**Rhodophyta (red algae)** has chlorophyll a and phycobilins. They can live in deep water due to phycobilins. **Phaeophyta (brown algae)** has chlorophyll a and c as well as fucoxanthin. **Chlorophyta (green algae)** has a carbohydrate cell wall and photosynthetic pigments that are similar to plants such as chlorophyll a.

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In plants, alternation of generations mean switching between haploid and diploid forms by using mitosis and meiosis processes throughout their lives. This is how they grow and reproduce.

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Multicellular algae can perform photosynthesis to make organic food sources and oxygen. Oxygen is released into the environment where it is used up by various organisms, such as us. The organic food source is consumed by many organisms, such as small fish. Without algae, many organisms will die.

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In their cells, red algae have phycobilin pigment that has the ability to obtain blue light. They are able to live in deep water because blue light can penetrate deep water.

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The diagram below shows the life cycle of a unicellular green alga called Chlamydomonas. It can reproduce through an asexual propagation of zoospores and it can reproduce sexually through a fusion called syngamy.