Algae :Algae The plant-like protists are called algae. Most are single-celled, but a few form large multicellular seaweed. The plant-like protists have chloroplasts. Some, like the Euglena, also have flagella for movement. Some, such as the diatoms, have calcium carbonate (chalk) or silica shells. When they die they form a layer on the bottom of an ocean or lake called diatomaceous earth.


Algae Blooms :Algae Blooms Algae blooms are the sudden growth of a large population of single celled algae. They occur near the coastlines, with the algae feed on fertilizer runoff and sewage. Algae blooms deplete the oxygen in the water, killing fish and other organisms. Some of the algae also secrete toxins. Red tide and Pfiesteria are examples of this.


Green Algae :Green Algae The green algae are the ancestors of plants. The term “plant” implies living on the land or derived from plants living on the land. Green algae and plants have very similar chloroplasts. Green algae have some unicellular species (such as Chlamydomonas), some simple colonies (such as Volvox), and some relatively complex multicellular organisms (such as Acetabularia). Green algae are haploid most of their live cycle, with only a very short diploid phase.


Multicellular Algae :Multicellular Algae The multicellular algae are commonly called seaweed. They can be classified into red, brown, and green algae. All have chloroplasts, but the pigments in the chloroplasts vary, giving the different colors. Some, like kelp, are very large and contain several different types of cells and tissues to do specialized work. These include leaves for photosynthesis, gas-filled bladders for buoyancy, the root-like holdfast, and tubes to transport nutrients throughout the body. Algae contain the polysaccharide “agar”, which is tasteless and is used to thicken foods such as soft ice cream.


Fungus-like Protists :Fungus-like Protists Water molds and slime molds Like fungi, they are heterotrophs: they get food and energy from other organisms. Many are decomposers of dead organisms. Unlike fungi, the fungus-like protists produce motile (moving) cells during part of their life cycle. Also, these protists surround and engulf bacteria as food. Slime molds live as separate cells most of their lives, feeding on bacteria. When conditions get harsh, they aggregate into a multicellular slug, which migrates to a new location. The slug then forms a fruiting body that generates spores. The spores from the fruiting body are very hardy.


More Fungus-like Protists :More Fungus-like Protists The water molds include some of the worst plant diseases. Phytophthora infestans causes rot in plants. In the 1840’s, Phytophthora caused the potato blight in Ireland. The Irish were poor and overcrowded, and lived mostly on potatoes. The blight caused crop failures in several years, resulting in the deaths of the population. Many Irish came to the US at that time.


Slime Molds :Slime Molds Slime molds can be rather large and colorful.