Problem 155 - Objective Biology for NEET

Question

Assertion: Vitamin \(-\) A deficiency produce night blindness. Reason: Vitamin \(-\) A forms retinal, a component of visual pigments in rods and cones.

Step-by-Step Solution

Answer

The assertion is true and reason is valid. A deficiency in Vitamin A can indeed lead to night blindness, as Vitamin A is required for the creation of retinal, which is an essential part of visual pigment in rods that are responsible for vision in low light.

Step 1: Understanding the assertion and the reason

Initially, we must understand the assertion and reason. The assertion is that a deficiency in Vitamin A results in night blindness. The reasoning given is that Vitamin A is converted to retinal, which is an important component of visual pigments present in the rods and cones of our eyes.

Step 2: Confirming the theory using reliable sources

Next, using a trustable source like a biology textbook or a reputable medical research paper, it can be confirmed that Vitamin A indeed converts into retinal, a component of visual pigments. It is known that the rods in our eyes are responsible for vision in dim light and any discrepancies in them can lead to night blindness.

Step 3: Concluding the connection

On correlating the information, it can be concluded that the reason is correct. This is because if there is a deficiency in Vitamin A, less retinal will be formed. As retinal is required for the visual pigments in rods which help in vision in dim light, a lower number of visual pigments results in a lower ability to see in dim light, causing night blindness. Therefore, Vitamin A deficiency does indeed cause night blindness.

Key Concepts

Night Blindness

Night blindness, or nyctalopia, is a condition where individuals find it challenging to see in dim light or darkness. This happens because the eye's vision adaption to low-light conditions is impaired. The root cause of night blindness is often linked to deficiencies in Vitamin A.
Vitamin A is crucial for maintaining proper vision as it helps produce the pigment retinal. Without adequate levels of Vitamin A, the eye cannot generate enough retinal, resulting in a deficiency of the pigments necessary for low-light vision.
Individuals with night blindness often struggle to see in dark environments. Activities such as driving at night or walking in poorly lit areas can become difficult. Addressing night blindness involves increasing Vitamin A intake through diet or supplements under medical guidance to restore vision capabilities in low-light scenarios.

Retinal

Retinal is a vital component of the visual pigment located within the photoreceptor cells in the eye. This molecule plays a significant role in the process of vision.
Retinal, derived from Vitamin A, combines with a protein named opsin to create rhodopsin, which is crucial for vision in dim lighting. The importance of retinal becomes evident as it acts as a chemical enzymatic trigger, allowing us to convert light into visual signals the brain can interpret.
In the absence of sufficient retinal, the formation of these critical visual pigments is hindered. Consequently, individuals may experience impaired vision, especially noticeable in low-light conditions. Ensuring enough Vitamin A intake is essential for the continuous production of retinal, thus supporting healthy vision.

Visual Pigments

Visual pigments are molecules found within the photoreceptor cells of the retina known as rods and cones. These pigments are pivotal for converting light into electric signals, which the brain turns into the images we see.
In rods, the primary visual pigment formed is rhodopsin, composed of retinal and opsin. Rhodopsin is sensitive to dim light, making it indispensable for night vision.
When light enters the eye, these visual pigments undergo a chemical change, initiating a cascade of events that lead to the perception of images. A deficiency in the components of visual pigments, such as retinal due to lack of Vitamin A, disrupts this process. This leads to difficulties in seeing, especially in low-light environments, manifesting as night blindness.

Rods and Cones

Rods and cones are the two types of photoreceptor cells located in the retina of the eye. These cells play a crucial role in the functioning of our vision.
Rods are highly sensitive to light and are responsible for our ability to see in low-light conditions, making them essential for night vision. Conversely, cones are responsible for color perception and function better in bright light conditions.
A sufficient amount of visual pigments in these cells is crucial for their optimal functioning. Retinal, a derivative of Vitamin A, is integral in forming these pigments. When Vitamin A levels are low, rods, which heavily rely on visual pigments for night vision, cannot function properly, leading to conditions such as night blindness. Maintaining a balanced diet including foods rich in Vitamin A can help support the health and functionality of rods and cones.