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The steps are :

(i) Plasmogamy : fusion of protoplasm of two motile or nonmotile gametes. 

(ii) Kayogamy : fusion of two nuclei. 

(iii) Zygotic Meiosis to form haploid spores. 

(iv) Dikaryophase in ascomycetes and basidiomycetes where before karyo gamy two nuclei per cell (dikaryon) are found.

R. H. Whittakar. Criteria for classification : Cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

Heterotrophic bacteria are Decomposes, help in making curd, production of antibiotics, N₂ fixation, cause diseases like cholera, typhoid.

Completely lack cell wall. Smallest living cells. Can survive without oxygen. Pathogenic in animals and plants is called Mycoplasma.

Demerits of Two Kingdom system - 

No difference in Eukaryotes and Prokaryotes. - 

Heterotrophic Fungi kept in Plantae. 

Viruses – Connecting link between living and non living. 

- Non cellular structure consisting of protein coat and Nucleic acid 

- Can reproduce within a host cell. 

- Viruses which infect bacteria are called Bacteriophage.

Viroids – Free RNA without protein coat. 

 RNA with Low molecular weight.

 The free RNAs without the protein coat are called viroids, while virus have a protein coat to protect the genetic material.

A rapid increase in the population of microscopic algae in an aquatic habitat is called algal bloom. The algal bloom involving the dianoflagellates is called the ‘red tide’ because of its red hue. Red tide can be harmful for other aquatic life forms. 

(a) Curd and antibiotic are made by using heterotrophic bacteria.

(b) Methanogens are responsible for production of biogas which can be used as fuel. The archaebacteria which live in extreme conditions give us a clue about the beginning of life on earth.

• Has bacteria a sole member. 

• Bacteria can have shapes like : Coccus (spheri cal), Bacillus (rod-shaped), Vibrio (comma shaped) and sprillum (spiral shaped). 

• Bacteria found almost everywhere and can be Photosynthetic autotrophs, Chemosynthetic au totrophs or Heterotrophs.

Bacillus (rod-shaped), Coccus (spherical), Vibrium (comma shaped) and Spirillum (spiral shaped).

The pigments present in cyanobacteria are: Chlorophyll 'a', phycobilin, phycoerythrin and phycocyanin.

Each filament of blue-green algae consist of a sheath of mucilage and one or more cellular strands called trichomes.

The filamentous blue-green algae possess special large sized cells called heterocysts. These are the sites of nitrogen fixation.

A multinucleate mass of protoplasm of slime moulds which creep like Amoeba is known as plasmodium.

Blue-green algae multiply asexually by the formation of small segments called hormogonia.

Features of Protista: 

(i) They are single celled colonial, filamentous eukaryotes. 

(ii) These grow in humid and moist environments. 

(iii) Some are photosynthetic but some are non- photosynthetic. 

(iv) Some forms are like animals whereas some are like plants. 

(v) They have membrane bound cell organelles. 

(vi) Examples are protozoa, slime moulds, Euglenoids, Chrysophytes protistan algae such as diatoms, dinoflagellates or phytoplanktons etc. 

(vii) The protozoan are unicellular (single celled) heterotrophs. Euglena is autotroph. 

(viii) Slime moulds are plant like or animal like. 

Theirsomatic body is called plasmodium (acellular, multinucleate, mobile mass of protoplasm lacking the cell wall). 

The major groups of this kingdom are: 

(a) Photosynthetic protist or protistan algae. 

(b) Consumer decomposer protists - Slime moulds. 

(c) Protozoan protists.

(i) Prokaryotes have a naked genetic material without being organised into a nucleus, a single envelope organisation, absence of spindle apparatus, meiosis and sexual reproduction. 

(ii) They are mainly unicellular.

Bacteria are classified as given below: 

(i) Cocci : They are oval or spherical in shape. When they occur singly, they are called Micrococcus; if in pairs Diplococcus; if in a chain, Streptococcus; and if occur in clusters, Staphylococcus. 

(ii) Bacilli: They are rod-like, with or without flagella. Flagella may be present at one or both the ends or around cells. Bacteria may occur singly, Bacillus; or in pairs, Diplobacillus or may form filaments, Streptobacillus. 

(iii) Vibrio : They are small and curved like commas. These are mostly motile. 

(iv) Spirillum : These are twisted like a screw. They have flagella at one end or both the ends. Certain bacteria possess flagella for locomotion.

(i) some bacteria can survive in extreme environmental conditions like high temperature, high concentration, in absence of oxygen or in presence of oxygen in high acidic or alkaline pH. Such bacteria are called archaebacteria. 

(ii) Their cell wall consists of non-cellulosic polysaccharide or protein and lacks peptidoglycan. This allows them to survive in extreme conditions.

(i) Cyanobacteria or blue-green algae are gram(+) photosynthetic prokaryotes which perform oxygenic photosynthesis 

(ii) Cell structure is typically prokaryotic-one envelope organisation with peptidoglycan wall naked DNA, 70S ribosomes, devoid of membrane bound cell organelles. 

(iii) The outer part of the protoplast contains a number of photosynthetic thylakoids. It is called as chromoplasm. 

(iv) Their membranes contain chlorophyll a, carotenes and xanthophylls. Chlorophyll b is absent. 

(v) DNA lies coiled generally in central part of the cytoplasm known as centroplasm. 

(vi) Small circular DNA segments may also occur in nucleoid, known as plasmid or transposons.

(i) Methanogens: (1) The archaebacteria are strict anaerobes. Nutritionally they are "autotrophs" which obtain both energy and carbon from decomposition products. 

(2) They occur in marshy areas where they convert formic acid and carbon dioxide into methane. 

(3) This capability is commercially exploited in the production of methane and fuel gas inside gobar gas plants. e.g., Methanobacterium, Methanococcus. 

(ii) Halophiles: (1) Halophiles are named so because they usually occur in salt rich substrata like salt plant, and salt marshes . ., Halobacterium, Halococcus. 

(2) They are aerobic chemoheterotrophs. Their cell membrane have red carotenoid pigment for protection against harmful solar radiations. 

(3) Halophiles are able to live under high salt conditions due to three reasons: 

(a) Presence of special lipids in the cell membranes. 

(b) Occurence of mucilage covering. 

(c) Absence of sap vacuoles and hence plasmolysis 

(iii) Thermoacidophiles : (1) These archaebacteria have dual ability to tolerate high temperature as well as high acidity. 

(2) They often live in hot sulphur springs where the temperature may be as high as 80°C and pH as low as 2, e.g., Thermoplasma thermoproteus.. 

(3) These archaebacteria are chemosynthetic. 

(4) Under aerobic conditions they usually oxidise sulphur to sulphuric acid. 

2S + 2H₂O +3O₂ → 2H₂SO₄ 

Thermoacidophiles are able to tolerate high temperature and high acidity due to two reasons: 

(a) Branched chain lipids in the cell membranes. 

(b) Presence of special resistant enzymes capable of operating under acidic conditions.

Lichens are symbiotic 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.