Green algae

Green algae are a fascinating group of plants that contain chlorophyll and make their own food through photosynthesis. They are found in many places, such as freshwater, oceans, and even on land. There are about 22,000 species of green algae, and they come in many shapes and sizes—from tiny single cells to large seaweeds you can see with your eyes.

Many green algae live most of their lives as single cells, but some form colonies, long threads, or even big, multicellular plants. Some other tiny creatures, like certain types of dinoflagellates, euglenids, and flatworms, depend on green algae to help them make food.

Green algae also have special relationships with fungi, forming what we call lichens. In these partnerships, the green algae provide food through photosynthesis, while the fungi offer protection and support. Without the algae, the fungi usually cannot survive on their own.

Cellular structure

Green algae have special parts called chloroplasts that contain chlorophyll a and b, which give them their bright green color. They also have other colorful substances like beta carotene and xanthophylls. Their cells are surrounded by walls made of a substance called cellulose, and they store energy as starch.

These algae also have structures called mitochondria that help them produce energy. Some green algae can move using tiny hair-like structures called flagella, which are anchored by a network of tiny tubes known as microtubules. Different types of green algae divide in slightly different ways, but they all have these basic cell parts that help them grow and live.

Origins

Photosynthetic eukaryotes began when a cell absorbed a tiny, plant-like organism called a cyanobacterium. This tiny organism lived inside the cell and changed over time to become a special part of the cell known as the plastid. This important event led to the creation of three groups of plant-like organisms: the (green) plants, the red algae, and the glaucophytes.

Evolution and classification

Green algae are a group of plants that, together with land plants, make up the green plant clade called Viridiplantae (or Chlorobionta). They are part of a larger group called Primoplantae, which also includes red algae and glaucophyte algae.

The green plants split into two main groups. One group is the Chlorophyta, which includes many common green algae. The other group is the Streptophyta, which includes charophytes and land plants. Scientists study these groups to understand how plants evolved.

Reproduction

Green algae are simple, plant-like organisms that can make their own food using sunlight. They have different ways of reproducing. Some green algae switch between two forms during their life cycle: one form has single sets of chromosomes, and the other has double sets. These forms can look the same or different.

In some green algae, small cells fuse with larger cells to create a new organism. This process is called fertilization. When certain thread-like green algae reproduce, they form bridges between cells and leave empty walls behind, which scientists can see under a microscope. This is called conjugation.

Some green algae, like Volvox, live in groups and can produce special chemicals called sex pheromones. These chemicals help the algae know when to reproduce sexually, especially when their water home is about to dry up.

Physiology

Green algae have been important for scientists studying how cells control water and salt. They help us learn about how membranes let things pass through, how cells keep their shape, and how they handle changes in salt levels. Researchers also study green algae to understand how cells move materials inside them and how they send electrical signals.