CBSE Class 12 Board Exams Questions and Answers

CBSE Class 12 Board Exams Algae Questions and Answers

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Products made from algae are the natural solutions to the energy, foods, economic, and climate challenges facing our whole world today.  Algae have the power to simultaneously put fuels in our vehicles and recycle CO2, provide nutrition for animals and people and create jobs for millions of Indian Algae? Naturally.

What is Algae

These are chlorophyll bearing, thalloid and simple thallophytes are placed in algae chlorophyll photosynthetic pigment) bearing thalloid plants. They synthesize their own food. Hence, algae are autotrophic (fungi lack chlorophyll and are heterotrophic). Besides, algae exhibit all the characteristics of thallophyta. They differ from bryophyta in many vegetative and reproductive features, such as absence of jacketed sex organs and formation of embryo.

What are Algae

The study of algae is known as algology or phycology (Phykos = alga). The most notable amongst the Indian algologists was Professor M.O.P lyengar from Madras whose valuable contributions to Indian algology earned him the honour of being called Father of Modern Indian Algology.

What is Habitat

Algae are mostly aquatic but are also found in other habitats. Some of the examples are given below.

Some other interesting habitats are listed below.

  1. Planktons. These are passively floating masses of plants (phytoplanktons) and animals (zooplanktons). Phytoplanktons consist mostly of diatoms.
  2. Red sea. It is a part of the mediterranean sea, where a blue green alga, Trichodesmium to grows on surface and imparts red colour.
  3. Red snow. Chlamydomonas nivalis and Haematococcus (green algac) inhabit ice or snow and develop red colour, hence the name red snow.
  4. Sargasso sea. It is a part of Atlantic Ocean, west of Africa, where broken fragments of Sargassum (brown alga) float on the surface.
  5. Water blooms. Blue green algae viz., Microcystis, Anabaena, Nostoc, etc., grow in abundance due to addition of nutrients to alter reservoirs. As a result, the water surfa is cove with bubbling masses of algae called water blooms.
  6. Red tide. Gonyaulax (red dinoflagellate undergo rapid multiplication and they make the sea appear red. Hence, it causes, what is popular known as red tide. Another dinoflagellate Karenia brevis (=Gymnodinium) common in Gulf of Mexico waters is responsible for Florida red tide. 

Types of Algae

Thallus Organisation

The vegetative of algae structure varies, The considerably in shape and size. There are small microscopic forms like Chlorella, Chlamydomonas, etc., consisting of only a single cell and also huge seaweeds like Laminaria, Macrocystis etc., which sometime measure more than 60 m in length. Not only the thalli vary in sizes but also show a great range of internal and external organizations. Some important types are described below. 

What are the three types of unicellular algae with example ?

  1. Unicellular algae. The thallus consists of a single cell. These may be of the following types.

(a) Motile. These unicellular algae possess flagella and are capable of movement eg, Chlamydomonas.

(b) Non-motile. These unicellular algae lack flagella, hence non-motile e.g., Chlorella.

What are the types of Multicellular algae with example?

What Is Multicellular Algae

The thallus is made of many cells forming either the colonies or filaments.

(a) Colonial Algae

In these algae many cells are grouped together to form a colony. The colony may be motile due to the presence of flagella (e.g., Volvox, Gonium, etc.) or may lack flagella and hence remains non-motile (e.g., Pediastrum,Hydrodictyon).

(i) Motile. 

In some of these colonies, the number of cells remain constant throughout the life; they are called coenobium; c.g., Volvox

(ii) Non-motile

There are non motile colonies in which the number of cells is not definite; these are called coccoid; e.g., Hydrodictyon.

(b) Filamentous algae

In these multicellular algae, the cells are arranged in a series, one over the other to form a filament. The filaments may be branched (e.g., Cladophora, Polysiphonia;

In some filamentous algae the thallus has two distinct systems prostrate or creeping that helps in attachment and erect or projecting which is green and hence photosynthetic. Such a thallus is known as heterotrichous. Fritschiella, a hetero- trichous alga, growing in moist soil is considered to be a link between aquatic habit and land habit.’ It is perhaps the seat of origin of land plants.

