Summary
Earth is endowed with living and nonliving things.
The attributes of living things include growth, metabolism, Reproduction,
Irritability and so on. Viruses are considered as Biological puzzle and exhibit
both living and non living characteristic features. They are ultramicroscopic,
obligate parasites and cause disease in plants and animals. They multiply by
lytic and lysogenic cycle.
Five Kingdom classification was proposed by
Whittaker, which include Monera, Protista, Fungi, Plantae and Animalia. Carl
woese divided the living world into 3 domains- Bacteria, Archaeae and Eukarya.
The domain Eukarya include Plantae, Animalia and Fungi. A new Kingdom called
Chromista was erected to include Diatoms, Cryptomonads and Oomycetes. Bacteria
are microscopic, prokaryotic organisms and possess peptidoglycan in their cell
wall. Based on Gram Staining method they are classified into Gram positive and
Gram negative type. They reproduce asexually by Binary fission. Sexual reproduction
occurs through Conjugation, Transformation and Transduction. Archaebacteria are
prokaryotic and are adapted to thrive in extreme environments.
Cyanobacteria are prokaryotic organisms and are
also called Blue Green Algae. The members of this group are ensheathed by
mucilage cover. They reproduce by vegetative and asexual methods.
Fungi are Eukaryotic, heterotrophic, unicellular or
multicellular organisms. The cell wall is made up of chitin.
They reproduce asexually by producing
sporangiospores, conidia, Thallospores, chlamydospores etc., The sexual
reproduction is isogamous, ansiogamous and oogamous. In addition, gametic
copulation, gametic fusion, spermatisation are also found. They are beneficial
to mankind. Some are known to cause disease in plants and human beings.
Rhizopus is
commonly called’ Bread mold fungi’.
It belongs to the class Zygomycetes. Asexual reproduction occurs by the
production of sporangiospores. During sexual reproduction gametangial
copulation occurs and zygospore is formed. Agaricus
belongs to the class Basidiomycetes.It is a saprophytic fungus. Three types of
mycelium , primary, secondary and tertiary mycelium are produced. Sexual
reproduction is present
Basidiocarps are produced after the sexual
reproduction. It bears basidia on which four basidiospores are produced.
The symbiotic association between the roots of
higher plants and fungal mycelium is called mycorrhizae. Lichen thallus
includes both phycobiont and mycobiont. It is an example for symbiotic
association.
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