The 3 Types of Algae
We recognize three types of algae, easily identified by colour. They are brown, red, and green algae. Most algae are classified under the kingdom Protista, so for our purposes they are protists under their own phylum.
They are all non-vascular so each is low-lying because they depend on diffusion between cells to move water and nutrients. Because of this they also all live in areas that are wet almost constantly. They can use photosynthesis.
They are all non-vascular so each is low-lying because they depend on diffusion between cells to move water and nutrients. Because of this they also all live in areas that are wet almost constantly. They can use photosynthesis.
Brown algae is from the phylum called heterokontophyta which is a mouthful to say but actually has meaning. "Hetero" means "different" and "konto" means "flagella." To me this is interesting because the sperm of brown algae have two flagella, one long and one short. It is most commonly found in marine and found in colder waters (temperate to arctic). Out of the three they grow to be the biggest size. They are yellow-brown or brown in colour due to the presence of chlorophylls a, c1 and c2, and are always lacking chlorophyll b. The pigment fucoxanthin helps give them their brown colour. Red algae is classified under rhodophyta. This name is easier to remember because both the colour and phylum start with "r."
It lives mostly in warm tropical waters (helping out coral reefs) but it can also be found in temperate zones in deeper waters because it can absorb blue light. It's reddish pigmentation comes from chlorophyll a, phycoerythrin and phycocyanin as well as a bunch of others. Red algae can be eaten by humans and can also be used to produce agar. Green algae is a member of chlorophyta, which is also easy to remember because chlorophyll is the green pigment in plants. Unsurprisingly, what makes green algae green are the chlorophylls a and b.
Green algae is easily the most diverse out of the three, as they can be unicellular, colonial or multicellular and can also be found in all environments, including salt water, fresh water and on land. Unicellular green algae are commonly found in fresh water as a part of phytoplankton. An example would be the chlamydomonas species. Colonial green algae either live in the form of long filaments or as spherical colonies (ex: volvox). Multicellular green algae are mostly marine and are thought to be the ancestors of today's plants. |
Plants Evolved From Algae
Because algae have soft bodies, their fossil record is poor. However, because of the characteristics multicellular green algae shares with bryophytes, we can conclude that algae were the first ancestor of plant kind.
In order to survive on land with drastically less water, algae had to make a few adaptations.
This effectively progressed into Bryophytes (mosses) who needs drastically less water than algae. Compared to other plants they still need quite a lot, but they no longer need to be submerged to survive. Natural selection explains well how algae could have selected for adaptations that would help them in dryer climates (click here for my evolution page explaining natural selection).
In order to survive on land with drastically less water, algae had to make a few adaptations.
- To prevent desiccation (drying out from evaporation) they developed a waxy cuticle that acts as a barrier to the sun. It is the outermost layer and it acts like the plant's "skin."
- For gas exchange through the cuticle stomata formed, which acts like a gateway for CO₂ in photosynthesis
- To depend less on diffusion, xylem was developed to transport water upwards and phloem to move nutrients from photosynthesis downwards.
- Embryos become protected, but not yet like seeds.
This effectively progressed into Bryophytes (mosses) who needs drastically less water than algae. Compared to other plants they still need quite a lot, but they no longer need to be submerged to survive. Natural selection explains well how algae could have selected for adaptations that would help them in dryer climates (click here for my evolution page explaining natural selection).