(c) Siphonaceous algae

In many algae, thalli are aseptate and thus nuclei remain scattered through out the tubular thallus. Such a multinucleate thallus is known as coenocytic; e.g., Vaucheria

(d) Pseudoparenchymatous algae

It is a thallus where the filaments are repeatedly branched and the branches are in close aggregation, giving an appearance of a parenchymatous organization. Such a thallus with a single large central (axial) filament is called uniaxial (e.g, Batrachospennun) and those with several axial filaments is known as multiaxial (e8, Polysiphonia).

(e) Parenchymatous algae 

In many algae (brown algae) parenchymatous thallus is formed due to extensive cell divisions. These thalli show elaborate internal differentiation; e.g Fucus, Laminaria.

Reproduction How Algae Grow

Reproduction of Algae 

Algae reproduce by vegetative, asexual and sexual methods.

  1. Vegetative reproduction. 

The most common method of vegetative reproduction is fragmentation. The thallus breaks into pieces and each piece is capable of regeneration. In blue- green algae such pieces of trichomes are called hormogonia.

  1. Asexual reproduction 

The cells taking part in reproduction undergo changes to form typical structures which germinate to give rise to a new plant. Asexual reproduction is characterised by chromnosome number which remains the same as that of the parent cells, meiosis being not involved.

Asexual reproduction of Algae

(a) Zoospores 

This is the most common method of asexual reproduction. Zoospores are uni-, bi, quadri- or multiflagellate asexual spores. The cell in which zoospores are formed is known as zoosporangium. Each zoosporangium may produce either one (e.g., Oedogonium) or many (e.g., Ulothrix) zoOspores.

(b) Aplanospores. 

These are non-motile spores and could be called zoospores arrested in their development. During their development, the units of protoplasm of the sporangium get enveloped by a new cell membrane just before zoospores could develop flagella; e.g., Ulothrix.

(c) Hypnospores. 

This is a type of aplanospore with a very thick wall. This permits the spore to remain dormant for a long time under unfavourable conditions; e.g., Vaucheria, etc.

(d) Palmella stage. 

It is a structure consisting of a large mucilage in which many non-motile cells are embedded. Palmella stage develops as a result of repeated divisions of the cells and concurrent dissolution of parent cell wall forming mucilage, e.g., Chlamydomonas, Ulothrix, ctc.

(e) Autospores. 

These are formed due to the division of the contents of the parent cell into many segments, each of them resembling the parent cell. Each autospore is surrounded by a distinct cell wall; e.g., Chlorella, etc.

(f) Akinete. 

These are non-motile spores with a very thick wall which remains fused with the wall of the parent cell. It contains a large amount of food material. In blue-green algae reserves (Cyanophyceae), akinetes are the major organs of reproduction. These are principal perennating structures and besides members of blue-green algae like Anabaena, Nostoc, etc. Akinetes are also found in Pithophora and Ulothrix.

(g) Other structures of Algae

Many different types of asexual spores, other than those described above, are found in algae. Some of them are endospores in Dermocarpa, monospores in Porphyra, tetraspores in Polysiphonia, statospores in diatoms, and cysts in Vaucheria.

Sexual Reproduction Of Algae

It involves formation of haploid gametes which fuse to form a diploid Zygote. Meiosis occurs during germination Zygote and the resultant new plant is a haploid gametophyte. Based on the size and movement of gametes, following types of sexual reproduction have been recognised.

(a) Plasmogamy. 

In this type, either both gametes or at least one is flagellated and. therefore, motile. Plasmogamy is of following types…

(i) Isogamy. 

