Algae – Definition, Types, and Uses

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What is Algae?

➧ Definition of Algae
❖ Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms.♦ Let’s discuss all the bold terms one by one.
• Contain 5 types of Chlorophyll (Chlorophyll a to Chlorophyll e)◘ Thalloid body (Thallus structure)
• Thalloid means a flat body with no differentiation into roots, stem and leaves.
• Just remember the word “Thali or Thela” which means Plate or dishes, and a plate contain only circular body. They don’t have legs (roots in case of algae) or head (Stem and leaves in case of algae).

• An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals.
• In greek word the term ‘Trophe’ means nourishment” or “food”.
• And we know the term ‘Auto’ means ‘Self’.
• The term autotroph was coined by the German botanist Albert Bernhard Frank

• Aquatic plants are plants that have adapted to living in aquatic environments both in saltwater and freshwater.

 Habitat of Algae

◘ They occur in a variety of habitats like moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).

➧ Cryophytic Algae
◘ Grow on snow
• Sphaerella/ Haematococcus :- Red snow ball ( due to haematochrome pigment)
• Chlamydomonas nivalis :- Red snow (Due to carotene pigment)
• Chlamydomonas Yellow stonensis :- Green snow.

➧ Thermophytes / Thermal algae
◘ Present in hot water spring (75 – 85 deg C)
Example :- • Phormidium
• Scytonema
• Synechococcus
• Mastigocladus.

➧ Epiphytic algae
◘ Grow on other plants.
Example :- • Oedogonium
• Cladophora
• Vaucharia & Rivularia.

➧ Halophytic algae
◘ Present in saline habitat
Example :-
• Chlamydomonas ehrenberghii (In Salt Lake)
• Enteromorpha species (In salt spring )

➧ Lithophytes algae
◘ Present on the moist surface or rock.
Example :- Diatoms

➧ Aquatic algae
◘ Present in water bodies
◘ Fresh water algae (Ponds, lakes, tanks , river)
Example :- • Zygnema
• Cladophora
• Ulothrix

➧Marine water algae
◘ Present in sea , ocean
Example :-
• Sargassum
• Ulva
• Codium

➧ Parasitic algae
◘ Grow as a parasite
Example :-
• Cephaleuros virescens on tea leaves :- Causative organism of Red Rust of Tea disease.
• Cephaleuros coffee algae on coffee leaves.

Form and Size of Algae

◘ The form and size of algae is highly variable.
• Algae range in size from picoplankton ( 0.2 to 2 micrometers in diameter) to giant kelp (large brown algae), which can be 50 metres (160 feet) long.

Macrocystis pyrifera
• Commonly known as giant kelp or giant bladder kelp, is a species of kelp (large brown algae).
• Giant kelp mainly found in the coast of the western Pacific Ocean, also found in the southern oceans near South America, South Africa, Australia, and New Zealand.

Microscopic unicellular forms of algae ➥ Chlamydomonas
Colonial forms of algae ➥ Volvox.
Filamentous forms of algae ➥ Ulothrix and Spirogyra.
Marine forms of algae ➥ kelps

 Types of Reproduction method in Algae

♦ The algae reproduce by 3 methods ….
◘ 1. Vegetative mode of reproduction.
◘ 2. Asexual mode of reproduction
◘ 3. Sexual methods of reproduction♦ Vegetative reproduction is by fragmentation. Each fragment develops into a thallus.♦ Asexual reproduction is by the production of different types of spores
• The most common being the zoospores.
• Zoospores are flagellated and motile
• The Zoospores germinate to gives rise to new plants.

♦ Sexual reproduction takes place through fusion of two gametes.
• Different types of Sexual reproduction. ….

Isogamous reprodution
• Isogamy is a form of sexual reproduction that involves gametes of similar morphology.
• Here similar morphology means similar in shape and size.
• In Isogamy the gametes can be flagellated (motile) or non-flagellated (non- motile)
• Flagellated (motile) algae Chlamydomonas.
• Non-flagellated (non-motile) algae Spirogyra.

