ALGAE

Cryptogams: These are those plants that do not bear flowers or seeds and are hence commonly known as flowerless or seedless plants.

Cryptogams are further divided into
(a) Thallophyta
(b) Bryophyta
(c) Pteridophyta

A. Thallophyta:
· Plant body is thallus i.e. not differentiated into leaf, stem, and root.
· It includes
(a) Algae: Thallophytes containing chlorophyll
(b) Fungi: Thallophytes without chlorophyll
(c) Lichens: Symbiotic association between algae and fungi
(d) Bacteria: Unicellular (prokaryotic) microscopic, non-green organism.


B. Bryophyta:
· The plant body is thalloid (prostate) or differentiated into stem, leaves but not true roots (erect body).
· There is a regular alternation of generation and the main body is always a gametophyte.
(a) Hepaticae (Liverworts): Bryophyte with thalloid body eg. Riccia and Marchantia.
(b) Anthocerotae (Hornwort): Plant body is simple and thalloid but the sporophyte is complex and semi-independent on the gametophyte eg. Anthoceros.
(c) Musci or Mosses: Bryophytes with leafy stem eg. Polytrichum, Spagnum.

C. Pteridophyta:
· The plant body is differentiated into root, stem, and leaf.
· Regular alternation of generation, sporophyte, and gametophyte are independent of each other often called vascular cryptogams.

ALGAE

· Supposed to be the most primitive plants.
· Study of algae: Phycology or Algology
· Father of Phycology: F.E. Fritsch
· The term algae was introduced by Linnaeus.

Various Types of Algae on the basis of Habitat.

· Holophytic (Photo-autotrophs) algae – able to synthesize their food themselves using light energy. 

· Phytoplanktons – aquatic freely floating algae on the water surface. They act as the producers in the pond ecosystem. e.g. Volvox
Benthic: Algae that grow on the bottom of water bodies.
Lithophytic: Attached to the moist surface of the rock.
Endolithic: Algae living inside the rock.
Periphyton: Algae attached to the submerged vegetation.
· The periphyton is epiphytic if attached to the surface of an aquatic plant. e.g. Spirogyra, Oedogonium
Endophyte: The periphyton growing inside the plants. E.g. Coleochaete nitelarum (inside Nitella)
Epizoic: Attached to the surface of the animals. E.g. Cladophora growing on the shells of Mollusca.
Endozoic: Found inside the body of animals.
Edaphophytes: Found in soil.
Epitphyllophytes: Algae growing on the leaves of the plant. e.g. Phycopetis
Aerial epilithic: Found on the surface of rocks and stones
Halophilic: Algae found in a highly saline environment.
Thermophiles: Algae growing in hot waters.
Cryophytic algae: Algae flourish well at low temperatures.
· Different colours of snow are due to cryophilic algae.
a. Red snow – Ulothrix, Chlamydomonas
b. Black snow – Rapidonema.

· Algae are generally autotrophic.
· Parasitic algae is Cephaleuros.
· Cephaleuros causes Red Rust of tea.
· Colourless parasitic algae which are Harveylla which belongs to Rhodophyceae.
· Body of algae is called Thallus.
· Thallus means undifferentiated body structure i.e. body is not differentiated into roots, stem, and leaf.
· Cell wall of algae is made up of cellulose i.e, cellulosic except blue-green algae (BGA).
NOTE: BGA is Prokaryote whose cell wall doesn't contain cellulose.
· Reserve food material in Algae is starch.
· Red algae which are not red in colour is Batrechospermus.
· Red colour of the red sea is due to Blue-green algae (Trichodesmium)
· Brown colour of algae is due to the pigment Fucoxanthin.
· Largest unicellular algae is Acetabularia.
· Largest multicellular algae is Macrocystis
Note: Macrocystis belongs to Phaeophyceae.
· Largest size algae of Phaeophyceae are called kelps or seaweed.
· Pigment common in all algae is Chlorophyll a and carotene.
· Pigments are similar in Red algae and blue-green algae (BGA).

Reserve food material in Algae

· In Cynophyceae [Blue green algae (BGA)]: Cynophycean starch
· In Chlorophyceae (Green algae): Starch
· In Phaeophyceae (Brown algae): Laminarian starch or mannitol
· In Rhodophyceae (Red algae): Floridian starch

Symbiotic Algae:

· Nostoc lives symbiotically in Anthoceros (Bryophyte)
· Nostoc/Anabaena – found symbiotically in the coralloid root of cycas.
· Anabena Azollae is found symbiotically in the leaf of Azollae.
Azolla (water fern) is an aquatic pteridophyte. It is the smallest pteridophyte used as a "Biofertilizer"
· Motility or Motile stages are absent in Red algae.
· Unicellular form is absent in Phaeophyceae or Brown algae.

Economic Importance of Algae

1. As food
· Algae are significant primary producers of organic matter in the ocean or aquatic environments.
· Spirulina (80% protein) is the richest source of protein and it is often cultivated in the water tank.
· An antibiotic chlorellin is obtained from chlorella.
· Chlorella is used in space travelling, hence called space algae.

2. Industries
Agar-agar used to prepare Semi-solid culture media is extracted from red algae (Gelidium and Gracillaria).
· Carageenin used for emulsifying chocolate, ice cream, cosmetics are produced from Chondrus crispus.
· Alginates is a colloidal gel used in rubber, textiles, and cosmetic industries is produced from Phaeophyceae.

3. Research
· Photosynthetic research is done in unicellular algae chlorella.

4. Others
· Iodine is obtained from large size brown algae known as kelp.
· Water bloom i.e. excessive growth of algae in ponds caused mainly by blue-green algae.
· Several algae may associate with parasitism in higher pants. eg. Cephaluros causes red rust of tea.

Reproduction in Algae

Reproduction occurs in 3 ways:

1. Vegetative Reproduction:
· Most common method of reproduction in algae.
· It occurs in one of the following ways.
(a) Fragmentation: E.g. in Spirogyra, Nostoc
(b) Fission in unicellular algae.
(c) Hormogones i.e. the short segment of trichome which is formed in the region of heterocysts. E.g. Nostoc
(d) Tubers e.g. Cladophora
(e) Budding e.g. Protosiphon

2. Asexual Reproduction: Occurs by spores.
A. Zoospore
· Motile, naked spore
· Produced under favourable conditions.
· Types:
Biflagellated: Chlamydomonas
Bi/quadriflagellated: Ulothrix
Multiflagellated: Oedogonium and Vaucheria

B. Aplanospores
· Thin-walled, non-motile (non-ciliated); asexual spore.
· Produced during unfavourable conditions.
E.g. Spirogyra, Vaucheria, Ulothrix

C. Akinetes
· Thick-walled; not motile spore; resting spores.
· Formed during the unfavourable conditions.
E.g. Nostoc, Spirogyra, Cladophora
D. Hypnospore
· Protoplasm of the cell separates from the cell wall and collects in the centre to form. Non-motile; and thick-walled, hypnospores
E.g. Chlamydomonas nivalis

E. Palmella stage
· Many zoospores / aplanospores come together and are covered by mucilage. This stage is known as the palmella stage.
E.g. Chlamydomonas, Ulothrix

3. Sexual Reproduction:
(i) Isogamous
· Fusion of morphologically similar, physiologically different gametes.
· Isogametes may be motile (zoogametes) e.g. in Chlamydomonas and Ulothrix or non-motile (aplanogametes) e.g. Spirogyra.

(ii) Anisogamous
· Fusion of gametes different in size but similar in structure.
· Larger one is considered as female and smaller one is the male gamete.
E.g. Chlamydomonas braunii and Pandorina

(iii) Oogamous
· Fusion of gametes different in size and structure.
· Male gamete is smaller and motile.
· Female gamete is larger and non-motile.
· Advanced type of reproduction.
E.g. Oedogonium, Vaucheria, Chlamydomonas

Classification of Algae

Fritsch (1935) classified the algae into 11 classes on the basis of pigments and reserve food materials: Chlorophyceae, Xanthophyceae, Bacillariophyceae Chrysophyceae, Cryptophyceae, Dinophyxeae, Chloromonadophyceae, Eugleuineae, Phaeophyceae, Rhodophyceae, Cynophyceae/Myxophyceae.

