2. CLASSIFICATION OF LIVING ORGANISMS
In this chapter you will learn
1.
2.
3.
4.
5.
1.1
Concept of classification and its need.
Micro-organisms as a diverse group of living organisms.
Nature of viruses and names of diseases caused by viruses.
Structure of bacteria and names of bacterial diseases.
Importance of bacteria and different methods of food preservation.
CLASSIFICATION
Organisms
An individual living thing that can react to stimuli, reproduce, grow and maintain homeostasis.
It can be avirus, bacterium, protist, fungus, plant or an animal.
Living organisms are arranged in different groups due to similarities and difference. The basic
unit of unit classification is species.
SPECIES: A group of closely resembling organisms. For example cat and rabbit are two species.
Need:The number is so large that each and every organism can't be studied separately. To
make the study convenient, easier, and quicker, we need classification. Therefore classification
of organisms is done by making groups.
3. 1.2 MICRO ORGANISMS
A microorganism (also spelled as microorganism) or microbe is an organism that is microscopic
(too small to be seen by the human eye).
There are different types of microorganism which are cyanobacteria, bacteria, protozoa, fungi
and viruses.
Micro-organisms differ from one another with regard to structure and mode of nutrition.
1.3
VIRUSES
Viruses are so small that they cannot be observed with light microscope but can be studied with
electron microscope and biochemical tests.
Types
Viruses of different shapes, some are rounded, a few are rod-shaped and few polyhedral while
some look tadpoles.
4. Tadpole
Polyhedral
Round
Rod-Like
Structure and Function
Viruses are small obligate intracellular parasites, which by definition contain either a RNA or
DNA genome surrounded by a protective, virus-coded protein coat. Viruses may be viewed as
mobile genetic elements, most probably of cellular origin and characterized by a long coevolution of virus and host. For propagation viruses depend on specialized host cells supplying
the complex metabolic and biosynthetic machinery of eukaryotic or prokaryotic cells. A
complete virus particle is called a virion. The main function of the virion is to deliver its DNA or
RNA genome into the host cell so that the genome can be expressed (transcribed and
translated) by the host cell. The viral genome, often with associated basic proteins, is packaged
inside a symmetric protein capsid. The nucleic acid-associated protein, called nucleoprotein,
together with the genome, forms the nucleocapsid. In enveloped viruses, the nucleocapsid is
surrounded by a lipid bilayer derived from the modified host cell membrane and studded with
an outer layer of virus envelope glycoproteins.
Diseases
Sometimes the virus and human immune system can establish a balance. However when
the human immune system is weak due to various reasons, the viruses can break the
balance and cause problems, became so called opportunist pathogen. For example, the BK
polyomavirus is presented in the kidney of ~80% population, however it only cause nephritis
in limited population. But that don't mean all viruses are not harmful, or opportunist
pathogens, some viruses can cause serious diseases, including AIDS, SARS, Hepatitis,
Herpes Simplex etc.
List of diseases caused by viruses:
5. Disease Name
Virus
Type
Organs Affected
Transmission
• Influenza
RNA
Respiratory Tract
Droplets
• Adenovirus Infections
DNA
Lungs, Eyes
Droplets, Contact
Droplets
• Respiratory Syncytial
Disease
RNA
Respiratory Tract
Droplets
• Rhinovirus Infections
RNA
Upper Respiratory Tract Droplets,Contact
• Herpes Simplex
DNA
Skin,Pharynx, Genital
organs
Contact
• Chicken pox ( Varicella) DNA
Skin, Nervous System
Droplets, Contact
• Measles (Rubeola)
RNA
Respiratory Tract, Skin
Droplets, Contact
• German Measles (
Rubella)
RNA
Skin
Droplets, Contact
• Mumps (Epidemic
Parotitis)
RNA
Salivary Glands, Blood
Droplets
• Small Pox (Variola)
DNA
Skin, Blood
Contact, Droplets
• Warts Kawasaki
Disease
DNA
Skin
?
• Yellow Fever
RNA
Liver, Blood
Mosquito (
AedesAegypti)
• Dengue Fever
RNA
Blood, Muscles
Mosquito (
AedesAegypti )
• Hepatitis A
RNA
Liver
Food, Water, Contact
• Hepatitis B
DNA
Liver
Contact with body
Fluids
