Chapter 2: Classification of Living Beings

Five Kingdom Classification chart showing Monera, Protista, Fungi, Plantae and Animalia branching from Organism through Prokaryotes/Eukaryotes, unicellular/multicellular, and nutrition type.

• All organisms of kingdom Monera have a prokaryotic cell (no true nucleus).
• Kingdom Protista includes unicellular eukaryotic organisms, e.g., Euglena.
• Fungi have a cell wall but no chlorophyll; they are saprotrophs that decompose dead and decaying matter.

• Cell wall is made up of cellulose.
• They are autotrophs (prepare their own food by photosynthesis).
• Some plants are flowering and some are non-flowering.
• On the basis of body structure, plants are classified into three divisions: Algae, Bryophyta and Tracheophyta.

• Unicellular or multicellular.
• Autotrophs due to presence of chlorophyll; food is stored as starch.
• Cell wall is composed of cellulose.
• Reproduce both sexually and asexually.
• Found in ponds, rivers, seas and marshy places.

Spirogyra, Volvox and Fucus specimens representing division Algae.

• Multicellular and autotrophic.
• Plant body is thallus or differentiated into rhizoid, stem and simple leaf.
• Found in moist and shady places.
• Dioecious; male plant produces gametes in antheridium, female plant in archegonium.
• No vascular tissue, so they grow only a few centimetres tall.

Marchantia, Moss and Riccia specimens representing division Bryophyta.

• Found in moist and shady places.
• No seed; body differentiated into root, stem (underdeveloped, rhizome) and feather-like leaf.
• Developed vascular tissue (xylem and phloem).
• Brown spots on the lower surface of leaves are called sori (singular: sorus); inside each sorus lies a sporangium that produces spores. A leaf with sori is a sporophyll, without sori a tropophyll.
• Plant body is called sporophyte because it produces haploid spores.
• Spores germinate into gametophytes called prothalli under suitable conditions.
• Shows alternation of generation; sporophytic phase is dominant and lasts longer.

Fern, horsetail and clubmoss representing sub-division Pteridophyta.

• First plants to produce seeds in the course of evolution.
• Bear cones instead of flowers; male and female cones are separate (unisexual); pollination through wind.
• No ovary in the cone, so no fruit; seed is naked.
• Leaves are elongated and needle-like; stem enclosed within thick bark.
• Shape is like an inverted cone, so also called coniferous plants.
• Roots spread far into the ground.

Pinus, Juniper and Cycas representing sub-division Gymnosperm.

• Most advanced plants of kingdom Plantae; found everywhere in land and water.
• Well-developed root, stem, leaf, flower and fruit.
• Bear real flowers; the flower contains both ovary and ovule.
• Some are bisexual, some unisexual; pollination by wind, water, insects or animals.
• Seeds are enclosed inside the fruit.

Bamboo and soybean representing real flowering plants of sub-division Angiosperm.

• Parallel venation in leaves.
• Fibrous root system.
• Usually hollow stem; nodes prominent at equal interval; leaf base forms a sheath covering the stem.
• Vascular tissue scattered within the stem.
• Floral parts are three or multiples of three.
• Seed has only one cotyledon.

Paddy, bamboo, turmeric, barley and banana representing monocotyledonous plants.

• Reticulate (net-like) venation with a mid-rib and branching veins/veinlets.
• Taproot system with a prominent main root.
• Stem solid, strong, mostly woody; nodes at unequal intervals.
• Vascular bundles arranged in a ring within the stem.
• Seed has two cotyledons; seeds enclosed within fruit.

Mustard, soybean, orange, bean and pea representing dicotyledonous plants.

• First multicellular organisms; no true tissue is developed (except in later phyla).
• Diploblastic (body develops from two germ layers).
• Body has pores; a larger pore is osculum and smaller pores are ostia; water enters through ostia and exits through osculum - this is the water canal system.
• Respire through the general body surface.
• Adult forms are found attached to a substratum; high regeneration capacity.
• Reproduce both asexually (budding, regeneration) and sexually.
• Mostly asymmetrical body.

