OCR GCSE Biology A: The eye, eye defects, the brain and limits of treatment (J247)

This guide follows the OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018. It covers statements B3.1d to B3.1h of topic B3.1, Coordination and control: the nervous system. Statements B3.1g and B3.1h are printed in bold in the specification, so they are tested in the Higher Tier papers only. Everything else here is assessed on both tiers. Neurones, reflex arcs and coordinated responses (B3.1a to B3.1c) are covered elsewhere on the site.

Related: revision notes, practice questions, the OCR GCSE Biology hub, the printable checklist and the free diagnostics.

What this unit covers

Statement	What you must be able to do	Tier
B3.1d	Explain how the cornea, iris, pupil, lens, retina, optic nerve, ciliary body and suspensory ligaments are related to their functions	Both
B3.1e	Describe colour blindness, short-sightedness and long-sightedness, and explain how some of these problems may be overcome	Both
B3.1f	Describe the structure and function of the cerebrum, cerebellum, medulla, hypothalamus and pituitary	Both
B3.1g	Explain difficulties of investigating brain function (obtaining and interpreting case studies, ethical issues)	Higher Tier only
B3.1h	Explain limitations in treating damage and disease of the brain and other parts of the nervous system	Higher Tier only

The specification also lists a mathematical outcome for this topic: extract and interpret data from graphs, charts and tables. Expect to be given data and asked what it shows.

B3.1d: the eye and how structure fits function

The eye is a sense organ. Its receptors detect light, and the brain builds the image you perceive from the impulses it receives. Nothing is sent out of the eye.

Structure	What it is	Function
Cornea	Transparent, curved front surface	Lets light in and bends (refracts) it, doing most of the focusing
Iris	Coloured ring of muscle	Changes the size of the pupil to control how much light enters
Pupil	Hole in the centre of the iris	Lets light through to the lens
Lens	Transparent, flexible, rounded on both sides	Refracts light further and adjusts to focus it onto the retina
Retina	Layer at the back containing light receptor cells	Detects light and changes it into nerve impulses
Optic nerve	Bundle of sensory neurones	Links the retina to the brain by carrying impulses
Ciliary body	Ring of muscle around the lens	Its shortening and lengthening alter how curved the lens is
Suspensory ligaments	Fibres joining the ciliary body to the lens	Transmit the pull that changes the lens shape

Two kinds of receptor cell are in the retina. Rod cells work in dim light but do not tell colours apart. Cone cells need brighter light and detect colour, and there are different types sensitive to different colours of light.

Controlling the amount of light

The iris has circular muscle fibres and radial muscle fibres. Bright light: the ring-shaped (circular) fibres shorten while the radial fibres, which run outwards like spokes, relax. The pupil narrows and less light reaches the retina. Dim light: the radial fibres shorten and the circular fibres relax, so the pupil widens. This protects the retina from damage in bright light and lets enough light in when it is dark.

Worked example 1 (interpreting data). A pupil has diameter 7.6 mm in a dim room and 2.2 mm in bright light. Describe the change and say what it does to the light entering.

1. Percentage decrease in diameter = (7.6 − 2.2) ÷ 7.6 × 100 = 71.1%.
2. The pupil is roughly circular, so the area of the opening is π × (diameter ÷ 2)². Dim: π × 3.8² = 45.4 mm². Bright: π × 1.1² = 3.80 mm².
3. Area ratio = 45.4 ÷ 3.80 = 11.9, so roughly twelve times as much light can enter in the dim room.
4. Cause: the iris muscles, with the circular fibres shortening in bright light.

A diameter fall of under three-quarters gives a far larger fall in the area of the opening.

Focusing: accommodation

Light from an object must be focused as a sharp image on the retina. The cornea does most of the bending, and the lens makes the fine adjustment by changing shape.

	Close object	Far object
Ciliary muscle (ring around lens)	Shortens	Lengthens, ring widens
Suspensory ligaments	Loose	Under tension
Lens shape	Fatter, more curved	Slimmer, flatter
Bending of light	Greater	Smaller

Light from near objects is spreading apart, so it must be bent more to meet on the retina. Distant objects send almost parallel rays that need less bending. Ligaments are not muscle; the muscle is in the ciliary body.

B3.1e: eye defects and how they are overcome

Short-sightedness (myopia)

A short-sighted person sees near objects clearly but distant objects look blurred. The eyeball is too long, or the lens is too strong (too curved), so the focus for distant objects forms in front of the retina and the image on the retina is out of focus.

Correction: a concave (diverging) lens, in glasses or contact lenses, spreads the light slightly before it reaches the eye so that the focus moves back onto the retina. Laser surgery that reshapes the cornea can also be used.

Long-sightedness (hyperopia)

A long-sighted person sees distant objects more clearly than near ones. The eyeball is too short, or the lens is too weak (cannot become curved enough), so light from near objects would focus behind the retina.

Correction: a convex (converging) lens adds extra bending of the light so that the focus moves forward onto the retina. Laser surgery or replacing the lens are other options.

Worked example 2 (interpreting data). A school records the near point (the closest distance at which print is clear) for volunteers of different ages.