Both the motile gametes are Similar in shape, size and structure, i.e., they are morphologically similar, e.g., Ulothrix, etc. However, in most of the isogametes male is more active than the female. Thus ,gametes which are morphologically similar are generally physiologically anisogamous. Both the gametes are

(ii) Anisogamy. 

flagellated and motile. The male gamete is smaller in size and invariably more active than the female e.g., Caulerpa, etc.

(iii) Oogamy. 

The male gamete is smaller and flagellated while the female gamete 1s larger and non-flagellated and thus passive. The male and female gametes are produced in specialised structures called antheridia and oogonia respectively. Oogamy is found in Oedogonium, Vaucheria, etc.

(b) Aplanogamy. 

Most of the algae reproduce by flagellated gametes (planogametes). However,in some algae like Spirogyra, diatoms, etc.,

Gametes lack flagella and are called aplanogametes. Such gametes fuse by a special process called conjugation.

Why Algae Is So Important 

The events of the past few years have made it clear that the United States can no longer ignore the threats to its economy, climate and national energy security rising from its dependence on petroleum fuel.

Social and political instability in or near major oil producing regions has led to frequent price spikes very high in the whole world ,and hampering an already-very slow economic recovery as consumers are forced to spend more of their limited income on gas and oil. Major spills in waterways like the Gulf of Mexico provide dramatic reminders of the risk inherent in oil exploration and production of oil and their effect on our natural environment is very bad.

The status quo is simply no longer an option. We must find new, sustainable and domestic alternatives to petroleum fuel and gas. Doing so will help us address the three most crucial issues of our good time:


Algae are useful as food, in industries, in agriculture, as medicine, source of minerals, etc. At the same time production of water blooms, toxicity, etc., are some of their harmful effects.

Useful Activities

The following are some of the important uses of algae.

Benefits Of Algae

[I] Algae as food

Algae are rich in carbohydrates, many inorganic and organic compounds, proteins, vitamins, etc. In some of the algae these substances are found in large amounts and are, therefore, used as food.

(1) The following members of Chlorophyceae (green algae) are used as food. Ulva (sea lettuce) is used as a vegetable

after drying and salting. Chlorella has a high percentage of proteins and lipids. Besides this, vitamins A and DD are also found in sufficient amounts. It has a very short life cycle and can be grown quickly. These characteristics make Chlorella a suitable food for future generations. It has also been grown easily in over-head tanks and was considered to be very suitable food for space flights.

(2) Members of Phaeophyceae (brown algae) used as food include Alaria, Laminaria, Sargassum, etc. The food value is due to proteins, fats and carbohydrates. They are rich in iodine and, therefore, goitre does not occur in the countries where these are eaten.

(3) Among Rhodophyceae (red algae) the genera commonly used as food are Chondrus (carrageen or Irish moss), Porphyra, Gigartina, Rhodymenia, etc. In species of Porphyra, vitamins C and B12 are found in sufficient quantities.

(4) A blue-green alga (Cyanophyceae) Nostoc commune is eaten as food in China, Java, etc. Another blue green alga, Spirulina is also used these days being very rich in proteins.

[II] Algae in industry

  1. Agar – Agar. These are obtained from members of Rhodophyceae, collectively called agarophytes e.g., Gelidium, Gracilaria, etc. Agar is a colloidal or jelly-like substance used for culturing bacteria and various other microorganisms. It is also useful in the preparation of medicines. Agar is also used in baking and confectionary
    industry as emulsifying agent and in cosmetics, textile, leather and paper industries. It is also useful as a laxative.
  2. Carrageenin. It is a cell wall derivative of a red alga-Chondrus crispus and is used as an emulsifying and stabilizing agent in ice creams, chocolates, cosmetics, tooth pastes, etc.
  3. Algin. This cell wall derivative of some brown algae like Alaria, Ascophyllum, Fucus, etc., is widely used in preventing formation of crystals in ice-creams. It is also used in the rubber, tyre and paint industry. Besides, it is also used to stop bleeding and in the preparation of. soups, creams, sauces, etc.
  4. Diatomite. It is a deposit of dead frustule styles or cell walls of fossil diatoms (Bacillariophycean The walls of diatoms have a heavy deposit of silicon dioxide (SiO). When the diatoms, which form a major part of planktons, die, the remainder of the cell wall are deposited at the bottom of the water reservoirs. These deposits are called (or kieselguhr). It has diatomaceous earth following uses.

