OCR GCSE Biology A B3.1 Coordination and Control: The Nervous System Exam Questions

About OCR GCSE Biology A B3.1 Coordination and Control: The Nervous System

B3.1 covers how the nervous system detects stimuli and coordinates rapid responses. On the OCR Gateway Biology A course it is the first part of Topic B3 Organism level systems, assessed in Paper 1 (Foundation) or Paper 3 (Higher). You study neurones, synapses and reflex arcs, the main regions of the brain and the eye as a sense organ. It links closely to the endocrine system in B3.2, which also coordinates responses but more slowly. Examiners often ask you to sequence a reflex arc, explain transmission across a synapse, compare nerves and hormones, and explain how the eye focuses or how lenses correct sight defects.

What you need to know

• Structure of the nervous system The central nervous system (CNS) is the brain and spinal cord. The peripheral nervous system connects receptors and effectors to the CNS through sensory and motor neurones.
• Neurones Neurones carry electrical impulses. They have a long axon, many dendrites to connect with other neurones, and a myelin sheath that insulates the axon and speeds up impulses.
• Synapses A synapse is a gap between neurones. When an impulse arrives, neurotransmitter chemicals are released, diffuse across the gap and bind to receptors on the next neurone, triggering a new impulse.
• Reflex arcs Reflexes are fast, automatic responses that protect the body. The pathway is stimulus -> receptor -> sensory neurone -> relay neurone (in the CNS) -> motor neurone -> effector -> response, bypassing conscious parts of the brain.
• The brain The cerebrum controls conscious thought, memory and language; the cerebellum coordinates movement and balance; the medulla controls unconscious actions such as heart rate and breathing. The brain is hard to study and treat because it is complex and delicate, though scans such as MRI help.
• The eye Light is refracted by the cornea and lens and focused on the retina, where rods and cones detect light. The ciliary muscles and suspensory ligaments change lens shape to focus (accommodation); short sight (myopia) is corrected with a concave lens and long sight (hyperopia) with a convex lens.

Common mistakes in B3.1 Coordination and Control: The Nervous System

• Saying the electrical impulse jumps across the synapse. The signal crosses as a chemical neurotransmitter that diffuses across the gap.
• Leaving the relay neurone or CNS out of a reflex arc. Reflexes pass through a relay neurone in the spinal cord or brain.
• Describing reflexes as controlled by the brain consciously. They are automatic and do not involve conscious thought.
• Mixing up lens corrections. Myopia (short sight) needs a concave (diverging) lens; hyperopia (long sight) needs a convex (converging) lens.
• Writing that the iris focuses light. The iris controls pupil size; the cornea and lens focus light.

Try three B3.1 Coordination and Control: The Nervous System exam-style questions