How it works
On this volvox quiz diagram a part is named and you tap it on the drawing. The colony comes first, cut through the middle, then three of its cells enlarged.
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Look-alikes on the colony
A gonidium is one large cell with a dark dot. A daughter colony is a ball with its own ring of tiny cells. The somatic cells are the small ones round the edge, each with two threads pointing outward. The gelatinous matrix is the plain filling, and the bracket at the left stands for the whole colony.
Look-alikes on the cell
Two clear circles at the front are the contractile vacuoles; the one dark oval at the side is the eyespot. Of the two round bodies the larger, upper one is the nucleus; the smaller one under it is the pyrenoid. Flagella point out of the colony; cytoplasmic strands run from cell to cell.
- A colony swims with one pole in front. The gonidia lie in its rear half, drawn here as the lower half.
Questions and answers
Is Volvox a plant or an animal?
It is a genus of green algae of the family Volvocaceae. Each cell has a chloroplast and makes its food from light, and the colony swims by its flagella. Older textbooks of botany and of zoology both describe it.
What did Volvox evolve from?
From single-celled ancestors, about 200 million years ago. Its living relatives run from Chlamydomonas, which is one cell, to small colonies such as Pandorina and Eudorina.
What is colony inversion in Volvox?
A young colony first forms inside out, with the ends of its cells that grow flagella turned inward. The sheet of cells then turns itself the other way, so the daughter colony ends with its flagella on the outside.
Are the cells of a Volvox colony connected?
Not in every species. In some, thin strands of cytoplasm join each cell to its neighbors, and the drawing shows them as in Volvox globator, the species of the textbook figures. Other species have no strands at all.