(1) It is used as an insulating agent in boilers, steam pipes, furnaces, etc., where the temperature rises to about 1000° F.

(2) It is used in car polishes, silver polishes and toothpastes.

(3) It is an absorbent for nitroglycerine, hence used in the transport of dynamite.

(4) Diatomite is also useful in oil refineries for the filtration process.

(5) It is useful in the preparation of paint, varnishes, abrasives, glass and porcelain.

[II] Algae as source of minerals

Seaweeds are very rich in minerals and form the commercial source of their extraction. Kelps, the members of Laminariales of Phaeophyceae (Ascophyllum, Ecklonia, Laminaria, etc.) were the chief source of iodine extraction in Europe. Bromine is extracted from members of Rhodophyceae like Polysiphonia, Rhodymenia, etc.

[IV] Algae as manure

In France, Iceland, Scotland and Norway, members of Phaeophyceae (brown algae) like Fucus Macrocystis, Sargassum, etc., are used as manure. Many useful inorganic minerals are obtained from them.

[V] Algae in nitrogen fixation

Blue-green algae (Cyanophyceae), viz., Aulosira, Anabaena, Nostoc, etc., fix elemental nitrogen and thus increase the soil fertility. These algae have special cells called heterocysts which are the sites for nitrogen fixation. P. K. De (1939) was the first to demonstrate N2 fixing ability of blue green algae. Fairly good yield of rice can be obtained over a number of years without addition of any nitrogenous fertilizer because of the presence of nitrogen fixing blue-green algae in the rice fields.

[VI] Algae in reclamation of Usar’ soils

of north India could be Saline Usar reclaimed by growing blue green algae, like Nostoc, Anabaena, Seytonema, etc, The algae increase the mineral content of the soil and thus the crop yield.

[VII] Antibiotic from algae

Chlorella (green alga) yields antibiotiC an chlorellin which is useful against both gram positive and gram negative bacteria. Besides this, Laminaria, Ascophyllum, Rhododmela, etc., also have antibiotic properties.

[VIII] Larvicidal properties of algae

Blue-green algae like Aulosira and Anabaena, and green algae like Chara and Nitella eliminate mosquito larvae from ponds and pools in which they grow.

[IX] Algae in biological research

Algae has always been useful for conducting physiological and genetic experiments since these can be easily grown and manipulated.

(1) Chlorella and Scenedesmus (green algae) have been extensively studying for photosynthesis.

(2) Acetabularia, a green alga, was used to establish the hereditary role of the nucleus.

(3) Halicystis, Valonia, etc., (green algae) are useful in the studies on permeability.

[X] In sewage disposal

The sewage dispOsal is an aerobic process and production of oxygen from algal photosynthesis helps it. Algae like Chlorella, Scenede smus, Pediastrum, Oscillatoria, etc., can grow in these rich organic wastes and provide oxygen to aerobic bacteria. Hence, an oxidation pond is an example of algal bacterial symbiosis.

  1. Harmful Activities

The following are some of the effects of algae causing damage.

[I] Water blooms

Algae grow abundantly in water reservoirs where and (especially nitrates of nutrients and excess sulphates) are available to them. Such an algal growth floats on the water surface and looks like foam or soap lather. It is called water bloom. members of Amongst bloom-forming algae, Anabaena, (e.g Microcystis, Cyanophyceae Oscillatoria, etc.) are common.

Water blooms deplete oxygen of water reservoirs and, therefore, aquatic animals die of deoxygenation. Bloom forming algae also release certain toxins which cause death of aquatic as well as domestic animals.

