Hint: The green colour generally denotes the plants or the parts of the plants. These parts of the plants performed the various functions such as photosynthesis, respiration etc. The green colour of plants is generally due to the presence of chlorophyll.
The algae are the photosynthetic organisms which contain chlorophyll to perform photosynthesis. They are generally green in colour due to the presence of chlorophyll and they do not possess any organs. The chlorophyll is a lipid-soluble pigment. They are simple, thalloid, autotrophic and largely aquatic organisms. They take place in the variety of other habitats such as moist stones, soils and wood. The form and size of algae are highly variable and ranges from the colonial form to the filamentous form. A few of the marine form of algae such as kelps which form the massive plant bodies.
The Chlorophyceae is the algae which are generally known as green algae. These algae are grass green due to the presence of the pigments chlorophyll a and chlorophyll b. These pigments are located in particular chloroplasts. The green algae generally have a rigid cell wall which is made up of an inner layer of cellulose and the outer layer of pectose.
Note: There are some algae which take place in the association with fungi and animals. The algae constitute polyphyletic groups and it shows a wide range of reproductive process from the simple asexual cell division to the most complex form of sexual reproduction.