IGCSE>CONTENT>SECTION-1>2-CLASSIFICATION
CLASS PRESENTATION:
CLASSIFICATION
- Nobody knows how many different kinds, or species, of living organisms there are on Earth.
- About 1.4 million species have been described and named. But many biologists think this may be only about one-tenth of all the species on earth.
- We have almost certainly discovered most of the large land animals, but there are probably many animals living in the deep oceans which have never been seen by humans. And biologists estimate that there are millions of insects and smaller animals and plants that have not yet been discovered.
- To make it easier to study these organisms, biologists have sorted them into groups. This sorting is called classification.
- Definition: The method of arranging and grouping of organisms on the basis of similarities and differences is called classification.
- Classification systems aim to reflect evolutionary relationships.
SIGNIFICANCE OF CLASSIFICATIONS
- Classification makes the study of various organism simpler and easier.
- Classification is essential to understand the interrelations between different organisms.
- Classification projects before us a good picture of all life forms at a glance.
- It serves as a base for the development of other biological sciences like bio-geography, ecology, behavioral sciences etc.
BASIS OF CLASSIFICATION
There are many possible ways of classifying organisms.
- Classification is traditionally based on studies of morphology and anatomy. Morphology is the study of external appearance of living organisms. Anatomy deals with the study of internal structure of living organisms.
- Modern classification are based on studies of sequences of bases in DNA and of amino acids in proteins. These classification are more accurate.
BINOMIAL NOMENCLATURE
- The living organisms that people are familiar with all have common names. People who speak English call a zebra ‘a zebra’. However, there are different kinds of zebras. For example, Grevy’s zebra and the plains zebra have different stripe patterns. In Swahili, the language of the people who share their home country with zebras, Grevy’s zebra is ‘kanjanga’ and the plains zebra is ‘punda mila’. Each language has its own name for a zebra, or for different kinds of zebras.
- To avoid confusion, biologists have given each kind of organism its own unique, two-word name. This is called a binomial (meaning ‘two name’). This idea was first thought of in 1735 by Linnaeus, a Swedish scientist. Linnaeus wanted to make sure that scientists all over the world could communicate about living organisms, even though they spoke different languages and so had different names for the same kind of organism. We still use Linnaeus’s naming system today.
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FIVE KINGDOMS CLASSIFICATION
Robert H. Whittaker (1969), an American taxonomist, divided the living world into five kingdoms: Monera, Protista, Fungi, Plantae and Animalia.
Five Kingdom System of Classification He used the following criteria for limiting the different kingdoms:
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TAXONOMIC HIERARCHY
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ANIMAL KINGDOM
INVERTEBRATES AND VERTEBRATES
Invertebrate: All the animals which do not have a vertebral column are often referred to as invertebrates. Those animals which have a vertebral column are called as vertebrates.
Invertebrate: All the animals which do not have a vertebral column are often referred to as invertebrates. Those animals which have a vertebral column are called as vertebrates.
Invertebrates: (Only one in syllabus)
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Vertebrates:(5 classes)
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INVERTEBRATES
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- These are often called 'roundworms'.
- Body is not divided into segments.
- They are circular in cross section.
- Pointed at both ends.
- Habitat: They are widely distributed, free-living in the soil or as parasites of plants and animals.
- Diseases: They can cause river blindness and elephantiasis.
2. ANNELIDA
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3. MOLLUSCA
4. ARTHROPODA (Jointed legs)
- Main features :
- Jointed limbs.
- They have hard, firm exoskeleton, which is called a cuticle, encloses their bodies.
- Phylum Arthropoda includes four classes.
CLASS: 1_ INSECTA
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CLASS: 2_ARACHNIDA
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CLASS: 3_CRUSTACEA
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CLASS: 4_MYRIAPODA
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Table: classes of Arthropoda
VERTEBRATES
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VIDEO: VERTEBRATES
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VERTEBRATES CLASSIFICATION
CLASS: 1_PISCES (FISH)
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CLASS: 2_AMPHIBIANS
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CLASS: 3_REPTILES
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CLASS: 4_AVES
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CLASS: 5_MAMMALS
PLANT KINGDOM
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Video : Plant classification
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NON FLOWERING PLANTS
- Algae
- Bryophytes
- Pteridophytes
- Gymnosperm
FLOWERING PLANTS (Angiosperms)
PROKARYOTES: BACTERIA
FUNGI
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VIRUS
Downloadable file: PPT