📚 Biology · Basic Level · Complete Notes
Classification &
Organic Evolution
Five Kingdom · Plantae · Animalia · Angiosperm · Vertebrata · Evolution
01
Concept of Five Kingdom System
Proposed by R.H. Whittaker (1969) — Based on cell structure, body organisation, mode of nutrition, reproduction & phylogenetic relationships. Before this, Linnaeus used Two Kingdoms (Plant & Animal).
🧠 Memory Trick — 5 Kingdoms
“My Pretty Funny Animal Pet”
Monera · Protista · Fungi · Animalia · Plantae
Monera
Prokaryotes
- No nuclear membrane
- No membrane organelles
- Unicellular
- Cell wall (mostly)
- Auto & Heterotrophic
- e.g. Bacteria, Cyanobacteria
Protista
Unicellular Eukaryotes
- True nucleus present
- Unicellular
- Auto or Heterotrophic
- Locomotion present
- e.g. Amoeba, Euglena, Paramecium
Fungi
Saprophytes
- Eukaryotic
- Chitin cell wall
- Absorptive nutrition
- Mostly multicellular
- e.g. Mushroom, Yeast, Penicillium
Plantae
Autotrophs
- Eukaryotic, multicellular
- Cellulose cell wall
- Chlorophyll present
- Photosynthesis
- e.g. Algae, Mosses, Trees
Animalia
Heterotrophs
- Eukaryotic, multicellular
- No cell wall
- Holozoic nutrition
- Locomotion present
- e.g. Sponge, Fish, Man
| Feature | Monera | Protista | Fungi | Plantae | Animalia |
|---|---|---|---|---|---|
| Cell Type | Prokaryote | Eukaryote | Eukaryote | Eukaryote | Eukaryote |
| Cell Number | Unicellular | Unicellular | Multi / Uni | Multicellular | Multicellular |
| Cell Wall | Present | Present / Absent | Chitin | Cellulose | Absent |
| Nutrition | Auto / Hetero | Auto / Hetero | Saprophytic | Autotrophic | Heterotrophic |
| Locomotion | Some | Present | Absent | Absent | Present |
| Example | Bacteria | Amoeba | Mushroom | Mango tree | Human |
⭐ Exam Points
- Whittaker (1969) — 5 Kingdoms; Linnaeus — 2 Kingdoms; Haeckel — 3 Kingdoms (added Protista); Carl Woese — 6 Kingdoms (split Monera).
- The 5 criteria used: cell structure · body organisation · mode of nutrition · reproduction · phylogenetic relationships.
- Fungi have chitin cell wall — unique among the kingdoms.
02
Divisions of Kingdom Plantae
Kingdom Plantae is divided into 5 major divisions based on presence of vascular tissue, seeds, and method of reproduction.
🧠 Memory Trick — Divisions in Order
“These Boys Play Guitars Amazingly”
Thallophyta · Bryophyta · Pteridophyta · Gymnospermae · Angiospermae
① Thallophyta Algae
- Plant body = thallus — no roots, stems or leaves
- No vascular tissue; mostly aquatic
- Contain chlorophyll → autotrophic
- Reproduce by spores or fragmentation
- Sub-groups: Chlorophyceae (green), Phaeophyceae (brown), Rhodophyceae (red)
📌 Examples: Spirogyra, Chara, Ulva, Volvox, Fucus, Ectocarpus
② Bryophyta Amphibians of Plant Kingdom
- First land plants — need water for fertilisation
- No true roots (rhizoids present); no vascular tissue
- Body divided into stem-like & leaf-like structures
- Dominant generation = gametophyte
- Reproduce by spores
📌 Examples: Funaria (moss), Marchantia (liverwort), Anthoceros (hornwort)
③ Pteridophyta First Vascular Plants — No Seeds
- True roots, stems and leaves present
- Vascular tissue (xylem & phloem) present — first time in plant evolution
- No seeds — reproduce by spores
- Dominant generation = sporophyte
- Moist & shady habitats
📌 Examples: Dryopteris (fern), Equisetum (horsetail), Selaginella, Marsilea
④ Gymnospermae Naked Seeds — No Fruit
- “Gymno” = naked; seeds not enclosed in fruit (exposed on cone scales)
- Vascular tissue well developed; heterosporous
- No true flowers; pollination by wind (anemophily)
- Perennial, mostly evergreen trees
📌 Examples: Pinus, Cycas, Cedrus, Abies, Gnetum, Ephedra
⑤ Angiospermae Covered Seeds — Most Evolved
- Seeds enclosed in fruit (ovary wall forms fruit wall)
- True flowers present; double fertilisation occurs
- Largest group (~250,000 species); dominant plant group on Earth
- Divided into Dicotyledonae & Monocotyledonae
📌 Examples: Mango, Wheat, Rice, Rose, Sunflower, Pea, Banana
| Division | Vascular | Seeds | Flowers/Fruit | Dominant Phase | Example |
|---|---|---|---|---|---|
| Thallophyta | No | No | No | — | Spirogyra |
| Bryophyta | No | No | No | Gametophyte | Funaria |
| Pteridophyta | Yes | No | No | Sporophyte | Fern |
| Gymnospermae | Yes | Naked | No | Sporophyte | Pinus |
| Angiospermae | Yes | Covered | Yes | Sporophyte | Mango |
03
Phyla of Kingdom Animalia
Kingdom Animalia has 9 major phyla, ranging from simple sponges (Porifera) to the most advanced Chordata. All are eukaryotic, multicellular, heterotrophic, and lack cell walls.
