Stigma

Definition

Stigma is a light-sensitive organelle found in certain unicellular eukaryotic organisms, such as algae and some protists. It helps the organism navigate toward light sources for photosynthesis.

5 Must Know Facts For Your Next Test

1. The stigma is also known as an eyespot.
2. It plays a crucial role in phototaxis, the movement of an organism toward or away from light.
3. Stigmas are commonly found in green algae such as Chlamydomonas.
4. They contain photoreceptor proteins that detect changes in light intensity and direction.
5. The structure of the stigma can vary between different eukaryotic microorganisms.

Review Questions

• What is the primary function of a stigma in unicellular eukaryotes?
• In which type of organisms is a stigma commonly found?
• How does the presence of a stigma benefit photosynthetic microorganisms?

Related terms

Phototaxis: Movement of an organism toward or away from a light source.

Chloroplast: A pigment-containing organelle where photosynthesis occurs.

Protist:

A diverse group of eukaryotic microorganisms, including algae, that are not plants, animals, or fungi.