Problem 86 - Objective Biology for NEET

Question

Quantum of light entering the eye through the pupil is dependent on (a) Ciliary body (b) Lens (c) Retina (d) Iris

Step-by-Step Solution

Answer

The correct answer is (d) Iris.

Step 1: Identify Functions of Eye Parts

The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens. The lens focuses light onto the retina, which perceives and processes the image. The iris is the colored part of the eye that controls the size of the pupil, through which light enters the eye.

Step 2: Relate Function to Light Entry

From the functions of these parts, only the iris function correlates directly with the control of light entry into the eye. Thus, the iris affects the amount of light that enters the eye by adjusting the size of the pupil.

Step 3: Choose the Correct Answer

Based on the identified functions, the correct answer is (d) Iris, as it controls the size of the pupil, and thereby the amount of light that enters the eye.

Key Concepts

Iris Function

The iris plays a vital role in our eye anatomy and overall vision. It is the colorful part of the eye surrounding the pupil, often seen in shades of brown, blue, green, or hazel. Its main function is to control the amount of light that enters the eye by adjusting the size of the pupil. Although it seems a small and simple task, the iris continuously works to regulate light exposure, ensuring we see clearly in various lighting conditions.

• The iris contains two groups of muscle fibers: circular and radial. These fibers are responsible for pupil constriction and dilation.
• In bright light, circular fibers contract, making the pupil smaller and reducing light entry.
• In dim light, radial fibers contract, enlarging the pupil to allow more light in.

The iris, working in tandem with the muscles, is a prime example of how our eyes automatically adapt to ensure optimal vision.

Light Entry into the Eye

Light enters the eye through the pupil, the dark center within the colored part of the eye—the iris. This process is critical as it forms the basis of how we perceive the world visually.

• The amount of light entering the eye affects how well and how accurately we see.
• The process begins when light from the environment passes through the cornea, the eye's outermost layer, then through the pupil.
• The lens focuses the incoming light onto the retina, where the image is converted into electrical signals for the brain to interpret.

This fascinating process of light entry is crucial for tasks ranging from reading to appreciating art, all relying on the seamless passage of light through the eye.

Pupil Size Control

Pupil size control is vital for regulating light entry and protecting our sensitive retinas. The pupil is essentially a "window" for light, and its size changes based on environmental conditions and various emotional and physiological states.

• The autonomic nervous system governs these adjustments, facilitating a response known as the pupillary light reflex.
• In bright environments, the pupil constricts (a process called miosis) to shield the eye from excessive light that may cause glare or discomfort.
• Conversely, in low-light settings, the pupil dilates (mydriasis), allowing more light to reach the retina, improving night and low-light vision.

Pupil size control, though involuntary, is a testament to the eye's dynamic ability to adapt and respond to changing light environments to maintain visual clarity and comfort.