1. Bacillariophyceae (Diatoms)
· Diploid thallus
· Chromatophores are golden, brown, or yellow.
· These are called “diatoms” due to the presence of an accessory brown pigment called Diatomin. 

Other pigments are chl-a & chl-c (but not chl-b), carotenes and xantophylls.
· Pigments are found in chromatophores.
· Reserve food materials are fats or protein (Volutin)
· Cell wall is silicified (called frustule) and consists of overlapping halves (epitheca and hypotheca)
· Cell wall composed of silica. So diatoms are commonly called “jewels of the ponds”/ “jewels of the plant kingdom”.
· Sexual reproduction occurs by auxospore formation.
· Used in making soundproof room, boot polish, paints cream
· Diatoms are also used during dynamite blasting.
· Eg: Pinnularia, Millosira


2. Chlorophyceae (Green algae)
· Mostly they are freshwater so, also called freshwater algae while some are marine (eg: Ulva). Ulva can be used as a vegetable (i.e edible).
· Reserved food material is starch. Starch is stored in pyrenoids.
· Motile gametes
· Cell wall is made up of cellulose
· Photosynthetic pigments are chlorophyll a chlorophyll-b, xanthophylls, and carotenes.
· Thallus range from unicellular to hetero-trichous form (i.ethallus with the erect and prostrate system)
· Most advanced algae (ancestor of the higher plant)
· They reproduce asexually and sexually.
· Cephalurus is a parasitic green alga.
· Chloroplast usually associated with one or more pyrenoids
· The pyrenoids are protein sheath surrounded by a starch sheath, functionally associated with synthesis and storage of starch.

a. Chlamydomonas
· Cup-shaped chloroplast
· Have two anterior flagella which help it to move in the water.
· Falls under the Volvocales order.
· Unicellular, motile, biflagellate, flagella usually from ‘Blepharoplast’ also known as “basal granule”
· Single large cup-shaped chloroplast with a pyrenoid present in it.
· Pyrenoid is made up of protein surrounded by starch plate or starch grains, it is the centre of the formation.
· A tiny spot of an orange or reddish-coloured spot known as stigma or eyespot (contains carotenoids) lies at the Anterior end. (@ it is the photoreceptive organ associated with the direction of light)
· Autotrophic nutrition is found in Chlamydomonas.

Various modes of asexual reproduction found in the Chlamydomonas are:
1. By zoospore: Zoospore is biflagellate
2. By aplanospore
3. By hypnospore
4. By palmella stage
5. By akinetes

Sexual reproduction: Gametic fusion may be Isogamous, anisogamous, and oogamous i.e sexual reproduction range from isogamy to anisogamy, and to oogamy occurs in the same genus Chlamydomonas.
Note: When a unicellular organism produces two types of gametes then such condition is called relative sexuality. (Discovered by Hartman)
· Life cycle in chlamydomonas is haplontic.
· If the zygote formed undergoes resting stage, it forms thick covering and is called a Zygospore.
· At the time of germination, meiosis takes place in the zygospore and 4 haploid spores are developed each giving a new thallus.
· Green algae found in fresh or stagnant water.

b. Chlorella
· Is a unicellular non-motile algae that is a rich source of protein.
· It's the source of antibiotic chlorellin
· It is useful in Research to detect the path of the carbon cycle.
· It is useful in space travel.
Note: Richest source of protein is spirulina which is often cultivated in the water tank.

c. Volvox
· Colon of motile algae which is also called Rolling algae.

d. Ulothrix
· Plant body is represented by an unbranched filament attached to the substratum with the help of ‘holdfast’Holdfast is hyaline (colourless) as it lacks chlorophyll.
· Cell wall consists of two-layer: the inner layer is made up of cellulose and the outer layer is mostly made up of protopectin which is insoluble in water.
· Filament is wet due to protopectin.
· Cell consists of single girdle-shaped chloroplast with 1 or more pyrenoids.

