Algae

Algae are photosynthetic organisms that must live in or near a source of water. Unlike land plants, most algae lack an internal system. That means that they don't have tubes to transport water and materials from one part of the plant to another.Most algae are multicellular, however they can be unicellular, therefore, come in a great variety of sizes. The cells of algae have a cell wall.

Chlorophyta- Green Algae

Green algae are found in moist areas on land and in fresh water. Multicellular green algae contain cellulose in their cell walls, and store food in the form of starch, similar to land plants.

Green Algae Spirogyra
This is a picture through a microscope of a preserved specimen.

Ulva 

Ulva is a bright green multicellular marine alga also known as "sea lettuce." Ulva is found along rocky seacoasts. Ulva plants are only two cells thick.

Algae are food for most of oceanic life. They are known as the grasses of the seas. Algae also provides homes and habitats for marine animals. Life would not be the same without algae, because they produce a big part of Earth's free oxygen through photosynthesis. Algae is also used for human food products, all well as laboratory experiments.