(a) State one important function of the following parts of the human eye: (i) Retina (ii) Pupil (b) State the role of ciliary muscles in focussing objects at varying distances from the eye.
(a) State one important function of the following parts of the human eye: (i) Retina (ii) Pupil (b) State the role of ciliary muscles in focussing objects at varying distances from the eye.
(a) Functions of the parts of the human eye:
- (i) Retina: It acts as a light-sensitive screen on which a real and inverted image of the object is formed. It contains an enormous number of light-sensitive cells that get activated upon illumination and generate electrical signals to be sent to the brain via the optic nerve.
- (ii) Pupil: It regulates and controls the amount of light entering the eye by adjusting its size.
(b) Role of ciliary muscles in focussing objects at varying distances:
The ciliary muscles modify the curvature of the eye lens, thereby changing its focal length to focus objects at different distances (accommodation):
- For viewing distant objects: The ciliary muscles relax, causing the eye lens to become thin. This increases its focal length, allowing parallel rays from distant objects to focus clearly on the retina.
- For viewing nearby objects: The ciliary muscles contract, which increases the curvature of the eye lens, making it thicker. This decreases its focal length, allowing diverging rays from nearby objects to focus clearly on the retina.
Marking Scheme
- 1Correct function of Retina (light-sensitive screen / image formation / signal generation) (1 mark)
- 2Correct function of Pupil (regulates/controls the amount of light entering the eye) (1 mark)
- 3Explaining the role of ciliary muscles during relaxation (for distant vision) and contraction (for near vision) (1 mark)
Hint
Think about where the image is formed in the eye, how the eye controls light entry in bright versus dark rooms, and how the lens changes shape when you look at a distant star versus a book.
Quick Oral Answer
The ciliary muscles change the focal length of the eye lens. When they relax, the lens becomes thin and its focal length increases for distant vision. When they contract, the lens becomes thick and its focal length decreases for near vision.
Analysis & Explanation
The human eye functions like a camera. The retina acts as the digital sensor or film, converting light energy into electrical impulses. The pupil acts as the aperture, changing its diameter to control light exposure. The ciliary muscles act as the focusing mechanism by physically altering the shape of the flexible, jelly-like crystalline lens. This ability to adjust focal length dynamically is known as the power of accommodation.
Common Mistakes
- 1Confusing the function of the iris with the pupil (the iris controls the size of the pupil, while the pupil regulates the amount of light).
- 2Stating that ciliary muscles contract to see distant objects (they actually relax for distant vision and contract for near vision).
Interesting Facts
The retina contains millions of photoreceptor cells. When light hits these cells, they convert it into electrical impulses in a fraction of a millisecond, which the brain processes so fast that we perceive motion seamlessly!
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2023?
This question carries 3 marks in the CBSE Class 10 Science 2023 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 "The Human Eye" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2023 paper?
This is a Short Answer question from Section C in the CBSE Class 10 Science 2023 paper.