The bewildering variety of life around ushas evolved on earth over millions ofyears.We do not have enough time to view eachand every fraction of these livingorganisms alone.Instead we look at them as a whole andfind similarities and dissimilarities amongthe organisms which allows us to classifythem into different types.
Attempts at classifying living thingsinto groups have been made since thetime immemorial. Greek thinker Aristotle classifiedanimals according to where they livedi.e. land, water or air. This was then rejected by the people ofthat time since it wasn’t anappropriate way to classify animals bythe basis of their habitat.
What is meant by characteristics?• When trying to classify a diverse group oforganisms, finding ways in which some of them aresimilar enough to be thought of together is theeasiest.• Characteristics mean a particular form orfunction. Eg. Humans have 5 fingers in each hand.
Characteristics for hierarchicalclassification -Characteristic No.1An eukaryotic cell has membrane bound organellesincluding a nucleus which allows cellular process to becarried out easily.Organisms which do not have a clearly demonstratednucleus need not have their biochemical practicesalways organized.This would effect every aspect of the cell design.
Characteristic No. 2• Cells that group together to form a singleorganism use the principle of division oflabour.• In such a cell type, all the cells wouldn’t beidentical .• Groups of cells will carry out specializedfunctions• Eg. An amoeba and a worm.
Characteristic No. 3• Some organisms can produce their own foodlike plants.• The other cannot produce their own food anddepend on the environment they live in for foodlike bear, lion, zebra.• The organisms which can produce food aremore organised and complex than the one’swho cant produce food on their own.
Characteristic No.4•There are different ways in whichsome animal’s body organs developfaster or more complexly from theother animals.•There are also some special organs fora particular function in some animals.Eg, A cheetah’s leg’s muscularcontraction and relaxation speed.
Classification and evolution• All living things are categorized on thebasis of their body design and function.• Once a certain body design comes intoexistence it will shape the effects of allother subsequent body designs.• There is an important role of time in thechange of characteristics.
• The classification of life forms are closelyrelated to their evolution.• Evolution means the accumulation of thechanges in body design which allow theorganism to survive better in itssurroundings.• Charles Darwin described this idea ofevolution in his book -The origin of species
An camel’s eye – Charles Darwin –His book The origin of species.
The hierarchy of classificationof groups• Biologists Ernst Haeckel, RobertWhittaker and CarlWoese have tried to classify all living organisms intobroad categories called kingdoms.• The classification RobertWhittaker proposed has fivekingdoms namelya) Monerab) Protistac) Fungid) Plantaee) Animalia
Monera• These organisms do not have a defined nucleusor organelles nor do any of them show multi-cellular designs.• Some have cell walls and some do not.• Can be seen only through a microscope.• Some synthesize their own food (autotrophic)and some get it from the environment(heterotrophic)• Eg. Bacteria, cyanobacteria and mycoplasma.
Protista• Includes many unicellular eukaryoticorganisms.• Some use appendages like cilia or flagella formoving around.• Mode of nutrition can be autotrophic orheterotrophic.• Eg.Unicellular algae, diatoms and protozoans.