Algae: General Characters (with Power Point Presentation – PPT)

Important Characteristics of Algae


“The life of the planet began the long, slow process of modulating and regulating the physical conditions of the planet. The oxygen in today’s atmosphere is almost entirely the result of photosynthetic living, which had its start with the appearance of blue-green algae among the microorganisms”

                                                                     Lewis Thomas, 1984

General appearance of algae

An Algal Bloom of Blue Green Algae

What are algae?

Algae is a group of chlorophyll containing thalloid plants which bear unicellular or multicellular sex organs and the sex organs are NOT protected in the sterile jacket cells. An undifferentiated plant body is known as ‘thallus’. In thalloid plants, there is no differentiation of plant body into true roots, stem and leaves.

The study of algae is known as PHYCOLOGY. The one who study algae is called Phycologist

General characters of algae

Ø  Thalloid plant body

Ø  In Eichler’s system of classification, algae are placed in the Division Thallophyta along with Fungi and Lichens.

Ø  Algae are autotrophs (synthesize food using light energy)

What is thallus?

Spirogyra Thallus *

Ø  Algae differ from fungi in:

⊕. Presence of photosynthetic pigment – chlorophyll
⊕. Mode of nutrition (autotrophs)

Ø  Majority of algae are in aquatic habitat (fresh water or marine), some algae are terrestrial also

Ø  Algae are present in all parts of the world including Arctic and Antarctic regions (universal occurrence)

Ø  Sex organs are unicellular or multicellular

Evolution of sex in algae

Oogonium (female sex organ) of Oedogonium *

Ø  Sex organs lack jacket cells around them (naked sex organs)

Ø  If jacket cells are present, they have different origin

Ø  There is a progressive complexity in the reproduction of different algal groups

Ø  Embryos is not formed after zygote formation

Ø  Show distinct alternation of generation

Ø  Cellular organization may be prokaryotic (blue green algae) or eukaryotic (all other algae)

Occurrence of algae:

Ø  Found in a variety of habitats (Fresh water, marine, on rocks, with in plants or animals)

Ø  Aquatic forms are most common

Ø  On the basis of habitat, algae are classified into three groups

1. Aquatic forms

2. Terrestrial forms

3. Algae of unusual habitats

chlamydomonas image

Chlamydomonas (Unicellular Flagellated Algae) #

(1). Aquatic algae:

Ø  Two types: Fresh water and marine forms

(a). Fresh water forms: Occurs in ponds, lakes, river etc. (Spirogyra)

(b). Marine water forms: Occurs in saline condition such as seas and oceans (Most of the Red and Brown algae such as Polysiphonia and Sargassum)

(2). Terrestrial Algae:

Ø  Found in/on soil, rocks, moist wall, tree trunks etc.

Ø  Example: Vaucheria and Fritschiella found on the surface of soil

Parasitic algae Cephaleuros

Red Rust on Leaves by Cephaleuros #

(3). Algae of unusual habitat:

Halophytic algae: algae present in highly saline water (Example: Dunaliella)

Epiphytic algae: algae grown on the surface of other plants/algae (Example Oedogonium)

Epizoic algae: algae grown on animals such as snails and fishes (Example: Cladophora grows on the shells of snails)

Endozoic algae:  algae growing inside the animals (Example: Zoochlorella grow inside Hydra)

Thallus organization in algae

Dunaliella (single celled algae) *

Symbiotic algae: Symbiotic (mutual) association with fungi in lichen, in Bryophytes (Anthoceros), in Pteridophytes (Azolla), gymnosperms (corolloid roots of Cycas) and in angiosperms.

Parasitic algae: grow as parasite on plants or animals (Example: Cephaleuros is a parasitic green algae grow on the leaves of many plants causing red rust diseases)

Thermophytic algae: grow in hot springs. (Example: Heterohormogonium)

Fluviatile algae: algae found in rapidly running water such as water falls (Example: Ulothrix occurs in mountains water falls

Thallus diversity in algae:

Ø  Wide range or thallus variation in algae

Ø  Thallus may be unicellular to multicellular and microscopic to macroscopic

Ø  Plant size range from few micron to several meters

Which is the largest algae

Largest Algae (Macrocystis pyrifera) *

Ø  Example: Chlamydomonas is a single celled algae whereas Macrocystis pyrifera, a marine brown algae, is multicellular, parenchymatous and several meters long.

