Algae : occurrence, classification and economic importance

Algae: Occurrence, types, classification, economic importance

Topics covered:

  • Introduction to algae.
  • Occurrence.
  • Characteristics.
  • Classifications.
  • Economic importance.

Introduction to algae

  • Linnaeus in 1753 was first to introduced the term algae (Latin- seaweeds) meaning, the Hepaticeae.
  • The algae (singular: alga) many of which are are unicellular.
  • Algae are ubiquitous, most of algae lives in aquatic environment but many also thrive a terrestrial and a subterranean alga.
  • Algae contains chlorophyll and are photosynthetic.
  • algae are of great general interest to all biologist because single algal cells are complete organism capable of photosynthesis and the synthesis of a multitude of other compounds which constitutes the cell.
  • The branch that deals with the study of algae are known as as phycology.
  • Algae chlorophyll bearing thalloid.

Occurrence

  • Algae are present everywhere in distribution.
  • They occur in great abundance in oceans, seas, ponds, fresh water, steams and Salt Lake.
  • Many are found in soil of dam, rocks, stones, and bark of tree and on other animals and plants surface.
  • Small aquatic forms make a large of the free floating microscopic life in water, called plankton.
    • Phytoplankton is made up of plants i.e. algal forms.
    • Zooplankton is composed of animal organisms.
  • Some Species of algae grow on the snow and ice of polar region and mountain peaks.
  • Some, algae grow in hot springes at temperature has high as 55°C.
  • Some are Endophytice. They are not free living but live in other organisms such algae are widespread in protozoa, molluscus, sponges and corals.

Characteristics of algae

Morphology

  • Algae have a wide range of size and shapes.
  • Algae that occur as unicellular and they are spherical, rod-shaped, club-shaped, or spindle shaped.
  • Many are multicellular and have understandable form, shape and various complexity.
  • Algal cells are eukaryotic.
  • In most of the algal species cell wall is very rigid and thin.
  • Cell wall of diatoms are contain silica which makes them thick and rigid.
  • The motile algae have flexible cell membrane called Periplasts. eg. Spirulina.
  • Algae contains a discrete nucleus.
  • Chlorophyll and other pigments are found in membrane bound organelles known as Chloroplast.
  • Within the plastid matrix or stroma are found flattened membranes vesicles called Thylakoid.

Algal pigments

  • There are three kinds of photosynthetic pigments are present in algae:
  • chlorophyll
  • carotenoid
  • biloproteins or phycobilins

Chlorophyll

  • There are five chlorophylls: A, B, C, D and
  • Chlorophyll A is present in all algae.
  • Chlorophyll B – Euglenophycophyta, Cholorophycophyta.
  • Chlorophyll C– Xanthophycophyta, Bacillariophycophyta, Chrysophycophyta, Cryptophycophyta.
  • Chlorophyll D – Rhodophycophyta
  • Chlorophyll E – Xanthophycophyta.

Carotenoids

There are two kinds of carotenoids:

  • Carotenes – linear, unsaturated hydrocarbon.
  • Xanthophyll – oxygenated derivatives.

Biloproteins or phycobilins

  • It is water soluble pigments.
  • Present in Rhodophycophyta.
  • Two types of phycobilins – Phycocyanin, Phycoerythrin

Reproduction

  • Algae may be reproduce asexually or sexually.

Asexual reproduction

  • Unicellular algae reproduce asexually by mitosis.
  • Multicellular algae also reproduce asexually either by vegetative means or by mitotically produced asexual spores called Mitospores.

Some common example of mitospores are:

  • Zoospores– flagellate motile spores.
  • Aplanospores– non- motile spores.
  • Autospores– non – motile produces by chlorella.

Sexual reproduction

Sexual reproduction involves:

  • Gamete formation
  • Fertilization
  • Meiosis

In algae three distinct type of sexual life cycles are reported.

