Question

t.In the chemistry of vision in mammals, the photosesst substance is called (a) rhodopsin (b) melanin (c) sclerotin (d) retinol.

Short answer

The photosensitive substance in the chemistry of vision in mammals is called (a) rhodopsin.

Step-by-step solution

Identify the photosensitive substance

In the mammalian eye, the retina contains photoreceptor cells. These cells contain a pigment that captures light and begins the process of sight. The substance that performs this role is specifically found in the rod cells of the retina.

Recall the function of the photoreceptor cells

The rod cells are responsible for vision in low light conditions and contain a pigment necessary for the initial step in the detection of light.

Choose the correct option

The pigment found in rod cells that is sensitive to light and triggers the signal that the brain interprets as vision is known as rhodopsin.

Key concepts

Rhodopsin

Rhodopsin, also known as visual purple, is a light-sensitive receptor protein that plays a pivotal role in the chemistry of vision in mammals. Located within the photoreceptor cells known as rods in the retina, rhodopsin is the substance that actually 'catches' photons of light, triggering a biochemical cascade that ultimately leads to visual perception.

Rhodopsin is composed of a protein called opsin and a light-absorbing molecule called retinal, which is derived from vitamin A. When a photon of light hits rhodopsin, it causes the retinal to change shape, initiating a process called phototransduction. This process converts the light signal into electrical signals that the brain can understand. Defects in rhodopsin can lead to visual impairments, illustrating its significance in vision.

Photoreceptor Cells

Photoreceptor cells are specialized types of neurons found in the retina that are capable of converting light into signals that can be processed by the brain. There are two main types of photoreceptor cells: rods and cones.

Rods are highly sensitive to light and allow us to see in low-light conditions but do not mediate color vision. Cones, on the other hand, require more light and are responsible for color vision and visual acuity. Rhodopsin is the pigment found in rods; cones contain photopigments known as cone opsins. Each type of photopigment reacts to different wavelengths of light, enabling the diversity of light perception humans experience.

The functioning of photoreceptor cells is fundamental to vision. These cells are key for both the perception of light intensity (brightness) and color, and their distribution across the retina allows for a detailed visual representation of the environment.

Retina

The retina is a thin layer of tissue lining the back of the eye on the inside and is crucial for vision. It contains millions of photoreceptor cells, including rods and cones, which respond to light and convert it into neural signals. These signals are then relayed via the optic nerve to the brain for visual recognition.

The retina is intricately organized into several layers, each with a unique role to process visual information. Apart from photoreceptor cells, it houses other cell types including bipolar cells, ganglion cells, and supporting glial cells. The region called the macula is responsible for high-resolution central vision, while the peripheral retina provides a broader field of view but with less detail.

Maintaining retinal health is essential for clear vision. Diseases such as macular degeneration and retinal detachment can severely affect vision, underscoring the retina's function as the foundation of visual perception in mammals.