Spongilla, Sycon and Euspongia representing phylum Porifera (sponges).

• Multicellular and diploblastic; the first tissue-graded animals.
• Have a hollow cavity called coelenteron (gastrovascular cavity) for digestion and transportation.
• Single opening of alimentary canal (mouth), surrounded by tentacles containing stinging cells (nematocysts) used to capture prey.
• Respire through the general body surface.
• Reproduce sexually and asexually (budding, regeneration).
• Radially symmetrical body; found in ponds, lakes and seas.

Hydra, Jellyfish and Coral representing phylum Coelenterata.

• Body flat, leaf-like or long ribbon-like; hence called flatworms ('platy' = flat, 'helminthes' = worms).
• Triploblastic (body develops from three germ layers).
• Mouth present at anterior-ventral surface but no anus; mouth surrounded by hooks to attach to the host; sucker helps absorb blood and nutrients.
• No well-developed organ system; space filled with parenchyma tissue; no circulatory system.
• Hermaphrodite (bisexual); fertilization is internal.
• Mostly parasites, a few free-living.

Tapeworm, Liverfluke and Bloodfluke representing phylum Platyhelminthes.

• Body elongated, cylindrical with tapering ends; bilaterally symmetrical; triploblastic.
• Developed digestive system with mouth, anus and sucker; no respiratory or circulatory system.
• Unisexual; reproduce sexually only, with internal fertilization.
• Mostly parasites (cause disease in host body); a few free-living.

Round worm, hook worm and pinworm representing phylum Nemathelminthes.

• Body elongated, cylindrical, segmented both externally and internally (metameric segmentation).
• Bilaterally symmetrical and triploblastic; skin is moist; respire through outer body surface.
• Excretion through nephridia; well-developed circulatory system with haemoglobin in blood.
• Nervous system with a nerve ring and nerve cord.
• Some hermaphrodite, some unisexual; high regeneration capacity.
• Found in moist land, water; some are ectoparasites.

Earthworm, Leech and Nereis representing phylum Annelida.

• Largest phylum of the animal kingdom.
• Body covered externally by a hard exoskeleton made of chitin; bilaterally symmetrical, triploblastic, segmented.
• Body divided into head, thorax and abdomen (sometimes fused as cephalothorax); head bears compound eyes, antennae and mouth parts.
• Legs are jointed, arising from the thorax; insects usually have two pairs of wings.
• Sexes separate; sexual reproduction; respire through body surface, gills or trachea.
• Found in all habitats: air, water and land.

Butterfly, crab, prawn, spider and centipede representing phylum Arthropoda.

• Soft-bodied animals; body divided into head, visceral mass, muscular feet and mantle.
• Most of body covered with a calcium exoskeleton (shell) for protection.
• Head bears tentacles and eyes; body is asymmetrical.
• Muscular feet help in swimming or gliding.
• Respire through body surface, gills or pulmonary sac.
• Well-developed digestive, circulatory and nervous systems.
• Usually unisexual, a few hermaphrodite; found in land and water.

Slug, snail, cuttlefish and octopus representing phylum Mollusca.

• Body externally covered by hard calcareous spines (spiny-skinned).
• Body shapes vary: globular, star-like, elongated, spherical; no distinct head.
• Triploblastic and radially symmetrical; move with the help of tube feet.
• Developed digestive system; respire through gills.
• Unisexual; reproduce sexually; regeneration is common.
• All are found in marine (sea) water.

Starfish, sea cucumber and sea urchin representing phylum Echinodermata.

• Body bilaterally symmetrical.
• Respiration through gills, moist skin or lungs.
• Poikilothermic (cold-blooded) animals: body temperature changes with the environment.
• Homeothermic (warm-blooded) animals: body temperature remains constant, slightly higher than the environment.
• Well-developed circulatory system; heart chambers range from two to four.
• Oviparous animals lay eggs; viviparous animals give birth directly to young ones.

Fish, snake, pigeon and tiger representing sub-phylum Vertebrata.

