Q.4. Describe foliaceous forms of thallus with example.
Ans. Foliceous forms (parenchymatous thallus): -
The plant body occurs in the form of multicellular, flat, plate-like or leaf like morphology. It develops a parenchymtous thallus in which the cells divide in more than one plane. Examples - UIva (Chlorophyta), Saragassum, Laminaria (Phaeophyta), Prophyra (Rhodophyta), etc.
Q.5. What are the salient features on which the classification of algae is based ? (1993, 96)
Ans. There are some important salient features on which the classification of algae is based. These are given below:
1. Organisation of the thallus: - In thallus organisation the algae shows much differentiation of plant body. Some points are as follows.
(a) Some algae are unicellular form these are two types-
(i) Non-Motile: - They include chlorela, chlorococum
(ii) Motile: - They include chlamydomonos
(b) Many algae are unbranched filamentous form and branched filament form.
(i) Unbranched filamentous form -
Example: - Spirogyra, Oscillatoria, Spirulina etc.
(ii) Branched filamentous form -
Eample: - Scystonema, Ectocarpus, Polysiphonia etc.
2. Algae cell structure: - Algae cells constituting of thalli are basically two kinds. Prokaryotic and eukaryotic. The prokaryotic cells differ from eukaryotic cells in the absence of nuclear membrane, mitochondria plastids and true nucleous.
(i) Prokaryotic cell (Blue green algae): - The thallus of blue green algae consists of prokaryotic cell. The prokaryotic cells have a cell wall which contain a specific stregthenic component not found in the cell walls of other algae it is mucopeptic component. This is not divide mitotic. DNA is the nuclear material and present centrally, e.g., Microcystis, Nostoc, Anabaena.
(ii) Eukaryotic cell: - A algae cell have developed cell organells, e.g. Chlorophyceal, Rhodophyceae, Pheaopeyceae Xanthohyceae etc.
3. Algae pigments: -Pigments have an important roll in the classification of algae. Definite chemical compound present in algae cell and a provide various colour in different classes. These are known as pigment. Thallus have a perticular colour due to predominant of one pigment in a combination of some others. Combination of pigments i.e. chlorophyll, caratenoids and phycobilins or biloproteins gives particular colour to algae in different classes. Thus the nature of pigment helps in primary classification of algae in to divisions.
Example: -
(i) Chlorophyceae (Grass green): - Chlorophyll a and b, carotene.
(ii) Xanthophyceae (Yellow green): - Chlorophyll a and e, carotene.
(iii) Phaeophyceae (Brown): - Chlorophyll a, b-carotene.
(iv) Rhodophyceae (Red algae): - Chlorophyll a, carotene and a-carotene.
4. Flagella type: - Motile algae cell have filament like structure.These are flagella.
Flagella in algae are two types: - (i) Whiplash and (ii) Tinsel
Whiplash flagellum is smooth surfaced. The tinsel flagellum bears longitudinal row of fine, minute flimmer hairs arranged along the axis almost to the tip of the flagellum.
Example: - Whiplash flagellum - Chlamydomonas
Tinsel flagellum: - Two types as follows: -
(i) Single row of Hairs: - Euglenophyta, and Pyrrophyta
(ii) Two row of Hairs: - Class-Chrysophyceae and Phaeophyceae.
5. Food reservers : - Reserve food material change group to group, and this plays an specific roll of preliminary classification of algae.
(i) True starch: - It is found in two algae division namely, Chlorophyta and Charophyta.
(ii) Cynophycean starch: - Found in division Cynophyta.
(iii) Floridean starch: - Characteristic of division Rhodophyta
Some other polysaccharides : -
Laminarin: - Found in brown algae i.e. division pheophyta.
Paramylon: - Characteristic of Euglenoids.
Leucosin: - It is peculiar to the Xanthophyta, Basillariophyta, and Chrysophyta.
Mannitol: - It is unique formely found in brown algae.
6. Reproduction: - Reproduction method vary on the nature of the thallus of algae.
The lower forms (Primitive algae) reproduce only by vegetative methods. But in the higher form both asexual and sexual reproduction are common occurence.
(a) Vegetative reproduction: - It occurs by :
(i) Fission (ii) Fragmentation (iii) Budding
(b) Asexual reproduction : -
(i) By spore formation: - Spores are reproductive unit, e.g., Chlamydomonas, Ectocarpus.
(ii) By Zoospores: - These are motile cell swime over the water e.g., Chlamydomonos, Uolthrix, Oedogonium.
(iii) By Aplanospore: - These are non-motile cell. Mainly found in terrestrial algae e.g., V’ ucheria, Microspora.
(iv) By Hypnospore: - These are thick walled cells called hypnospores, e.g., Chlamydomonas nivalis.
(v) Akinetes: - These are resting cells, and contain reserve food e.g. Pithophors.