🧠 Memory Trick — 9 Phyla
“Please Come Play And Eat More Apples Every Cartoon”
Porifera · Coelenterata · Platyhelminthes · Aschelminthes · Echinodermata · Mollusca · Annelida · Arthropoda · Chordata
Phylum 01
Porifera Sponges
- Simplest multicellular animals
- Body full of pores (Ostia & Osculum)
- No true tissues or organs
- Sessile & aquatic
- Canal system & spicules present
- Asexual & sexual reproduction
📌 Sycon, Spongilla, Euspongia
Phylum 02
Coelenterata Cnidaria
- Diploblastic (2 cell layers)
- Radial symmetry
- Cnidoblasts (stinging cells) present
- Two forms: polyp & medusa
- No circulatory or respiratory system
- First animals with tissue-level organisation
📌 Hydra, Aurelia (jellyfish), Corals, Obelia
Phylum 03
Platyhelminthes Flatworms
- Bilaterally symmetrical; triploblastic
- Dorsoventrally flattened body
- Acoelomate (no body cavity)
- No circulatory or respiratory system
- Mostly parasitic
- Flame cells for excretion
📌 Planaria, Taenia (tapeworm), Fasciola (liver fluke)
Phylum 04
Aschelminthes Roundworms
- Cylindrical, unsegmented body
- Pseudocoelomate (false coelom)
- Complete digestive system (mouth to anus)
- Sexes separate (dioecious)
- Mostly parasitic
📌 Ascaris, Wuchereria (filaria), Ancylostoma
Phylum 05
Annelida Segmented Worms
- True segmented body (metamerism)
- True coelom (first time)
- Closed circulatory system — first time
- Nephridia for excretion
- Setae for locomotion
- Triploblastic
📌 Earthworm (Pheretima), Leech (Hirudo), Nereis
Phylum 06
Arthropoda Largest Phylum
- Jointed appendages
- Exoskeleton of chitin
- Open circulatory system
- Compound eyes
- Head, thorax, abdomen
- ~80% of all animal species
📌 Cockroach, Mosquito, Crab, Spider, Scorpion
Phylum 07
Mollusca 2nd Largest
- Soft-bodied, usually with shell
- Mantle (fold of skin) present
- Radula for feeding
- Open circulatory system
- Kidney-like excretory organs
📌 Snail, Octopus, Squid, Clam, Oyster
Phylum 08
Echinodermata Spiny-Skinned
- Water vascular system (unique)
- Radial symmetry in adults
- Endoskeleton of calcareous ossicles
- Tube feet for locomotion
- Exclusively marine
📌 Starfish, Sea urchin, Sea cucumber, Sea lily
Phylum 09 — Most Advanced
Chordata Backbone Animals
- 3 Defining Characters:
- ① Notochord (at some stage)
- ② Dorsal hollow nerve cord
- ③ Pharyngeal gill slits
- Post-anal tail present
- Closed circulatory system
- Sub-phylum Vertebrata: backbone replaces notochord
📌 All fish, frogs, snakes, birds, mammals
04
Classification of Angiospermae up to Class
Angiospermae (Flowering Plants) is divided into 2 Classes based on the number of cotyledons (seed leaves) in the embryo.