e. Oedogonium:
· Plant body is filamentous, unbranched, and attached to the substratum by means of holdfast.
· Each cell consists of one or more transverse ring-like structures known as apical cap cell with apical cap is called ‘cap cell’.
· Zygospores are uninucleated and multi-flagellated
· Reticular-shaped chloroplast.

f. Ulothrix:
· Ulothrix, a genus of filamentous green algae (family Ulotrichaceae) found in marine and freshwaters.
· Each cell contains a distinct nucleus, a central vacuole, and a large thin chloroplast with at least one pyrenoid.
· The specialized cell for attachment is called the holdfast, and the filaments are typically unbranched.
· In most species, all the cells can form reproductive bodies.

Ulothrix reproduces via
1. Vegetatively by fragmentation
2. Asexually by nonmotile resting spores (aplanospores), motile quadriflagellate spores (zoospores), by hypnospores, by akinetes, and by palmella stage.
3. Sexually by biflagellate gametes.

Fig: Showing Ulothrix

g. Vaucheria:
· Plant body is siphonaceous i.e thallus is siphon-like.
· Thallus is aseptate, multinucleate, coenocytic.
· Zoospore is multinucleated, multi-flagellate. So, it is also called a coenozoospore or compound zoospore.

h. Zygnema: star-shaped chloroplast.
hi Acetabularia: green algae.

SPIROGYRA

Systematic position:
Kingdom: Plantae
 Subkingdom: Thallophyta.
  Phylum: Chlorophyta
   Class: Chlorophyceae
    Order: Conjugales
     Family: Zygnematceae

      Genus: Spirogyra

· Often called water silk or pond silk or pond scum.
· Freshwater algae
· Plant body is gametophytic thallus, which is a multicellular, unbranched silky thread-like structure.
· The plant body consists of an unbranched filament without a distinct base and apex, all the cells are cylindrical, identical, and placed end to end in a single row.
· The plant body is a gametophytic thallus.
· Spirogyra comes on the surface of the water in light due to oxygen bubbles adhered to it making it buoyant.
· Number of chloroplast per cell ranges from 1 to 16.
· Chloroplast is non-granal.
· Cytoplasm is peripheral due to the presence of central vacuoles; this type of cytoplasm is called the primordial utricle.
· Cells are uni-nucleated.
· Presence of cytoplasmic strands.
· Unbranched filamentous algae living in ponds.
· Characteristically slimy due to mucilaginous covering so it is called water silk, pond silk, or pond scum.
· Cell wall is a two-layered outer wall is made up of pectin and the inner layer is cellulosic.
· There are one or more spiral bands of chloroplast which is the distinct feature of spirogyra.
· All the cells contain chloroplast except holdfast that doesn't contain chloroplast.
· Each chloroplast band has numerous pyrenoids.
· Pyrenoid helps in the synthesis and storage of starch.
· Pyrenoids are proteins surrounded by starch.

Reproduction:

Occurs in 3 ways: Vegetative, asexual, and sexual.

A. Vegetative Reproduction: Occurs by fragmentation.
B. Asexual Reproduction
· Rarely occurs by 2 types of spores.
(i) Akinetes
(ii) Aplanospores
· Zoospores absent.
C. Sexual Reproduction: Is isogamous and occurs by conjugation i.e. Scalariform and lateral.
· Gametes are non-flagellated (aplanogametes) and morphologically similar but physiologically different i.e. Physiological Anisogamy.
· Scalariform conjugation takes place between the cells of two different filaments; i.e. in dioecious.
· Lateral conjugation occurs between two adjacent cells of the same filament; i.e. in monoecious.
· Zygospore (2n) is formed after the fusion of gametes.
· Meiosis takes place during the germination of zygospore whereby 3 out of 4 haploid nuclei degenerates.
· Thus each zygospore gives a single filament.
· Life cycle of spirogyra is haplontic.
· Sexual reproduction is isogamous and takes place by conjugation.
· In spirogyra, meiosis followed by mitosis occur during germination of zygospore.

