Algae Nutrition and Photosynthesis

Algae Characteristics

• Algae manufacture their own carbohydrate food from carbon dioxide and water through the agency of sunlight.
• Aquatic forms obtain water and carbon dioxide by osmosis and diffusion, respectively, from the medium in which they grow.
• Aerial forms obtain H2O from the damp substratum and CO2 from the air.
• Algae synthesize oil and proteins from the carbohydrates they manufacture, and the soluble forms of nitrogen and other minerals available in solution in the water in which they grow.

Environmental Factors

• Favorable temperature, suitable light, proper supplies of oxygen, carbon dioxide, and essential elements favor the growth of algae.

Reproduction in Algae

• Algae exhibit three types of reproduction: vegetative, asexual, and sexual reproduction.

Vegetative Reproduction

• Fission: unicellular forms reproduce by vegetative method called fission or cell division, resulting in two daughter cells that separate immediately.
• Fragmentation: multicellular forms with a filamentous thallus reproduce by breaking into small portions of living cells called fragments, which grow into new individuals.
• Akinetes: single-celled resting fragments, specially modified to function as a means of perennation and multiplication, formed either singly or in chains in the vegetative filament.

Asexual Reproduction

• Asexual reproduction is the commonest method of multiplication among algae under favorable conditions.
• Spores involved in asexual reproduction include zoospores, aplanospores, autospores, hypnospores, carpospores, tetraspores, endospores, and exospores.
• Zoospores are the most important kind of asexual spore, provided with one or more flagella and containing a chromatophore, a nucleus, and an eye spot.

Sexual Reproduction

• Sexual reproduction takes place under unfavourable conditions.
• Gametes (male and female) are produced within gametangia.
• The plant may be homothallic (producing male and female gametes in the same individual) or heterothallic (producing male and female gametes in separate individuals).
• Sexual reproduction can be categorized into two types: isogamous and heterogamous.

Isogamous Type

• Both male and female gametes are morphologically similar but differ physiologically.
• This type is common among unicellular algae and considered to be primitive.

Heterogamous Type

• Both male and female gametes differ both morphologically and physiologically.
• Male gametes are usually smaller in size.
• This type can be further categorized into anisogamous and oogamous.

Anisogamous Type

• Both fusing gametes are motile, but the male gametes are comparatively smaller in size and more active.

Oogamous Type

• It is considered the most advanced type of sexual reproduction.
• It is common among the higher algae.
• The male gametes are motile and found in large numbers, whereas the female gametes are non-motile and bigger in size.

Life Cycle in Algae

• Three different types of life cycles exist, depending on when meiosis occurs, the type of cells produced, and if there is more than one free-living stage present in the life cycle.