJ m⁻² yr⁻¹) through each trophic level.” 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 competition for a limited resource can affect the carrying capacity of a population in an ecosystem.
[3 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Explain how competition for a limited resource can affect the carrying capacity of a population in an ecosystem.” Their response addresses only this point: “Defines carrying capacity as the maximum population size that an environment can sustainably support given its available resources.” 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 - 23.
Extension practice (HL content beyond the prescribed SL syllabus): Outline the process of primary succession, from bare rock to a more established community.
[3 marks] · no calculator - 24.
Marking analysis: A learner attempts the following task: “Extension practice (HL content beyond the prescribed SL syllabus): Outline the process of primary succession, from bare rock to a more established community.” Their response addresses only this point: “States that primary succession begins on newly exposed, lifeless substrate (e.g. bare rock) with no existing soil.” 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 one method that estimates animal population size from directly sampled individuals and one method that uses indirect signs to estimate relative abundance in the field.
[2 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Outline one method that estimates animal population size from directly sampled individuals and one method that uses indirect signs to estimate relative abundance in the field.” Their response addresses only this point: “Outlines a direct method, e.g. the capture-mark-release-recapture technique, where a sample is captured, marked, released, and a second sample is later captured to estimate total population from the proportion of marked individuals recaptured.” 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 - 27.
Outline the process by which nerve impulses are transmitted across a chemical synapse.
[4 marks] · no calculator - 28.
Marking analysis: A learner attempts the following task: “Outline the process by which nerve impulses are transmitted across a chemical synapse.” Their response addresses only this point: “States that an arriving nerve impulse causes calcium ion channels to open, allowing Ca²⁺ to enter the presynaptic neuron.” 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 - 29.
Outline how the antibody-mediated (humoral) immune response leads to the production of antibodies against a specific pathogen.
[4 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Outline how the antibody-mediated (humoral) immune response leads to the production of antibodies against a specific pathogen.” Their response addresses only this point: “States that a B-lymphocyte with a receptor complementary to a specific antigen on the pathogen binds to that antigen.” 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 - 31.
A food chain transfers energy from producers storing 10,000 kJ m^-2 year^-1. Assuming 10% is transferred at each step, calculate the energy available to (a) primary consumers, (b) secondary consumers and (c) tertiary consumers. Explain how the decline in available energy limits food-chain length.
[4 marks] - 32.
Marking analysis: A learner attempts the following task: “A food chain transfers energy from producers storing 10,000 kJ m^-2 year^-1. Assuming 10% is transferred at each step, calculate the energy available to (a) primary consumers, (b) secondary consumers and (c) tertiary consumers. Explain how the decline in available energy limits food-chain length.” Their response addresses only this point: “Calculates energy available to primary consumers as 10,000 × 0.10 = 1,000 kJ m⁻² year⁻¹.” 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.
A population of deer introduced to an island shows exponential growth initially, but the growth rate slows and eventually levels off as the population approaches the island's carrying capacity. Explain two factors that could limit further population growth as the population nears carrying capacity.
[3 marks] · no calculator - 34.
Marking analysis: A learner attempts the following task: “A population of deer introduced to an island shows exponential growth initially, but the growth rate slows and eventually levels off as the population approaches the island's carrying capacity. Explain two factors that could limit further population growth as the population nears carrying capacity.” Their response addresses only this point: “Explains a valid density-dependent limiting factor, such as food/resource availability becoming scarce as more deer compete for a fixed supply of vegetation, reducing survival and reproduction rates.” 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.
Explain how carbon moves from the atmosphere into living organisms, and then back into the atmosphere, as part of the carbon cycle.
[3 marks] · no calculator - 36.
Marking analysis: A learner attempts the following task: “Explain how carbon moves from the atmosphere into living organisms, and then back into the atmosphere, as part of the carbon cycle.” Their response addresses only this point: “Explains that producers (plants, algae) remove carbon dioxide from the atmosphere through photosynthesis, converting it into organic carbon compounds (e.g. glucose).” 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 - 37.
A student counts a moss species in five equal quadrats beneath trees and five equal quadrats in an open area. Counts beneath trees are 12, 9, 15, 10 and 14; open-area counts are 3, 5, 4, 2 and 6. (a) Calculate the mean count for each habitat. (b) State the pattern shown. (c) Identify one limitation of the investigation. (d) Suggest one improvement that directly addresses that limitation.
[4 marks] · no calculator - 38.
Marking analysis: A learner attempts the following task: “A student counts a moss species in five equal quadrats beneath trees and five equal quadrats in an open area. Counts beneath trees are 12, 9, 15, 10 and 14; open-area counts are 3, 5, 4, 2 and 6. (a) Calculate the mean count for each habitat. (b) State the pattern shown. (c) Identify one limitation of the investigation. (d) Suggest one improvement that directly addresses that limitation.” Their response addresses only this point: “Calculates a mean of 12 moss plants per quadrat beneath trees.” 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