8. Explain the structure and working of a human eye.

The human eye is a complex organ responsible for vision. Its structure and working involve several components that work together to collect, focus, and transmit visual information to the brain. Here's an overview of the structure and functioning of the human eye:

1. Cornea: The cornea is the transparent outer layer of the eye that covers the iris, pupil, and anterior chamber. It helps in focusing light into the eye.

2. Pupil: The pupil is the black circular opening in the center of the iris that regulates the amount of light entering the eye by dilating or constricting in response to light intensity.

3. Iris: The iris is the colored part of the eye surrounding the pupil. It controls the size of the pupil and thus the amount of light entering the eye.

4. Lens: Behind the iris and pupil is the lens, a transparent, flexible, and biconvex structure that focuses light onto the retina.

5. Retina: The retina is a thin layer of tissue lining the back of the eye. It contains photoreceptor cells called rods and cones that convert light into electrical signals.

6. Rods and Cones: Rods are sensitive to low light levels and are responsible for peripheral and night vision, while cones are responsible for color vision and detail in bright light.

7. Optic Nerve: The optic nerve is a bundle of nerve fibers that carries visual information from the retina to the brain.

8. Vitreous Humor: The vitreous humor is a gel-like substance that fills the space between the lens and the retina, helping to maintain the shape of the eye and transmit light to the retina.

Working of the Human Eye:

1. Light enters the eye through the cornea, where it is refracted (bent).
2. The iris adjusts the size of the pupil to control the amount of light entering the eye.
3. The light then passes through the lens, which further refracts it to focus it onto the retina.
4. The retina contains photoreceptor cells (rods and cones) that convert light into electrical signals.
5. These signals are then transmitted through the optic nerve to the brain.
6. In the brain, the visual information is processed, allowing us to perceive and interpret the images we see.

Overall, the human eye functions like a sophisticated camera, capturing and processing visual information to enable sight.