InstaCue - Biology - Class-11

Kingdom-Monera
- Bacteria are the sole members of this kingdom.
- Bacteria are the most abundant microorganisms occurring in air, water, soil as well as in extreme habitats like deserts, snow, hot springs, etc.
- Bacteria have been grouped under four categories based on their shape
- Coccus (cocci) - Spherical
- Bacillus (bacilli) - Rod-shaped
- Vibrium (vibrio) - Comma-shaped
- Spirillum (spirilla) - Spiral-shaped.
- Bacteria show a wide range of mode of nutrition. They may be autotrophic (synthesise their own food from inorganic substrates), chemotrophic (photosynthetic autotrophic), saprophytic or heterotrophic (depend on other organisms for food).
- Bacteria are further divided into Archaebacteria and Eubacteria.

Archaebacteria
- Archaebacteria live in extreme environmental conditions. These include
- Halophiles Bacteria residing in salty areas.
- Thermoacidophiles Bacteria residing in hot springs.
- Methanogens Bacteria which survive in marshy areas (these are present in gut of many ruminant animals like cows and buffaloes).
- Archaebacteria differ from other bacteria in having different cell wall structure. Their cell wall is made up of murein and contains high amount of unsaturated fatty acids, which is responsible for ensuring their survival in extreme conditions.

- Another class-Eubacteria is also known as 'true bacteria'.
- These have rigid cell wall made up of peptidoglycan.
- They could be photosynthetic autotrophs, chemosynthetic, autotrophs and heterotrophic bacteria.
- Photosynthetic autotrophs include blue-green algae, which have chlorophyll- $a$ similar to green plants. Also known as cyanobacteria.
- These could be unicellular, colonial or filamentous, freshwater/marine or terrestrial algae.
- Some bacteria can fix atmospheric nitrogen in specialised cells known as heterocyst, e.g. in Nostoc and Anabaena.
- Some bacteria utilise inorganic substances like nitrate, nitrite, ammonia, etc., for oxidation and release of energy for ATP production. These are known as chemosynthetic autotrophic bacteria.
- Heterotrophic bacteria (most abundant in nature) are dependent on other organisms for nutrition. These include $\mathrm{N}_2$-fixing bacteria, pathogens, etc.

Kingdom-Protista
- All single-celled eukaryotes are placed under Protista.
- Members of kingdom-Protista are the connecting link between prokaryotic monerans and complex multicellular kingdoms-Fungi, Plantae and Animalia.
- These include chrysophytes, dinoflagellates, euglenoids, slime moulds and protozoans.
- These show a well-defined nucleus and membrane bound organelles.
- They reproduce asexually and sexually by a process involving cell fusion and zygote formation.
- Kingdom-Protista has been further divided into the following groups
- Chrysophytes include diatoms and golden algae known as desmids. They are found in marine environment.
- The cell wall of diatoms is embedded with silica and forms two thin overlapping sheath as in soap box.
- Diatomaceous earth is the large amount of cell wall deposits of diatoms in their habitat. These are used in polishing, filtration of oils and syrups.

Kingdom-Fungi
- These are heterotrophic organisms with their cell wall made up of chitin.
- These have cosmopolitan distribution and are found in warm and humid places.
- Fungal body consists of long, thread-like structures called hyphae, which together form a network called mycelium. In certain organisms, hyphae are continuous tube with multinucleated cytoplasm (coenocytic), while others have septae or cross walls.
- Their mode of nutrition is saprophytic and parasitic. They can also live as symbionts in association with algae as lichen and with roots of higher plants as mycorrhiza.
- Reproduction in fungi occurring by vegetative means, includes fragmentation, fission and budding, asexually by zoospore production conidia, etc., and sexually by oospores, ascospores and basidiospores.
- Sexual cycle involves plasmogamy (fusion of two protoplasts), karyogamy (fusion of two haploid nuclei) and meiosis.
- In some fungi, two haploid cells result in diploid cells. In some cases, dikaryon stage occurs in which two nuclei are present within a cell. This phase is known as dikaryophase of fungus.

Kingdom-Animalia
- Animals are motile organisms showing holozoic nutrition. They follow a definite growth pattern.
- They directly or indirectly depend on plants for food.
- Sexual reproduction is by copulation of male and female gametes followed by embryo development.
Viruses, Viroids, Prions and Lichens
- Viruses and viroids are the non-cellular organisms, which are not characterised in the system of classification given by Whittaker.
- They have both living and non-living characteristics.
- They form inert crystalline structure outside the living cell, but inside the host cell they can multiply easily.
- They take over the host machinery and replicate themselves.
- Pasteur and DJ Ivanowsky gave the name virus, which means venom or poisonous fluid.
- MW Beijerinck in 1898, called fluid obtained from infected tobacco plant as Contagium vivum fluidum (infectious living fluid).