DIVERSITY IN LIVING ORGANISMS

IMPORTANT TERMS

Biodiversity                  Biodiversity means variety and variability of various lives on Earth.

Classification                Classification is the arrangement of organisms into groups and subgroups on the basis of their similarities and dissimilarities. 

Kingdom                      It is a taxonomic category having the highest ranking in which all forms of life having certain fundamental characteristics in common have been grouped together.  

Species                       It is the basic unit of biological classification. It is a group of closely related organisms that are capable of interbreeding and producing fertile offspring.

Prokaryote                   It is a unicellular organism that lacks a membrane-bound nucleus as well as any other membrane-bound organelle.

Eukaryote                    Eukaryotes are organisms whose cells have a well-defined membrane-bound nucleus and organelles.

Autotrophs                   An organism that is able to synthesizing its own food from inorganic substances using light or chemical energy. Green plants, algae, and certain bacteria are autotrophs.

Heterotrophs                They are not capable of producing their own food. Therefore, they obtain their energy requirements by feeding on organic matter or another organism. All animals, some fungi and most bacteria are heterotrophs.

Cold blooded                Body temperature of cold blooded animals changes according to the surrounding temperature. Therefore body temperature of these animals does not remain constant.

Warm blooded             Body temperature of warm blooded animals remains constant regardless of the surrounding temperatures.

BIODIVERSITY

The variety of living organisms present on a particular geographical area is called biodiversity of that area. Term "Biodiversity" was coined by "Walter G. Rosen" in 1986.

 MEGADIVERSITY

• The warm and humid tropical regions of the earth between the tropic of Capricorn and the tropic of Cancer, are rich in diversity of living biota. This is called the region of "Megadiversity".
• There are 12 megadiversity centres in the world, which are rich in biodiversity: Brazil, Colombia, Ecuador, Peru, Mexico, Zaire, Medagascar, Australia, China, Indonesia, Malaysia and India.

CLASSIFICATION

• Organisms are classified into groups and subgroups on the basis of their similarities and dissimilarities. It is necessary for easier study of living organisms. Aristotle classified living beings according to whether they lived on land, in water or in air. He classified them into two groups
• Charles Darwin first described the idea of evolution in 1859 in his book, "The Origin of Species". Organisms are classified based on body design, hierarchy in developing, relation to evolution
• Haeckel, Whittaker and Carl Woese tried to classify all living organisms into broad kingdoms.
• Hierarchy: It refers to the taxonomical classification of living organisms in successive levels of complexity. 
• Category: Complex organisms (Plants and animals) are arranged in categories such as Kingdom, Phylum (for animals) or Division (for plants), Class, Order, Family, Genus and Species.
• Taxon: It is defined as a unit of classification of organisms that can be recognised to a definite category at any level of classification e.g. birds, worms etc.

Kingdom → Largest Group

        Phylum (for animals) / Division (for plants)

               Class     

                    Order         

                          Family                

                              Genus                      

                                  Species → Lowest group

 

FIVE KINGDOM CLASSIFICATIONS

It is given by Robert Whittaker (1959), which is the most accepted system of classification.

Monera

They are unicellular, prokaryotic organisms (do not have defined nucleus and organelles). They may or may not have cell wall.  Mode of nutrition is either autotrophic (Blue-green algae) or heterotrophic (Mycoplasma and most bacteria). Ex. bacteria, blue green algae (cyanobacteria) and mycoplasma.

Protista

They are unicellular, eukaryotic organisms (presence of true nucleus and membrane bound other cell organelles). Some of them are covered with cell wall (most photosynthetic protists) while others do not possess it (e.g., protozoan protists). They are either autotrophic (algae and diatomes) or heterotrophic (protozoans). Some organisms have cilia (e.g. Paramecium), flagellum (e.g. Euglena) and pseudopodia (e.g. Amoeba) for locomation. Sexual reporduction is present but an embryo stage is absent.

Fungi

These are multicellular eukaryotic organisms with cell wall, made of chitin. Mode of nutrition is heterotrophic. Food is gained by either saprophytically (from dead organic matter) or parasitically (from other living tissues). Some fungi live in symbiotic relationship with bluegreen algae (or cyanobacteria). These symbiobic life forms are called lichens.

Plantae

These are multicellular and eukaryotic with cell wall made of cellulose. They are mostly autotrophs. Presence of chlorophyll is a distinct characteristic of plants, because of which they are capable of doing photosynthesis. Cell wall is present. Ex. Maize, Sunflower etc.