3. PHAEOPHYCEAE (Brown algae)
· Found in cold marine seawater.
· No unicellular forms, only multicellular forms are present.
· Cell wall is made up of cellulose and alginic acid.
· Stores carbohydrates as laminarian starch or Mannitol.
· Chlorophyll a and c, Fucoxanthin, and Carotenoids are the main photosynthetic pigments.
· Extra brown pigments are called fucoxanthin.
· Larger size Brown algae are called 'kelps'.
· They are exclusively marine and marine algae and seaweeds are a rich source of iodine.
· Trumpet hyphae (analogous to sieve tube) are found which helps in the conduction of food.
· Pyrenoids are present.
· Motile reproductive cells are pear-shaped and biflagellated.
· Meiosis occurs during gametogenesis.
· Sex organs develop in a special cavity called ‘conceptacle’.
· Algin is extracted from the cell wall of brown algae.
E.g. Macrocystis, Fucus (Rockweed), Ectocarpus, Laminaria Sargassum (gulf weed)

NOTE: Macrocystis – Multicellular and Largest algae & Laminaria – Rich source of iodine.

4. RHODOPHYCEAE (Red algae)
· Mostly found in warm marine water and some in freshwater.
· Cell wall has cellulose and pectin.
· Store carbohydrate as Floridian starch
· Non flagellated male gamete i.e motility is absent in Red algae.
· Plant body is mostly heterotrichous.
· Calcium carbonate is deposited in the cell wall.
· Red colour is due to the presence of special pigment, r-phycocyanin, and r-phycoerythrin.
· Male and female sex organs are ‘spermatangia’ and ‘carpogonia’.
· Male gametes are non-motile and are called ‘spermatia’ instead of antherozoid.
· Carpogonium consists of a long narrow neck-like structure and ‘Trichogyne’ which acts as a receptive spot.
· Carrageenin is extracted from the cell wall of red algae.

Examples:

Batrachospermum (Red algae but green in colour)
Harveylla (colourless parasitic algae)
Gelidium, Gracillaria.
Note: Gelidium and Gracillaria are the sources of Agar-agar, which is a polysaccharide useful for tissue culture medium. Agar-agar makes liquid nutrient media semi-solid.

5. CYNOPHYCEAE or MYXOPHYCEAE
· Members of this class are commonly known as blue-green algae or cyanobacteria.
· Prokaryotic cell structure.
· Cynophycean starch as a reserve food material.
· Sexual reproduction is totally absent but asexual reproduction by Hormogonia (a short piece of trichome), fission, and akinetes.
· They perform oxygenic photosynthesis (1st oxygenic photosynthesizer)
Note: Oxygenic photosynthesis – oxygen released during photosynthesis e.g. green plants and cyanobacteria.
· Anoxygenic photosynthesis–no release of oxygen during photosynthesis. e.g. Bacteria.
· O2 is not evolved in bacterial respiration because hydrogen donor in bacterial respiration is H2S instead of H2O.
· Photosynthetic pigments are Chl. a, b-carotene, C-Phycoerythrin, Phycocyanin, and allophycocyanin.
· Ground is slippery in the rainy season due to BGA.
· The blue-green colour is due to the presence of phycobilin pigment c-phycocyanin (also c-phycoerythrin)
· All the blue-green algae are prokaryotic, so kept in monera.
· Cell wall is made up of substance mucopeptide. (not found anywhere else)
· Pyrenoids are absent.
· Many filamentous forms possess some specialized cells of disputed nature heterocysts. (probably nitrogen fixation)
· As they lack a true nucleus, they reproduce only vegetatively: (fragmentation, Hormogones, Heterocyst, Akinetes)
· Red colour of the red sea is due to the extensive growth of Trichodesmium erythrium.
· Member of Cyanophyceae show adaptability to extremes of Environment because of their gelatinous sheath, compactness of molecule in protoplasm.
E.g. Nostoc, Anabena, Oscillatoria.

