Biology SL
Theme B: Form and function — Theme B
- 1.
A cubic cell has sides of length 2.0 cm. Calculate its surface-area-to-volume ratio. Compare it with a cubic cell of side 1.0 cm and explain one consequence for exchange with the environment.
[5 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “A cubic cell has sides of length 2.0 cm. Calculate its surface-area-to-volume ratio. Compare it with a cubic cell of side 1.0 cm and explain one consequence for exchange with the environment.” Their response addresses only this point: “For the 2.0 cm cube, calculates surface area = 24 cm².” 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 - 3.
Extension practice (includes HL content beyond the prescribed SL syllabus): Explain what happens to a plant cell placed in a hypotonic solution. Refer to water potential, osmosis and the cell wall.
[4 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Explain what happens to a plant cell placed in a hypotonic solution. Refer to water potential, osmosis and the cell wall.” Their response addresses only this point: “The external solution has a higher water potential than the cell contents.” 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 - 5.
Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of the rough endoplasmic reticulum and the Golgi apparatus in the production and secretion of a protein.
[4 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of the rough endoplasmic reticulum and the Golgi apparatus in the production and secretion of a protein.” Their response addresses only this point: “States that ribosomes on the rough endoplasmic reticulum synthesize the protein, which enters the RER lumen.” 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 how the fluid mosaic model describes the structure of the plasma membrane.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain how the fluid mosaic model describes the structure of the plasma membrane.” Their response addresses only this point: “States that the membrane consists of a phospholipid bilayer, with hydrophilic heads facing outward and hydrophobic tails facing inward.” 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.
Explain why a decreasing surface-area-to-volume ratio can limit the size of a cell that increases in size without changing its shape or exchange adaptations.
[3 marks] · no calculator - 10.
Marking analysis: A learner attempts the following task: “Explain why a decreasing surface-area-to-volume ratio can limit the size of a cell that increases in size without changing its shape or exchange adaptations.” Their response addresses only this point: “States that as a cell increases in size, its volume (and hence its metabolic demand for nutrients and oxygen, and waste production) increases faster than its surface area.” 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 - 11.
Outline primary active transport across a plasma membrane, and explain how ATP hydrolysis drives movement against a gradient.
[3 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Outline primary active transport across a plasma membrane, and explain how ATP hydrolysis drives movement against a gradient.” Their response addresses only this point: “States that primary active transport uses specific membrane pumps to move a substance against its concentration gradient, or electrochemical gradient for ions.” 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.
Distinguish between a monosaccharide, a disaccharide and a polysaccharide, giving one example of each.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Distinguish between a monosaccharide, a disaccharide and a polysaccharide, giving one example of each.” Their response addresses only this point: “States that a monosaccharide is a single sugar unit, 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 - 15.
Extension practice (HL content beyond the prescribed SL syllabus): Outline the level of protein structure at which hydrogen bonding creates an alpha helix or beta pleated sheet.
[2 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Extension practice (HL content beyond the prescribed SL syllabus): Outline the level of protein structure at which hydrogen bonding creates an alpha helix or beta pleated sheet.” Their response addresses only this point: “States that this is the secondary structure of a protein.” 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 - 17.
Explain how the alveoli of the human lung are structurally adapted for efficient gas exchange. Refer to surface area, diffusion distance and blood supply.
[4 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Explain how the alveoli of the human lung are structurally adapted for efficient gas exchange. Refer to surface area, diffusion distance and blood supply.” Their response addresses only this point: “States that alveoli provide a very large total surface area for diffusion.” 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 - 19.
Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of villi and microvilli in increasing the efficiency of absorption in the small intestine.
[3 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of villi and microvilli in increasing the efficiency of absorption in the small intestine.” Their response addresses only this point: “States that villi are finger-like projections of the intestinal wall, and microvilli are even smaller projections on the surface of the epithelial cells covering each villus.” 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 - 21.
Explain gas exchange between alveolar air and blood in the lungs, referring to diffusion driven by partial-pressure differences.
[4 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Explain gas exchange between alveolar air and blood in the lungs, referring to diffusion driven by partial-pressure differences.” Their response addresses only this point: “States that oxygen partial pressure is higher in alveolar air than in the venous blood arriving at the lungs, so oxygen diffuses into the blood.” 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.
Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of the SA node and AV node in coordinating the cardiac cycle.
[3 marks] · no calculator - 24.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Outline the roles of the SA node and AV node in coordinating the cardiac cycle.” Their response addresses only this point: “States that the sinoatrial (SA) node, located in the right atrium, acts as the heart's natural pacemaker, generating an electrical impulse that triggers atrial contraction.” 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.
Extension practice (HL content beyond the prescribed SL syllabus): Explain how the structure of the nephron enables both filtration and selective reabsorption during urine formation.
[3 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Extension practice (HL content beyond the prescribed SL syllabus): Explain how the structure of the nephron enables both filtration and selective reabsorption during urine formation.” Their response addresses only this point: “States that in the glomerulus, high blood pressure forces water and small solutes (e.g. glucose, salts, urea) out of the capillaries and into the Bowman's capsule, while blood cells and large proteins are retained (ultrafiltration).” 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 - 27.
Extension practice (includes HL content beyond the prescribed SL syllabus): Explain the role of haemoglobin in the transport of oxygen in the blood, referring to its structure.
[3 marks] · no calculator - 28.
Marking analysis: A learner attempts the following task: “Extension practice (includes HL content beyond the prescribed SL syllabus): Explain the role of haemoglobin in the transport of oxygen in the blood, referring to its structure.” Their response addresses only this point: “States that haemoglobin is a globular protein found in red blood cells, made of four polypeptide subunits, each containing a haem group with an iron ion.” 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.
Extension practice (HL content beyond the prescribed SL syllabus): Explain how antagonistic pairs of muscles, such as the biceps and triceps, bring about movement at a joint.
[3 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Extension practice (HL content beyond the prescribed SL syllabus): Explain how antagonistic pairs of muscles, such as the biceps and triceps, bring about movement at a joint.” Their response addresses only this point: “States that a contracting skeletal muscle pulls rather than pushes; opposing muscles can therefore produce movements in opposite directions at a joint.” 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.
Explain, in terms of hydrogen bonding, why water has a high specific heat capacity, and explain one biological advantage this property provides to aquatic organisms.
[3 marks] · no calculator - 32.
Marking analysis: A learner attempts the following task: “Explain, in terms of hydrogen bonding, why water has a high specific heat capacity, and explain one biological advantage this property provides to aquatic organisms.” Their response addresses only this point: “States that water molecules form extensive hydrogen bonds with one another.” 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 - 33.
Explain how the structure of alveoli in the lungs is adapted to maximize the rate of gas exchange.
[3 marks] · no calculator - 34.
Marking analysis: A learner attempts the following task: “Explain how the structure of alveoli in the lungs is adapted to maximize the rate of gas exchange.” Their response addresses only this point: “States that the very large number of small alveoli provides a large total surface area for gas diffusion.” 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 why increasing the temperature beyond an enzyme's optimum causes a sharp decrease in reaction rate, with reference to enzyme structure.
[3 marks] · no calculator - 36.
Marking analysis: A learner attempts the following task: “Explain why increasing the temperature beyond an enzyme's optimum causes a sharp decrease in reaction rate, with reference to enzyme structure.” Their response addresses only this point: “States that an enzyme's active site has a specific three-dimensional shape, maintained by hydrogen bonds and other interactions within its tertiary structure.” 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