After days of rain, you may notice green patches on your terrace or in between the cracks in your store room. These are nothing but algae. Are they plants? – May be, may be not.
So what’s an alga? This is a question that has kept scientists busy for years. There is no one fixed definition for algae. Algae may be classified as plants as they make their own food by photosynthesis. But they do not have distinct features like leaves, stem, root and branches with distinct functions. They can also be called Protists – a term used to refer to organisms that are neither animal, plants, fungi nor bacteria.
Algae consist of a large group of diverse organisms. They may be unicellular or multicellular – microscopic or large. They are found everywhere on the planet. They live in water, land and even on the fur of animals. They are described as polyphyletic, meaning that not all members of the group share a common ancestor. Almost all algae live in or near water, fresh or salty. There are a few types that live in the soil.
Like plants, algae too use up carbon dioxide for photosynthesis and release oxygen, which contributes to 70 per cent of all the air we breathe. They also play an important role in many ecosystems.
Algae can be divided into a number of sub-groups, based on the types of pigments they utilise for photosynthesis.
Green algae are thought to be the ancestor of land plants and they also use the green pigment chlorophyll. Majority of them are aquatic but they are also found on tree trunks and damp walls.
Mostly marine organisms such as seaweed, get their colour from the pigments phycoerythrin and phycocyanin. They have the ability to photosynthesise deep under the ocean.
Brown algae are a diverse group. They include diatoms (the microscopic, single-celled forms) and kelp seaweeds.
Earlier called blue-green algae, cyanobacteria are more like bacteria, but the only difference is that they photosynthesise. It is believed that these algae may have been the first organisms to use photosynthesis.
Relationship with other organisms
The photosynthesising ability of algae is exploited by other organisms such as fungus, coral reefs and sea sponges. While algae help them with food, the host organisms pay back in the form of protection. This is called a symbiotic relationship and the respective algae are called symbiont. The algae that combine with fungi make lichen. The fungus keeps the algae protected from drying, while algae give back to the fungus because it can gather energy from the sun. Lichen is the blue-green smudges you see growing on tree trunks and rocks.
For the past two week, Chile has been experiencing perhaps the worst ‘red tide’, which is nothing but a population explosion of algae. It has turned Southern Chile’s waters toxic and resulted in the mass beaching of whales, sea lions and the death of fish. It has also driven away sea birds.
This algal bloom can occur from time to time on coastlines and freshwater lakes. Reasons for the sudden outburst vary from climatic changes to fertiliser contamination. The overabundance of algae reduces the oxygen content of the water and some species produce toxins that can kill or harm other organisms.
Benefits of Algae
* Algae are major food for fish
* They release oxygen through photosynthesis which is used by aquatic animals
* They consume CO2 and therefore help in mitigating global warming
* Seaweed can be eaten
* Kelp, which can grow 100 feet below water, are used as a fertilizer
* Some species are also used in medicine, cosmetics and paints
* Microalgae can be used to produce biofuelsR. Keerthana