NEET BIOLOGY

Detailed explanation-1: -Euglena rotates about its long axis as it swims, and thus in the presence of light from one side the photoreceptor will be periodically shaded by the eyespot. It has been suggested1 that this shading causes a succession of phobic responses (shock reactions) which act to point the organism towards the light source.

Detailed explanation-2: -Because the Euglena can undergo photosynthesis, they detect light via eyespot and move toward it; a process known as phototaxis. When an organism responds to light, a stimus (plural, stimuli), they move either toward or away from light.

Detailed explanation-3: -Euglenids have many unique cellular structures, some of which include their flagella, eyespot, contractile vacuole, and chloroplasts. The eyespot helps the organism to detect light sources in order to photosynthesize.

Detailed explanation-4: -Euglena also have an eyespot at the anterior end that detects light, it can be seen near the reservoir. This helps the euglena find bright areas to gather sunlight to make their food.

Detailed explanation-5: -A red eyespot (stigma) is located near the base of the reservoir (Fig. 3.4) and this filters the light and focuses it on the paraflagellar body, and is involved in the phototaxis of this alga (Häder and Iseki, 2017). Euglena lacks a cell wall.