(c) Sexual reproduction: - It is greatly special type of reproduction and not known in Myxophyceae. There are two main types.
1. Isogamy: - The fusion of similar motile gametes e.g., Spirogyra, Ectocarpus.
2. Heterogamy: - It is most advanced type of sexual reproduction as compared with isogamy. It includes the fusion of dissimilar gametes.
(i) Anisogamy: - In this type both gametes are motile but male gametes are comparatively smaller in size and more active, e.g., Chlamydomonas braunii.
(ii) Oogamy: - The male gametes are motile and are formed in large number where as female gametus are non-motile and bigger in size, e.g., Oedogonium, Vaucheria, Chara.
Q.6. Describe the different ways of reproduction in algae. (2009)
Related Question -
Q. Name two algae which produce multiflagellated zoospores. (2006)
Ans. Reproduction in Algae: -
In algae, reproduction found by the following methods :
1. Vegetative reproduction: - In Chlamydomonos , reproduction takes place by cell-division. In Ulothrix, Oedogonium and Vaucheria vegetative reproduction occurs by fragmentation in which filaments break into many small fragments and each fragment grows into a new filament. It takes place by means of hormogonia in Nostoc and Oscillatoria. For vegetative reproduction Bulbils and amylum stars are present in Chara and Nitella etc.
2. Asexual reproduction: - In algae, asexual reproduction takes place by different types of spores. These spores give growth to new plant after germination. Asexual reproduction occurs during suitable conditions. It takes place by the following methods :
(a) By Zoospores: - In algae, zoospores are formed during suitable conditions. In unicellular algae e.g., Chlamydomonos, zoospores are developed by the division of protoplast of parent cell. Zoospores are liberated by the rupturing of plant cell wall and give rise to new cells. In filamentous algae e.g., Ulothrix, Cladophora, Oedogonium and Vaucheria, zoospores are formed inside the zoosporangium. Zoospores of Cladophorra are biflagellate whereas the zoospores of Ulothrix are biflagellate or quadriflagellate. In addition to this, multiflagellate zoospores are found in Oedogonium and Vaucheria.
(b) Palmell stage: - In some algae like Chlamydomonas and Ulothrix, parent cell divides into many daughter cells. These daughter cells do not come out but redivide and become surrounded by mucilagenous sheath. Under favourable conditions, this sheath ruptured and daughter cells get free and functions as zoospores.
(c) By Aplanospores: - In some algae, e.g., Ulothrix, Microspora and Chlorococus, non-flagellate, thick walled aplanospores are formed instead of zoospores, under adverse conditions. In favourable conditions, these aplanospores come out and germinate to give rise to new plant.
(d) By Hypnospores: - When aplnospores of some algae like Pediastrum secrete thick wall around themselves then they are called hyphnospores. They germinate under favourable conditions.
(e) By Akinetes: - During adverse conditions, the whole cell of some algae like Cladophora and pithophora become thick walled to form akinetes which germinate during favourable conditions.
(f) By Autospores: - Parent cells of algae like Chlorella, Chlorococcus and Scendesmus form into resting spores which are called autospores. They are thick walled and liberate only when the parent cell ruptures.
(g) By Cysts: - Many speta are formed in the filament of Vaucheria and each filament divides into a number of segments. A thick wall is formed in each segment during unfavourable conditions.
(h) By Endospores: - Tetraspores formed in Polysiphonia are called endospores. These spores after liberating from the sporandia germinate to give new plant.
3. Sexual reproduction: - There are three types of sexual reproduction takes place in algae.
(a) Isogemous: - This type of sexual reproduction is found in Chlamydomonas, Ulothrix and Cladophora. The size of the gametes taking part in this sexual reproduction is similar, but their physiology is different, e.g., one gamete is of plus (+) strain called female and other gamete is of minus (-) strain called male.
(b) Anisogemous: - It is occuring Chlamydomonas braunni, Udorina and Pandoria. The gametes of this type are dissimilar in size and physiology, i.e.male gamete is smaller in size and more active whereas female gamete is larger in size and sluggish.
(c) Ooggamous: - This is the most advanced type of sexual reproduction. It occurs in C. coccifera, Oedogonium, Volvox and Vaucheria. Male and female gametes are clearly distinct from each other. Male gamete is smaller, bilagellae, motile and active which goes near to the female gamete during fertilization. In contrast to this female gamete is very large, non-flagellate and non-motile. Sperm is formed within the antheridium and egg within the Oogonium in Volvox, Oedogonium and Vaucheria.
Advanced oogamy is found in the members of Phaeophyceae e.g., Ectocarpus siliculosus, Sargassum and Fucus. Similarly, most advanced oogamous type sexual reproduction occurs in the members of Rhodophyceae e.g., Batrachospermum and Polysiphonia. Their female sex organs carpogonia are flask-shaped with long trichogyne. Their male gametes are motile which goes near the trichogyne to perform fertilization.