Taxonomic Hierarchy: Kingdom → Division → Class → Order → Family → Genus → Species
“King David Came Over For Good Soup”
Class: Dicotyledonae
~200,000 species
- 2 cotyledons in seed
- Tap root system
- Reticulate (net-like) venation in leaves
- Flowers pentamerous (5 parts) or tetramerous
- Vascular bundles in ring arrangement in stem
- Cambium present → secondary growth possible
- Pollen tricolpate (3 furrows)
Sub-classes:
- Polypetalae – free petals (e.g. Rose, Mustard, Pea)
- Gamopetalae – fused petals (e.g. Potato, Sunflower, Datura)
- Monochlamydeae – single or no perianth (e.g. Casuarina)
📌 Mango, Rose, Pea, Neem, Sunflower, Tomato, Beans, Mustard
Class: Monocotyledonae
~50,000 species
- 1 cotyledon in seed
- Fibrous (adventitious) root system
- Parallel venation in leaves
- Flowers trimerous (3 parts or multiples of 3)
- Vascular bundles scattered in stem (no ring)
- No cambium → no secondary growth
- Pollen monosulcate (1 furrow)
Important Families:
- Gramineae / Poaceae – wheat, rice, maize, bamboo
- Liliaceae – lily, onion, garlic, aloe
- Palmae / Arecaceae – coconut, date palm
📌 Wheat, Rice, Maize, Bamboo, Banana, Onion, Coconut, Sugarcane
| Character | Dicotyledonae | Monocotyledonae |
|---|---|---|
| Cotyledons | Two | One |
| Root System | Tap root | Fibrous root |
| Leaf Venation | Reticulate (net-like) | Parallel |
| Flower Parts | 4 or 5 (multiples) | 3 (multiples of 3) |
| Vascular Bundles | In ring, with cambium | Scattered, no cambium |
| Secondary Growth | Present | Absent |
| Pollen | Tricolpate | Monosulcate |
| Example | Mango, Rose, Pea | Wheat, Rice, Onion |
05
Classification of Vertebrata up to Class
Vertebrata = Sub-phylum of Phylum Chordata. Notochord is replaced by vertebral column (backbone). Divided into 2 Super-classes: Pisces (fish) & Tetrapoda (four-limbed).
🧠 Memory Trick — 7 Classes
“Cats Often Arrive Ready After Much Maintenance”
Cyclostomata · Osteichthyes · (Chondrichthyes) · Amphibia · Reptilia · Aves · Mammalia
SUPER-CLASS: PISCES (Aquatic — Gilled Vertebrates)
Class 1: Cyclostomata
- Most primitive vertebrates
- No paired fins, no jaws
- Circular sucking mouth
- Cartilaginous skeleton
- Ecto-parasitic on fish
- No scales; 6–15 pairs of gills
- Cold-blooded
📌 Petromyzon (lamprey), Myxine (hagfish)
Class 2: Chondrichthyes
- Cartilaginous skeleton
- Jaws present
- No operculum (gill cover)
- Placoid scales (rough skin)
- Cold-blooded; marine
- Spiracle present
- Viviparity in some
📌 Shark, Dogfish, Rays, Torpedo, Pristis
Class 3: Osteichthyes
- Bony skeleton
- Operculum covers gills
- Cycloid / ctenoid scales
- Swim bladder for buoyancy
- Largest class of vertebrates
- Marine & freshwater
📌 Rohu, Catla, Labeo, Hippocampus, Tuna
SUPER-CLASS: TETRAPODA (Four-Limbed Vertebrates)
Class 4: Amphibia Dual Life
- First terrestrial vertebrates
- Moist, smooth glandular skin — no scales
- Breathe via lungs AND moist skin
- Aquatic larvae → terrestrial adults
- 3-chambered heart
- Cold-blooded (poikilothermal)
- External fertilisation; lay eggs in water
📌 Frog (Rana), Toad (Bufo), Salamander, Hyla, Ichthyophis
Class 5: Reptilia Crawlers
- Dry, scaly skin (epidermal scales)
- Lungs for respiration
- 3-chambered heart (except crocodile — 4)
- Cold-blooded
- Internal fertilisation; cleidoic eggs
- Dominated Mesozoic Era (Age of Reptiles)
📌 Snake, Lizard, Turtle, Crocodile, Chameleon, Gecko
Class 6: Aves Birds
- Feathers — unique to birds
- Forelimbs modified into wings
- Hollow (pneumatic) bones → light for flight
- 4-chambered heart
- Warm-blooded (homeothermal)
- Beak present, no teeth (modern birds)
- Air sacs connected to lungs
- Oviparous (egg-laying)
📌 Pigeon, Sparrow, Peacock, Penguin, Ostrich, Eagle
Class 7: Mammalia Most Advanced
- Mammary glands (milk production) — unique
- Hair / fur on body
- 4-chambered heart
- Warm-blooded (homeothermal)
- External ears (pinnae) present
- Diaphragm separates thorax & abdomen
- Heterodont teeth
- Viviparous (live birth); some oviparous
📌 Human, Cat, Dog, Whale, Bat, Dolphin; Platypus (oviparous)
| Class | Heart | Skin/Cover | Temperature | Key Feature |
|---|---|---|---|---|
| Cyclostomata | 2-chambered | Smooth, no scales | Cold | Jawless, circular mouth |
| Chondrichthyes | 2-chambered | Placoid scales | Cold | Cartilage skeleton |
| Osteichthyes | 2-chambered | Bony scales | Cold | Swim bladder, bony skeleton |
| Amphibia | 3-chambered | Moist, glandular | Cold | Dual life; breathe through skin |
| Reptilia | 3-ch (croc: 4) | Dry, epidermal scales | Cold | Amniotic egg on land |
| Aves | 4-chambered | Feathers | Warm | Hollow bones; feathers |
| Mammalia | 4-chambered | Hair / fur | Warm | Mammary glands; diaphragm |
06
Organic Evolution & Classification
Core Idea: Classification is NOT random — it reflects the evolutionary history (phylogeny) of organisms. Related organisms share common ancestors. Modern taxonomy = phylogenetic classification.
