Category: Biology Second Paper Lecture Sheet

When filaments and colonies of multicellular algae are divided into two or more segments by injury or physical reasons, a new algae is formed from each segment. E.g. Ulothrix, Oedogonium, Spirogyra, Nostoc, Oscillatoria etc.

1. By fission: Unicellular algae grow in size by taking food and divide into two new algae by fission process. Like- Chlorella, Euglena, Navicula, Diatom, Protococcus, Gloeocapsa, Synechococcus etc.
2. Segment: When filaments and colonies of multicellular algae are divided into two or more segments by injury or physical reasons, a new algae is formed from each segment. E.g. Ulothrix, Oedogonium, Spirogyra, Nostoc, Oscillatoria etc.
3. Budding: In favorable environment, the algae grows in size by taking food and outgrowths form from the side of the body. A bud or bud is then produced from the subgrowth and the bud separates from the mother body to give rise to new algae. Eg- Protosiphon.
4. Hormogonia: Trichrome of blue-green algae breaks down to form hormogonia. The hormogonium is covered by a thick wall to form the hormocyst. New algae are produced from hormogonia in favorable conditions. Eg Nostoc, Oscillatoria etc.
5. Hormocysts: In unfavorable environment hormogonium of algae is covered by thick wall to form hormocyst. Under favorable conditions, hormocysts germinate and give rise to new algae. Eg Nostoc, Oscillatoria etc.
6. Tuber/Bulbil: Tuber or bulbil is produced by the accumulation of food above and below the rhizoid in some algae. These separate from the mother body and form new algae. Like- Chara, Cladophora, Botrydium etc.
7. Akinity: In unfavorable environment, one or more cells of some protozoan algae swell to store large amounts of food and develop into resting spores covered by a thick wall. These cells are called akinites. Each actinomycete germinates into a new alga in a favorable environment. Such as Nostoc, Oscillatoria, Pithophora, Ulothrix, Gloeotrichea, Revularia etc.
8. Star stach: White matter accumulates in the body of some algae and forms a star-shaped organ. They are called starch stars or amylum stars. Later new algae are born from the starch star. Like Chara, Botrydium etc.
9. Protonema: Protonema is formed from the rhizoids of some algae. New algae grow from these protonema. Like- Chara, Nitella etc.

Stirring ocean water in the tropics ignites fire and produces light. This is called bioluminescence. Pyrrophyta is caused by algae. They create red tides. Pyrrophyta algae contain luciferin. Luciferin is phosphorylated by ATP to form new molecules. The resulting material reacts with oxygen in the presence of the enzyme luciferase to emit light.

1. Cell wall: The cell wall of algae has two layers. The outer layer is composed of pectose and the inner layer is composed of cellulose, pectin or mucilage. Flagellated algae do not have cell walls. The cell walls of diatoms are composed of two layers of siliceous membranes. The siliceous cell wall of an intact diatom is called a frustule. Euglenophyta have membranes called periblasts instead of cell walls.
2. Plasma membrane: The fine and thin membrane inside the cell wall is called plasma membrane. It is composed of lipids and proteins. The plasma membrane of flagellated algae is rigid in nature. This plasma membrane is called periplast.
3. Protoplasm: All the living parts of the cell inside the cell wall are collectively called protoplasm. It consists of two parts. Cytoplasm and nucleus.
(i) Cytoplasm: Different parts of cytoplasm are-
Plasted: Plasted is a dye. Green colored plastids are called chloroplasts. Algae contain blue phycocyanin, red phycoerythrin, brown pheophanin and yellow-brown phycoxanthin along with chloroplasts. They carry out photosynthesis.
Pyrinoid: Pyrinoid is a protein aggregate. Chloroplasts contain one or more pyrenoids. It stores carbohydrates.
Cell vacuole: Each cell has a small cell cavity. It is filled with tissue.
Food: Sugar or starch or white matter is stored as food in green algae. Laminarin and mannitol in brown algae, volutin and fat in golden-yellow algae, and floridian starch in red algae are stored as stored food. Some algae contain leucosin and paramylum as stored food.
(ii) Nucleus : Each cell of algae contains one or more well-formed nuclei. It controls all biological functions of cells.
The body of sinocytic algae is cylindrical, branched, wallless and multinucleated. The body of acinocytic algae is walled and the cells contain one or more nuclei.

The body of some algae is made up of three parts. Hold fast, stipe and frond. Fronds are flat like leaves. Such a structure is called a complex body. Such as- Fucus, Laminaria, Sargassum.

Their body consists of Parva and Parvamadhya. Lateral branches arise from the pars. Like- Chara, Nitella etc.

The body of polysiphon algae consists of many siphons or hollow cylindrical parts. Its central sinusoid is called central siphon and surrounding sinusoid is called pericentral siphon. Eg- Codium, Polysiphonia.

Algae with hollow cylindrical body are called siphon algae. These hollow tubes are called sinusites. Such as Vaucheria, Botrydium, Protosiphonia etc.

The thallus of algae consists of two parts. Recumbent part and aerial part. A thallus with such features is called heterotrichous. Such as Coleochaete, Fritschiella, Stigeoclonium, Trentepohlia etc.

If the cells of algae divide and form a thin and flat leaf-like thallus, it is called thalloid. For example, Enteromorpha, Porphyra, Ulva etc.