Tag: biology

In the eye of the bird, a comb-like structure is present. It is called as pectin. It is soft and vascular. It is a rectangular plate. It projects into the vitreous humor from the blind spot. So, the correct answer is option B.

Iris is the part of the eye, which acts like the diaphragm of a camera, dilating and constricting the pupil to allow more or less light into the eye. The iris works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light is entering the eye.
The two eyelids act to protect the front of the eye and excessive light by their closure. The inner layer of the cornea is made up of transparent tissue, which allows light to pass. The pupil is the dark opening in the centre of the coloured iris, that controls how much light enters the eye. The ciliary body is a structure located behind the iris which produces aqueous fluid that fills the front part of the eye and thus maintains the eye pressure. It also allows focusing of the lens. 

In the rods of fresh water fishes, rhodopsin is replaced by the purple photolabile pigment porphyropsin. This participates in a retinal cycle identical in form with that of rhodopsin, but in which new carotenoids replace retinene and vitamin A.

The back of the eye is lined by a layer called as the retina, which acts like the film inside a camera. The retina is a thin layer of nerve tissue, that contains photoreceptors. Photoreceptors convert light rays into electrical impulses, which are then sent through the optic nerve to the brain, where an image is perceived. As with a camera, if the film is bad in the eye (i.e., the retina is damaged or diseased), no matter how well the rest of the eye is functioning, a good picture is not possible.

The ora Serrata is a toothlike junction between the peripheral retina and the pars plana and is composed of forward extensions of the retina and backward extensions of the ciliary body. So, the correct answer is option A.

A myopic eyed person focuses the light rays from a distant object in front of the retina, it can not focus distant objects sharply on the retina. Emmetropic eyes are characterized by sharp focusing of parallel light rays from distant objects on the retina when the ciliary muscle is completely relaxed to make the person see all the distant objects clearly. Hypermetropic eyes can not sufficiently bend the parallel light rays from the distant object to focus it on the retina in time.

The compound eyes of arthropods are composed of units called as ommatidia. An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells.

The retina contains the cells, that respond to light. These specialized cells are called as photoreceptors. There are 2 types of photoreceptors in the retina: rods and cones. 

In order to reduce the amount of light entering into the eye, pupils constrict, and this constriction helps to decrease the strong light, which can be harmful to cells in the retina. The retina is the innermost layer of the eye which contains photoreceptor cells, that are useful for the formation of the image and perceiving an object. Another advantage of constriction of the pupil is to improve the clarity of image by blocking some of the rays of light, which can optically cause distortion of the image. The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle.

Rhodopsin is a light-sensitive receptor protein. It is a biological pigment in photoreceptor cells of the retina. It is the primary pigment found in rod photoreceptors. They are extremely sensitive to light, enabling vision in low-light conditions.