All the multicellular eukaryotic plants are placed in Kingdom Plantae. They are autotrophic, i.e. they manufacture their food by photosynthesis.
FOLLOWING PLANT GROUPS ARE INCLUDED IN KINGDOM-PLANTAE:
(a) Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic plants.
(b) Term "Algae" was given by Linnaeus
(c) Phycology- Study of algae
(d) Father of Phycology- Fritsch → Book → "Structure & Reproduction of algae"
(e) Father of Indian phycology- Mandayam Osuri Parthasarathy Iyengar
3. Sexual Vegetative Reproduction
1. Vegetative reproduction is by fragmentation, where each fragment develops into a thallus.
2. Asexual reproduction is by the production of flagellated zoospores which on germination give rise to new plants.
3. Sexual Reproduction
ALGAE IS DIVIDED INTO FOLLOWING DIVISIONS
1. Chlorophyta: Green Algae
2. Phaeophyta: Brown Algae
3. Xanthophyta: Yellow- Green Algae
4. Rhodophyta: Red Algae
(a) Green algae are the most advanced algae. It is believed that green algae are the ancestors of the higher plants.
(b) Habitat: Green algae are cosmopolitan in nature.
Different forms of Green algae (Structure): Green algae are found in many forms.
1. Unicellular: A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell.
(a) Chlamydomonas: Motile unicellular algae. This algae moves with the help of flagella.
(b) Chlorella: Non-motile unicellular alga.
Chlorella Unicellular Alga
(c) Acetabularia: Umbrella plant - It is the largest unicellular plant. The diameter of its cell is 10 cm.
Acetabularia umbrella Plant
2. Coenocytic: Some green algae are coenocytic i.e. multi-nucleated.
Note: According to five kingdom system the algae described above should be placed in Protista but exceptionally due to their life cycle, it is similar to green algae. They are placed in Plantae. But now modern scientist place above algae in protista.
3. Colonial: Some green algae are found in colonies. They form a colony of cells. The number of cells in a colony is fixed. Colony with fixed number of cells is called coenobium.
Example: Volvox- Motile colony Hydrodictyon- Non-motile colony (called as water net).
4. Multicellular filamentous: Mostly algae are multi-cellular filamentous.
Example: Ulothrix- Known as pond wool, Spirogyra- Known as pond silk.
Some green algae are heterotrichous i.e. two types of branches, prostrate and erect- Fritschiella, Stigeoclonium, Coleochaete (Fritschiella tuberosa has approach to the early land plants).
5. Multicellular thalloid or Parenchymatous: Some algae are multi-cellular in length & width.
Example: Ulva- Also called as sea lettuce.
Chlorophyll- Chl 'a' and Chl 'b'
Carotene- b carotene
Xanthophyll- Luteaxanthin and Violoxanthin- Yellow coloured
Note: The green colour of green algae is due to chlorophyll.
Stored food: In green algae, the food is stored in the form of starch.
Note: On the basis of pigments (Chl 'a', Chl 'b', Carotenoids), stored food (starch) & cell wall (made up of cellulose or pectin), green algae are considered similar to higher plants.
1. Food: Chlorella is used as food, because after Spirulina, Chlorella has largest amount of protein.
2. Antibiotics: Chlorellin antibiotic is obtained from Chlorella.
3. Space research: In space, Chlorella is used as a source of food and O2.
4. Parasitic algae: Cephaleuros algae remains parasitically in the leaves of tea plant and causes disease 'red rust'.