 

NOSTOC

· Nostoc is a common blue-green algae of filamentous form, species of Nostoc commonly occur in ponds ditches, and other pools of water and also in wet soil often as somewhat firm masses of jelly.
· It is a colonial prokaryotic Blue Green Algae or Cyanophycean.
· Found in both aquatic (fresh & sea) and terrestrial habitat.
· Some species are associated with lichens, bryophyte thalli (e.g. Anthoceros), roots of cycads, and other plants. This association is helpful in fixing atmospheric nitrogen.
· Nostoc forms shining mucilaginous colonies popularly known as Moonspit or Star Jelly or Witches butter.
· Land becomes slippery during rain due to BGA.
· They show Gaidukov’s phenomenon; i.e. change colour in different wavelengths of light.

Cell Structure:
· Cell membrane lacks sterol.
· Outer peripheral coloured (pigmented) region is called chromoplasm; the colourless central region is called centroplasm.
· The colour of chromoplasm is due to photosynthetic thylakoids.
· Phycobilisomes are attached to thylakoids.
· Phycobilisomes possess 3 pigments called phycobilins.
(i) C-phycocyanin (bluish) – Light absorbing pigment
(ii) C-phycoerythrin (red)
(iii) Allophycocyanin (blue)
· Cytoplasm contains 70s ribosomes for the synthesis of proteins; mitochondria, dictyosomes, and ER absent.
· Cyanophycean starch is a-granules.
· Volutin granules (polyphosphate bodies) & polyhedral bodies rich in Rubisco are present.

Reproduction:
· Sexual reproduction is absent (being prokaryotes).
· Multiplies asexually by 4 methods.
(i) Fragmentation
(ii) Hormogones – These are short segments of the trichome that are formed in the region of Heterocyst due to mechanical disturbance or death of vegetative cells.
(iii) Akinetes
(iv) Heterocyst
· Heterocyst are specialized for Nitrogen fixation.

Economic Importance of Nostoc:
(i) Larger colonies of Nostoc are edible. They are rich in nitrogen substances.
(ii) Active Nitrogen fixers.
· Aulosira fertilisima is the most active Nitrogen fixer in the rice fields.
(iii) Biofertilizer
· Azolla has Anabaena in its leaves to fix Nitrogen.
(iv) It is helpful in reclaiming saline or alkaline soils because of its mucilaginous secretion, ability to fix N2, rapid growth, and formation of abundant organic matter.

Economic Importance of Algae:

Useful Aspect:
Many algae are used by human beings for food, manufacture iodine for some other purposes from ancient times. Many types of research are being done in phycology (study of algae) and many workers are trying to find out the food value of algae, their importance in industries, and their importance in agriculture.

The importance of the role played by algae in the world is becoming more appreciated each day because of the increased utilization that many of them are valuable to man.

1. Algae as food: Large numbers of Algae are used as a source of food by human beings. They are rich in carbohydrates, inorganic substances, and vitamins. Vitamins A C D and E are the main constituents of these plants.

Parphyratenesa is very popular and eaten throughout Japan.

Kambu is another product of algae.

Laminaria is used in Japan as standard food.

Spirogyra is the chief source of food Ulva (sea lettuce) is also used by man as food.

Recently green algae chlorella has drawn the attention of psychologists. The percentage of Protein in this algae is too much than other vegetables or eggs. It contains vitamins A to D. Algae is used to decorate pastries, sandwiches, rice, fish, cakes, and jelly cakes in Japan.

Agar-Agar is also used in the preparation of ice cream and jellies. Geliduim, Gracillaria algae are the chief sources of agar.

Another algae Rhodomenia palmata is chewed like tobacco in Scotland.

Hair vegetable is eaten in China and algae Nostoc commune is one of its constituents.

Minute algae Chlorella has also been found as a food source for humans and animals.

Many algae are used as food for animals like sheep, goats, and cattle in New Zealand.

2. Algae in the industry: Diatoms (algae) prepare diatomaceous earth and are extensively used in sugar refineries and soap manufacture. It is also helpful in the cement industry, in the manufacture of dynamite, rubber, and blotting paper. It is also used in isolation of boilers, blast furnaces, and at various other places where very high temperature (1000°C) is required.
Algin is extracted by boiling algae in a washing soda solution and rollers of typewriters are prepared from it. Japanese prepare artificial wool from sargassum. Agar-Agar obtained from algae-like Geliduim is used in the sizing of textiles.

