Courses for Kids
Free study material
Offline Centres
Store Icon


share icon
share icon

What is Algae?

Algae is a group of organisms that are predominantly aquatic, nucleus-bearing, and photosynthetic. Unlike plants, algae do not have stems, leaves, roots, or reproductive structures like plants. Algae consist of cells that are not found among any plants or animals. even the photosynthesis pigments are a lot different than that of plants.

The smallest Algae picoplankton can range in size anywhere between 0.2 to 2 micrometers and at the same time, the giant kelp can be as big as 60 meters.  

Algae cells can possess one single nucleus or even multiple nuclei. Algaes are eukaryotic organisms with three varied types of double membrane-bound organelles. It has a nucleus, mitochondria, and chloroplast.

There are few species of Algae that produce toxins and are harmful to fish, finfish, and shellfish, and hence these fishes are harmful if consumed. The dinoflagellates that release toxins in water are harmful to aquatic life and are also responsible for red tides. The toxins released in the air by dinoflagellates can also cause health issues for any organisms that breathe air. 

Algae play quite a few important roles in Earth’s atmosphere. Algae is responsible for producing about half the oxygen and storing carbon dioxide to ensure it is out of the Earth’s atmosphere. 

Algae - Classification, Life Cycle and Uses

The word algae address a large diversity of eukaryotic organisms ranging from unicellular microalgae to multicellular organisms such as giant kelp. In general, algae are plant-like organisms that are subdivided into two parts: photosynthetic and aquatic. Although it is a plant-like organism, it still does not have true roots, stems, leaves, and vascular tissue but possesses simple reproductive structures. Algae or their spores can be found in a variety of environments such as freshwater, marine water, air, soil, or other organisms. The majority of the variety of algae found are microscopic, yet some variety is found to be very large, such as marine seaweeds which can grow up to 50m in length. They are subdivided into two parts: Microalgae and the other is Macroalgae.

  1. Microalgae: It is the unicellular form of algae.

  2. Macroalgae: It is the multicellular form of algae.

Microalgae are photosynthetic, heterotrophic organisms that have an extraordinary potential for cultivation as energy crops. Algae has its nature that it can grow or can be cultivated under any difficult climatic conditions. Algae produce various commercial by-products such as fats, oils, sugars, and other useful bioactive compounds. The term also includes some members of the red, brown, and green algae. They are photosynthetic in nature and "simple" because they don’t possess the bunch of complicated organs as found in land plants. Hence they are excluded from being considered as plants.  

The algae possess chlorophyll in their structure which is responsible for the manufacturing of their own food by the photosynthesis process within the membrane-bound structure called the chloroplasts. Almost all the algae are eukaryotes except the Cyanobacteria (which is a bacterial organism traditionally included as algae), which possess a prokaryotic cell structure. Algae are extremely important species. They produce the highest amount of oxygen as compared to all the living land plants in the world as well as being an important food source for many animals such as little shrimps and huge whales. Thus, they are at the bottom of the food chain because many living organisms are dependent on them.

Recent research has proved that the algae can be used for producing Biodiesel, which possesses certain advantages like biofuel of algae, is non-toxic, contains no sulfur, and is highly biodegradable. Moreover, they are high-yielding as compared to other energy crops. The estimates suggest that microalgae are capable of producing up to 15,000 gallons of oil per hectare a year. This oil can be converted into fuels and chemicals and more. They can provide much higher yields of biomass and fuel, 10-100 times higher than comparable any energy crops. Also, they have the potential to grow under any conditions which may be unsuitable for conventional crop production. Micro-algae have the capacity to reduce atmospheric CO2 levels, thus fixing the increasing percentage of CO2 in the atmosphere, responsible for the global pollution problem.

Classification of Algae

Taxonomic classification of algae is based upon the same rules that are used for the classification of land plants. Microscopic research has shown differences in the features of algae which contributes to another method of their classification. Various features that differentiate various types of algae are: organelle structure, flagellar apparatus, and cell division process. Division-level classification (kingdom-level classification) is negligible for algae. Some scientists place classes like Xanthophyceae, Bacillariophyceae, in division Chromophyta, whereas some scientists place each class in the division: xanthophyll, Bacillariophyceae.

