- The food reserves are stored as glycogen or fat.
- Most of them are capable of locomotion.
- They have a definite shape and size and follow a definite growth pattern also.
- The sexual reproduction takes place by copulation of male and female followed by embryological development.
VIRUSES, VIROIDS AND LICHENS
- The name virus was given by Pasteur. D.J. Ivanowsky (1892) is credited with the discovery of virus. Beijerinck (1896), called it
contagium vivum fluidum. - The viruses are ultramicroscopic, highly infectious agents and non-cellular organisms characterised by having an inert crystalline
structure outside the living cell. - Once they infect a cell they take over the machinery of the host cell to replicate themselves, killing the host.
- Viruses contain capsid, the proteinaceous covering and genetic material, that could be either DNA or RNA.
- Viruses that infect plants have single stranded RNA while those that infect animals have either single or double stranded RNA or
double stranded DNA. Bacteriophages are usually double stranded DNA viruses. - In humans, viruses cause diseases like mumps, smallpox, herpes, influenza and AIDS.
- In plants, the symptoms of virus infection can be mosaic formation, leaf rolling, yellowing, leaf curling and stunted growth.
- Stanley (1935) crystallised Tobacco Mosaic Virus (TMV) for the first time.
- An inert virus is called virion that can be crystallised and stored indefinitely.
- Viroids are the smallest self replicating particles discovered by Diener (1971).
- Viroids are infectious RNA particles devoid of protein coat.
- Like viruses, they are obligate parasites.
- Viroids are known to cause diseases in plants only, e.g., Potato spindle tuber chrysanthemum stunt.
- Lichens are dual organisms or entities which contain a permanent association of a fungus or mycobiont and an alga or
phycobiont. - The algal component is autotrophic while fungal component is heterotrophic.
- Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for algae.
- Lichens cannot tolerate air pollution especially due to sulphur dioxide.
Prions are highly resistant glycoprotein particles which function as infectious agents. Prions are not affected by proteases, nucleases,
temperature upto 800°C, UV radiation and formaldehyde. Prions accumulate in nervous tissue and bring about its degeneration.
Common diseases caused by them are mad cow disease, scrapie of sheep, kuru, Creutzfeldt-Jakob disease (CJD). Prions were
discovered by Prusiner (1983).- Name the scientist who crystallised Tobacco Mosaic Virus (TMV) for the first time.
- Why deuteromycetes are called imperfect fungi?
- Mention various methods by which sexual reproduction takes place in fungi.
- Ann Madona Shaju- Calicut, Kerala
April 2018
- Mycoplasma Pg. 33 Winner
- Phycoerythrin Pg. 39
- Prothallus Pg. 41
- Pollen mother cell Pg. 62
ANSWERS WHO AM I ...