Information+1

conjunctiva cornea sclera choroid retina iris lens** ciliary body optic nerve**
 * ​1. Describe the anatomy and function of the human eye, including the:
 * aqueous and vitreous humour

The human eye is an organ that enables the body to detect light and form sharp colour images in conjunction with the brain. The eyeball is enclosed by 3 layers of fibrous tissue, which are covered by a thin layer of epithelial cells called the conjunctiva. The conjunctiva keeps the outer surface of the area moist. The cornea is located at the front of the eye to protect it. The three layers are the sclera on the outside which covers it. The sclera supports and protects the eye, serves as an attachment for the extrinsic eye muscles and helps in focusing. The second layer is called the choroid, situated between the sclera and the retina. It serves as an additional protection and support for the eye and extends into the iris at the front of the eye. The inner layer is the retina, containing photoreceptors, a pigment layer, nerves, blood cells; photoreceptor cells respond to light and the adjacent neurons do some preliminary processing, before the information goes to the central nervous system. The central area of the retina focuses images most sharply and is called the fovea. The cornea is transparent and allows light into the eye. The iris surrounds a small opening called pupil. Muscles in the iris contract to change the diameter of the pupil. The lens is a transparent bioconvex disc made of protein. It focuses the light onto the retina. The anterior cavity produces a fluid called aqueous humour, which fills the cavity. The posterior cavity produces a jelly-like vitreous humour, which fills the eyeball and maintains the volume of the eye. Both also help focus the light onto the retina. The ciliary body is a structure that extends from the cornea and the sclera and attaches to both the iris and the lens. It holds the lens in place, allowing flexibility. The optic nerve transmits visual information to the brain for central processing. The optic nerve leads out of the posteriors of the eyeball to the brain stem and to the optic chiasma at the base of the brain. The main function of the human eye is to provide vision by working with the brain by translating light waves into eyesight from different distances and different situations all the time.



The diagram represents a visual view of all the parts of the eye and their location in and around the eyeball.


 * 2. Identify the limited range of wavelengths of the electromagnetic spectrum detected by humans and compare this range with those of other vertebrates and invertebrates**

Electromagnetic waves all travel at the speed of light but differ in their wavelengths. So they range from very short wavelength rays and X-rays with wavelengths of 0.001 micrometres to very long radio waves with wavelengths of 1 or more metres. Visible light is between wavelengths of 400-700 nm, the only radiation human eye cones can detect. This is different to other vertebrates and invertebrates. Infra-red light is invisible to humans, e.g. snakes use it to detect prey. Platypus uses electromagnetic receptors on its bill. Electric eels emit electrical signals that create an electrical environment.


 * 3. Use available evidence to suggest reasons for the differences in range of electromagnetic radiation detected by humans and other animals**

There is differences in the range of electromagnetic radiation detected. Humans only recognise visible light. The eyes range in complexity from simple collections of photoreceptor cells, through compound eyes, the simple singl-lens eyes of many invertebrates to the more complex single lens eyes of vertebrates including humans. Despite these variations the photoreceptors in all eyes contain pigment which absorb light. Humans live in terrestrial environments where vision is a suitable sense, whereas other aquatic animals live in environments in which vision is limited(less light available), Humans also cannot detect electrical, magnetic fields and waves which some animals use.


 * 4. Identify the conditions under which refraction of light occurs**

Refraction of light is the bending of light. When light enters another medium of a different density, whether high to low density or vice versa, the light travels at a different speed and is refracted. If the light travels to a denser medium, it is bent towards the normal and if the light goes to a less dense medium, it is bent away from the normal.

This diagram shows examples of the refraction of light that occurs in the human eye.


 * 5. Identify the cornea, aqueous humor, lens and vitreous humor as refractive media**

Refraction occurs when light passes from air into the denser material of the cornea. The cornea has a density close to that of water. The light then passes from the cornea into the aqueous humour. It is refracted again when the light passes from the aqueous humour. It is refracted again when the light passes from the aqueous humour into the denser lens. This provides the extra refraction required to focus the rays of light on a point on the retina called the focal point. These are all refractive media.