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Algae Definition, Characteristics and Examples

Algae are chlorophyll bearing, simple, thalloid, autotrophic and large aquatic organisms. Due to their ability to grow under various circumstances, they are found in various habitats like moist stones, soil, lake, pond, wood, etc. Various types of algae are present in this world. Algae can reproduce very fast, and they can cover the entire surface over a short period. Excessive growth of algae in the water is known as an algal bloom. They occupy the bottom-most place in a food chain and play a significant role in the ecosystem. They are considered a food source for several aquatic and non-aquatic species.

Size and Form

The form and size of algae are highly variable. However, based on the size, they can be of the following two types:

  1. Microalgae: It includes microscopic unicellular organisms (Chlamydomonas). For single-celled algae, the thallus is the body of the vegetative form of algae.
  2. Macroalgae: It includes macroscopic multicellular, colonial organisms (for e.g., Volvox) and filamentous species like Spirogyra. It also includes massive algal forms, including giant Kelps, which reside in marine water.

The highly filamentous and massive shape of the algae helps inefficient movement with the waves of water.

Habit and Habitat

The spores of algae are found everywhere in the environment, such as air, water, soil, and bodies of various animals. Algae can also grow in association with fungi in the form of lichen. This is an example of a symbiotic relationship.

Types of Algae

Algae can be divided into three main classes based on the following features, which will be discussed ahead:

  1. Habit
  2. Cell wall
  3. Pigments
  4. Reserve food material and motility
  5. Number and structure of flagella
  6. Type of reproduction

1. Green algae

The agricultural implements are beneficial in the following ways:

  • It is also known as Chlorophyceae
  • It is generally found in freshwater, brackish water and saltwater Its cell wall is made up of cellulose and pectose It contains some essential pigments like Chlorophyll-a, Chlorophyll-b, Carotene and Xanthophyll It is motile and contains starch as a reserve food material.

2. Brown algae

  • It is also known as Phaeophyceae
  • It is rarely found in freshwater and present in abundance in saltwater and brackish water
  • It has a cell wall of cellulose and phycocolloid (algal Colloids) substance like alginic acid
  • It contains pigments like Chlorophyll-a, Chlorophyll-c, Xanthophyll and the most dominating Fucoxanthin and beta-carotene.
  • It is motile and contains mannitol and laminarin (a polysaccharide of glucose) as reserve food material
  • It has 2 heterokont and laterally inserted flagella
  • Its mode of reproduction is isogamous, anisogamous and oogamous

3. Red algae

  • It is also known as Rhodophyceae
  • Some species are found in freshwater, but mostly, the red algae are found in saltwater and brackish water
  • Its cell wall is made up of cellulose, pectin, xylan or mannan fibrils, poly-sulphated esters like agar and carrageenin.
  • It contains pigments like Chlorophyll-a, Chlorophyll-d, Carotene, Xanthophylls, phycoerythrin and Phycobilins
  • It is non-motile and contains Floridean starch as reserve food material
  • Flagella are absent
  • It reproduces by oogamy

Reproduction in Algae

The three reproduction modes in Alage include sexual reproduction, Vegetative and Asexual reproduction. They are explained further as:

  1. In vegetative reproduction, there is a fragmentation of the parent algae in two parts, and the fragment develops by replicating the rest of the bodies into a separate thallus.
  2. Asexual reproduction occurs by the formation of different types of spores:
  3. Asexual reproduction occurs by the formation of different types of spores:
    1. Zoospores: These are motile asexual spores formed during favourable conditions and are without a cell wall
    2. Aplanospore: These are thin-walled, non-motile spores that are formed from a portion of the protoplasm of the parent cell.
  4. Reserve food material and motility
  5. Number and structure of flagella
  6. Type of reproduction
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