[II] Parasitism

Cephaleuros virescens, a green alga, is a parasite and causes red rust of tea in some tea growing parts of India, especially Assam. It is known to cause extensive damage to this crop.

Algae Kingdom Classification or CLASSIFICATION OF ALGAE

different proposed Many algologists have classifications of algae. These are based on different characters. However, the algal pigments have still remained the major basis of algal classification. Other characters, often considered include external forms, reserve food products, nucleus, life history, reproduction, etc. The classification given by a famous British phycologist F. E. Fritsch (1935, 1945) is widely used even today. He has divided algae into 11 classes.

  1. Chlorophyceae
  2. Xanthophyceae
  3. Chrysophyceae
  4. Bacillariophyceae
  5. Cryptophyceae
  6. Dinophyceae
  7. Chloromonadineae
  8. Euglena
  9. Phaeophyceae
  10. Rhodophyceae
  11. Myxophyceae

Some of the characteristics of major algal classes are summarised in.


Spirogyra is represented by about 300 species. It is a freshwater alga found free floating on the surface of stagnant pools, ponds, ditches, etc. A few species are also known to grow attached to the substratum. Spirogyra is commonly known as water silk or pond silk since it forms green silky floating masses.

Thallus Structure

The thallus is an unbranched and uniseriate filament where cells are arranged in a single row… All the cells of a filament are similar. In some species holdfast is present (e.g.. S. fluviatilis) The cells are mostly rectangular and longer than broad. The cell wall is two layered; the outer layer is of pectic substances and the inner 0 cellulose. The outer pectin layer dissolves in water and forms a slimy mucilaginous envelope around the filament. This explains the smooth silky nature of the filament and hence the name water silk. The mucilage checks the growth of epiphytes on the filaments.

The transverse wall between the adjacent cells is generally simple and plain, but it may also be replicate, collegiate, etc. In the replicate type middle lamella forms a ring-like structure while in collegiate type distinct H- shaped pieces are formed between the adjoining cells. Cytoplasm is present in the form of a layer close to the cell wall; it is called a primordial utricle. It surrounds a large central vacuole. A single nucleus present in the centre of the cell is held by thin cytoplasmic strands which traverse through the vacuole

The most characteristic feature of the cell is the ribbon or strap-shaped chloroplasts. They are arranged in left handed or counterclockwise spirals in the peripheral region of the cell. The number of chloroplasts varies from to 16. Margins of the chloroplast may be either Smooth or serrated. Many pyrenoids are situated in the chloroplasts at regular intervals. Each pyrenoid consists of a central proteinaceous core surrounded by starch plates. It is the site of starch formation and accumulation. 

Examples of Algae

  • Ulothrix
  • Porphyra
  • Spirogyra

More Questions About Algae

What is Algae
What are Algae
What is Habitat

Types of Algae

Thallus Organisation
What are the three types of unicellular algae with example ?
What are the the types of Multicellular algae with example?

What Is Multicellular Algae

Colonial Algae



Filamentous algae

Siphonaceous algae

Pseudoparenchymatous algae

Parenchymatous algae 

Reproduction How Algae Grow

Reproduction of Algae 

Vegetative The reproduction

Asexual reproduction 

Asexual reproduction of Algae




Palmella stage



Other structures of Algae

Sexual Reproduction Of Algae






Why Algae Is So Important 


Benefits of Algae
Algae as food
Algae in industry
Algae as source of minerals
Algae as manure
Algae in nitrogen fixation
Algae in reclamation of Usar’ soils
Antibiotic from algae
Larvicidal properties of algae
Algae in biological research
In sewage disposal

Harmful Activities

Water blooms

Algae Kingdom Classification or CLASSIFICATION OF ALGAE

Thallus Structure

Reproduction Of Algae

Vegetative reproduction
Asexual reproduction



Examples of Algae

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