BIOLOGY 2 Marks Questions

Prion : In modern medicine certain infectious. neurological diseases were found to be transmitted by an agent consisting of abnormally folded protein. The agent was similar in size to viruses. These agents were called prions. The most notable diseases caused by prions are bovine spongiform encephalopathy (BSE) commonly called madcow disease in cattle and its analogous variant Cr- Jacob Disease (CJD) in humans.

All bacteria come under the kingdom Monera. These are found everywhere. They have the highest number among microorganisms. They are also found in adverse habitats like hot water springs, ice, deep sea and desert etc. Many bacteria live as parasites on or inside other organisms.
Bacteria have been divided into four groups on the basis of their shape (spherical Coccus, rod shaped - Bacillus, comma shaped, Vibrium and spiral Spirillum). These are simple in structure. They can synthesise their food from inorganic substances. They are photosynthetic or chemosynthetic autotrophs, that is, they do not synthesise their own food but depend on other living organisms or dead organic matter for food.

1. Presence of chlorophyll and they are autotrophic
2. Plant body thallus like and sexual organs are unicellular or multicellular.
3. The cell wall is made of cellulose.
4. They are usually found in habitats with water or moisture. Example: Members of Chlorophyceae, Phypophyceae, Chrysophyceae etc

The usefulness of algae is as follows:
(1) These are rich sources of Vitamin A and B.
(2) Provide food for fishes.
(3) Many seaweeds are important sources which contain iodine, potassium and other minerals.
(4) Some algae fix atmospheric nitrogen. Due to which they are a source of natural fertiliser for plants.
(5) A class of algae (diatoms) contain silica in their walls. After death these creatures become fossils. Their deposits are used in large quantities in making filters and furnace linings.

(1) Mushrooms like 'Gucchi' (Agaricus compestris) are eaten.
(2) Yeasts are used in bread, beer, soya sauce, 'cheese' and liquor etc.
(3) Mycorrhizal fungi are found living with the roots of plants. With this type of association, the roots of the plants obtain minerals from the environment while the fungus obtains food prepared from the plant.
(4) Neurospora It is used in experiments conducted in the field of genetics.
(5) Many antibiotics are obtained from fungi. Penicillin is obtained from Penicillium notatum. Discovery of its antibacterial effect was done by Alexander Fleming in 1927.

Those parasites which are found only on a particular plant, if that plant is not available to them then they themselves get destroyed or are unable to earn their living. Example: Fungus called Albugo or Cystopus (the parasitic fungi on mustard).

Slime moulds are saprophytic protists. The body moves along decaying twigs and leaves engulfing organic material. Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet. During unfavourable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their tips. The spores possess true walls. They are extremely resistant and survive for many years, even under adverse conditions. The spores are dispersed by air currents.

Life cycle of plants has two distinct phases-the diploid sporophytic and the haploid gametophytic-that alternate with each other. The lengths of the haploid and diploid phases, and whether these phases are free-living or dependent on others, vary among different groups in plants. Haploid (2n) spores are formed by meiosis division in the zygote (n). These spores germinate and form gametophytes. Gametes (male and female) are formed on the gametophyte which fuse again to form a diploid zygote. Sporophyte develops from zygote. This process is called alternation of generation. Example: Ulothrix and Albugo.

A good indicator of pollution is lichen. Lichens are symbiotic associations i.e. mutually useful associations, between algae and fungi. The algal component is known as phycobiont and fungal component as mycobiont, which are autotrophic and heterotrophic, respectively. Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner.