(i) Growth promotion Fungus produces growth promoting hormones. In the absence of this association, Pinus and Betula show stunted growth despite providing all types of nutrients.
(ii) Antimicrobial substance Fungus protects the root from parasitic fungi and harmful bacteria by secreting antimicrobial substances.
(iii) Nourishment In orchids, the fungus absorbs nourishment from outside transports it over to the germinating seed.
(iv) Adverse environment Allows plants to grow in mineral deficient soil, saline soil, unfavourable pH and temperature.
(v) Absorption of water Fungal association increases water availability to the root.

(i) Toadstools
(ii) Mushrooms and young puffballs
(iii) Brewer's yeast (Saccharomyces cerevisiae)
(iv) Truffles (tuber-like underground fungus)
(v) Rhizomorphs perennate during periods of scarcity of food and water.
(vi) Basidiospores (develop exogenously)
(vii) Sclerotia under favourable conditions each one forms a new mycelium

(i) Heterocysts are present in some cyanobacteria. It is a large-sized, pale coloured, thick-walled cell which occurs in terminal, intercalary or lateral position in filamentous cyanobacteria,.e.g., Nostoc.
(ii) Features of cyanobacteria are
(a) Mucilage sheath is present.
(b) Thylakoids lack phycobilins. Therefore, photosynthesis is absent, but cyclic photophosphorylation occurs.
(c) Heterocyst is dependent for its nourishment on adjacent vegetative cells.
The thick wall is impermeable to oxygen, but permeable to nitrogen. It has enzyme nitrogenase which is specialised to perform nitrogen-fixation

(i) The interior of bacterial cell seems simple and granular because the membrane bound organelles are not present in it.
(ii) Mucilage, cell wall and plasma membrane are together called cell envelope.
(iii) Mucilage or glycocalyx gives gummy or sticky trait to cells.
Though it is not essential for bacterial survival, glycocalyx has several functions such as
(a) Protection from desiccation and toxins.
(b) Preventing host phagocytes to get attached to the bacterium.
(c) Holdings cells together.
(d) Storing chemicals for virulence.

Biological classification keeps with our understanding of life forms, Initially, new characters were taken by Aristotle, Theophrastus, John Ray and Linnaeus. Linnaeus divided plants on the basis of sex organs only.
As more and more knowledge gathered for delimitation of taxa, the ways for natural system of classification became clear.
This can be understood by following examples :
(i) Two kingdom classification was replaced by three kingdom classification when Haeckel (1866) proposed the kingdom of Protista.
(ii) It was converted into four-kingdom classification by Copeland when he proposed the kingdom-Monera.
(iii) Whittaker in 1969 proposed five kingdom classification
(iv) As the information about biochemistry of archaebacteria gathered, Carl Woese in 1990 raised another kingdom - Archaea.