The organ which is sensitive to light in Euglena is the

1. Analyze the question The question asks which part of Euglena detects light. Euglena is a unicellular, flagellated organism found in ponds and stagnant water. It photosynthesizes like a plant but can also move like an animal.

2. Explain the concept Each structure in Euglena has a specific job:

• Gullet (A): A canal-like depression at the anterior end. The flagellum arises from it, and it is also associated with the contractile vacuole. It is not light-sensitive.
• Flagellum (B): A whip-like structure used for locomotion. It moves the organism toward light but does not detect it.
• Chloroplast (C): Contains chlorophyll and carries out photosynthesis. It uses light but does not sense it.
• Eyespot / stigma (D): A red pigmented spot near the base of the flagellum. It is photosensitive, so it detects the direction and intensity of light.

3. Show the solution

• The question says "sensitive to light", which means detection, not use of light.
• Detection is done by the eyespot (stigma).
• The eyespot helps Euglena move toward favourable light, a response called phototaxis. The flagellum then carries out the movement.

4. Answer The correct option is D. eyespot.

5. Exam tip Link each structure to its function:

• Eyespot → Eyes → detects light
• Flagellum → Forward movement
• Chloroplast → Creates food (photosynthesis)
• Gullet → entrance or canal at the front

If a question uses words like "sensitive to" or "detects", think of a receptor. If it says "uses light to make food", think of chloroplast.