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TNPSC Science Notes - 6th Standard - Diversity of Organisms

Diversity of Organisms 
6th Std Science Series - 4

Charles Darwin
  • The book titled ‘Origin of Species’ published in the year 1859. It was written by a scientist Charles Darwin was sold in large number and paved way for the maximum criticism.
  • Darwin sailed to several important islands of the world in the ship H.M.S.Beagle.
  • Organisms differ in their character, habit, size, structure, nutrition and habitat. This is known as Bio-diversity. 
Organisms in different forms
  • Organisms exist in different forms such as microorganisms, plants, animals,worms, insects and birds. 
  • Organisms that can be seen only under a microscope are called micro-organisms. They can be either unicellular or multicellular. 
  • They occur in air, water, land, food and even in other living organisms. 
  • Bacterium, virus, fungus, alga, protozoan etc. are micro-organisms.
  • Bacterium and protozoan are unicellular micro-organisms. 
  • Most of the fungi and algae are multicellular micro-organisms.
  • Many people suffering from diseases like swine flu, bird flu, chikungunya, jaundice, polio, chicken pox, rabies and AIDS, these are caused by viruses. Viruses cause many diseases in plants and animals. They infect us if we are not aware of them. 
Diseases caused by Viruses
  • Common Cold - Rhino Virus
  • Polio - Polio Virus
  • Chicken pox - Herpes Virus
  • T o b a c c o Mosaic Disease - Tobacco Mosaic Virus (TMV)
  • AIDS - HIV
  • Rabies - Rabdo Virus
  • Bacteria, a micro-organism, which was discovered by Anton Van Leeuwenhoek in 1675.
Beneficial activities of bacteria:

  • Curdling of milk
  • Decomposition of organic
  • Wastes into manure.
  • Fermentation of idly and dosai flour
  • Act as bio-fertilizer increasing the yield.
Diseases caused by bacteria

  • Plants – citrus canker, blight disease of tomato
  • Animals – anthrax, tuberculosis
  • Man – pneumonia, tetanus, tuberculosis
  • Unicellular plants and animals belong to the kingdom Protista.
  • Example: Chlamydomonas,
  • Amoeba, Euglena, Plasmodium.
  • Most of the fungi are multicellular organisms. Penicillin is extracted from the fungus Penicillium notatum. 
  • It was discovered by SirAlexander Flemming in 1928. 
  • Certain fungi cause diseases like dandruff formation on our scalp 
  • Algae are unicellular and multicellular organisms. They have chlorophyll pigment which helps them to prepare their own food by the process of photosynthesis.
  • Chlamydomonas is a motile, unicellular plant. It is an alga.
  • e.g.Chlamydomonas, Volvox, Spirogyra
  • Micro-organisms are the most diversified organisms on earth.
  • A dot can be filled with 70,000 amoebae.17,000 types of micro-organisms live in a human body
  • Algae which can be seen only under a microscope (microscopic algae) are called micro algae. 
  • e.g. Chlamydomonas, Volvox.
  • Algae which can be seen with naked eyes are called macro algae.
  • These are found in pond and sewage.
  • e.g. spirogyra.
  • Some algae are used as food for man and aquatic animals. They enrich the soil.
  • In some plants, the seeds are exposed without any covering. These are naked seeded plants. These
  • plants are found in snow-covered mountains and cool places.
  • Eg. Cycas, Pine
Plant Kingdom

1. Cryptogams (non-flowering plants)
  • Thallophyt - Algae e.g. chlamydomonas and Fungi e.g. mushroom
  • Bryophyta
  • Pteridophyta
2. Phanerogams (flowering plants)
  • Gymnosperms (naked seeded plants) - e.g. cycas
  • Angiosperms (closed seeded plants)
  • Dicot plant -e.g. mango tree
  • Monocot plants -e.g. coconut tree
  • Based on the presence and absence of backbone, animals are classified as vertebrates and invertebrates.
Worms :
  • Worms like tapeworm, hook worm and roundworm live in the small intestine of man. These cause indigestion, stomach ache, dysentery, stomatitis in man. Intake of well cooked food and boiled water is good for our health.
  • It has segmented body. It feeds on organic matter in the soil and is called the friend of farmers. Preparation of vermicompost is carried out extensively using this organism.
Insects :
  • Insects like mosquito, housefly, honeybee are found everywhere. They have compound eyes. They are both beneficial and harmful to us
  • These are softbodied organisms. They have muscular foot which helps in slow movement. They posses shell . 
  • Eg: Snail
  • Some of these are exclusively marine. Eg: starfish, sea cucumber. Their skin is covered with calcareous spines. Using these spines they attack their enemies. They can regenerate the broken or lost parts.
  • These are aquatic. The body is covered with scales. Respiration takes place through the gills.
  • These are amphibians which can live both on land and in water. The body is covered with moist skin. Respiration occurs through lungs, skin and gills. These are oviparousn (egg laying).
  • These belong to the class reptilia. 
  • They respire through lungs. Heart is three chambered. These are oviparous.
  • It is 5.5m long. It is the biggest poisonous snake. A drop of its venom can kill 30 people.
  • Except for a few, most of the snakes are non-poisonous. Killing of snakes leads to their extinction
  • They are oviparous. Their body is covered with feathers. Respiration occurs through lungs. Among the birds, ostrich lays the largest egg. It is almost the size of a coconut
  • Their heart is four chambered. They feed their young ones with the help of milk producing glands. They have hairs, sweat glands and oil glands all over their body. Monkey, elephant, bat, cat, rat, blue whale and man are examples of mammals.
Examination Points:
  • The branch of science that deals with bacteria is called Bacteriology.
  • The branch of science that deals with viruses is called Virology
  • The study of micro-organisms is called Microbiology.

  • Humming Bird is the only bird that can fly forwards, backwards and sideways.
  • Crocodile is the only living organism that cannot protrude its tongue. 
  • Anaconda, the world’s biggest snake is viviparous. (gives birth to young ones)
  • Crocodiles are colour blind.
  • The tongue of a chameleon is twice as long as its body
  • Electron microscope was invented by Ernst Ruska and Max Knoll in 1931
  • Robert Gallo - In 1984, Robert Gallo discovered HIV which causes AIDS
  • The study of micro-organisms - Microbiology
Fill in the blanks by choosing the correct option

1. __________ discovered bacteria.

(Anton Van Leeuvenhoek / Alexander Flemming)

Answer: Anton Van Leeuvenhoek 

2. _________ is a motile plant.

(Amoeba / Chlamydomonas )

Answer: Chlamydomonas

3. ________ is the friend of farmers.

(locust / earthworm)

Answer: Earthworm

4. __________ disease is caused by virus.

(Polio / Cholera)

Answer: Polio

5. Chicken pox is caused by ______________

( virus / fungi)

Answer: Virus 

Choose the correct answer

1. Unicellular plant

a) Euglena b) Amoeba c) Chlamydomonas

 Answer: Amoeba

2. To which class does man belong?

a) aves b) mammals c) reptiles

Answer: Mammals

3. Which is a vertebrate?

a) jelly fish b) starfish c) eel

Answer: Starfish

4. Which is a monocot plant?

a) mango b) jack fruit c) paddy

Answer: Paddy

5. Which is the characteristic feature of a dicot plant?

a) tap root b) parallel venation c) fibrous root

Answer: Fibrous root


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