Anisogamous reprodution
•Fusion of two gametes dissimilar in size, as in some species of Chlamydomonas is termed as anisogamous.

oogamous reprodution
• Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete is termed oogamous, e.g., Volvox, Fucus.

Types of Algae

◘ The algae are divided into three main classes ….
• 1. Chlorophyceae (Green algae)
• 2. Phaeophyceae (Brown algae)
• 3. Rhodophyceae (Red algae )➲ Chlorophyceae (Green algae)
Plant body of Green algae
▶ Plant body may be ….
• Unicellular
• Filamentous
Types of chlorophyll in Green algae
▶ Always grass green due to the dominance of two pigments.
• Chlorophyll a and
• Chlorophyll b

Shape of chloroplasts in Green algae
▶ The chloroplasts of Chlorophyceae family may be
• Discoid
• Plate-like
• Reticulate
• Cup-shaped
• Spiral or ribbon-shaped

Storage body of Green algae
▶ Storage body of green algae is known as Pyrenoids
• Pyrenoids located in the chloroplasts.
• Pyrenoids contain protein and starch.
• Some algae may store food in the form of oil droplets.

Cell wall of Green Algae
• Usually have a rigid cell wall.
• Cell wall of green algae made of …
– Cellulose (inner layer) and
– Pectose (outer layer).

Reproduction mode of Green Algae
▶ Vegetative reproduction takes place by …..
• Fragmentation or
• by the formation of different types of spores.
▶ Asexual reproduction takes place by flagellated zoospores.
▶ The sexual reproduction may be …
• Isogamous
• Anisogamous
• oogamous.

Example of Green Algae
▶ Some commonly found green algae are ….
• Chlamydomonas
• Volvox
• Ulothrix
• Spirogyra
• Chara

➲ Phaeophyceae (Brown algae)
Habitat and Forms of Brown Algae
▶ Phaeophyceae family algae primarily found in marine habitats.
▶ They shows various forms like …
• Simple branched
• Filamentous forms (Ectocarpus)
• Profusely branched forms (Kelps)

Types of chlorophyll in Brown Algae
▶ They contain three types of pigments ..
• Chlorophyll a, c
• Carotenoids
• Xanthophylls (fucoxanthin)
▶ Due to presence of these pigments the ocolour of brown algae varies from olive green to various shades of brown.

Food storage in Brown Algae
▶ Food is stored as complex carbohydrates
▶ The complex carbohydrates stored in the form of laminarin or mannitol.

Cell wall of Brown Algae
▶ The vegetative cells have a cellulosic wall
▶ The cellulosic wall covered by a gelatinous coating of algin.

Reproduction in Brown Algae
▶ Vegetative reproduction takes place by fragmentation.
▶ Sexual reproduction may be isogamous, anisogamous or oogamous.
▶ Asexual reproduction in brown algae is by pear-shaped biflagellate zoospores

Example of Brown Algae
▶ The common brown algae are ..
• Ectocarpus
• Dictyota
• Laminaria
• Sargassum
• Fucus

➲ Rhodophyceae (Red algae)
Habitat of Red Algae
▶ Majority of the red algae are marine
▶ Largely found in the warmer marine areas.

Pigments in Red Algae
▶ Predominance of the red pigment, r-phycoerythrin

Storage in Red Algae
▶ The food is stored as floridean starch.

Reproduction in Red Algae
▶ Usually reproduce by vegetative fragmentation.
▶ They reproduce asexually by non-motile spores.
▶ Also They reproduce sexually by non-motile gametes.
▶ Sexual reproduction is oogamous

Example of Red Algae
▶ The common members are
• Polysiphonia
• Porphyra
• Gracilaria
• Gelidium

Main Characteristics of Algae in Brief Tabular format

Classes Common Name Major Pigments Stored Food Cell Wall
Chlorophyceae Green algae Chlorophyll a, b Starch Cellulose
Phaeophyceae Brown algae Chlorophyll a, c,
Mannitol, laminarin Cellulose and algin
Rhodophyceae Red algae Chlorophyll a, d
Floridean starch Cellulose, pectin and
poly sulphate esters

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