What is the cornea and what does it do?

It is the transparent front of the eye and it refracts the light entering the eye, doing most of the focusing.

The hole in the middle of the iris through which light passes into the eye.

How does the iris control how much light enters the eye?

Its circular and radial muscles contract and relax to make the pupil small in bright light and wide in dim light.

What is the function of the retina?

It carries the light receptor cells that detect light and turn it into electrical impulses.

What does the optic nerve do?

It carries electrical impulses from the retina to the brain.

OCR GCSE Biology A J247

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

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Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition and trophic levels Pyramids of biomass and the efficiency of transfer

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Asexual and sexual reproduction compared Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination, multiple genes and Mendel's work Variation within a population, and classification Natural selection and evolution Evidence for evolution, and the work of Darwin and Wallace

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Food security, agricultural and biotechnological solutions Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples Physical and chemical plant defences White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc The eye and its common defects The structure and function of the brain Hormones and the endocrine glands Hormones in reproduction and the menstrual cycle Methods of contraception Tropisms, auxin and the roles of plant hormones Homeostasis, and the skin in temperature control Insulin and the control of blood glucose Type 1 and type 2 diabetes Osmotic changes in body fluids, and the kidneys Kidney structure and the parts of the tubule

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Organism Level Systems

The eye and its common defects

3 things to know
Paper 1

Overview

The cornea, pupil, iris, retina with its rods and cones, and optic nerve, how the ciliary muscles and suspensory ligaments change the lens to focus on near and distant objects, red-green colour blindness, the causes of short- and long-sightedness and the concave and convex lenses that correct them, and contact lenses and surgery.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the pupil?

Key term

Name the two kinds of light receptor cell in the retina and say what each detects.

Key term

Explain how the ciliary body and suspensory ligaments let the eye focus on a nearby object.

Questions from this subtopic

Each one with the model answer underneath.

1
What is the cornea and what does it do?
Model answer
It is the transparent front of the eye and it refracts the light entering the eye, doing most of the focusing.
2
What is the pupil?
Model answer
The hole in the middle of the iris through which light passes into the eye.
3
How does the iris control how much light enters the eye?
Model answer
Its circular and radial muscles contract and relax to make the pupil small in bright light and wide in dim light.
4
What is the function of the retina?
Model answer
It carries the light receptor cells that detect light and turn it into electrical impulses.
5
Name the two kinds of light receptor cell in the retina and say what each detects.
Model answer
Rods, which work in dim light but see only in black and white, and cones, which detect colour but need bright light.
6
What does the optic nerve do?
Model answer
It carries electrical impulses from the retina to the brain.

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Cell Level Systems

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Genes, Inheritance and Selection

Global Challenges

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AA diet high in sugar and fat leads to obesity.

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