NCERT Biology Class 11 – What are Algae and their types?
What are Algae? (Algae meaning)
Generally, algae are referred to as plant-like organisms that are typically photosynthetic and aquatic. They do not have true roots, stems, leaves, vascular tissues, as they possess simple reproductive structures. They are distributed worldwide in the sea, in freshwater and in moist situations on land. Most algae are microscopic, but some are very large, for example, some marine seaweed can exceed 50 m in length.
The algae have chlorophyll and thus, can manufacture their own food through the process of photosynthesis. Algae are classified in the kingdom of Protista, which consists of a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms that have cells with a membrane-bound nucleus.
Algae are eukaryotic organisms, they have a membrane-bound structure called chloroplasts, which has chlorophyll, and this helps in carrying out photosynthesis. The chloroplasts contain DNA. The exact nature of the chloroplasts is different among different types of algae.
Cyanobacteria are algae, which have a prokaryotic cell structure typical to that of bacteria. Cyanobacteria perform photosynthesis directly within the cytoplasm, but not in a specialized organelle.
Algae have photosynthetic pigments that are more complex and varied as compared to plants. They are ecologically beneficial for producing oxygen, together with a major contributing role in producing food for most of the aquatic life forms. Economically, they are used as a crude oil source and also in a number of pharmaceutical industries contributing to the assistance of mankind.
TYPES OF ALGAE
i. They are unicellular organisms that belong to the kingdom Protista.
ii. Most diatoms exist in a singular form, but some join to form colonies.
iii. They are typically yellowish or brownish and are found in fresh- and saltwater, in moist soil, and the moist surface of plants.
iv. They reproduce asexually by cell division. When aquatic diatoms die, they accumulate at the bottom, and the shells do not decay, but they simply collect in the ooze and finally form the material known as diatomaceous earth.
v. Diatoms can occur in a more compact form as a soft, chalky, lightweight rock, called diatomite. This diatomite is used as an insulating material against both heat and sound. It is also used in making dynamite and other explosives etc. Diatoms have deposited most of the earth’s limestone, and much petroleum found inside the earth is of diatomic origin.
i. This division of kingdom Protista consists of the photosynthetic organism usually known as green algae.
ii. The various species of green algae are either unicellular, multi-cellular, coenocytic (having more than one nucleus in a cell), or colonial.
iii. Chlorophyta is aquatic (marine), but few types are terrestrial, occurring on moist soil, on the trunks of trees, on moist rocks and in snowbanks. Various species are highly specialized.
iv. Green algae have chlorophyll a and chlorophyll b and store food as starch in their plastids.
i. This phylum of the kingdom Protista consists of mostly unicellular aquatic algae. Most live in freshwater.
ii. There are some euglenoids that contain chloroplasts with the photosynthetic pigments. While others are heterotrophic and can ingest the food.
iii. Reproduction occurs by longitudinal cell division.
iv. The typical example is Euglena, which is commonly found in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used.
i. It is a large group of flagellate Protists.
ii. Some species in this group are heterotrophic, but most of them are photosynthetic organisms containing chlorophyll. Various other pigments sometimes mask the green colour of these chlorophylls.
iii. Some species are also endosymbionts of marine animals and protozoa and play an important part in the biology of coral reefs.
iv. While some other dinoflagellates are colourless predators on other protozoa, and some forms are parasitic also.
v. Reproduction in most dinoflagellates is asexual, through simple division of cells following the process of mitosis. The dinoflagellates are important plankton and are primary food sources in warmer oceans.
vi. Many forms of dinoflagellates are phosphorescent; they are responsible for the phosphorescence visible at night in tropical seas.
i. These algae are known as golden algae, found mostly in freshwater.
ii. The cell walls of many chrysophytes are composed of cellulose with large quantities of silica.
iii. The photosynthetic pigments present in these are chlorophyll a and c.
iv. Under some circumstances, they reproduce sexually, but the usual form of reproduction is asexual by cell division.
i. This phylum consists of brown algae.
ii. Most of the world’s familiar seaweeds are members of Phaeophyta. There are several brown carotenoid pigments as fucoxanthin (in their cell chloroplasts) present in these organisms which give them brown colour.
iii. Brown algae are mostly marine, growing in the colder oceans of the world, many in the tidal zone, where they have great stress from wave action, while others grow in deep water.
