Q.31. Write a short note on Phytoplankton. (2008, 11)
Ans. Phytoplankton: -
The plankton plays a very important role in the ocean ecosystem. The planktonic organisms may be zooplankton or phytoplankton. The dominant producers in the photic zone are passively drifting or floating algae, called phytoplankton, although in some locations the algae attached to the bottom also become important as producers.
These are microscopic (minute), floating or suspended lower plants (algae) that are distributed throughout the water, but mainly in the photic zone. Most of them are filamentous algae such as Spirogyra, Ulothrix, Zygnema, Cladophora and Oedogonium. These also occur some chlorococcales (e.g. Chlorella), Clostrium, Cosmarium, Eudorina, Pandorina, Pediastrum, Scendesmus, Volvox, Diatoms, Anabaena, Gloeotrichia, Microcystis, Oscillatoria, Chlamydomonas, Spirulina, etc. and some flagellates.
Q. 32. Write short note on the planogamy. (2009)
Ans. Planogamy: -
Planogamy is also known as planogametic copulation. It is a type of sexual reproduction in algae. In planogamy fusion of naked zoospores take place. Planogainetic copulation or planogamy is of three types:
(i) Isoplanogamy, (ii) Anisoplanogamy and, (iii) Ooplanogamy
Q. 33. What is the difference between aplanospore and synzoospore? (2006, 10, 11)
Related Question-
Q. Write short note on Synzoospore.
Ans. Aplanospores: - Aplanospores are formed during unfavourable and drought conditions. During the formation of aplanospores the protoplast of parent cell is contracted and comes into centre and forms a spore like structure. After some time a thin wall is developed around this spore. These are generally formed at the anterior ends of the filaments. These aplanospores are liberated by the bursting of parent cell wall and forms new plant in favourable conditions.
Example : Chlamydomonas, Ulothrix, Vaucheria etc.
Synzoospores: - These are formed during favourable conditions on the erect branches of thallus or plant. During the formation of synzoospores erect branches of thallus are swollen and form a spherical structure. This structure is separated from reamining filaments by a septum. Now this structure is called zoosporangium.
Protoplasm of each zoosporangium shrinks and nuclei accumulates at the periphery. Each nucleus produce two cilia. Thus, each nucleus forms a unicelluar zoospore.
All zoospores unite and forms a multiflagellate compound zoospore which is called as synzoospore. Each synzoospore liberate into water from apical pore of mother cell. After swimming in water for sometime, the flagella of zoospores are vanished and comes under resting stage. In favourable conditions it germinates and forms two or three tubluar outgrowths. After sometime holdfast also develop and in this way new plant is developed. Example - Vaucheria.
Q.34. Give the general characteristics of Cyanobacteria. (2009,10,11)
Ans. General Characteristics of Cyanobacteria: -
1.The members of this group appear blue coloured due to presence of pigment c-phycocyanin. The pigments of cyanophyceae are chlorophyll ‘a’, carotene and c-phycoerythrin and phycocyanin.
2. Their pigments are not present in chromatophores but dispersed in cytoplasm.
3. True nucleus is absent in the members of this group. Incipient nucleus is present.
4. Nucleus is devoid of nuclear membrane of nucleus.
5. Cell division takes place by direct division of cytoplasm.
6. The reserve food material are sugar and glycogen.
7. Reproductive units are always non-motile.
8. Sexual reproduction is completely absent.
9. Thallus is covered by mucilagenous or gelatinous sheath.
10. Pyrenoids are absent.
11. Heterocysts are present in some members of this group.
12. They are prokaryotes, in which plastids, vacuoles, mitochondria, golgibodies and E.R. absent.
13. Cell wall is devoid of cellulose.
14.The cell wall contains peptides. Further, a diaminopimalic acid and glucossamine are also present.
Q. 35. What is the difference between unilocular and plurilocular sponrangium? (2006)
Ans. The plant of Ectocarpus may be haploid or diploid. The diploid plant reproduce asexually by forming zoospores in unilocular sporangia and plurilocular or neutral sporangia.
Differences between Unilocular and Plurilocular sporangia: -
