[Biology Class Notes] on Green Algae Pdf for EXAM

Introduction

Green Algae are a group of algae belonging to Chlorophyta and capable of photosynthesis. We are mostly familiar with common groups of algae-like pond scum, seaweeds, lake algal blooms, etc. They are abundant and are present around us. There are about 9000 to 12000 species in the group of green algae. They have the pigment chlorophyll and hence they are capable of photosynthesis. These algal life forms are important organisms. They play a vital role in the ecosystem and the emergence of life.

What is Green Algae?

Algae is referred to as a group of organisms capable of photosynthesis. They have some similar traits as to plants but lack most of the plant features like leaves, stem, roots, a vascular system, etc. Algae are mostly unicellular organisms appearing in a variety of shapes and sizes. Naturally, they do not have a definite body structure. Algae are very diverse in nature. They may be microscopic or macroscopic and live in colonies. Or they can even be multicellular organisms. Seaweeds have a leafy appearance. Generally, they vary in size from 0.2 to 2 micrometres. However, some macroscopic algae can be as big as 60 meters in size. And, they are found in both freshwaters as well as saline water. They do not have a natural unit which may indicate they descended from a common ancestor. They may be prokaryotic or eukaryotic, but still, all of them are generally referred to as algae.

 

Cellular Structure

• All green algae have chloroplast with chlorophyll a and b pigments and accessory pigments beta carotene, xanthophylls stacked in the thylakoid.

• Its cell wall consists of cellulose and pectin and it functions to store carbohydrates in the form of starch.

• They have mitochondria with a flat crista. 

• Flagella may or may not be present and are used to move the cell.

• All algae possess a central vacuole.

• Green algae vary in shapes and sizes, for example- single-celled Chlamydomonas, colonial Volvox, Filamentous Spirogyra and Tubular Caulerpa.

• They can reproduce sexually or asexually by cell division, sporulation, and fragmentation.

• Occurrence- Green algae mostly occur in freshwater. They are found attached to submerged rocks or as scum on stagnant water. Some species are also seen in terrestrial or marine habitats. Some aquatic organisms feed on free-floating microscopic species of green algae. 

Examples of Green Algae

Marimo

Marimo is a different and unusual growth form of green algae that grows as round green and puffy balls. The species is normally found in Japan and Northern Europe in freshwater sources. It is a eukaryotic alga with a fluffy green appearance. 

Sea Lettuce

It comprises the genus Ulva. It is a group of edible green algae widely found along the coasts of oceans around the world. Sea lettuce is eaten by several different sea animals, including manatees and the sea slugs. Many species of sea lettuce are also eaten raw by humans as a salad. It’s nutritious and a source of proteins, dietary fibres, and vitamins. 

Ulva Intestinalis

This green alga is also known as gutweed, sea lettuce, and grass kelp. They are tubular and belong to family ulvaceae.

Order: Ulvales

Haematococcus Pluvialis

This is a freshwater species of Chlorophyta belonging to the family Haematococcaceae. This species is known to have the high content of antioxidant astaxanthin and it has its application in aquaculture and cosmetics.

Codium Fragile or Dead man’s fingers

Codium fragile is generally called Dead Man Fingers because it resembles one in appearance, or Green Sea Fingers, Forked Felt-Alga, Felty Fingers, Stag Seaweed, Green Sponge, Sponge Seaweed, Green Fleece, and Oyster Thief. It is a seaweed genus in the Codiaceae family.

Chlorella

Chlorella is a single-celled or unicellular green that is triangular in shape. Its diameter ranges from 2 to 10 μm. They do not possess flagella.

Water Silk

Is a green alga of the genus spirogyra. It is named so because of the spiral arrangement of the chloroplast which is also a characteristic of this genus. There are approximately 400 species of spirogyra found across the world and they live in freshwater habitats. The slimy filamentous green masses on the surface of the water are spirogyra.