Animalia

These are multicellular eukaryotic organisms without cell wall. Mode of nutrition is heterotrophic. . Ex.Human, Fish etc.

 

KINGDOM PLANTAE

The Plant Kingdom can be further classified into five divisions. Their key characteristics are given below:

Thallophyta

The plant body is not differentiated into root, stem and leaves. The plant body is simple thallus type. They are commonly known as algae. Plants are predominantly aquatic. Examples: Spirogyra, chara, volvox, ulothtrix, etc

Bryophyta

Plant body is differentiated into stem and leaf like structure. There is no specialized tissue for transportation of water, minerals and food. Bryophytes are also known as the amphibians of the plant kingdom, because they need water to complete a part of their life cycle. These are the simplest and the most primitive land plant.  Examples: Moss, marchantia.

Pteridophyta

Plant body is differentiated into root, stem and leaf. They have specialized tissue (Vascular system) for the conduction of water and other substances from one part of the plant body to another Examples: Marsilear, ferns, horse tails, etc.

The reproductive organs of plants in the thallophytes, the bryophytes and the pteridophytes groups are very inconspicuous, and they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’. These groups have naked embryos that are called spores.

Gymnosperms

The word ‘gymnos’ means naked and ‘sperma’ means seed. They bear naked seed. The seeds are not enclosed inside fruits. Plants are usually perennial, evergreen and woody. Examples: Pine, cycas, deodar, etc.

Angiosperms

The word ‘angio’ means covered and ‘sperma’ means seed. The plants of this group produce seeds inside an organ called ovary, which is modified in to fruit. These are called flowering plant. There is great diversity in species of angiosperm. Angiosperms are further divided into two groups, viz. monocotyledonous (single cotyledon in their seeds) and dicotyledonous (two cotyledons in a seed). Examples of monocots: Lily, coconut, wheat, maize etc. Examples of dicots: Gram, Pea, Mustard, Ipomoea etc.

KINGDOM ANIMALIA

The animal kingdom is classified into different phyla. Their detail is given below:

Sponges (Poriferans)

• The word porifera means organisms with holes (pores all over their body).
• They mostly live in salty sea water fixed to some object.
• The pores lead into the canal system. Water flows through the canal system and facilitates entry of food and exchange of other materials.
• Their body is not differentiated into tissues. It is covered with a hard outer skeleton.
• Example- Sycon, spongilla, euplectelea, etc.

 

Cnidarians (Coelenterata)

• They are aquatic animals having marine habitat.
• There is a cavity (coelom) in the body. Body is tube like with one opening called mouth.
• The body wall is made up of two layers of cells (diploblastic).
• Mouth is surrounded by tentacles used for capturing prey.
• They have radially symmetrical body.
• Example- Hydra, Jelly fish, Sea anemone

 

Platyhelminthes (Flatworms)

• The body is flattened from top to bottom and hence the name platyhelminthes
• They can be found in marine/fresh water.
• Body is bilaterally symmetrical. The body wall is triploblastic. Because of three layers, it is possible to form some organs as well.
• A proper ceolom is absent in platyhelminthes and hence proper organs are absent.
• Body is having a single opening.
• They are free-living or parasitic animals.
• Example-Tapeworms, Liverfluke.

 

Nematoda

• Body is bilaterally symmetrical. The body wall is triploblastic.
• A pseudocoelom is present and hence organs are absent.
• Animals are cylindrical in shape
• Found in fresh/marine water or on land.
• They have unsegmented body.
• Body has two openings mouth and anus.
• Most of them are parasites and reproduce sexually by laying eggs.
• Example-Pinworm, Ascaris. Wuchereria

 

Annelids (Segmented worms)

• Body is bilaterally symmetrical. The body wall is triploblastic.
• True body cavity is present in these animals.
• The body is divided into segments and hence the name annelid. Each segment is lined one after another and contains a set of organs.
• Found in marine and fresh water.
• They have special organs of excretion called nephridia
• Example-Earthworm, Leech.

 

Arthropods (Animals with jointed legs)

• They have jointed appendages which gives the name arthropoda.
• They  have segmented bilaterally symmetrical body
• Body is divided into three regions- Head, Thorax and Abdomen.
• Body has tough outer covering called exoskeleton
• Circulatory system is open, which means blood flows in the coelomic cavity.
• This is the largest group of animals
• Examples: cockroach, housefly, spider, prawn, scorpion, etc.

