Note: (Complete chapter removed from syllabus for 2020-21 academic session)
Introduction to Taxonomy
- Diversity is the presence of different organisms in the same ecosystem or geographical location.
- Diversity gives a chance for a more balanced ecosystem.
- Evolution is the slow process by which the organisms change according to the needs to survive the environment around them.
- Evolution leads to the formation of new organisms and more diversity in the ecosystem.
- Charles Darwin was an English biologist and a naturalist.
- He travelled on HMS Beagle to Galapagos Island in South America.
- Using his observation, he proposed the theory of evolution in his book On the Origin of Species.
Taxonomy is the branch of science that deals with the classification of organisms.
Hierarchy of Classification
- Organisms are arranged into groups/levels according to their similarities.
- As we go up the hierarchy, the organisms have lesser similarity.
A kingdom is the highest level of classification which consists of a number of phyla or divisions(in case of plants) with similar characteristics.
Phylum/Division is a level of classification which consists of a number of classes with similar characteristics.
A class is the level of classification which consists of a number of orders with similar characteristics.
An order is the level of classification which consists of a number of families with similar characteristics.
A family is the level of classification which consists a number of Genus with similar characteristics.
Genus is the level of classification which consists of a number of species with similar characteristics.
Species is the level of classification which consists of a number of organisms with similar characteristics and can interbreed to give rise to a fertile offspring.
- Carolus Linnaeus is a Swedish botanist and physician who also called ‘Father of taxonomy‘.
- He introduced the Binomial nomenclature and laid the ground rules which paved way for modern taxonomy.
- Binomial Nomenclature was introduced by Linnaeus as a method of naming organisms in taxonomy.
- It consists of two parts.
- The first part is the Genus name which is written in capital.
- The second part is the species name, which is not capitalised.
Five Kingdom Classification
5 Kingdom classification
- 5 Kingdom classification is the most accepted system of classification given by R.H.Whittaker.
- This classification solved most of the issues in taxonomy related to the placement of bacteria and fungi.
- The 5 kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
- All the prokaryotic organisms are placed in this Kingdom.
- Bacteria and their ancient cousin, archaebacteria are the organisms that makeup Kingdom Monera.
- These are prokaryotic, unicellular, autotrophic/heterotrophic organisms.
- Bacteria have a cell wall made up of polysaccharides.
- The category in the kingdom Monera which consists of the organisms surviving in extremely hot conditions.
- They are considered to be the most ancient living organism present on the planet.
- Eubacteria is phylum of Monera consists of all the bacteria that survive in a normal environment.
- All the major helpful and pathogenic bacteria we know today fall under this category.
Gram +ve/-ve bacteria
- Some bacteria have a very thick cell wall which makes them take up Gram stain and appear violet.
- There are other bacteria which have a thin cell wall and on Gram staining appear pink.
- Usually, gram +ve bacteria are pathogenic in nature.
- Kingdom Protista is made up of all the eukaryotic unicellular organism except yeast.
- Protozoans are the unicellular eukaryotic organisms that come under the Kingdom Protista.
- Examples include paramecium, amoeba, Plasmodium, euglena, leishmania etc.
Fungi like Protists
- This kingdom includes unicellular fungi like yeast and moulds.
- Kingdom Protista includes some unicellular algae which are photosynthetic.
- The organisms of Kingdom Fungi are mostly saprophytic.
- It is the only Kingdom which has the multicellular and unicellular organisms.
- Majority of them have a cell wall made up of chitin.
- All plants and trees we see around us come under this Kingdom.
- All of them are autotrophic with chloroplast in their cell.
- Their cell wall is made up of cellulose.
- The plant kingdom is classified into two major divisions as Cryptogams and Phanerogams.
- Cryptogams literally mean ‘plants with hidden reproductive parts’
- Cryptogams are plants that produce spores to reproduce instead of seeds.
- So these plants do not have flowers or fruits.
- Cryptogams are further classified as thallophytes, bryophytes and pteridophytes.
- Phanerogams are plants that produce seeds for reproduction.
- Some of them do not produce flowers, while the others produce flowers.
- Phanerogams are further classified as gymnosperms and angiosperms.
- Thallophyta is the first division of plant kingdom.
- It consists of red, green and brown algae.
- They don’t have a lot of differentiated structure.
- Bryophyta is the 2nd division of plant kingdom.
- These are the first plants to have differentiated roots and shoots.
- Pteridophyta is the 3rd division of plant kingdom.
- These plants have proper differentiation of roots, stem and leaves.
- Gymnosperm stands for naked seed.
- They are the first phanerogams since they produce seeds, which is not enclosed in a fruit.
- Angiosperm is the last division of plant kingdom and has what scientist assume, the most evolved organisms on the planet.
- They bear flowers and fruits, inside which the seeds are found.
- Cotyledons are structures present in seeds for nutrition during germination when leaves are not yet developed.
- Angiosperms either have two cotyledons making them dicots or only one, making them monocot.
Dicots and Monocots
- Angiosperms, the highly evolved plants on the planet Earth, are further classified based on the number of cotyledons their seeds have.
- When seeds have two cotyledons, they are called dicots.
- Dicots have tap root system and reticulate venation. Examples: Mango, Pea, Beans etc.
- If seeds have only one cotyledon, they become monocots.
- Monocots show fibrous root system and parallel venation.
- Examples: all grains like wheat, maize, rice etc.
- Kingdom Animalia is made up of eukaryotic, multicellular, heterotrophic organisms.
- Mode of nutrition is holozoic and they are either herbivores or carnivores.
- Most animals are motile, they can move independently in search of food, shelter or mate.
- Animals are made up of many organ systems, that aids in performing specific functions that are necessary for the survival of the organism.
