Algae – Classification, Life Cycle and Uses of Algae | Biology

Overview of Algae

Algae are a large group of prokaryotic, photosynthetic lifeforms. Since these organisms don’t share a common ancestry, hence, they are not related to each other. Therefore, they are also termed polyphyletic due to this attribute.

Algae can survive in any kind of environment. Being photosynthetic they can harness light energy, and convert this to make their food. Algae can be found in various places ranging from freshwater bodies to moist soils. They are prominent in oceans, mountains, rivers, and ponds.

Characteristics of Algae

Algaes are anatomically similar to land plants, but the difference lies in their structural components. The differences that can be noticed are ems, shoots, and leaves. Furthermore, they also lack nutrient and water circulating tissues i.e. xylem and phloem present in plants.

Here are some important characteristics of algae mentioned below.

1. Cellular Structure

Algaes can exist in both the forms unicellular and multicellular forms. Yet, the algae do not possess any specialized tissues and organs found in higher plants, including roots, leaves, or stems.

• Chlamydomonas are unicellular, simple life forms, that carry out their own all necessary life functions.
• Ulva (Sea lettuce), is an example of multicellular algae. It has a complex structure, with cells organized into simple tissues.

2. Photosynthetic Pigments

Different types of algae have different colored pigments offering specific functions. Algae possess photosynthetic pigments, that are green in color, responsible for converting light energy for photosynthesis.

• Fucoxanthin has brown colored pigment, red algae have phycoerythrin, and blue-green algae (cyanobacteria) have phycocyanin.
• The colored pigments help the algae to absorb light energy at different wavelengths, giving them life support to thrive in different light conditions.

3. Mode of Reproduction

The mode of reproduction for algae is both sexual and asexual. When the mode of reproduction is asexual, there is no fusion of gametes. It reproduces through fragmentation, division, budding, and sporulation. Whereas, in sexual reproduction, there is a fusion of gametes and it occurs through autogamy, hologamy, isogamy, anisogamy, and oogamy.

• Binary fission, a form of asexual reproduction, occurs in Chlamydomonas.
• Fragmentation occurs in Spirogyra, where thallus(body), breaks into fragments. These fragments further grow in new individual plant bodies.
• Algaes also reproduce through sporulation.
• Zoosprores(motile spores) are common in algae like Ulothrix and Chlamydomonas.
• Aplanospores(non-motile spores) are formed by algae in unfavorable conditions.
• Autospores, are non-motile spores found in some unicellular algae. In this, the parent cell divides, internally and forms daughter cells. These cells are called daughter cells, released as parent cells rupture.
• Budding can be also seen in some algae. On the surface of the parent cell, tiny buds develop; these buds eventually separate and become new individuals.

4. Habitat

Algae are known to survive in a range of different habitats. The primary habitats of algae are aquatic environments like – lakes and ponds, where they get the base of their food.

• Common organisms found in these environments are – Diatoms(Bacillariophyta), and Green algae (Chlorophyta).
• Phytoplankton, free-floating organisms, including various algae types, are responsible for oxygen production and nutrient cycling.
• Algaes found in rivers or streams are often found hooked up in rocks or submerged surfaces. Flowing water provides them with nutrients for growth.
• Algae are abundant in wetlands like marshes and swamps. Example – Chara((stoneworts) thrive in such environmental conditions.
• Brown algae such as – Kelps, are common in cold-water coastlines.
• Red algae (Rhodophyta) are found in warmer water bodies at depth, as they can absorb blue light.

Classification of Algae

Algae are classified on different criteria including structural composition, cell wall, physiological traits, and others. The major groups of algae are listed below.

1. Chlorophyta (Green algae)

The algae contain photosynthetic pigment, which is responsible for converting light energy into food. The stored food in them is starch. The cell wall is composed of cellulose. Found in habitats such as freshwater, marine, and terrestrial environments. Examples include –

• Chlamydomonas
• Volvox
• Spirogyra.

2. Phaeophyta (Brown Algae)

They are marine algae, found in cold water bodies. The presence of Fucoxanthin helps them provide a brown color to the algae. They can form large underwater forests due to their heavy growth capacity.

