State one function of the crystalline lens in the human eye.
State one function of the crystalline lens in the human eye.
The crystalline lens of the human eye provides the finer adjustment of focal length required to focus objects at different distances on the retina. It forms a real and inverted image of the object on the retina. The curvature (and hence focal length) of this lens can be changed by the ciliary muscles to clearly see objects placed at varying distances.
Marking Scheme
- 11 mark: Stating any one correct function of the crystalline lens (e.g., finer adjustment of focal length, or forming a real inverted image on the retina).
Hint
Think about what happens to light after it passes through the pupil and before it reaches the retina. The lens is responsible for fine focusing.
Quick Oral Answer
The crystalline lens provides the finer adjustment of the focal length of the eye so that objects at varying distances can be focused on the retina, forming a real and inverted image.
Analysis & Explanation
The human eye works very much like a camera. Light entering the eye is refracted mainly at the outer surface of the cornea. The crystalline lens, located behind the iris and pupil, does the fine-tuning of this refraction. By changing its curvature with the help of ciliary muscles, the lens adjusts its focal length — this property is called the power of accommodation. Thus, whether you are looking at a distant tree or reading a book held 25 cm away, the crystalline lens modifies its shape so that the image is always formed sharply on the retina. Because the question asks for ONE function, mentioning the focal-length adjustment OR image formation is sufficient for full credit.
Common Mistakes
- 1Confusing the role of the cornea with that of the crystalline lens (cornea does most of the refraction; the lens does the fine adjustment).
- 2Writing that the lens only refracts light without mentioning the retina/image.
- 3Mentioning colour detection, which is a function of the retina, not the lens.
Interesting Facts
The crystalline lens of a newborn is almost perfectly transparent; with age it may become milky — a condition known as cataract.
The lens is composed of a fibrous, jelly-like material with no blood supply; it gets nourishment from the aqueous humour.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2012?
This question carries 1 mark in the CBSE Class 10 Science 2012 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Crystalline lens of the human eye" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2012 paper?
This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.