- Most of the animals are bilaterally symmetrical, while primitive animals are asymmetrical and cnidarians and echinoderms are radially symmetrical.
- This phylum consists of the sponges.
- They are mostly marine, very few are freshwater.
- All the animals are sessile (fixed in one place).
- Cells are loosely arranged (cellular grade of the organization).
- Animals are diploblastic with outer ectoderm and inner endoderm held with jelly-like mesoglea.
- Exoskeleton in the form of spicules made up of silica or calcium carbonate.
- Sponges have pores all over the body. Body pores are called Ostia.
- Water from outside enters the body through Ostia and leaves through one large opening called the osculum.
- These animals are aquatic, mostly marine.
- They are solitary or colonial. Each individual is known as zooid.
- Animals are radially symmetrical.
- Sessile forms are called Polyps and free-living forms are called Medusa
- Cells are organized into tissues (tissue grade of the organization).
- Animals are diploblastic, outer ectoderm and inner endoderm. Mesogloea separates these two layers.
- The body has a single opening called hypostome surrounded by sensory tentacles.
- Body cavity (coelom) acts as gastrovascular cavity i.e.coelenteron.
- special types of cells called Nematocysts are present for capturing and paralyzing pray, present in tentacles.
- Examples: Hydra, Jellyfish, Corals, Obelia, Sea-anemone.
- This phylum consists of the organisms are bilaterally symmetrical, triploblastic and flattened.
- Organ- system grade of the organization is seen.
- Animals are triploblastic with outer ectoderm, middle mesoderm and inner endoderm.
- Acoelomate i.e No body cavity.
- The digestive system is incomplete or absent.
- Mostly parasites, few are free living.
- Examples: Liver fluke, Tapeworm.
- These organisms have bilaterally symmetrical, triploblastic and cylindrical body.
- Organ system grade of the organization is seen.
- Pseudocoelom is present.
- Have a tubular digestive system with openings at both the ends.
- They are endoparasites.
- Mouth is provided with hooks and suckers.
- Examples: Ascaris, hookworm, filarial worm etc.
- These organisms have bilateral symmetry and triploblastic.
- They are mostly aquatic, few are terrestrial.
- These are the first organism to have a true coelom.
- Coelome is compartmentalized by intersegmental septa.
- Body long and metamerically segmented (segmentation from outside and inside of the body).
- Examples: leech, earthworm etc.
- This is the largest phylum with 80% of all known living animals.
- Animals with jointed appendages (in Greek Arthron: jointed, poda: legs).
- The body has three segments/regions as head, thorax and abdomen.
- Body is covered by an exoskeleton made of chitin.
- They are bilaterally symmetrical and have an open circulatory system.
- Compound eyes are present
- Examples: insects, scorpions, spiders, millipedes, centipedes, crabs, lobsters etc
- They are bilaterally symmetrical, with a reduced coelomic cavity and little segmentation.
- They have an open circulatory system and kidney like organs for excretion.
- Body is soft and usually enclosed in a shell. The shell may be external or internal.
- They show the presence of Foot, Mantle and Mantle cavity.
- Examples: pearl oysters, bivalves, sepia, octopus, snail, slug etc.
- They are spiny skinned and free-living, exclusively marine.
- The animals are usually pentamerous.
- They are triploblastic and have a coelomic cavity.
- They have a water driven tube system for moving forward.
- Examples: starfish, sea urchin, sea cucumber, sea lily etc.
- Hemichordata is bilaterally symmetrical and triploblastic.
- In addition to these, they have a notochord that runs along the back of the animal and separates the nervous tissue from the gut.
- They are marine animals and bridge non-chordates to chordates.
- Porifera to Echinodermata are non-chordates/invertebrates.
- Example: Balanoglossus, also called acorn worm.
- Presence of dorsal, tubular, hollow nerve cord.
- Presence of notochord.
- Presence of pharyngeal gill slits.
- Presence of post-anal tail.
- Bilaterally symmetrical body.
- Presence of three germ layers.
- Organ-system level of organization.
- Presence of ventral heart and hepatic portal system.
- Presence of well developed endocrine glands
- Except for a few primitive forms, the animals have vertebral column instead of the notochord. These animals are called vertebrates.
- Class Pisces include all bony and cartilaginous fishes.
- They are exclusively aquatic.
- Body is streamlined with paired and unpaired fins.
- These are cold-blooded vertebrates
- Heart is two-chambered.
- Lateral line system is well developed.
- Examples: Sharks, Rays, Rohu, Mrigal, Green carp etc
- Amphibians live both, on land and in water, and lay their eggs in water.
- Respiration is through gills in the larval stage and through lungs in adults.
- They are cold-blooded animals.
- They have a three-chambered heart.
- Examples: frog, toads, salamander etc
- These are the first completely land animals.
- Reptiles are cold-blooded and breathe through their lungs.
- They have a three-chambered heart (exception crocodile) and lay eggs with tough coverings.
- Body is covered with scales, scutes or hard plates.
- Examples: snakes, crocodiles, turtles, lizards etc.
- All birds belong to this class.
- They are warm-blooded, have a four-chambered heart and breathe through lungs.
- They have their forelimbs modified into wings which help in flight.
- Jaws are modified into beaks.
- Bones are hollow and most of them are fused to reduce body weight.
- An exoskeleton is in the form of feathers.
- They are warm-blooded, breath through lungs and have a four-chambered heart.
- Presence of hair on their body, sweat and oil glands are exclusive characters of mammals.
- Presence of pinna i.e external ear is also seen only in mammals.
- They also have the mammary glands to feed their young ones.
- They usually give birth to live young ones.
- Examples: humans, cattle etc