i. The members of this phylum consisting of the photosynthetic organisms commonly known as red algae.
ii. These organisms bear red or purple colour due to the presence of accessory pigments called phycobilin.
iii. They are multicellular and are characterized by too much branching, but without dividing into complex tissues.
iv. Seaweeds belong to this group. Red algae are found in almost all the oceans, but they are most common in warm-temperate and tropical climates, where they may occur at greater depths than any other photosynthetic organisms. Few species are also found in freshwater.
v. Most of the coral forming algae, which secrete calcium carbonate and play a major role in building reefs, belong to this group.
i. This group consists of prokaryotic aquatic bacteria that obtain their energy through photosynthesis.
ii. They are generally referred to as blue-green algae.
iii. Cyanobacteria may be single-celled or colonial. The type of species and environmental conditions determine whether the colonies will form filaments, sheets or hollow balls.
iv. Unlike bacteria, cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and carry out photosynthesis.
v. Hence, cyanobacteria are producers of their own food from simple raw materials. Nitrogen-fixing cyanobacteria need only nitrogen and carbon dioxide to live. They fix nitrogen gas (which cannot be absorbed by plants) into ammonia (NH3), nitrites (NO2) or nitrates (NO3). These compounds are absorbed by plants and converted to protein and nucleic acids.
vi. Cyanobacteria are found everywhere, from oceans to freshwater to bare rock to soil.
Mode of Reproduction in Algae
Algae reproduce by both sexual and asexual ways involving various reproductive strategies. Asexual reproduction occurs through normal cell division or fragmentation, without the union of two cells or without the combination of different genetic material in minor algae species. In the case of higher algae, reproduction occurs through spores. Sexual reproduction also occurs that involves the process of meiosis where genetic material from two different parent cells combines. Different environmental events influence and regulate sexual reproduction.
What are the characteristics of algae?
The special characteristics of algae are the same for both plants and animals. For example, algae can photosynthesize like plants, and they have specialized structures and cell organisms, such as centrioles and flagella, found only in animals. The general characteristics of algae are listed below.
- Algae are photosynthetic organisms
- Algae can be single-celled or multicellular organisms
- Algae do not have a precisely defined body, and therefore do not have structures such as roots, stems or leaves.
- Algae are found where there is sufficient moisture.
- Reproduction in algae occurs in sexual and sexual forms. Spores are caused by fertilization.
- Algae survive independently, although some can establish a spontaneous relationship with other organisms.
What is the importance of Algae? – Economic importance of algae
These eukaryotic marine organisms have no roots, flowers or twigs. It plays an important role in the recovery of alkali used as a soil binding agent. They are economically important in various ways as discussed below:
- Diet: Algae are rich in carbohydrates, fats, proteins, vitamins A, B, C, and E as well as iron, potassium, magnesium, calcium, manganese and zinc. Therefore, people in Ireland, Scotland, Sweden, Norway, North and South America, France, Germany, Japan, and China use it as a food ingredient.
- Fodder: Algae are used as fodder to feed livestock and livestock. It is used as a grain in various countries including northern European countries such as Denmark, Sweden and Norway.
- Fish farming: Algae play an important role in fish farming as it helps in the production process. Fish used plankton and plankton as food. This helps maintain the health of the marine habitat, as algae naturally absorb carbon dioxide and provide oxygen to the water.
- Fertilizers: Algae are rich in minerals and vitamins. Therefore they are used as a liquid fertilizer, which helps to improve the amount of nitrogen contained in the soil.
- Alkaline recovery: Blue-green algae help reduce high levels of alkalinity in the soil.
- Binding factor: Algae act as a binding agent against natural processes such as erosion.
- Biological Indicators: Algae are very sensitive, their pigments can change or die if there is even a slight change in the environment.
Algae are important in the natural habitat because they account for about half of the photosynthesis of terrestrial organisms. They serve as food for aquatic life. Some of them even live in coexistence like lichens. Lichens are an innate link between algae and fungi in terrestrial habitats. The presence of lichens indicates the level of pollution in the environment.
Algae are used in various industries. For example, kelp (brown macroscopic algae) is harvested, dried and processed for commercial production of soap and glass. They are also used as fertilizer. They are also used in the production of agar, which is used as a growth medium in microbiological studies. They are an important source of vitamins (A, B1, B2, B6, niacin, C), iodine, potassium, iron, magnesium, and calcium.
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