Age (years)	10	30	50	60
Near point (cm)	8	12	50	100

1. Describe the trend: the near point gets further away as age increases, and the change is much faster after 30.
2. Calculation: from 30 to 50 years, change = (50 − 12) ÷ 12 × 100 = 317% increase.
3. Explanation (extension of the idea above): with age the lens becomes less able to become curved, so close objects can no longer be focused. This resembles long-sightedness, and a convex lens in reading glasses helps.
4. Limitation: only four ages are shown, and the number of people tested is not given.

Colour blindness

Colour blindness is an inherited condition in which one or more types of cone cell do not work properly, or are missing. The commonest form makes it hard to tell some reds from some greens.

Overcoming it: there is no cure that restores the faulty cones. Colour-filter lenses or glasses can help some people tell certain colours apart, and people adapt by using other clues such as position and brightness. State clearly that this is help with the problem, not repair of the receptors.

B3.1f: the brain

The brain is part of the central nervous system. Different regions have different jobs.

Region	Structure	Function
Cerebrum	Large, folded, divided into two halves (hemispheres); the folded outer layer is the cortex	Conscious thought, memory, language, intelligence; receives sensory information; controls voluntary movement
Cerebellum	Smaller, at the back and below the cerebrum	Coordinates movement and muscle activity; maintains balance
Medulla	At the base, joining the brain to the spinal cord	Controls unconscious actions such as breathing rate and heart rate
Hypothalamus	Small region deep in the brain	Monitors and controls body temperature and water balance
Pituitary	Small gland attached beneath the hypothalamus	Secretes hormones, several of which act on other glands, so it is called the “master gland”

The hypothalamus and pituitary link the nervous and hormone systems: the hypothalamus detects changes in the blood and controls the pituitary, which releases hormones into the blood.

Worked example 3 (applying brain regions). A person has a stroke damaging a small area at the back of the brain below the cerebrum. Their speech and memory are normal, but their walking is clumsy and they sway when standing still. Which region is most likely affected?

1. Speech and memory are cerebrum functions, and they are normal, so the cerebrum is probably not damaged.
2. Clumsy movement and poor balance are signs of cerebellum damage.
3. Breathing and heart rate seem normal, so the medulla is probably unaffected.
4. Answer: the cerebellum.

B3.1g: difficulties of investigating brain function (Higher Tier only)

The brain has billions of neurones with an enormous number of connections, and many regions work together. Several things make it hard to study.

• Access. The brain is protected by the skull and is soft and delicate, so you cannot look inside a healthy, working brain without risk of harm.
• Case studies are hard to obtain. They depend on people who happen to have a brain injury or disease, so they are rare, and no two injuries are in exactly the same place or of the same size. Researchers also rarely know how the person functioned before the injury.
• Case studies are hard to interpret. A single patient is a very small sample. Damage may spread beyond the area found, and other regions may take over some tasks. A loss of function shows an area is needed for something, not that it is the only area involved. A link between damage and symptoms may also be a correlation that other factors explain.
• Ethical issues. Deliberately damaging a human brain to see what happens is not acceptable. Patients with brain damage may be unable to give informed consent, and their records must be kept confidential. Experiments on animals raise concerns about suffering, and an animal brain may not work in the same way as a human one.

Scans let living brains be studied without surgery, but they are costly, and an area being active during a task does not by itself prove it causes the task. Finding willing, suitable volunteers also limits sample sizes.

B3.1h: limitations in treating nervous system damage (Higher Tier only)

• Limited ability to repair nervous tissue. Once damaged, many neurones in the brain and spinal cord are not readily replaced. Damage from a stroke, injury or a disease that destroys neurones may therefore be permanent.
• Irreversible damage to surrounding tissues. Reaching a tumour or a damaged area may mean cutting through healthy tissue, and treatments such as radiation can also affect healthy tissue nearby. Losing healthy neurones can cause new problems that cannot be undone.
• Difficulties with accessing parts of the nervous system. The brain is enclosed by the skull and the spinal cord by the backbone. Parts lie deep inside, so surgery is risky. The blood supply to the brain also limits which drugs reach it.

For these reasons treatments for conditions such as Parkinson’s disease often reduce symptoms but do not replace the lost neurones.

Worked example 4 (explain). Explain why a person with a spinal cord injury may not regain movement even with surgery.

1. Neurones in the spinal cord have limited ability to repair themselves, so the broken pathway may not regrow.
2. The cord is surrounded by bone and is delicate, so reaching it risks further, irreversible damage to the cord and nearby tissue.
3. Impulses cannot pass the damaged region, so muscles below it may not receive them.

Common errors

• Saying the iris “lets light in”. The pupil is the opening; the iris controls its size.
• Mixing up the lens corrections: short-sight needs a concave lens and long-sight a convex lens.
• Saying “the eye is too long” for long-sightedness. Long-sight comes from a short eyeball.
• Saying the cerebellum controls “thinking” or the cerebrum controls “balance”.
• Answering B3.1g with only “it is unethical”. Name a specific issue.

Official syllabus

OCR, GCSE (9-1) Gateway Science Biology A (J247), Version 4.0 (August 2026), for first assessment in 2018: statements B3.1d to B3.1h.