Topics:
Animal Physiology, Animal Refresher
True Statements About Vision
Which of the following statement(s) is/are true about vision?
- Cones are required for daylight vision while rods are required for night vision
- Majority (95%) of the photoreceptor cells are rod cells
- Rod cells are about 300 times more sensitive to light than cone cells
- All the above — Correct Answer
Explanation:
Correct Answer: All the above
All three statements about vision are factually correct:
- Statement 1: Cones → Daylight vision; Rods → Night vision ✓ — Cones (photopic system) are activated by bright light and provide colour discrimination. Rods (scotopic system) are activated by dim light and provide high-sensitivity monochromatic vision.
- Statement 2: 95% of photoreceptors are rod cells ✓ — The retina contains ~120 million rods (95%) and ~6 million cones (5%). This high rod-to-cone ratio enables detection of light under dark conditions.
- Statement 3: Rods are ~300 times more sensitive than cones ✓ — Rods contain rhodopsin which can be activated by even a single photon of light. This extraordinary sensitivity makes rods ideal for night vision. A single photon can theoretically trigger a nerve impulse in a rod cell.
Clinical Note
- Vitamin A (retinol) deficiency impairs rod function first → night blindness (nyctalopia). In severe deficiency, cone function is also affected.
- Example: Cattle and sheep grazing on Vitamin A–deficient dry pasture during drought may develop night blindness.
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