• Examples include kelps, such as Laminaria and Macrocystis.
• Brown algae are commercially used in food processing industries in the form of – alginates.

3. Rhodophyta (Red Algae)

They are mostly marine algae and are found mostly in tropical and sub-tropical environments.

• Red algae contain the pigment phycoerythrin, responsible for absorbing blue light and surviving in deep water.
• Red algae is used widely in food industries. For example – One popular red algae used in sushi is called Porphyra (nori).
• Agar and carrageenan are also used as gelling agents in food industries.

4. Cyanobacteria (Blue-Green Algae)

They are prokaryotic algae, more closely related to bacteria than to other algae. The blue-green algae are responsible for the nitrogen cycle and can fix atmospheric nitrogen.

• Cyanobacteria are commonly found in environments, including freshwater, marine, and terrestrial habitats.
• Example – Anabaena, forms symbiotic relationships with plants like water ferns.

5. Diatoms (Bacillariophyta)

These algae are found in mainly oceans, freshwater, and soils. They are district from other algae as they have silica cell walls with intricate patterns.

• As primary producers and a significant part of phytoplankton, diatoms are essential to aquatic ecosystems.
• Diatoms are helpful in global carbon cycle fixation in the environment.

What is the Lifecycle of Algae?

The life cycle of algae includes growth, reproduction, and death continuously. Let’s have a look at the life cycle of the algae below.

1. Growth – Algae grow by cell division, and this means cells divide into daughter cells. Algae proliferate and form colonies rapidly because they reproduce quickly through cell division.
2. Reproduction – Algae can reproduce both sexually and asexually. Sexual reproduction occurs through the fusion of gametes. The gametes can be similar, or non-similar as well, depending on species. Asexual reproduction involves the division of individual cells into two new cells.
3. Death – The algae no longer functions, when the cells no longer divide its cells. Therefore, reproduction stops and algae is not functional anymore, leading to the death of algae.

The Economic and Ecological Significance of Algae

Algae play an important ecological and economic factor in the environment. They help maintain a balance between the food chains and the ecosystem. Here is a brief of the importance of algae as an economic and ecological point of view.

• Algae such as Cyanobacteria help in nitrogen fixation from the environment.
• They are responsible for oxygen production on earth and contribute to carbon removal.
• Through photosynthesis, algae help in converting organic matter into food, which is consumed by herbivores.
• Algae like Porphyra (nori) and Chlorella are economically important as food, consumed directly.
• Algae have the potential to produce biofuels sustainably.
• They can be used in wastewater treatment by removing the nutrients and contaminants from water.

FAQs on Algae

What is called algae?

Algae are a diverse group of photosynthetic organisms found primarily in aquatic environments. They can vary significantly in size, shape, and color, and they play a crucial role in aquatic ecosystems as primary producers. Algae are not classified as plants, animals, or fungi but belong to a separate category known as protists.

Are algae unicellular?

While some algae are unicellular, existing as single-celled organisms, others are multicellular, forming complex structures such as seaweeds. This diversity allows algae to thrive in various environments, from freshwater to marine ecosystems.

Who eats algae?

Algae serve as a vital food source for many organisms, including herbivorous fish, zooplankton, and even some terrestrial animals. They form the base of the food web in aquatic ecosystems, supporting a wide range of marine life.

What is the 2nd name of algae?

The term phytoplankton is often used to refer to microscopic algae that drift in ocean currents, highlighting their role in the aquatic food chain. However, there is no widely accepted second name for algae as a whole; they are generally referred to simply as algae.

Are algae fungi?

Algae are not fungi; they are distinct organisms that perform photosynthesis, unlike fungi, which are heterotrophic and obtain nutrients by decomposing organic material.

Is algae a decomposer?

While algae can contribute to decomposition by breaking down organic matter in aquatic environments, they are primarily known as producers, converting sunlight into energy through photosynthesis and releasing oxygen as a byproduct.

Is algae a producer?

Yes, algae are producers. The process of photosynthesis performed by algae is essential for sustaining life in aquatic ecosystems and contributes significantly to the overall health of our planet.