Ø  On the basis of thallus organization algae are following five types:-

(1). Unicellular forms (Example: Chlamydomonas, Chlorella)

(2). Colonial forms (Volvox, Pandorina)

(3). Filamentous forms

(a). Un-branched filamentous (Spirogyra, Oedogonium)

(b). Branched filamentous (Cladophora, Pithophora)

(4). Siphonaceous forms (Vaucheria)

(5). Parenchymatous forms (Sargassum, Laminaria)

Pigmentation in algae:

Ø  Algae also shows great diversity in pigmentation

Ø  Different groups of algae have different pigment composition

Ø  Distribution pattern of pigments has great taxonomic significance in algae

Ø  The classification of algae by Fritsch is primarily based of the pigmentation in algae

Ø  Pigments in algae belongs to three major categories:

(1). Chlorophylls

(2). Carotenoids

(3). Phycobilins

Ø  All major algal groups have at least one characteristic pigment

Cyanophyceae (blue green algae): Phycocyanin

Chlorophyceae (green algae): Chlorophyll b

Pheophyceae (brown algae): Fucoxanthin

Rhodophyceae (red algae): Phycoerythrin

Chlorophyll a is universally present in all algal grous

Plastids in algae:

Ø  Except in Cyanophyceae (blue green algae, BGA) pigments in algae are found in membrane bound organelles called plastids

Ø  In BGA, plastids are absent, pigments located at peripheral cytoplasm called chromoplasm

Ø  Plastids are two types:

(1). Leuoplast: – Colourless plastids

(2). Chromoplast: – Coloured plastids

Plastid forms in algae:

Ø  Algae shows great diversity in plastid shape, Plstids may be:

Chloroplast diversity in algae

Spiral Shaped Chloroplast (Spirogyra) *

Cup shaped: Clamydomonas, Volvox

Discoid: Voucheria, Chara

Girdle shaped: Ulothrix

Reticulate: Oedogonium, Hydrodictyon, Cladophora

Spiral: Spirogyra

Stellate (star shaped): Zygnema


Ø  They are proteinacious bodies present in chromatophores

Ø  Considered as the organelle of synthesis and storage of starch

what is pyrenoid

Pyrenoid of Chlamydomonas *

Ø  In some Chlorophyceae pyrenoids are surrounded by starch grains

Ø  Pyrenoids arise de-novo or by the division of preexisting pyrenoids

Ø  Pyrenoids absent in blue green algae

Reserved food materials in algae:

Ø  It is also called as food reserve. It is the stored form of food in the cells for energy. Different algal groups have different types of reserved food materials. Similar to pigmentation in algae, the distributional difference in reserved food is also in the classification of different algal groups.

Cyanophyceae: cyanophycean starch

Chlorophyceae: Starch

Rhodophyceae: Floridean starch

Phaeophyceae: Laminarin, manitol and oil

Learn more: Lichen – General Characters

Fungi – General Characters

Bryophytes – General Characters

Reproduction in algae:

Ø  Algae reproduce by three methods:

(1). Vegetative reproduction: Cell division, fission, fragmentation, Hormogonia, formation of adventitious branches, tubers, buddings etc. are the important vegetative reproduction methods in algae.

(2). Asexual reproduction: By a variety of motile or non-motile spores. Zoospore, aplanospore, hypnospore, tetraspore, autospore, akinetes etc are the important spore types in algae

(3). Sexual reproduction: here the union of gametes are involved: Autogamy,  hologamy,  isogamy, anisogamy and oogamy are the different types of sexual reproduction algae.

Alternation of generation:

Ø  Alternation of generations (also known as alternation of phases) is a term primarily used to describe the life cycle of plants

Ø  Most algae have an alternation of many celled haploid gametophytic generation with many celled diploid sporophytic generation, which alternate regularly.

Life cycle in algae:

Ø  The growth and development consists of a number of distinct morphological and cytological stages

Ø  The sequence of these orderly changes is called life cycle

Ø  Life cycle: sequence of all different phases or events through which an organism passes from zygote (diploid) of one generation to the zygote of the next generation through gametes (haploid)

Ø  There are five types of life cycles in algae based on the number of haploid and diploid generation

Life cycle in algae:

(1). Haplontic: simple type, major stages in the life cycle are haploid, the diploid stage is represented by only the zygote. Zygote undergo meiosis to produce spores (Chlamydomonas, Ulothrix)

(2). Diplontic: Just reverse of the haplontic type. Major stages in the life cycle are diploid, the haploid stages are represented only by gametes. (Sargassum, Codium)

(3). Haplobiontic: Three phases in life cycle. Among three phases, two are haploid and one is diploid (Batrachospermum, Coleochaete)

(4). Diplobiontic: Three phases in life cycle, two are diploid and one is haploid. Majority of marine Red algae are this type (Polysiphonia)

Major Classes of Algae (algal systematics)

(1). Cyanophyta: Blue green algae (BGA), prokaryotes

(2). Euglenophyta: Motile, protozoan like algae lack true cell wall

(3). Crysophyta: Golden-brown algae = diatoms

(4). Pyrrophyta: Dinoflagellates

(5). Chlorphyta: Green algae

(6). Rhodophyta: Red algae

(7). Paeophyta: Brown algae

* Images taken from wikipedia
# Images taken from flickr

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