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Old Saturday, November 19, 2011
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Characteristics Of Living Organisms:


Following are the main characteristics of living beings which are not present in non-living organisms.
i) Metabolism
ii) Growth
iii) Irritability
iv) Reproduction
v) Movement
vi) Nutrition
vii) Respiration
viii) Excretion

Virus:

• Viruses are the micro-organisms which are strict or obligate parasites of animals or plant cells.

• Many of the viruses are also parasites on bacteria.

• A large number of viruses cause diseases in plants and animals.

Characteristics Of Virus:
• A virus consists of two components, a protein coat and a core of nucleic acid which is either DNA or RNA.

• DNA viruses are called adenoviruses and RNA viruses are called retroviruses.

• The shape of a virus is due to its protein coat.

• Viruses are of many shapes i.e. rods, spherical, hexagonal or icosahedral.

• Sometimes their shape is complicated.

• Virus replicate inside a living cell and many viruses are synthesized along with their protein coats and nucleic acid.

• The nucleic acid contains instructions for the shape of the virus.

Diseases Caused By viruses:
i) Polio
ii) AIDS
iii) Smallpox
iv) Measles
v) Hepatitis

Bacteria:


Characteristics Of Bacteria:
• Bacteria are unicellular prokaryotic organisms which generally divide by transverse binary fission.

• They possess rigid cell walls and act as pathogens

• Nucleus is not well organised

• No definite chloroplast, chlorophyll is dissolved in chromoplasm.

• There are three forms of bacteria which are:
i) Round called Cocci
ii) Rod like called Bacilli
iii) Spiral called Spirrila

Classification Of Bactria According To Mode Of Nutrition:

According to mode of nutrition, there are three types of Bactria:
a) Parasitic:
• Devoid of chlorophyll
• Are heterotrophic and get food from living animals and plants

b) Saprophytic
• Lack chlorophyll hence cannot prepare their own food.
• Get food from dead organic remains

c) Autotrophic
• Contain chlorophyll
• Can synthesis food by photosynthesis
• Few get their food by chemosynthesis

Reproduction In Bacteria
i) Vegetative: By Binary Fission
ii) Asexual: By Formation of Endospores
iii) Sexual: By Conjugation
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