Microbes and food 2. Microbe facts
Alga photomicrograph
Picture 2.4a the threads of an alga. You can see they are a string of cells.
2.4 Algae (singular: alga)
Algae are diverse. Their main characteristics are:
  • their cells have membrane-bound nuclei (we call them eukaryotic)
  • they contain chlorophyll and carry out photosynthesis.

Most algae are green. However, some algae contain other photosynthetic pigments which make them red.

They come in a number of forms:

  • single celled - e.g. diatoms
  • colonies e.g. Volvox
  • filaments e.g. Spirogyra.
  • macroscopic e.g. seaweeds.

The first three are microscopic. However, seaweeds grow up to 30 metres long and are not considered to be micro-organisms.

Lichen photo
Picture 2.4b Lichen growing on a rock - an example of symbiosis between algae and fungi.
Where do they live?

Most algae are free living although some form symbiotic relationships with other organisms. Lichens are an example of symbiosis between algae and fungi. Algae usually live in aquatic habitats of all types; some are found in soil or vegetation where there is enough moisture. They are rarely parasitic.

Spirogyra photomicrograph
Picture 2.4c Spirogyra.

How do they move and reproduce?
Some algae are motile. Single-celled algae often have flagella and move in a spiralling manner. Others do not have flagella but secrete a sticky substance which attaches them to the substrate, enabling them to glide along leaving a trail of slime behind.

Algae can reproduce asexually by fragmentation, binary fission and spore formation. They can also reproduce sexually.