How it works
Algae come in many forms, from single cells to threads and sheets of many cells. This algal cell diagram shows Chlamydomonas, a green alga that is one swimming cell and the one textbooks most often draw.
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Front end first
The two flagella mark the front. Just under them are two contractile vacuoles. The eyespot, at one side near the front, senses light.
One chloroplast, shaped like a cup
The chloroplast fills the back and sides of the cell, and the nucleus lies in its hollow. In the thick base of the cup is the pyrenoid, ringed with starch.
- Pyrenoid and nucleus are both round: the nucleus sits in the hollow of the cup, the pyrenoid inside its base.
Questions and answers
What is the structure of an algae cell?
This one has a cell wall, two flagella, a single cup-shaped chloroplast with a pyrenoid, a nucleus, an eyespot and two contractile vacuoles. Other green algae differ: some are threads or sheets of many cells.
How is an algal cell different from a plant cell?
Chlamydomonas swims, which no leaf cell does: it has flagella, an eyespot and contractile vacuoles. It has one large chloroplast where a leaf cell has many small ones, and its wall is glycoprotein, not cellulose.
Do algae cells have a nucleus?
Green algae such as Chlamydomonas do: they are eukaryotes, like plants. Blue-green algae are different. They are bacteria, also called cyanobacteria, and have no nucleus.
What does the pyrenoid do?
The pyrenoid is a body inside the chloroplast of many algae. Starch, the food the cell stores, is formed round it, which is why it is drawn with a ring of starch plates.