In general and widely accepted terms, the classification of algae is done based on the following six types:

  1. Nuclear Organization – prokaryotic or eukaryotic

  2. Nature of Cell Wall – cellulosic or non-cellulosic (protein, acid, polysaccharide)

  3. Pigmentation and Photosynthetic Apparatus – 3 pigments (chlorophylls, carotenoids, and lipoproteins)

  4. Nature of Reserve Food – Starch, oil, mannitol, leucosis, etc. is the various types of reserve food in various classes.

  5. Flagellation – Type, number, and position of flagella determine the class.

  6. Type of Life Cycle – complete absence or presence and the complexity of cycle.

Properties of Algae

Different algae have different requirements. Hence, several essential factors such as water, carbon dioxide, minerals, and light play important roles in the cultivation of algae. 

  • Size and Structure

For single-celled algae, the thallus is the body of the vegetative form of algae and for multi-celled algae; the thallus consists of the entire, continuous organism. The thallus is an example of complex algae, which appears to be a macroscopic, and multicellular organism but is one giant, unicellular structure only. The aquatic habitat is a relatively benign and uniform place, which helped the organisms to get into shape. Because water supports the algal plant body, they easily flow with the water currents and waves. Since water surrounds the plant on all sides, individual algal cells absorb moisture (water), minerals, and sunlight directly from the surrounding. Mostly they are photosynthetic in nature, possess four different kinds of chlorophyll pigments (include blue, red, brown, golden) may be microscopic and float in the surface waters (phytoplankton) or macroscopic and live attached to rocky coasts (seaweeds). Size ranges from the size of bacteria (0.5 µm) to over 50 m long. 

  • Temperature 

The temperature of the water must be in a range that will support the growth of specific algal species. Temperature plays a major role in the growth of any algal species. The optimal temperature for phytoplankton cultures is between 20-30 oC. If the temperature is <16 oC it slows down the growth and a temperature >35 oC is lethal for a number of species.

  • Light

A light that is very strong or very low hinders the algae growth. In most algal-cultivation systems, light only penetrates the top 3 - 4 inches of the water. As the algae grow and multiply vigorously and become dense, they block light penetration into ponds, tanks, etc. the light required by algae is only 1/10th of sunlight received by other plants. Direct and strong sunlight is harmful and destroys the growth of algae.

Where do Algae Grow?

The habitat of algae can be anywhere and everywhere. Algae are the most robust organism in terms of habitat, as they can grow in a wide range of conditions. Algae can be found in both environments: terrestrial and aquatic. Moreover, it’s more common to find algae in moist regions than dry ones, as algae do not have vascular tissues and other adaptations for living on land. Yet algae can be found in any and every part of the world. The examples include snails, turtles, worms, rotifers, worms, alligators, three-toed sloths, aquatic ferns, freshwater sponge, aquatic plants, on and inside water plants.

The Chemical Composition of Algae

Algae are Composed of Two Types of Cells: eukaryotic or prokaryotic cells. These are cells with nuclei and organelles. The functional systems of algae are plastids, which are bodies with chlorophyll and carry out photosynthesis. Some have only Chlorophyll A, some A, and B, A and C, etc. the primary composition of algae is made up of proteins, carbohydrates, fats, nucleic acids, in varying proportions. All types of algae found completely comprise of the following, in varying proportions: Proteins, Carbohydrates, Fats and Nucleic Acids. While the percentages vary with the type of algae, types of algae are there, some of them comprising up to 40% of their overall mass by fatty acids. This fatty acid from the algae can be extracted and converted into biodiesel. Algal oil is very high in unsaturated fatty (UFA) acids which include Arachidonic acid (AA), Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA), Gamma-linolenic acid (GLA), Linoleic acid (LA), etc.

Lifecycle of Algae

Four main patterns of lifecycle in the algae are:

1. Hypotonic Life Cycle –The plant body is a gametophyte. The gametophytic plant produces haploid gametes. The gametes fuse to form a zygote, which is diploid. Thus, diploid represents the sporophytic phase (diploid phase) of their lifecycle. This lifecycle is also known as the monogenic lifecycle and is found to be active in a majority of classes.

2. Diplontic Life Cycle – The plant body is a sporophyte. The sex organs produce gamete by meiosis, and they represent the gametophytic stage. The gametes soon unite and fertilize to form a zygote. The zygote does not undergo any meiosis. The zygote is only responsible for giving rise to new sporophytic plant bodies.