Algae Chondrus and Careragaenium which yield mucilage are used in the manufacture of left hats as a stiffening agent. It has the properties of agar and is therefore used as an ingredient of cosmetics, shaving creams, shoe polishes, and shampoos. Various red algae like laminaria yield Iodine.

Several seaweeds also yield bromine, acetic acid, formic acid, and acetone.

3. Algae in Agriculture: The presence of mucilage in most of the members of Myxophyceae helps in the development and better nourishment for nitrogen-fixing bacteria. Some of them like Anebena, Nostoc, etc are able to utilize and fix atmospheric nitrogen, thus increasing soil fertility. Some members of Myxophyceae were able to fix 20 Lbs. of atmospheric nitrogen per acre in a rice field.

4. Medicinal Use of Algae: Green unicellular algae chlorella yield an antibiotic known as chlorellin. It is crystalline and stable at 120°C. With an average composition of carbon 77.3%, Hydrogen 16.6%, and oxygen 10.99%. It has a marked effect on gram-positive and gram-negative bacteria.

The presence of Chara and Nitella algae in a pond cause death of mosquito larvae thus helping in the control of malaria to some extent.

5. Algae in Biological research: Photosynthesis and metabolism are based on studies of unicellular algae such as chlorella. Certain algae-like Chlamydomonas are being used in genetic studies. Chlamydomonas was the first haploid organism on which successful hybridization was accomplished.
Certain algae-like Acetabularia, Valonia, and Nitella show great success in studies on morphogenesis, nuclear function, nuclear-cytoplasmic relationship, and ionic exchange with the environment.
From the above discussion, it is clear that algae are of great importance for human being.

Harmful Aspect:
Water bloom (extensive growth of algae in the pond)is caused by Blue-green algae and Green algae.
Important algae causing water bloom are Macrocystis, Oscillatoria, etc.
Diseases:
Red rust of tea: By Cephaleuros virescence
Red rust of coffee: By Cephaleuros arabica.
[coffee is obtained from seeds of Coffea Arabica (family Rubiaceae)]

 

High Yielding Points from ALGAE:

1. Nostoc lives symbiotically in Anthoceros (Hornwort).

2. Anabaena azollae is found symbiotically in the leaf of Azolla.

3. Food is stored in the form of Floridian starch in Red algae and in the form of Laminirian starch or mannitol in Brown algae.

4. Spirulina is the richest (80%) source of protein and is often cultivated in water tanks.

5. An antibiotic Chlorellin is obtained from Chlorella.

6. Chlorella is used in space travelling.

7. Agar is obtained from Red algae namely Gelidium and Gracilaria.

8. Carrageenin is obtained from Chrondus cripsus and Alginates is produced from Phaeophyceae.

9. Chlorella used in photosynthesis experiments is an algae.

10. Water bloom is due to BGA.

11. Vegetative reproduction by HORMOGONES occurs in NOSTOC.

12. Asexual reproduction by:
a. Zoospore (Motile spore):
Biflagellated: Chlamydomonas @BC.
Quadriflagellated: Ulothrix
Multiflagellated: Odogonium and vaucheria (@ VOM)
b. Aplanospore (non motile spore) eg: spirogyra
c. Akinetes (non-motile ): Nostoc, spirogyra
d. Hypnospore: Chlamydomonas nivalis (cause red snow)
e. Palmella stage: Chlamydomonas, ulothrix (@ CPU)

13. Sexual reproduction:
a. Isogamous: Spirogyra
b. Anisogamous: Chlamydomonas, pandorina
c. oogamous: Chlamydomonas, vaucheria oedogonium

14. Algae are autotrophic except Cephaleurus which is parasitic.

15. Colourless parasitic algae is Harvelia.

16. The non-motile cell bodies are found in Rhodophyceae

17. Only multicellular form (no unicellular form) is present in Brown algae.

18. Bryophyta + Thallophyte = halodiplobiontic life

Also, Read Notes of Other Lessons of Botany:

• Bacteria
• Algae
• Fungi
• Lichens
• Virus
• Bryophytes
• Pteridophytes
• Gymnosperms