 Molluscs (soft bodied shelled animals)

• Animals have soft un-segmented body which is enclosed in a hard shell.
• They have bilaterally symmetrical body.
• Circulatory system is open and kidney like organ is present for excretion
• The body has well developed muscular feet for locomotion.
• Example-Squid, snail, octopus .

 

 Echinoderms (Spiny-skinned animals)

• They are marine animals having spines all over the body.
• Body is radially Symmetrical
• The animals have well developed water canal system, which is used for locomotion.
• Skeleton is made of calcium carbonate.
• Body has two openings mouth and anus.
• They have tube like feet having suckers
• Example-Starfish, Sea urchins. 

Chordata

• Animals have notochord, pharyngeal gill slits and post anal tail; for at least some stages of life.
• Phylum chordata is divided into three sub-phyla; Craniata (Vertebrata), Tunicata (tunicates, or urochordates), Cephalochordata.
• Urochordata and Cephalochordata are collectively known as protochordates.

Protochordata

• They are bilaterally symmetrical, triploblastic and ceolomate.
• They are marine animals.
• Notochord is present at least at some stages of life
• Notochord is a long rod-like structure which runs along the back of the animal. This provides attachment points for muscles.
• Notochord separates the nervous tissues from the gut.
• Examples: Balanoglossus, herdmania, amphioxus, etc.

VERTEBRATES

The notochord is replaced by a spinal column during embryonic stage. Following are the main characteristics of vertebrates.

• Notochord present; which is replaced by spinal column.
• Dorsal nerve chord is present.
• Animals are triploblastic and coelomate.
• Animals have paired gill pouches.

Pisces (fish)

The body is streamlined and covered with scales. Muscular tail is present which assists in locomotion. Paired gills are present that can breathe oxygen dissolved in water. They are cold-blooded animals. The heart has only two chambers. They lay eggs. They can be bony (e.g., Rohu and katla) or cartilaginous (e.g., Shark).

Amphibia

These animals are adapted to live both in water and land. Mucus glands on skin keep the skin moist. The animals breathe through skin when in water and through lungs when on land. The heart has three chambers. These are cold blooded animals. Examples: Frog, toad, salamander, etc.

Reptilia

These animals show crawling movement for locomotion. Skin is hardened to form scales. Most of the reptilians have three chambered heart but crocodile has four-chambered heart. They don’t need water to lay eggs, rather eggs are covered with hard shells and laid on land. Examples: snakes, lizards, crocodile, turtle, etc.

Aves

The body is covered with feathers. Forelimbs are modified into wings. These are warm-blooded animals. The heart has four chambers. Bones are hollow (pneumatic); which assists in flying. All the birds belong to this class.

Mammalia

The body is covered with hairs. Skin has sweat glands and sebaceous glands. Mammary glands are present in females and are used for nourishing the young ones. Most of the mammalians give birth to young ones and are called viviparous e.g. human, chimpanzee, lion, horse, etc. Two of the mammals lay eggs and are called oviparous i.e platypus and spiny anteaters.

BINOMIAL NOMENCLATURE OF ORGANISMS:

• The system of binomial nomenclature was proposed by Carolus Linneaus (1707 – 1778). Conventions of writing biological name are as follows:
• The biological name is composed of two terms. The first term is called genetic name starts with a capital letter and the second term is called species name starts with a small letter. Both term are to be written in italics.
• Example: Binomial Nomenclature of Mango is called Magnifera indica.

INTERESTING FACTS

• There are about ten million species on the planet, although we actually know only one or two millions of them.
• Amazon rainforests is the largest biodiversity hotspot in the world that produces more than 20 percent of the world oxygen.
• Molluscs “the largest marine phylum” comprises around 23% of all the marine organisms.
• Echinoderms do not have head.
• Centipedes and millipedes both are classified as arthropods but centipedes are carnivorous while millipedes are herbivores.
• Vertebrates account for about 3% of all known species on our planet. The other 97% of species alive today are invertebrates.
• The male birds are generally much more colorful than the females.
• The Blue Whale is a vertebrate that is the world's largest animal.
• The bat is the only mammal that can fly.
• Dolphins can swim and sleep at same time, but they sleep with one eye open.
• Caterpillars have 4000 muscles while humans have only 629.
• Although crocodile belongs to reptiles but it has four chambered heart like aves and mammals.