BIOLOGY – 25
MICROBES
BACTERIA
• Study of bacteria - Bacteriology
• The bacteria are unicellular and prokaryotic
• first observed and reported by Anton Von Leeuwenhoeck in 1676.
• Their size and shape varies as per the species.
• Bacteria are autotrophic, heterotrophic as well as saprophytic.
• In bacteria reproduction takes place by both Asexual and Sexual
• Majority of Bacteria are in the size range of 0.5 to 50 µ,
❖ Smallest - Pasteurella (0.7µ)
❖ Largest - Beggiota (15-22 µ).
SHAPES OF BACTERIA
• Bacteria are the monocellular microorganisms which are found in almost
places in singleton form or in group.
• The cellular wall of the bacteria is thick and it is made from chitin, Murine
etc.
They have different shapes
1. Coccus (spherical)
2. Bacillus (rod shaped)
3. Vibrio (comma shaped)
4. Spirillum (cork screw shaped)
VIRUS
• Study of Virus- Virology
• A virus is a small collection of genetic code (either DNA or RNA) surrounded by a protein
coat.
• Discovered by mitri Ivanovsky in 1892.
• A virus is an acellular organism which are 10 to 100 times smaller than bacteria, about 20-
300 nm in size.
• Viruses can infect a variety of living organisms, including bacteria, plants, and animals.
• The infective, extracellular (outside the cell) form of a virus is called the virion.
• They lack metabolic machinery of their own to generate energy or synthesize proteins.
• They can reproduce only within a living cell – hence they are obligate intracellular parasites.
• They take over the functions of the host cell hence causing infection.
• Viruses are inactive outside the host (crystallized form) and active inside.
• This puts them in the unique criteria of living as well as the non-living entity or ‘not truly
living’.
• As viruses don’t have the same components as bacteria, they cannot be killed by antibiotics.
• Antiviral medications or vaccines can eliminate or reduce the severity of several viral
diseases.
Classification based on nucleic acid type
1. DNA viruses – can be single-stranded or double-stranded
2. RNA viruses – can be single-stranded or double-stranded
FUNGI
• Fungi are among the most primitive members of the plant
kingdom.
• Study of the fungi is called mycology.
• The fungi are non-chlorophylous, nucleatedthallophytic micro
organism
• due to lack of chlorophyll they do not prepare their own food.
• The fungi - thallophytes or plants with a thallus - have no
roots, stems, flowers and seeds - structures we commonly
associate with higher plants.
• The thallus of a fungus is usually made of branching threads
called hyphae.
fungi are of three types
1. Saprophytes
2. Parasites
3. Symbiotic
ALGAE
• Algae (seaweeds) are usually aquatic, either marine or
fresh water plants.
• A few algae also occur in terrestrial habitats such as
moist soils, wet rocks, tree trunks, etc.
• These are unicellular or multicellular, autotrophic
plants which don’t have vascular tissues (tissues that
provide mechanical strengh) and their body are called
thallus.
TYPES OF ALGAE
1. Green Algae or Chlorophyceae
2. Brown algae or Phaeophyceae
3. Red Algae or Rhodophyceae
4. Blue Green Algae or Cyanophyceae
PROTOZOA
• Protozoans are the single-celled eukaryotes, either free-living or parasitic, which
feed on organic matter such as other microorganisms or organic tissues and debris.
• Eukaryotes are organisms whose cells have a nucleus enclosed within membranes,
unlike prokaryotes, which have no membrane-bound organelles.
• A parasite is an organism that lives on or in a host and gets its food from or at the
expense of its host. E.g. plasmodium parasite which causes malaria.
Habitat
Mostly they are aerobic (with oxygen) but some are anaerobic (without oxygen)
and present in the rumen or human intestine.
Size and Shape
The size and shape of Protozoa vary greatly,
from microbial (1µm) to large enough and can be seen
by the naked eye.
Nutrition
Protozoans are heterotrophs and
have holozoic nutrition.
Holozoic nutrition
method of nutrition which involves the
ingestion of some complex organic substances (such as
parts of a plant or animal) that may be in the solid or the
liquid form.
