Problem 65 - Objective Biology for NEET

Question

Choroid is blue due to (a) Lack of \(\mathrm{O}_{2}\), in tissues (b) Due to pigment (c) Excess of blood vessels (d) None of these

Step-by-Step Solution

Answer

(b) Due to pigment

Step 1: Understanding of Choroid

Choroid is a part of the eye. It provides oxygen and nutrients to the outer layers of the retina. It is known to be dark blue or brown in color. By knowing this fact, an analysis of the proposed options can be performed.

Step 2: Evaluate each option

(a) Lack of \(\mathrm{O}_{2}\) in tissues: This is not a valid option as Choroid has a rich supply of blood vessels which ensures adequate oxygen supply to the tissues. So, lack of oxygen cannot make it blue. (b) Due to pigment: This seems more plausible as the color of any body part is usually due to the presence of specific pigments. (c) Excess of blood vessels: While it's true that Choroid has abundant blood vessels, they are not directly responsible for the blue color. The vessels are there to supply nutrients and oxygen to the retina.

Step 3: Choose the correct answer

After analyzing all options, it appears that the choroid's blue color is primarily due to the presence of a pigment, making option (b) the correct choice.

Key Concepts

Eye Anatomy

The human eye is a complex and fascinating organ that allows us to perceive the world around us. It's made up of several key parts, each playing a crucial role in the process of sight. At a basic level, the eye consists of:

• The Cornea - The transparent front layer that focuses incoming light.
• The Lens - Adjusts its thickness to focus light directly onto the retina.
• The Retina - A layer of light-sensitive cells that detect light and send signals to the brain.
• The Optic Nerve - Transmits visual information from the retina to the brain.
• The Choroid - A vascular layer filled with blood vessels, situated between the retina and sclera.

The choroid is particularly important as it supplies blood and nutrients to the retina. Its network of blood vessels ensures the proper functioning of the retinal cells by providing essential nutrients and oxygen. The eye operates as a cohesive system; any disruption in one part can affect the entire process of vision.

Oxygen Supply in Retina

The retina needs a constant supply of oxygen to work efficiently and maintain vision. This is where the choroid comes into play. Located behind the retina, the choroid is responsible for delivering oxygen and nutrients. It does this through its rich network of capillaries.

This rich supply is crucial because the retina is highly active and requires significant oxygen to convert light into electrical signals.

• High oxygen requirement - The retina consumes more oxygen compared to other tissues.
• Choroidal blood flow - Supports the metabolic activity of photoreceptors.
• Prevents ischemia - Sufficient oxygen supply avoids tissue damage from lack of oxygen.

Most of the oxygenation occurs in the outer layers of the retina, where photoreceptor cells are densely located. This abundant oxygen supply ensures these cells function without interruption, maintaining clear vision.

Pigmentation in Eye

Pigmentation in the eye mainly refers to the color of various parts, which is influenced by pigments. The choroid appears dark, often described as blue or brown, primarily due to the presence of specific pigments such as melanin. These pigments serve multiple purposes:

• Light Absorption - Melanin absorbs excessive light that enters the eye, reducing photobleaching.
• Protection - Prevents ultraviolet or radiation damage to delicate retinal cells.
• Coloration - The pigment is responsible for the characteristic color of the choroid.

Melanin, a key pigment, is not only present in the choroid but also in other parts of the eye, such as the iris. In the choroid, this pigment helps manage light efficiently, ensuring that only the necessary amount of light reaches the photoreceptors. Thus, the pigmentation of the eye plays a significant role in both vision and protection.