Algae, the Plant-like Protist

Contributor: Felicia Sabur. Lesson ID: 12012

Would you protest if you found algae in your swimming pool, fish tank, or bird bath? It's just innocent protist, trying to photosynthesize and divide! Learn more about this common, colorful organism!


Life Science

learning style
personality style
Grade Level
High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


When you think of algae, do you think of polluted pools and fouled fishbowls? Or do you think of graceful aquatic scenery? What gives plant-like protist known as algae their color?

In the previous three Related Lessons in our Kingdom Protista series, found in the right-hand sidebar, you learned about protozoans, the animal protist that are unicellular heterotrophs.

In this and the final Related Lesson, you will dive into the world of algae, the plant-like protist. Here is some useful vocabulary you need to know for these lessons:

  • Algae are photosynthesizing protists. They can contain up to four different types of chlorophyll, along with other photosynthetic pigments. The pigments in algae can create a variety of colors in algae, including purple, green, dark red, yellow, and brown. These colors are used to classify the algae into groups. Algae can be unicellular or multicellular organisms.
  • Chlorophyll is a greenish pigment that exists in all green plants and in cyanobacteria. It is responsible for the absorption of light in order to provide energy for photosynthesis.
  • Photosynthesis is a process used by plants and some other organisms, by which sunlight is used to make nutrients from carbon dioxide and water. The process of photosynthesis also generates oxygen as a by-product, so the more trees you have in your area, the cleaner the air!


This is a picture of a species of red algae in the sea. What other colors of algae have you seen in the ocean or a pond near your home?

Life cycles

The life cycle of all plants and some algae has a pattern that is called alternation of generations. This means that the organism alternates between haploid and diploid generation, which is explained in the video clip from On Alternation of Generations by Maximus Thaler:


As the video explained, the haploid form of the organism is known as a gametophyte, because it produces gametes, the male or female reproductive cells that contain half of the genetic material of the organism. A male and female gamete fuse to form a zygote, from which a diploid organism called a sporophyte grows and develops.

The sporophyte is what you would normally think of when you see the algae floating on the water. The red algae in the picture above is in the sporophyte stage. Certain cells in this stage undergo meiosis (cell divisions) and eventually become haploid spores that can develop into gametophytes.

If you would like to watch a time-lapse video of algae dividing, check out the Time-lapse Video - Cell Divison of Micrasterias Algae (1) from Microscopic World (below):


Read more about the Alteration of Generations at biology dictionary.

Algae are photosynthesizing protists that contain chlorophyll, along with other photosynthetic pigments. Algae can be unicellular or multicellular organisms, and they are classified into six phyla. The life cycle of algae has a pattern called "alternation of generations" that allows them to alternate between haploid and diploid generation.

In the Got It? section, you will be drawing an example of the algae lifecycle.

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