IB DP Biology: Nervous system, brain, spinal cord and reflexes (DP Biology) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

These questions cover statements C3.1.1 to C3.1.10 of the IB Biology guide, first assessment 2025, for DP Biology. All are SL and HL, and they apply to the examination sessions that follow that first assessment. Learn the content first from the study guide and the revision notes. Track progress on the IB DP Biology hub and the printable checklist.

Questions

1. (a) List these in order from smallest to largest: organ system, tissue, cell, organism, organ. [1] (b) State what is meant by system integration. [1] (c) Explain what an emergent property is, using an example from an animal. [2]

2. State four differences between signalling by the nervous system and signalling by the endocrine system. [4]

3. Describe two examples of the blood system transporting a material between organs, naming the substance and the organs. [4]

4. (a) Distinguish between a conscious process and an unconscious process. [2] (b) Give one example of each. [2] (c) State the region of the spinal cord where integration of an unconscious process takes place. [1]

5. Describe the pain reflex arc that withdraws the hand from a sharp object. [6]

6. A pain signal travels 1.0 m from the foot to the spinal cord. In a myelinated fibre the speed is 50 m/s. In an unmyelinated fibre the speed is 1.0 m/s. (a) Calculate the time taken in each fibre, in seconds. [2] (b) Calculate how many times faster the myelinated fibre is. [1] (c) Explain why most of the fibres in a reflex pathway for sharp pain are expected to be myelinated. [2]

7. A micrograph shows a transverse section of a nerve. A scale bar 18 mm long represents 90 µm. The nerve measures 54 mm across on the micrograph. In a sampled area there are 150 myelinated and 90 unmyelinated fibres. (a) Work out the magnification of the micrograph. [2] (b) Work out the real diameter of the nerve in µm. [2] (c) Calculate the percentage of fibres that are myelinated. [1] (d) State one structure visible in the section that protects the nerve fibres. [1]

8. In a ruler-drop test, a person catches a falling ruler. The distance it falls before being caught is measured over five trials, before and after a week of daily practice.

	Distance fallen (cm)
Before practice	21, 19, 18, 20, 17
After practice	16, 14, 13, 15, 12

Reaction time t is given by t = √(2d ÷ g), where d is distance in metres and g = 9.81 m/s². (a) Calculate the reaction time for the mean distance before and after practice, to 3 significant figures. [3] (b) Calculate the percentage change in reaction time. [2] (c) Suggest two reasons why this response is slower than a withdrawal reflex. [2]

9. Twelve volunteers with cerebellar damage and twelve controls walked heel to toe along a line for 20 steps. The mean number of steps that left the line was 1.5 for the controls and 11.4 for the cerebellar group. (a) Calculate the percentage of steps off the line for each group. [2] (b) Calculate how many times greater the mean for the cerebellar group is. [1] (c) Explain how the data relate to the role of the cerebellum. [3] (d) State two limitations of drawing a conclusion from this investigation. [2]

10. A person has a complete injury to the spinal cord in the mid-back. A pinprick on the sole of the foot is not felt, yet the foot withdraws. (a) Explain why the person does not feel the pinprick. [2] (b) Explain how the foot can still withdraw. [3] (c) Explain why the person cannot voluntarily move the leg. [2] (d) Explain how this supports the idea that the spinal cord integrates unconscious processes. [2]

11. A goalkeeper dives to save a penalty kick. (a) Outline how information from the kick leads to muscle contraction, from receptor to effector. [4] (b) State two ways in which the cerebellum contributes. [2] (c) Explain how the blood system supports the working muscles. [2] (d) Explain why the save is an emergent property of the body. [2]

Answers

1. (a) Cell, tissue, organ, organ system, organism [1] (b) Coordination of the parts of a system so that they work together to do an overall function [1] (c) An emergent property is a feature of the whole that none of its parts has alone [1]; for example, the heart pumps blood although a single cardiac muscle cell cannot, or an animal can hunt only because senses, brain, muscles and circulation work together [1] [4] Examiner insight: Credit tends to follow when the example states what the whole does that a part cannot; naming a system without that comparison is usually too vague.

2. Any four differences, each with both sides stated, for example: Nervous uses electrical impulses along neurons, endocrine uses hormones carried in the blood [1] Nervous acts on specific targets joined by neurons, endocrine acts on any cell with receptors for the hormone [1] Nervous is very fast, endocrine is slower [1] Nervous effects are short, endocrine effects usually last longer [1] [4] Examiner insight: A one-sided statement such as “nerves are fast” is a weak comparison; state both systems in each point.

3. Any two, each with substance and organs, for example: Oxygen [1] from lungs to muscles [1] Glucose [1] from the small intestine or liver to the brain [1] Urea from the liver to the kidneys; hormones from a gland to target cells; carbon dioxide from muscle to lungs [4] Examiner insight: “Blood transports oxygen” earns little without the two organs; give origin and destination.

