SCIENCE GRADE 8TH

CHAPTER =1

Ø  Concept of classification & its need

·         Classification

·         Units of classification

·         Basic unit of classification

·         Importance/need of classification

Ø  Micro-organisms

·         Definition

·         Micro-organisms as a diverse group of living organisms

·         Difference b/w different micro-organisms

1)      How viruses differ from other micro-organisms?

2)      How bacteria differ from other micro-organisms?

3)      How algae & bacteria differ from fungi?

Ø  Viruses

·         Definition

·         Shapes

·         Composition

·         Structure

·         Mode of nutrition

·         Mode of transmission

·         Diseases caused by viruses in;-

1)      Human/Animals

2)      Plants

·         SARs (severe Acute Syndrome)

Ø  Bacteria

·         Habitat

·         Types

·         Nature

·         Structure

·         Characteristics

·         Mode of nutrition

·         Mode of transmission

·         Importance

1)      Advantages

2)      Disadvantages

·         Pathogenic bacteria

Ø  Methods of preservation

·         Sterilization

·         Pasteurization

·         Low temperature

·         Drying process

·         By radiations

·         High temperature

v  Concept of classification & its need

v  Classification;-

“Living organisms are arranged into different groups due to some similarities & differences. This grouping is called classification.”

v  Units of classification;-

In classification organisms are placed into following different units;-

1)      Species

2)      Genus

3)      Family

4)      Order

5)      Class

6)      Phylum

7)      Kingdom

v  Basic unit of classification;-

The basic unit of classification is “species”.

Species;-

“A group of closely resembling organism that can interbreed with one another in nature.”

Example;-cat and rabbit are two species.

v  Importance/need of classification;-

1)      It is necessary for the study of living organisms to classify them into different groups.

2)      It tells us inter-relationship among species members.

3)      In classification organisms are identified on the basis of their structures and other characteristics, so we can study them systematically & logically.

v  Micro-organisms;-

v  Definition;-

“Micro means “small” & and Organism means “living things” .So micro-organisms are those organisms that are so small that cannot seen with naked eye.

v  Micro-organisms as a diverse group of living organisms;-

Micro-organisms form a diverse group b/c it includes different kinds of organisms such as;-

1)      Virus

2)      Bacteria

3)      Unicellular plant & animals

4)      Algae

5)      Fungi

v  Differences among different organisms;-

Micro-organism differ from one another on the basis of;-

1)      Structure

2)      Mode of nutrition

·         How viruses differ from other micro-organisms;-

On the basis of structure “viruses” are NOT CELLULAR while “other organisms” are CELLULAR.

·         How bacteria differ from other micro-organisms;-

“Bacteria “have no organized nucleus while “other micro-organisms” have organized nucleus.

·         How Algae & bacteria differ from fungi;-

According to mode of nutrition” algae are autotrophic while fungi are heterotrophic.

v  Viruses;-

v  Definition;-

“Virus is a Latin word which means ‘poison ’.Viruses are so small that they cannot be observed with light microscope but can be studied with electron microscope.

v  Shapes;-

Viruses are of following shapes;

1)      Round

2)      Rod-shaped

3)      Polyhedral

4)      Tadpole

v  Composition;-

Structurally viruses are not cellular but made up of;

1)      Nucleic acid

2)      Protein

v  Structure;-

Viruses consists of following two PARTS;-

1)      Outer coat;-made up of proteins.

2)      Inner core;-made up of DNA or RNA

v  Mode of nutrition;-

All viruses are parasites & obtain their food from other organisms.

v  Mode of transmission;

Viruses in living organisms are transmitted by;-

1)      Air

2)      Contaminated water

3)      Contaminated food

4)      Insects

5)      Coughing & sneezing

6)      Through contact

v  Diseases caused by viruses in;-

·         Human beings;-Measles ,Small pox, Cancer, Influenza, AIDs, Cold, Hepatitis B & C,SARs

·         Plants;-viruses cause diseases in plants of Tobacco, potato, tomato & cabbage

v  SARs(severe acute respiratory syndrome)

It is pneumonia like viral disease in which at first temperature of patient rises. He feels cold, irritation in throat, difficulty in breathing & suffocation. Sometimes death occurs.

v  Bacteria ;-

v  Habitat;-found everywhere.

v  Types ;-on the basis of shape & form, bacteria are of following FOUR types;

1.      Round

2.      Rod-shaped

3.      Spiral

4.      Comma

·         Nature;-

Bacteria are found;

1.      Singly

2.      In groups

3.      In beaded form

·         Structure;-

·         A distinct NUCLEUS is ABSENT in bacteria.

·         A single large circular molecule of DNA is present.

·         Bacterial cell is surrounded by a CELL WALL.

·         A few bacteria have additional SLIME CAPSULE around their cell wall.

·         Some bacteria have one or more thread like FLAGELLA, which help in locomotion.

·         Characteristics;-

1.      Bacteria are UNICELLULAR.

2.      Some are AUTOTROPHS while majority of them are HETEROTROPHS.

3.      Mode of nutrition;-

Parasitic bacteria;

Bacteria which live on other living organisms for their nutrition are called parasitic bacteria.

4.      Pathogenic bacteria;

The parasitic bacteria cause diseases in plants & animals are known as pathogenic bacteria.

5.      Mode of transmission;-

Bacteria are transmitted from one organism to another by;-

1.      Touch

2.      Air

3.      Insects

4.      Contaminated water

5.      Contaminated food

·         Importance;-

·         Advantages;-

1.      Bacteria act as decomposers; they decompose dead bodies of plants & animals so increase the SOIL FERTILITY.

2.      Use in industries & commercial areas;

Bacteria are used for manufacturing of;-

·         Butter

·         Tobacco

·         Cheese

·         Coffee

·         Yogurt

·         Leather

·         Processing of vinegar

3.      Preparation of antibiotics;

Streptomycin, tetracycline, & terramycin are obtained from bacteria.

v  Disadvantages ;-

1.      Food is decomposed and putrefied by bacteria.

2.      Bacteria cause harmful diseases in plants, animals & humans.

·         In plants;-

Ø  Canker disease in citrus fruits

Ø  Fire blight in peach, pear, & apple

Ø  Scab in potatoes

·         In animals;-

Ø     T.B

Ø  Anthrax

·         In humans;-

Ø  T.B

Ø  Whooping cough

Ø  Typhoid

Ø  Pneumonia

Ø  Leprosy

Ø  Plague

Ø  Tetanus

Ø  Diphtheria

Ø  Cholera

v  Methods of preservation;

1.      Sterilization;-

The process in which food & other things are preserved by heating it from 120C*-126C* for 12-90 minutes under suitable pressure.

2.      Pasteurization ;-

The process in which milk is heated for half an hour at 62C*for 15 seconds at 71C*to make it free from bacteria

3.      Low temperature:-

Most of bacteria are killed at very low temperature(10C*-50*)for many days.

4.      Drying process;-

Spoilage of food can be prevented by drying process.

5.      By radiations;-

Bacteria can be killed by exposing the food to radiations.

6.      High temperature;-

Cooked food & other eatables are first heated at a high temperature that kills bacteria & then sealed in metallic containers.