Problem 79 - Objective Biology for NEET

Question

Find out the incorrect statement: (a) Lens is a transparent and crystalline structure. (b) Iris is pigmented and opaque layer. (c) The aperture surrounded by iris is called pupil. (d) Twilight vision is the function of cones.

Step-by-Step Solution

Answer

The incorrect statement is (d) Twilight vision is the function of cones.

Step 1: Understanding Statements

Read all the statements carefully and understand their meanings related to human eye anatomy and functions.

Step 2: Evaluating Each Statement

Evaluate each statement against known facts regarding the human eye structure and its function. Apply knowledge on the lens, iris, pupil, and the concept of twilight vision related to cones in the human eye.

Step 3: Identifying Incorrect Statement

Identify the statement which does not align with the known facts about the human eye. The lens is indeed a transparent and crystalline structure which helps in focusing light on the retina. The iris is a pigmented and opaque layer which regulates the amount of light entering the eye. The aperture surrounded by the iris is known as the pupil. However, the function of twilight vision, also called scotopic or night vision, is not a function of cones but, in fact, the function of rods in the human eye. Cones are responsible for day or photopic vision.

Key Concepts

Lens

The lens in the human eye is a transparent structure. It is crystalline, which means it is clear and glass-like in appearance. The primary function of the lens is to focus light onto the retina, enabling the eye to see clearly. This ability to focus light is crucial for our vision because it helps us see objects at various distances. Additionally, the lens is flexible and can change shape to fine-tune focus, a process known as accommodation.

• The lens is important for adjusting vision based on the distance of objects.
• It works with the cornea to refract light precisely.

By understanding the role of the lens, we can appreciate how it is essential for sharp and accurate vision, providing us with a detailed view of the world.

Iris

The iris is the colored part of the eye, and it surrounds the pupil. It acts like a curtain, regulating the amount of light that enters the eye. Think of the iris as a camera shutter—it opens wider or constricts smaller depending on the lighting conditions.

• In bright environments, the iris constricts to reduce light intake.
• In dim lighting, it dilates to allow more light in, assisting proper vision.

The pigment of the iris provides eye color, and its opacity prevents light from passing directly through, ensuring that light enters only through the pupil. The iris makes sure our eyes receive the right amount of light, protecting the sensitive internal structures from damage due to excessive brightness.

Pupil

The pupil is the dark spot in the center of the eye, surrounded by the iris. It is essentially an opening through which light enters the eye. The size of the pupil is adjusted by the action of the iris to control how much light gets in.

• In bright surroundings, the pupil becomes smaller to protect the inner eye from too much light.
• In darkness, it expands to capture as much available light as possible.

The functioning of the pupil is a reflex action, happening without conscious thought. This constant adjustment helps maintain optimal vision by balancing light levels, so our eyes aren't overwhelmed by drastic changes in brightness. The pupil is central to how we perceive the world visually, allowing us to adapt to varying lighting conditions efficiently.

Twilight Vision

Twilight vision—or night vision—is what allows us to see in low light conditions, like dusk or dark interiors. This type of vision is managed by the rod cells in the retina. Unlike cones, which are responsible for color vision and work best in bright light, rods are highly sensitive to low light, making them crucial for seeing when it's dark.

• Rods respond to low light and help us detect shapes and movements.
• They are distributed throughout the retina, providing peripheral vision in dim settings.

Understanding twilight vision helps clarify why colors seem less vivid in low light—the cones are less active, while rods take over to ensure we can navigate in near darkness. This division of labor between rods and cones allows humans to maintain vision across a wide range of environments.