Chrysophytes are unicellular algae that live in fresh water and contain chlorophyll a and chlorophyll c, which are photosynthetic pigments used to transform sunlight into energy. These are also known as golden algae because they have golden silica scales. There are 500 known species of chrysophytes. Some chrys-ophytes are amoeboid that attack bacteria by engulfing and destroying it.
Diatoms are unicellular algae that have a hard, double outer shell made of silica. Nutrients pass through pores in the shell, then through the diatom's plasma membrane contained within the shell. There are 5,600 known species of diatoms, most of which are phototrophic and contain chlorophyll a and chlorophyll c pigments. They also contain carotenoids, which are yellow and orange pigments. Some diatoms are heterotrophs and break down and use organic matter as nutrients. Diatoms accumulate at the bottom of the sea and are commercially mined for both their value as an abrasive and their filtering and insulating capabilities (used in the filters in pools).
Dinoflagellates are unicellular algae that have the capability of self-movement through the use of tail-like projections called flagella. The flagella are located between grooves in the cellulose plates that cover the dinoflagellate's body. These flagella pulsate in both an encircling motion around the body and in a perpendicular motion, causing the dinoflagellates to rotate like a top. There are about 1,200 known species of dinoflagellates that inhabit both fresh water and seawater.
Dinoflagellates live in seawater. Some are heterotrophs and break down organic matter for nutrients. Some seawater dinoflagellates are luminous, giving a twinkle to the sea at night. Freshwater dinoflagellates are phototrophic: They synthesize nutrients from sunlight using photosynthesis.
Many dinoflagellates have chlorophyll a and c pigments as well as the yellow and orange pigments, carotenoids. Depending on their photosynthetic pigment, dinoflagellates can appear yellow-green, green, brown, blue, or red. When dinoflagellates undergo a population explosion, the sea changes color from an ocean blue to a sea of red or brown.
Some dinoflagellates, such as Gonyaulax (plankton), can be fatal to humans because they produce neurotoxins. These dinoflagellates are eaten by fish and are absorbed by oysters, clams, and other shellfish (mollusks). The neurotoxins build up in their tissues, making the seafood poisonous to humans. These dinoflagellates also cause "red tides" that have a devastating effect on the fish population.
Red algae, also known as Rhodophyta, are algae that form colonies in warm ocean currents and in tropical seas. They contribute to the formation of coral reefs that can be found as deep as 268 meters below the surface of the ocean. Their stone-like appearance is caused by a build-up of calcium carbonate deposits on their cell walls.
There are 4,000 known species of red algae, of which fewer than 100 are found in fresh water. Red algae get their color from the phycobilins and chlorophyll a pigments contained in their cells. Phycobilins pigment absorbs green, violet, and blue light, which are light waves that are capable of penetrating the deepest waters. It is for this reason that red algae can survive at great depths. The pigment that makes the algae red is called phycoerythrin.
As you learned in Chapter 6, red algae are used to make agar. Agar is the culture medium that is extracted from the cell wall of red algae and is used to grow bacteria. Red algae are also used as a moisture-preserving agent in cosmetics and baked goods. Red algae are used as a setting agent for jellies and desserts.
Brown algae, also known as phaeophyta, are multicellular organisms. Some brown algae are commonly called kelp; they live in the northern rocky shores of North America and can grow up to 30 meters. There are 1,500 known species of brown algae.
Brown algae have chlorophyll a and b photosynthetic pigments. They also have carotenoids. Brown algae can appear dark brown, olive-green, and even golden depending on the type of pigments in their cells. The pigment that makes the algae brown is called fucoxanthin. Algin is a gummy substance found in the cell walls of some species of brown algae and is used as a thickening, emulsify-
ing, and suspension agent for ice cream, pudding, frozen foods, toothpaste, floor polish, cough syrup, and even jelly beans.
The organic matter that kelp produces supports the life of invertebrates, marine mammals, and fish.
Green algae can live in moist places on land, such as tree trunks and in the soil, as well as in water. There are 7,000 species of green algae that are diverse in size, morphology, lifestyle, and habits. Scientists believe that some members of the species are linked structurally and biochemically to the Plant kingdom. Two common green algae are:
1. Spirogyra: Spirogyra are freshwater algae that have tiny filaments, each containing spiraling bands of chloroplasts.
2. Volvox: Volvox are colonial multicellular green algae that have flagella and live in marine, brackish, and freshwater environments.
Was this article helpful?