🔬 What is Organic (Biological) Evolution?
- Gradual change in heritable characteristics of populations over generations
- Species change over time → new species form
- All life descended from common ancestors
- Proposed by Charles Darwin (1859) — On the Origin of Species
- Mechanism: Natural Selection — “survival of the fittest” (Herbert Spencer)
📋 What is Classification (Taxonomy)?
- Systematic arrangement of organisms based on similarities & differences
- Father of Taxonomy: Carolus Linnaeus
- Modern taxonomy = Phylogenetic classification
- Uses: morphology, anatomy, genetics, fossils, embryology
- Each taxonomic rank reflects degree of evolutionary relationship
MAJOR THEORIES OF EVOLUTION
① Lamarck’s Theory (1809)
- Use & disuse of organs
- Inheritance of acquired characters
- Classic example: Giraffe’s long neck — stretched over generations and passed to offspring
- Now largely discredited (acquired characters are NOT inherited)
- Published in: Philosophie Zoologique
② Darwin’s Theory — Natural Selection (1859)
- Overproduction — more offspring than can survive
- Variation — individuals differ from each other
- Struggle for existence — competition for food, space, mate
- Survival of the fittest — best-adapted survive
- Heredity — favourable traits passed to offspring
- New species formed over long time
③ De Vries — Mutation Theory (1901)
- New species arise suddenly by mutations, not gradually
- Worked on Evening Primrose (Oenothera lamarckiana)
- Mutations are raw material for evolution
- Did not support gradual, slow change
④ Modern Synthetic Theory (Neo-Darwinism)
- Combines Darwin + Mendel + Mutations + Population genetics
- Genetic variation via mutation & recombination
- Natural selection acts on genetic variation
- Genetic drift, gene flow, reproductive isolation
- Currently the most accepted theory
🔗 Evidence of Evolution Used in Classification
- Fossils — show ancestral forms; Archaeopteryx links reptiles & birds
- Homologous organs — same origin, different function → common ancestry (e.g. forelimbs of whale, bat, human)
- Analogous organs — same function, different origin → convergent evolution (e.g. wings of bat vs. bird)
- Vestigial organs — remnants of once-functional organs (e.g. appendix, coccyx in humans)
- Comparative embryology — similar embryos suggest common ancestor (e.g. gill slits in vertebrate embryos)
- Molecular biology — DNA/protein similarities reveal evolutionary relationships
- Biogeography — geographic distribution of species reflects evolutionary history
- Connecting links — Archaeopteryx (reptile + bird); Platypus (reptile + mammal)
| Concept | Definition | Significance in Classification |
|---|---|---|
| Phylogenetic classification | Based on evolutionary relationships | Most natural & scientific system |
| Cladistics | Classification based on shared derived characters | Produces cladograms showing ancestry |
| Divergent evolution | One ancestor → many different species | Explains diversity within a taxon |
| Convergent evolution | Unrelated species develop similar features | Warns against misclassifying look-alikes |
| Adaptive radiation | Rapid evolution from one ancestor into many forms | Explains diversity within a class/order |
| Speciation | Formation of new species from existing ones | Creates taxonomic diversity over time |
⭐ Key Exam Statement — Must Learn
- “Natural / Phylogenetic classification is the most scientific system because it groups organisms according to their evolutionary relationships.”
- “The higher the taxonomic rank two organisms share, the more recent their common ancestor — so classification is a direct reflection of organic evolution.”
- Taxonomy without evolution = arbitrary arrangement; Evolution without taxonomy = unorganised data — both are inseparable.
- Connecting links are living proof of evolution that bridge two groups (Archaeopteryx = reptile + bird; Platypus = reptile + mammal; Euglena = plant + animal).