. Explain General characteristics of Protista
1. They are solitary unicellular or colonial unicellular eukaryotic organisms.
2. Mostly they are aquatic organisms. Many protists are planktons. Some forms are parasites.
3.Protists have different body shapes. The cell wall, when present, contains cellulose. pellicle, shell, etc. may be present.
4. Cytoplasm contains membrane bound cell organelles; many have centrioles also.
5. The protoplasm is surrounded by a distinct plasma membrane made of lipoprotein.
6. Cytoplasm shows streaming movement.
7. Photosynthetic forms contain chloroplasts with internal thylakoids and act as chief producers of food in the oceans and fresh waters.
8. Nucleus has typical structure viz. porous nuclear envelope, chromatin material, nucleoplasm and nucleolus.
9. A mesokaryon occurs in dinoflagellates.
10. They commonly move with the help of pseudopodia, flagella or cilia. Flagella have (9 + 2) organization of microtubules that are composed of a protein named tubulin.
11. Nutrition may be photosynthetic, holozoic, saprobic or parasitic. Some protists have mixotrophic nutrition (photosynthetic and saprobic) as in euglenoids.
12. Food reserve can be starch, paramylum. chrysolaminarin, glycogen and fat.
13. Reproduction occurs by both asexual and sexual methods. An embryo stage is absent.
14. In protists asexual reproduction is a rapid method of multiplication and occurs by binary fission, multiple fission, spore formation, budding, cyst formation, etc.
15. Sexual reproduction is believed to have originated in primitive protists. It involves meiosis and syngamy.
16. Sexual reproduction may be isogamous (e.g., dinoflagellates and a cellular slime moulds) or anisogamous (e.g. Ceratium, a dianoflagellate) or oogamy (e.g. protozoans).
17. Life cycle may show zygotic meiosis (e.g. dinoflagellates and cellular slime moulds) or gametic meiosis (e.g., diatoms and acellular slime moulds).
18. Parasitic protists may cause diseases such as dysentery, malaria, sleeping sickness, etc.