    1. Halpontic
    2. Diplontic
    3. Haplodiplontic.
  • Sex organs of algae is Gametangia.
  • Antheridium – Male sex organs.
  • Oogonium – Female sex organ.
  • If the two gametes are look alike neither male nor female, such gametes are called, isogametes, infusion process is isogamous. Example – In spirogyra.
  • If the two gametes differ in size, these gametes are Anisogametes and the fusion process of anisogametes are referred as Anisogamous Example – In Chlamydomonas.
  • Smaller one is male and the larger one is female.
  • The female gamete (egg) is large and non motile and the male gamete is small and motile such gametes are oogametes and fusion process is Known as oogamy. Example – In Volvox, fucus.

Classification of alage

The are three main groups of algae being:

    1. Green algae
    2. Red algae
    3. Brown algae.

They are classified on the basis of following characteristics:

    1. Primary photosynthetic pigments.
    2. Storage product.
    3. Cell wall composition.
    4. Type and location of flagella.

Green algae – Chlorophyceae

  • Habitat – Freshwater, Marine and terrestrial.
  • Photosynthetic pigments- Chlorophyll A and B carotenoid.
  • Cell wall components- Cellulose.
  • Storage food- Starch (stored inside the plastids).
  • Flagella- Two flagella per cell.
  • Asexual reproduction- reproduce vegetatively by fermentation or by formation of mitospores.
  • Sexual reproduction- reproduction is of Isogamous, Anisogamous, Oogamous.

Example- Chlamydomonas, Volvox, ulothrix, chara, ulva (sea lettuce).

Red algae – Rhodophyceae

  • Habitat- Marine and freshwater.
  • Photosynthetic pigment- Chlorophyll A and D, carotenoids and phycobilins. Commonly called red alage because of presence of red pigment – phycoerythrin.
  • Cell wall components- Cellulose
  • Stored food- Floridian starch (alpha -1,4 glucon) stored in cytosol.
  • Flagella- Absent.
  • Asexual reproduction- By fragmentation or by non-motile mitospores.
  • Sexual reproduction- Oogamous and gametes are non- motile.
  • Example – Polysiphoria, Gracilaria and Gelidium.

Brown algae – Phaeophyceae

  • Habitat- marine and freshwater.
  • Photosynthetic pigment- chlorophyll A and C, carotenoids and phycobilins.
  • Shades of brown depends on xanthophyll pigment, fucoxanthin, present.
  • Cell wall components- cellulose and alginic acid.
  • Cellulose is covered by a gelatinous coating of Algin.
  • Stored food- Laminarin, mannitol
  • Flagella- 2, unequal, lateral.
  • Asexual reproduction- by fragmentation or by motile zoospores.
  • Sexual reproduction- is isogamous, anisogamous, Oogamous.
  • Example – Ectocarpus, Laminaria, fucus.

Economic importance of algae

  • Algae as primary producers- algae provides the base or beginning of most aquatic animals or organisms because of their photosynthetic activities so it is also known as primary producers of organic matter.
  • Commercial products from algae- many products are derived from algal cell wall for economic value. Three of these are: Agar Alginic Acid, and Carrageenan, are produced from the walls of algae.
  • Carrageenan is produced from the walls of several red algae. Species of Chondrus, Gigartina are mostly used.
  • Agar is well known as a solidifying agent in the preparation of microbiological media. It is obtained from red algae. Species of Gelidium and Gracilaria are extensively used.
  • Alginic acid and its salts are obtained from the wall for brown algae. Species of brown algae producing this compound include- Macrocystis, Laminaria, Fucus.
  • Algae as food- many species of algae are (mostly red and brown algae) are used as food in the far east.
  • Red algae one of the most important is Porphyra: it is used as food in Japan where it is called
  • Other red algae such as Chondrus, Nemalion are locally collected and prepared.

Reference and Sources

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Algae: occurrence, types, classification, economic importance

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