3. Diplohaplontic Life Cycle – In this type, both the diploid and haploid phases are equally present and prominent, expressed by two distinct vegetative individuals. There is a difference in both only in terms of chromosome numbers and functions. The diploid (sporophytic stage) reproduces by the asexual process, while the haploid (gametophytic stage) reproduces by the sexual method. This kind of life cycle has two types: isomorphic (homologous) and heteromorphic (heterologous).

4. Triphasic Life Cycle – In this type, there is a succession of three distinct generations. This type of lifecycle has two types: Haplobiontic and diplobiotonic type.

Use of Algae

Algae are used in various fields such as in the food industry as a food supplement, in waste-water purification as a bio-filter, in laboratory research systems, in space biotechnology, etc. Algae are commercially cultivated for pharmaceuticals, nutraceuticals, cosmetics, and aquaculture purposes. It is also used as a fuel source, stabilizing agent, and fertilizer.

Ecological and Commercial Importance of Algae

Algae use photosynthesis to create organic food molecules from carbon dioxide and water by capturing energy from sunlight. Plants are absent in the oceans so nearly all aquatic life depends upon Algae like land plants as they are at the bottom of the food chain. Aquatic animals like sea stars, whales, fishes, prawns, turtles, seals, octopuses, clams, worms, and lobsters are dependent on Algae. As a byproduct of photosynthesis, algae create oxygen in addition to organic molecules. Algae are thought to create between 30 and 50 percent of the net global oxygen accessible for human and other terrestrial animal respiration.

Crude oil and natural gas are the remains of ancient algae's photosynthetic products, which were then transformed by bacteria. The North Sea oil deposits are thought to have developed from coccolithophore algae (family Prymnesiophyceae), while the Colorado oil shales are thought to have formed from an alga similar to Botryococcus. Botryococcus now generates blooms in Lake Baikal, releasing so much oil onto the lake's surface that it can be collected with a specific skimming apparatus and used as a fuel source. Several firms have extracted oil from oil-producing algae grown in high-salinity ponds as a potential replacement for fossil fuels.

Want to read offline? download full PDF here
Download full PDF
Is this page helpful?

FAQs on Algae

1. Does Algae need water to survive? 

Algae is a marine or aquatic organism and hence it needs water to survive. Though Algae spores can survive without water. Algae also need sunlight as the cells have chlorophyll that helps algae to photosynthesize by using sunlight in converting carbon dioxide into cell material. We can find Algae laying dormant on various items that interact with water, especially swimwear, pool accessories, vacuum hoses, leaf nets or even wall brushes. Hence Algae needs water to survive but it can survive without water in a dormant state.

2. What does Algae eat? 

Algae do not survive on organic materials. It feeds on the waste of the aquatic animals as well as the waste materials from the decomposing materials. Algae are found in lakes, oceans, etc where the sun rays can penetrate through the water usually at the depth of the photic layer.  The survival and growth of Algae majorly depend upon the process of photosynthesis. Here, the bacteria-forming organisms produce energy using the sun rays. 

3. Why are Algae green? 

Chlorophyll does not have only one molecule. There are various forms of chlorophyll that absorb the wavelength differently so that the process of photosynthesis is efficient enough for the plants or Algae. There is a green wavelength found in sunlight. While Algae and other plants absorb the sunlight from the sun they absorb all colors but due to the green wavelength present chlorophyll makes the plants and algae look green. Hence, Algae is green.

4. What eats Algae in a food chain?

Algae are found mostly at the depth of the ocean and most of the aquatic animals depend upon Algae for food. There are certain species in the ocean that survive only by consuming Algae. The different types of Algae consumed by aquatic animals are microalgae, green film algae, diatoms, brown film algae, detritus, hair algae and red slime algae. The various aquatic species that survive on Algae are fishes, sea urchins, crabs, snails, etc.

5. Is Algae a Bacteria or Plant? 

Algae is called a eukaryotic organism that has a nucleus (single or multiple nuclei) and it also photosynthesizes like plants but it lacks the reproductive structure like stems, roots, leaves, etc. Algae and Bacteria are both microorganisms and they both photosynthesize as well. They are both crucial elements in the food chain. While Algae Fuels the ecosystem by being part of the aquatic food chain,  bacteria break down dead matter and make it part of the soil. 

Competitive Exams after 12th Science