Algae are eukaryotic organisms that have no roots, stems, or leaves but do have chlorophyll and other pigments for carrying out photosynthesis. Algae can be multicellular or unicellular. Unicellular algae occur most frequently in water, especially in plankton.

The typical green algal cell, which can be motile or nonmotile, has a central vacuole, pigments contained in plastids that vary in shape in different species, and a two-layered cellulose and pectin cell wall. Food is stored as starch in pyrenoids (proteinaceous cores within the plastids).

• Algae are unicellular, filamentous, or multicellular (thallic).
• Most algae live in aquatic environments.
• Algae are eukaryotic; most are photoautotrophs.
• The thallus of multicellular algae usually consists of a stipe, a holdfast, and blades.
• Algae reproduce asexually by cell division and fragmentation.

Green algae are food for sea animals and humans. Green algae are used in cancer treatment. They could help reduce carbon dioxide in the atmosphere.

All algae are eukaryotic organisms. All algae, therefore, have a nucleus enclosed within a membrane and chloroplasts bound in one or more membranes.

Characteristics of Algae

• Algae are photosynthetic organisms.
• Algae can be either unicellular or multicellular organisms.
• Algae lack a well-defined body, so, structures like roots, stems or leaves are absent.
• Algaes are found where there is adequate moisture.
• Reproduction in algae occurs in both asexual and sexual forms.

Euglena is a large genus of unicellular protists: they have both plant and animal characteristics. All live in water, and move by means of a flagellum. This is an animal characteristic. Most have chloroplasts, which are characteristic of algae and plants.

Euglena cannot be mechanically or physically controlled, except by replacing the pond water. Exchange of water from a well or other source that does not have an algae bloom will dilute the algae in the pond.

Euglenas are typically green in appearance due to the presence of chloroplasts, but some species appear red in color because they contain a large amount of carotenoids, the same pigment that gives reddish color to ripe tomatoes and autumn leaves.

They can survive in both fresh and salt water. Euglena lies inactive and forms a protective wall around itself when in low moisture conditions, it does this until the environmental conditions change. Euglena can be a friend and a foe. Euglena is good but also bad for the environment.

A negative phototaxis is one in which the organism moves away from the light source as demonstrated by certain insects such as cockroaches.

Phototaxis can be advantageous for phototrophic bacteria as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite.

Phototaxis is the ability of organisms to move directionally in response to a light source. Many cyanobacteria exhibit phototaxis, both towards and away from a light source. In the environment, the ability to move into optimal light conditions for photosynthesis is likely to be an advantage.