6.2: Protist Nutrition

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What can photosynthesize AND hunt for food?

No, there are no man-eating plants or leaf-growing animals. The idea of an organism both photosynthesizing and hunting for food might seem strange, but this isn't science fiction. These organisms, examples of Euglena, are protists that can feed like an animal or use the energy of the sun to make food like a plant.

Protists Nutrition

The cells of protists need to perform all of the functions that other cells do, such as grow and reproduce, maintain homeostasis, and obtain energy. They also need to obtain "food" to provide the energy to perform these functions.

Recall that protists can be plant-like, fungi-like, or animal-like. That means that protists can obtain food like plants, fungi, or animals do. There are many plant-like protists, such as algae, that get their energy from sunlight through photosynthesis. Some of the fungus-like protists, such as the slime molds (Figure below), decompose decaying matter. The animal-like protists must "eat" or ingest food.

Some animal-like protists use their "tails" to eat. These protists are called filter-feeders. They acquire nutrients by constantly whipping their tails, called flagellum, back and forth. The whipping of the flagellum creates a current that brings food into the protist.

Other animal-like protists must "swallow" their food through a process called endocytosis. Endocytosis happens when a cell takes in substances through its membrane. The process is described below:

The protist wraps around its prey, which is usually bacteria.
It creates a food vacuole, a sort of "food storage compartment," around the bacteria.
The protist produces toxins which paralyze its prey.
Once digested, the food material moves through the vacuole and into the cytoplasm of the protist.

Also, some of the animal-like and fungi-like protists are parasitic, harming their hosts as they obtain nutrients. Fungi-like protists absorb nutrients meant for their host, harming the host in the process.

Summary

Some protists are plant-like and photosynthesize.
Some protists absorb nutrients from decaying matter like a fungus.
Some protists hunt their food or act as parasites.

Review

How do algae obtain food?
How do animal-like protists "swallow" their prey?
What is a filter-feeder?
How do slime molds get their energy?