Diversity in living organisms
Diversity in living organisms
Biodiversity term is used to define the diversity of life forms.
Biodiversity is a word more often used to refer to the variety of life forms found in a particular geographic region.
Diversity of life forms of a geographic region provides stability in the respective region.
Need for Classification: Classification is necessary for easier study of living beings. Without proper classification, it would be impossible to study millions of organisms which exist on this earth.
Base of Classification
Greek thinker Aristotle first classified animals based on their place of residence whether they lived on land, in water, or in the air.
Later, all the living organisms are identified and categorized on the basis of their body design in form and function.
The idea of evolution was first described by Charles Darwin in 1859 in his book namely – The Origin of Species.’
Charles Darwin first described this idea of evolution in 1859 in his book, ‘The Origin of Species.’
Organization of nucleus:
Nucleus may or may not be organized in an organism. On this basis, organisms can be divided into two groups, viz. prokaryotes and eukaryotes.
(a) Prokaryotes: When nucleus is not organized, i.e. nuclear materials are not membrane bound; the organism is called prokaryote.
(b) Eukaryotes: When nucleus is organized, i.e. nuclear materials are membrane bound; the organism is called eukaryote.
Number of cells:
An organism can be composed of a single cell or many cells. An organism with a single cell is called unicellular organism. On the other hand, an organism with more than one cell is called multicellular organism.
Mode of Nutrition:
On this basis, organisms can be divided into two broad groups, i.e. autotrophs and heterotrophs. An autotroph makes its own food, while a heterotroph depends on other organisms for food.
Level of Organisation:
Classification and Evolution:
Hierarchy of Classification Groups
Some biologists, namely Ernst Haeckel (1894), Robert Whittaker (1959), and Carl Woese (1977) have attempted to classify all living organisms into broad categories and named them ‘Kingdoms.’
Whittaker categorized into five kingdoms namely −
Monera
Protista
Fungi
Plantae
Animalia
Further, these kingdoms have been classification by naming the sub-groups at various levels as −
Monera: These are prokaryotes; which means nuclear materials are not membrane bound in them. They may or may not have cell wall. They can be autotrophic or heterotrophic. All organisms of this kingdom are unicellular. Examples: bacteria, blue green algae (cyanobacteria) and mycoplasma.
2. Protista: These are eukaryotes and unicellular. Some organisms use cilia or flagella for locomotion. They can be autotrophic or heterotrophic. Examples: unicellular algae, diatoms and protozoans.
3. Fungi: These are heterotrophic and have cell wall. The cell wall is made of chitin. Most of the fungi are unicellular. Many of them have the capacity to become multicellular at certain stage in life. They feed on decaying organic materials. Such a mode of nutrition is called saprophytic. Some fungi live in symbiotic relationship with other organisms, while some are parasites as well. Examples: yeast, penicillium, aspergillus, mucor, etc.
4. Plantae: These are multicellular and autotrophs. Presence of chlorophyll is a distinct characteristic of plants, because of which they are capable of doing photosynthesis. Cell wall is present.
5. Animalia: These are multicellular and heterotrophs. Cell wall is absent.
Plantae
The first level of classification among plants depends on whether the plant body has well differentiated, distinct components.
The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances within it.
Further classification looks at the ability to bear seeds and whether the seeds are enclosed within fruits.
Thallophyta
Plants don’t have well differentiated body design.
commonly known as algae.
Plants are predominantly aquatic.
Examples are Spirogyra, Ulothrix, Cladophora and Chara
Bryophyta
Called the amphibians of the plant kingdom.
Plant body is commonly differentiated to form stem and leaf-like structures.
Do not have specialised tissue for the conduction of water and other substances from one part of the plant body to another.
Examples are moss (Funaria) and Marchantia.
Pteridophyta
The plant body is differentiatedinto roots, stem and leaves.
Has specialised tissue for the conduction of water and other substances from one part of the plant body to another.
Some examples are Marsilea, ferns and horse-tails.
NOTE:
Thallophytes, bryophytes and the pteridophytes have naked embryos that are called spores. The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called
‘cryptogamae’, or ‘those with hidden reproductive organs’.
plants with well differentiated reproductive tissues that ultimately make seeds are called phanerogams. Seeds are the result of the reproductive process. They consist of the embryo along with stored food, which serves for the initial growth of the embryo during germination. This group is further classified, based on whether the seeds are naked or enclosed in fruits, giving us two groups: gymnosperms and angiosperms
Gymnosperms
This term is made from two Greek words: gymno– means naked and sperma– means seed.