4. (a) A conscious process involves awareness and a decision by the cerebral hemispheres [1]; an unconscious process occurs without awareness or choice [1] (b) Conscious: choosing to pick up a cup [1]. Unconscious: the pain withdrawal reflex [1] (c) The grey matter [1] [5] Examiner insight: An example must be a process, not a body part; “reflex” alone is less secure than naming the withdrawal reflex.

5. Free sensory nerve endings in the skin of the hand act as pain receptors [1]; a sensory neuron carries the impulse to the spinal cord [1], entering through the dorsal root [1]; in the grey matter, an interneuron receives it across a synapse [1]; a motor neuron receives it across a second synapse and leaves through the ventral root [1]; the effector, a skeletal muscle, contracts and pulls the hand away [1] [6] Examiner insight: Sequence matters in this kind of answer; use words such as “then” and name each structure so the route can be followed.

6. (a) Myelinated: 1.0 ÷ 50 = 0.020 s [1]; unmyelinated: 1.0 ÷ 1.0 = 1.0 s [1] (b) 1.0 ÷ 0.020 = 50 times [1] (c) Myelinated fibres conduct impulses much faster [1], so the foot is withdrawn before further damage [1] [5] Examiner insight: Show the division with units; a time given with no unit, or a ratio inverted, is a common way to lose credit.

7. (a) Magnification = 18 ÷ 0.090 [1] = ×200 [1] (b) 54 ÷ 200 = 0.27 mm [1] = 270 µm [1] (c) 150 ÷ (150 + 90) × 100 = 62.5% [1] (d) The (connective tissue) protective sheath [1] [6] Examiner insight: Convert the scale bar to the same unit as the image before dividing; the units of the final answer should be stated.

8. (a) Mean before = 19 cm, mean after = 14 cm [1]; t = √(2 × 0.19 ÷ 9.81) = 0.197 s [1]; t = √(2 × 0.14 ÷ 9.81) = 0.169 s [1] (b) (0.169 − 0.197) ÷ 0.197 × 100 [1] = −14.2% (a decrease of about 14%) [1] (c) The response is voluntary, so the signal goes to the cerebral hemispheres [1]; more neurons and synapses, and a longer pathway, add delay compared with the short reflex arc [1] [7] Examiner insight: Calculate the mean before converting to metres, then keep consistent units; percentage change is divided by the original value.

9. (a) Controls: 1.5 ÷ 20 × 100 = 7.5% [1]; cerebellar group: 11.4 ÷ 20 × 100 = 57.0% [1] (b) 11.4 ÷ 1.5 = 7.6 times [1] (c) Those with damage left the line much more often [1], showing poorer coordination and balance [1], consistent with the cerebellum coordinating muscle contractions and maintaining balance [1] (d) Any two: small sample of twelve [1]; mean only, with no measure of spread [1]; damage may differ in extent or location; ages and fitness may differ [8] Examiner insight: A conclusion should refer to the data and to the function; saying only “the cerebellum controls movement” is too general to explain the evidence.

10. (a) The signal cannot travel up the cord past the injury [1]; feeling occurs only when the signal reaches the cerebral hemispheres [1] (b) The pain receptor and sensory neuron send impulses into the cord below the injury [1]; an interneuron in the grey matter passes the signal to a motor neuron [1]; the motor neuron stimulates the muscle to contract without any signal from the brain [1] (c) Impulses from the motor area of the cerebral hemisphere cannot pass down the cord past the injury [1]; the motor neurons below receive no voluntary instruction [1] (d) The withdrawal happens without awareness [1]; integration occurs in the grey matter of the cord alone [1] [9] Examiner insight: Mention where the pathway breaks (above or below the injury); an answer that says “the brain is damaged” does not match the information given.

11. (a) Photoreceptors in the eye detect the ball [1]; sensory neurons carry impulses to the brain [1]; the cerebral hemispheres combine the input with other information and send impulses down motor neurons [1]; motor neurons stimulate skeletal muscle to contract [1] (b) Coordinates the timing and force of muscle contractions [1]; maintains balance during the dive [1] (c) Blood delivers oxygen and glucose to the muscles [1]; it removes carbon dioxide (or heat) [1] (d) The save depends on sensing, brain, muscles and circulation all being coordinated [1]; no single organ or system could produce it alone [1] [10] Examiner insight: In extended questions credit is spread over several short points; give each part its own sentence so none is lost inside a long paragraph.

Where marks are usually lost

• Writing “brain” for the centre of a reflex arc.
• Missing the dorsal and ventral roots or mixing them up.
• Placing the interneuron in white matter.
• Giving a hierarchy in the wrong order, or leaving out organ systems.
• Describing transport without saying from which organ to which.
• Forgetting to convert units in magnification.
• Dividing by the new value in a percentage change.
• Not comparing both sides when asked for differences.
• Describing the cerebellum as starting movement instead of coordinating it.

Next steps

• Read the revision notes.
• Re-read the study guide.
• Return to the IB DP Biology hub and the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

IB Diploma Programme Biology guide, first assessment 2025, published by the International Baccalaureate Organization. Section C3.1, Integration of body systems, statements C3.1.1 to C3.1.10.