Understanding the Cellular Structure and Role of Green Algae
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?
[Image will be uploaded Soon]
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
[Image will be uploaded Soon]
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.
Class: Ulvophyceae
Phylum: Chlorophyta
Scientific name: Aegagropila linnaei
Family: Pithophoraceae
Sea Lettuce
[Image will be uploaded Soon]
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.
Scientific name: Ulva Lactuca
Phylum: Chlorophyta
Class: Ulvophyceae
Order: Ulvales
Family: Ulvaceae
Rank: Species
Ulva Intestinalis
[Image will be uploaded Soon]
This green alga is also known as gutweed, sea lettuce, and grass kelp. They are tubular and belong to family ulvaceae.
Scientific name: Ulva intestinalis
Rank: Species
Higher classification: Sea lettuce
Phylum: Chlorophyta
Family: Ulvaceae
Order: Ulvales
Haematococcus Pluvialis
[Image will be uploaded Soon]
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.
Scientific name: Haematococcus pluvialis
Phylum: Chlorophyta
Higher classification: Haematococcus
Order: Chlamydomonadales
Rank: Species
Family: Haematococcaceae
Codium Fragile or Dead man’s fingers
[Image will be uploaded Soon]
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.
Phylum: Chlorophyta
Scientific name: Codium fragile
Rank: Species
Higher classification: Codium
Class: Ulvophyceae
Order: Bryopsidales
Chlorella
[Image will be uploaded Soon]
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.
Rank: Genus
Class: Trebouxiophyceae
Phylum: Chlorophyta
Order: Chlorellales
Higher classification: Chlorellaceae
Water Silk
[Image will be uploaded Soon]
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.
Kingdom: Plantae
Class: Zygnematophyceae
Scientific name: Spirogyra
Division: Charophyta
Order: Zygnematales
FAQs on Green Algae: Comprehensive Guide for Students
1. What are green algae?
Green algae, belonging to the class Chlorophyceae, are a large group of simple, plant-like aquatic organisms. They are known for their characteristic grass-green colour due to the dominance of pigments chlorophyll a and b within their chloroplasts. Their plant body, or thallus, can be unicellular (like Chlamydomonas), colonial (like Volvox), or filamentous (like Spirogyra).
2. What are the key characteristics of Green Algae?
The main characteristics of green algae (Chlorophyceae) are:
Pigments: They possess chlorophyll a and b, as well as carotenoids and xanthophylls, housed in distinct chloroplasts.
Stored Food: They store food primarily as starch. Many also have one or more storage bodies called pyrenoids located in the chloroplasts, which contain protein besides starch.
Cell Wall: They have a rigid cell wall, with an inner layer of cellulose and an outer layer of pectose.
Habitat: Most are freshwater organisms, but they are also found in marine environments, on moist soil, tree trunks, and rocks.
3. What are some common examples of green algae as per the NCERT syllabus?
Common examples of green algae studied in the CBSE/NCERT curriculum include unicellular, colonial, and filamentous forms. Five key examples are:
Chlamydomonas (unicellular, motile)
Volvox (colonial, motile)
Ulothrix (filamentous, unbranched)
Spirogyra (filamentous, unbranched, known for spiral chloroplasts)
Chara (a more complex, branched form)
4. Why are green algae considered the ancestors of modern land plants?
Green algae are widely believed to be the evolutionary ancestors of higher land plants (like mosses, ferns, and flowering plants) due to several striking similarities. These shared characteristics suggest a common origin:
Both have the same photosynthetic pigments: chlorophyll a and chlorophyll b.
Both store their reserve food material in the form of starch.
The cell walls of both are primarily composed of cellulose.
5. How does reproduction occur in green algae?
Reproduction in green algae shows significant variation and can occur through three different methods:
Vegetative Reproduction: This typically happens through fragmentation, where the parent thallus breaks into smaller pieces, each growing into a new individual.
Asexual Reproduction: This commonly occurs by the formation of flagellated zoospores produced within zoosporangia.
Sexual Reproduction: This involves the fusion of gametes and can be isogamous (fusion of similar-sized gametes), anisogamous (fusion of dissimilar-sized gametes), or oogamous (fusion of a large, non-motile female gamete with a smaller, motile male gamete).
6. What is the importance or use of green algae?
Green algae are ecologically and economically important in several ways:
Primary Producers: They are major producers of oxygen through photosynthesis, forming the base of most aquatic food chains.
Food Source: Species like Chlorella are rich in protein and are used as food supplements.
Biofuel Research: Due to their high lipid content and rapid growth, they are being researched as a potential source for producing biofuels.
Sewage Treatment: They are used in oxidation ponds to help decompose sewage by providing oxygen for aerobic bacteria.
7. Can green algae be harmful to the environment?
While most green algae are beneficial, they can become harmful under certain conditions. When nutrient pollution (from fertilizers, for example) enters a water body, it can trigger a rapid, excessive growth of algae, an event known as an algal bloom. While toxic blooms are more often caused by cyanobacteria (blue-green algae), dense green algae blooms can also damage the ecosystem by blocking sunlight to submerged plants and, upon their death and decomposition, consuming large amounts of dissolved oxygen, leading to hypoxia which can kill fish and other aquatic animals.
8. How does the body structure of green algae relate to its function and habitat?
The diversity in the body structure of green algae is an adaptation to different aquatic lifestyles. For instance, the motile, unicellular form of Chlamydomonas allows it to move freely in the water column as plankton. The Volvox colony represents a simple form of multicellular organisation, allowing for coordinated movement. Filamentous forms like Spirogyra and Ulothrix are well-suited to attach to substrates in ponds and slow-moving streams, maximising their exposure to sunlight for photosynthesis.