• Body elongated, flat, streamlined, covered by scales; divided into head, trunk and tail (no neck).
• Gills on the lateral side of head for respiration; paired and unpaired fins for locomotion; air sacs present.
• Two-chambered heart; poikilothermic; unisexual.
• Mostly oviparous, a few viviparous; mostly external fertilization (internal in sharks).

Seahorse, fish and shark representing class Pisces.

• Body covered by moist skin; divided into head and trunk (tail in some); two pairs of limbs.
• Poikilothermic; young ones (tadpoles) respire through gills, adults through lungs and moist skin.
• Three-chambered heart; unisexual; oviparous, lay eggs in water; external fertilization; need water for reproduction.

Toad, frog and salamander representing class Amphibia.

• Body covered with dry, horny scales; divided into head, neck, trunk and tail.
• Two pairs of limbs, crawl on the ground; poikilothermic; respire through lungs.
• Three-chambered heart (crocodile has four-chambered heart).
• Unisexual; internal fertilization; oviparous; mostly found on land.

Snake, lizard, crocodile and tortoise representing class Reptilia.

• Body covered with feathers; divided into head, neck, trunk and tail.
• Forelimbs modified into wings; hind limbs used for walking; hollow pneumatic bones make the body lighter for flying.
• Homeothermic; respire through lungs; four-chambered heart.
• Unisexual; internal fertilization; oviparous; have air sacs.

Duck, lophophorus, hen, parrot and peacock representing class Aves.

• Body covered with hair; divided into head, neck, trunk and tail.
• Developed mammary glands (suckle milk to young ones); respire through lungs.
• Homeothermic; four-chambered heart.
• Unisexual; internal fertilization; viviparous (except a few like platypus).

Whale, bat, rat and lion representing class Mammalia.

• Prokaryotic organisms (Monera) evolved first on Earth, followed by eukaryotic organisms (Protista), and then multicellular fungi, plants and animals evolved gradually.
• Classification is the process of grouping organisms based on similarities and differences; evolution is the gradual change of living beings from simpler to more complex forms.
• Comparing heart chambers: Pisces have a two-chambered heart, Reptilia a three-chambered heart, while Aves and Mammalia have a four-chambered heart - showing that advanced animals developed from less developed ones.
• Aves and Mammalia share more common features with each other than with Pisces, suggesting Aves and Mammalia diverged from a common ancestor more recently than Pisces did.

Tree diagram showing evolution and classification of the five kingdoms (Monera, Protista, Fungi, Plantae, Animalia).

• Do not confuse a thallus (undifferentiated body of algae/some bryophytes) with a fully differentiated root-stem-leaf body.
• Do not say gymnosperms bear fruit - they have naked seeds without fruit.
• Do not classify an animal only by habitat (land/water); always check vertebral column, body covering and heart structure.
• Remember crocodile has a four-chambered heart but is still a reptile, not a bird or mammal.
• Do not confuse hermaphrodite (bisexual) organisms with unisexual organisms; always check the example given.
• Always write the correct number of phyla (8 invertebrate + 1 Chordata = 9 total) in kingdom Animalia.

• Five kingdoms: Monera, Protista, Fungi, Plantae, Animalia (Whittaker).
• Plantae divisions: Algae (thallus, water), Bryophyta (amphibian plants, alternation of generation), Tracheophyta (root-stem-leaf, vascular tissue).
• Tracheophyta sub-divisions: Pteridophyta (spores, sori), Gymnosperm (naked seed, cones), Angiosperm (real flower, fruit - monocot/dicot).
• Animalia phyla (invertebrates): Porifera, Coelenterata, Platyhelminthes, Nemathelminthes, Annelida, Arthropoda, Mollusca, Echinodermata.
• Chordata sub-phylum Vertebrata classes: Pisces (2-chambered heart), Amphibia (3-chambered), Reptilia (3-chambered, crocodile 4), Aves (4-chambered, feathers), Mammalia (4-chambered, hair, mammary glands).
• Classification and evolution are related: organisms with more common features share a more recent common ancestor.