Question

Eyespot or stigma is present in ………………………
A. Spirogyra
B. Ulothrix
C. Nostoc
D. Chlamydomonas

Answer 1

Hint: It is the photosensitive receptors that are found mostly in the unicellular organism like euglenoids. But it is found in one of the green algae that is having similar size flagellated gametes. Eyespot is basically present for the perception of optimum sunlight.

Complete Answer:
Eyespot is generally the light reception apparatus found in the flagella of green algae and other unicellular photosynthetic organisms like euglenoids. It is the tactile apparatus that moves the organism to the direction where optimum light is present thus helping in carrying out the photosynthetic reactions.
- Eyespots are the most common and the simplest eyes found in nature that are composed of photoreceptors and areas of bright orange red pigment granules.
- The eyespot is thus found in Chlamydomonas and some of the euglenoids for carrying out the photosynthetic process by deriving optimum sunlight.

The correct option is D i.e. Chlamydomonas.

Additional information: The tactile response of the organism can be positive or negative. If it is positive then the organism moves towards the light while if it is negative then the organism moves away from the light.
The eyespot apparatus is having some proteins that are responsible to sense light. There are basically two types of proteins found in the photoreceptor. These are:
- Flavoproteins: it contains flavin molecules as chromophores that is likely found in Euglena.
- Rhodopsin: it is also called as retinylidene proteins that contain retinal and is characteristically found in Chlamydomonas.
Besides these 2 proteins, there are some structural, metabolic and signaling proteins that are also present.

Note: Chlamydomonas is a green algae belonging to the class chlorophyceae containing chlorophyll a and b as a main pigment. It stored food in the form of starch. Besides starch, oil droplets are also present that are responsible for storage of food material. The gametes of Chlamydomonas are flagellated and of similar size. Thus the isogamous type of reproduction takes place in them. In Chlamydomonas, the eyespot proteome comprises roughly 200 different proteins.