These plants bear naked seeds and are usually perennial, evergreen and woody.
Examples are pines and deodar.
Angiosperms
This word is made from two Greek words: angio means covered and sperma– means seed.
Seeds develop inside an organ which is modified to become a fruit.
Also called flowering plants.
Plant embryos in seeds have structures called cotyledons.
Cotyledons are called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates. Thus, cotyledons represent a bit of pre-designed plant in the seed.
Angiosperms are divided into two groups on the basis of the number of cotyledons present. Monocotyledonous or monocots: Plants with seeds having a single cotyledon.
Dicots: Plants with seeds having two cotyledons.
ANIMALIA
3. Platyhelminthes: The word Platyhelminthes means organisms with flatworms (dorsocentrally flattened)”. They are bilaterally symmetrical Triploblastic (three layers of cell), either free-living or parasitic. No true Coelom is present – Acoelomates. Ex. Planaria (Free living), Tape worm( Parasitic)
4. Nematoda: The word Nematoda “means organisms with roundworms”. They are bilaterally symmetrical Triploblastic (three layers of cells), familiar with parasitic worms. The false Coelom is called as Pseudocoelome. Ex. Ascaris, Wuchereria (Filarial worm causes elephantiasis).
5.Annelida: The word Annelida “ means organisms with metameric-segmented”.They are bilaterally symmetrical Triploblastic (three layers of cells) with closed circulatory system, familiar with earth worms. The Coelom is called as true Coelom. Ex. Neris, Earth worm, Leech .
6. Arthropoda: The word Arthropoda “means organisms with jointed legs” They are bilaterally symmetrical Triploblastic(three layers of cells ), familiar with cockroaches. The Coelom is blood filled called as Haemo Coelom. Ex. Prawn, Scorpion, Housefly.
7. Mollusca: The word Mollusca “means organisms with soft body” They are bilaterally symmetrical, Triploblastic(three layers of cells), familiar with Octopus, Pila. Foot is for moving, kidney like organ for excretion, with open circulatory system. Ex. Unio, chiton.
8. Echinodermata: The word Echinodermata “means organisms with spiny skinned”. Exoskeleton is with calcium carbonate. They are radially symmetrical Triploblastic (three layers of cells) with coelomic cavity, familiar with Star fish. They are exclusively free-living marine animals. Ex. Sea Cucumber, Feather Star .
II.CHORDATES: They are further classified as two major groups such as Protochordata &Vertebrata
(A).Protochordata: Notochord present in at least larval forms, but very rudimentary. It is a rod like supporting structure, runs along with nervous tissue from the gut of animal. They are bilaterally symmetrical, triploblastic (three layers of cells) with a Coelom, familiar with Amphioxus. Ex. Balanoglossus.
(B).Vertebrata: Notochord is replaced by vertebral column and internal skeleton. They are bilaterally symmetrical, triploblastic, coelomic and segmented having paired gill pouches. Vertebrates are grouped into five classes.
1. Pisces: These are commonly called as “fishes”, exclusively aquatic. Body is streamlined and a tail for locomotion. Gills for respiration, heart is two chambered, cold blooded, skin is covered with scales, plates. They are cold-blooded animals. Skeleton of bone ( Rohu) / cartilage( Shark). They lay eggs. Ex. Lion Fish, Dog Fish.
2. Amphibians: These are commonly called as “Amphibians” because they can live on land and in water”. Body is streamlined and a webbed foot/ foot for locomotion. Gills or lungs or skin for respiration, heart is three chambered, cold blooded, skin is lack of scales, plates. They are cold-blooded animals. They lay eggs. Ex. Rana, Hyla .
3. Reptilia: These are commonly called as “Reptilians”. A lung for respiration, heart is three chambered (Crocodile heart is four chambered), skin have scales. They are cold-blooded animals. They lay eggs. Ex. Snakes, Turtles
4. Aves :These are commonly called as “Birds”. A lung for respiration, heart is fourchambered, fore limbs are modified for flight, skin has feathers. They are warm-blooded animals. They lay eggs. Ex. Ostrich (Flightless Bird), Pigeon, Sparrow .
5. Mammalia: These are commonly called as “animals with mammary glands for producing
milk to nourish their young ones”. A lung for respiration, heart is four chambered, skin has
hairs, sweat or oil glands. They are warm-blooded animals. They lay eggs (Platypus, Echidna), give birth to young ones poorly developed (Kangaroo) & give birth to developed young ones (Human beings). Ex. Lion, Whale, Bat