Biology HL
Theme B: Form and function (HL) — Theme B HL
- 1.
Explain how the cohesion-tension theory accounts for the rise of water through the xylem of a tall tree.
[4 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “Explain how the cohesion-tension theory accounts for the rise of water through the xylem of a tall tree.” Their response addresses only this point: “States that water evaporates from the mesophyll cells and leaves the stomata during transpiration, lowering water potential in the leaf.” 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 the pressure flow (mass flow) hypothesis for translocation of sugars in phloem sieve tubes.
[4 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Outline the pressure flow (mass flow) hypothesis for translocation of sugars in phloem sieve tubes.” Their response addresses only this point: “States that sucrose enters sieve tubes at a source, lowering water potential. In an actively loading species, energy-dependent loading concentrates sucrose in the phloem; passive loading occurs in other species.” 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.
A student measures the transpiration rate of a leafy shoot using a potometer at three different humidity levels. Predict and explain the effect of increasing humidity on the rate of water uptake.
[3 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “A student measures the transpiration rate of a leafy shoot using a potometer at three different humidity levels. Predict and explain the effect of increasing humidity on the rate of water uptake.” Their response addresses only this point: “Predicts that the rate of water uptake will decrease as humidity increases.” 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.
Explain why mature xylem water-conducting vessel elements are dead and hollow, whereas phloem sieve tube elements and their companion cells remain living in a flowering plant.
[4 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain why mature xylem water-conducting vessel elements are dead and hollow, whereas phloem sieve tube elements and their companion cells remain living in a flowering plant.” Their response addresses only this point: “States that xylem transports water and dissolved minerals passively, driven by transpiration pull, which does not require living cell processes.” 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 - 9.
A ring of bark and phloem is removed from around the trunk of a tree (girdling), leaving the xylem intact. Predict what will happen to the roots and explain your reasoning.
[3 marks] · no calculator - 10.
Marking analysis: A learner attempts the following task: “A ring of bark and phloem is removed from around the trunk of a tree (girdling), leaving the xylem intact. Predict what will happen to the roots and explain your reasoning.” Their response addresses only this point: “Predicts that the roots will eventually die (or stop growing and be starved).” 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.
Explain how the structure of guard cells enables stomata to open in response to light.
[4 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Explain how the structure of guard cells enables stomata to open in response to light.” Their response addresses only this point: “States that light stimulates guard cells to actively pump H+ ions out, and K+ ions are then taken up into the guard cells.” 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 - 13.
Outline one adaptation of xerophytic plants that reduces water loss, and explain how it achieves this.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Outline one adaptation of xerophytic plants that reduces water loss, and explain how it achieves this.” Their response addresses only this point: “Names a valid xerophytic adaptation, for example sunken stomata (in pits), a thick waxy cuticle, or reduced leaf surface area (e.g. spines instead of leaves).” 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.
Using the sliding filament model, outline the role of calcium ions in initiating muscle contraction.
[4 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Using the sliding filament model, outline the role of calcium ions in initiating muscle contraction.” Their response addresses only this point: “States that a nerve impulse arriving at the neuromuscular junction triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.” 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.
Explain why skeletal muscles function in antagonistic pairs, using the biceps and triceps at the elbow joint as an example.
[3 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Explain why skeletal muscles function in antagonistic pairs, using the biceps and triceps at the elbow joint as an example.” Their response addresses only this point: “States that muscles can only actively contract and pull; they cannot actively push or extend themselves.” 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 the process of ultrafiltration in the nephron, including the role of the pressure difference between the glomerulus and the Bowman's capsule.
[4 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Outline the process of ultrafiltration in the nephron, including the role of the pressure difference between the glomerulus and the Bowman's capsule.” Their response addresses only this point: “States that the afferent arteriole entering the glomerulus is wider than the efferent arteriole leaving it, creating high hydrostatic pressure within the glomerular capillaries.” 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 - 21.
Explain how root pressure contributes to the movement of water into the xylem, and state one piece of evidence for its existence.
[3 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Explain how root pressure contributes to the movement of water into the xylem, and state one piece of evidence for its existence.” Their response addresses only this point: “States that living root cells load mineral ions into the xylem, using active transport; the increased solute concentration lowers xylem water potential. Root hairs take ions up from the soil but do not directly line the xylem.” 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.
Outline the role of antidiuretic hormone (ADH) in regulating the water content of the blood.
[4 marks] · no calculator - 24.
Marking analysis: A learner attempts the following task: “Outline the role of antidiuretic hormone (ADH) in regulating the water content of the blood.” Their response addresses only this point: “States that a decrease in blood water potential (an increase in solute concentration) is detected by osmoreceptors in the hypothalamus.” 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 - 25.
Outline how the loop of Henle creates a concentration gradient in the medulla that allows for the reabsorption of water from the collecting duct.
[5 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Outline how the loop of Henle creates a concentration gradient in the medulla that allows for the reabsorption of water from the collecting duct.” Their response addresses only this point: “States that the water-impermeable thick ascending limb uses energy-dependent NaCl reabsorption to help establish the medullary gradient; the thin ascending limb, where present, transports salt passively.” 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 - 27.
Describe the structure of a sarcomere, identifying the arrangement of actin and myosin filaments.
[4 marks] · no calculator - 28.
Marking analysis: A learner attempts the following task: “Describe the structure of a sarcomere, identifying the arrangement of actin and myosin filaments.” Their response addresses only this point: “States that a sarcomere is the repeating structural and functional unit of a myofibril, bounded at each end by a Z line.” 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.
Distinguish between slow oxidative (Type I) and fast glycolytic (Type IIx) muscle fibres, in terms of their structure and function. Do not generalise the glycolytic description to all Type II fibres: Type IIa fibres also have substantial oxidative capacity.
[4 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Distinguish between slow oxidative (Type I) and fast glycolytic (Type IIx) muscle fibres, in terms of their structure and function. Do not generalise the glycolytic description to all Type II fibres: Type IIa fibres also have substantial oxidative capacity.” Their response addresses only this point: “States that slow-twitch fibres contain more mitochondria and myoglobin, and rely mainly on aerobic respiration, contracting slowly but resisting fatigue for a long time.” 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.
Explain how hydrostatic and oncotic pressure differences influence fluid filtration across systemic capillaries, and explain the role of the lymphatic system in returning filtered fluid to the blood.
[4 marks] · no calculator - 32.
Marking analysis: A learner attempts the following task: “Explain how hydrostatic and oncotic pressure differences influence fluid filtration across systemic capillaries, and explain the role of the lymphatic system in returning filtered fluid to the blood.” Their response addresses only this point: “Explains that capillary hydrostatic pressure tends to drive fluid outward, opposed by interstitial hydrostatic pressure; the balance is a pressure difference across the barrier.” 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 - 33.
Explain how changes in thoracic volume bring about inhalation, in terms of pressure changes described by Boyle's law.
[4 marks] · no calculator - 34.
Marking analysis: A learner attempts the following task: “Explain how changes in thoracic volume bring about inhalation, in terms of pressure changes described by Boyle's law.” Their response addresses only this point: “States that contraction of the external intercostal muscles and the diaphragm increases the volume of the thoracic cavity.” 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