The effect of fungi on human life may be harmful or beneficial.
1. Harmful Fungi:
(i) They cause diseases in important crops, e.g., late blight of potato (Phytophthora infestans), black stem rust of wheat (Puccinia graminis), brown spot of rice (Helminthosporium oryzae), etc.
(ii) They induce animal and human diseases, e.g., mycosis caused by infestation of Aspergillus, Cercospora and Cryptococcus.
(iii) They also spoil fruits, vegetables and all kinds of foodstuff.
2. Beneficial Fungi
Fungi form the most useful basis in industries like, baking and brewing (Saccharomyces), preparation of cheese (Penicillium) and commercial production of citric acid (Aspergillus niger).
Wonder drug, penicillin, is an antibiotic extracted from fungus Penicillium notatum.
Fungus, Claviceps pupurea, contains a number of alkaloids which are utilized in medicine and useful in controlling haemorrhage during child birth.
Used as Food:
Fungi like mushrooms, morels and truffles are used as food.
Majority of known fungi along with bacteria live on dead organic matters, decompose them performing a very useful service in returning to the soil the nutrients.
Fungi imperfecti (Deuteromycetes) :
Members of the fungi imperfecti lack a sexual cycle and include all the existing fungi which reproduce solely by asexual means and even those which produce no spores at all. E.g., Aecidium, Uredo, Caeoma and Peridermium, etc
Lichen is a permanent association of a fungus and an alga. The fungal component is called mycobiont and the algal component is known as phycobiont. Fungus always envelops the algal component of the association. This association is regarded as symbiosis in which both the participants are benefited the alga supplies food to the fungus which in return gives protection to the alga.
Lichens perform the work of breaking down the hard rock surfaces and preparing a soil on which highly developed plants can grow, e.g., Lecanora.
Food for Animals:
Many lichens might be used as fodder for animals, e.g., Lobaria, Evernia and Ramalina, etc. Cladonia, the well-known 'reindeer-moss' is the most favourite lichen food for reindeer and cattle.
Food for Human Beings:
Lichens contain a carbohydrate very much allied to starch, which can be used as good food. Cetraria, the 'Iceland moss' is used as food by the natives of Sweden, Norway and other western countries. In India Parmelia is used as food and to prepare curry.
Source of Medicine:
Various medicinal benefits of lichens have been described since, Pre- Christian times. A preparation of Peltigera has been used to cure hydrophobia, Parmelia can cure epilepsy, Usnea and Evernia were used in haemorrhages and Cladonia was found valuable in whooping cough.
Useful in Perfumery:
French perfumers extract an excellent perfume from Evernia and Lobaria. The thalli of Usnea possess the power of retaining scent and are utilized in perfumery.
Preparation of Dyes:
Orchil and cud bear blue dyes are obtained from lichens, Roccella. Litmus solution is also made by grinding the lichen, Roccella.
The word virus is derived from Latin which means poison. They are cellular obligate intracellular parasites having nucleic acid (DNA or RNA) enclosed in a protein coat. They lack their own enzyme system and depend on the host for all metabolic activities.
For this reason, viruses can multiply only inside the living cells. They were discovered by M.W. Beijernick in 1899. Many biologists regard viruses as intermediate between non-living matter and living organisms. They are responsible for a large number of important plant and animal diseases.
They are virus like bodies having a cell membrane without any cell wall and are resistant to penicillin. They transmit a number of diseases in plants such as aster yellows, potato witch's broom, mulberry dwarf, maize stunt, rice-yellow dwarf and several clover diseases.
Rickettsias morphologically resembles bacteria but are biologically related to viruses. They contain both DNA and RNA and a considerable amount of enzymes. They reproduce by binary mission similar to bacteria and are found typically in arthropods. They are responsible for typhus fever in man.