Diversity of Life: Classification, Kingdoms and Plant Morphology
Diversity of Life
1. Biodiversity and the Need for Classification
Biodiversity is the variety of living organisms. Classification groups organisms, aids identification, avoids confusion from local names and shows similarities, differences and evolutionary relationships.
2. Artificial, Natural and Phylogenetic Classification
Artificial classification uses a few characters. Natural classification considers many characters. Phylogenetic classification groups organisms by evolutionary history and common ancestry.
3. Taxonomy and Systematics
- Taxonomy deals with identification, nomenclature and classification.
- Systematics studies diversity and evolutionary relationships, including taxonomy.
4. Species and Taxonomic Hierarchy
A species is a group of similar organisms that naturally interbreed and produce fertile offspring.
Hierarchy: species → genus → family → order → phylum/division → kingdom.
5. Binomial Nomenclature
Each scientific name has two words: genus and specific epithet. Names are Latin or Latinised; the genus begins with a capital letter and the species with a lowercase letter. Printed names are italicised; handwritten names are underlined separately.
6. Father of Taxonomy
Carolus Linnaeus developed systematic classification and popularised binomial nomenclature.
7. Herbarium
A herbarium is a collection of dried, pressed, mounted and labelled plant specimens used for identification and taxonomic research.
8. Taxonomic Key
A taxonomic key identifies organisms using contrasting pairs of observable characters; each pair is a couplet.
9. Two-, Three-, Four- and Five-Kingdom Classification
The two-kingdom system (Plantae and Animalia) fails to separate prokaryotes from eukaryotes, unicellular from multicellular organisms, and fungi from plants. Whittaker’s five kingdoms (1969) are Monera, Protista, Fungi, Plantae and Animalia.
10. Whittaker’s Criteria
Cell structure, body organisation, nutrition, reproduction and phylogenetic relationships.
11. Advantages of the Five Kingdoms
The system separates prokaryotes from eukaryotes, unicellular from multicellular organisms, and fungi from plants, and considers nutrition and evolutionary relationships.
12. Kingdom Monera
Mostly unicellular prokaryotes lacking a true nucleus and membrane-bound organelles. DNA lies in the nucleoid, and ribosomes are present. A cell wall is usually present, but absent in Mycoplasma. Nutrition is autotrophic or heterotrophic; reproduction is mainly by binary fission.
13. Cyanobacteria vs Heterotrophic Bacteria
Cyanobacteria are photosynthetic autotrophs with chlorophyll a; Nostoc and Anabaena fix nitrogen. Heterotrophic bacteria obtain organic food from organisms or decaying matter; many are decomposers, symbionts or pathogens.
14. Kingdom Protista
Mostly unicellular eukaryotes, mainly aquatic, with a true nucleus and membrane-bound organelles. Nutrition is autotrophic or heterotrophic; movement occurs via cilia, flagella or pseudopodia. The group includes chrysophytes, dinoflagellates, euglenoids, slime moulds and protozoans.
15. Fungi
Fungi are eukaryotic, non-chlorophyllous heterotrophs that absorb nutrients. Their cell walls contain chitin, and hyphae form a mycelium. They may be saprophytic, parasitic or symbiotic and reproduce vegetatively, asexually or sexually.
16–17. Lichens: Phycobiont and Mycobiont
Lichens are symbioses between a fungus and an alga or cyanobacterium. The phycobiont photosynthesises and supplies food; the mycobiont provides structure, protection, water and minerals.
18–19. Viruses: Features and Structure
Viruses are acellular infectious agents containing DNA or RNA inside a protein capsid; some have a lipid envelope and spikes. They lack cytoplasm, ribosomes and independent metabolism and replicate only inside living host cells.
20. Viroids
Viroids are very small infectious agents made of short, circular, single-stranded RNA without a protein coat; they mainly cause plant diseases.
21. Status of Viruses and Viroids
They lie at the boundary of living and non-living: inert outside hosts but able to replicate inside living cells.
Kingdom Plantae and Morphology
1. Major Plant Groups
Algae are simple and mostly aquatic; bryophytes lack vascular tissue; pteridophytes have vascular tissue but no seeds; gymnosperms bear naked seeds; angiosperms produce flowers and seeds enclosed in fruits.
2. Bryophytes
Small plants of damp, shady places that lack true roots, stems, leaves and vascular tissue. Rhizoids anchor them. The gametophyte is dominant, and fertilisation needs water, so they are called the amphibians of the plant kingdom.
3. Pteridophytes
Seedless vascular plants with true roots, stems and leaves. The sporophyte is dominant; spores form in sporangia, often grouped in sori. The gametophyte is a small prothallus that requires water for fertilisation.
4. Gymnosperms
Vascular seed plants whose ovules and seeds are not enclosed in fruits. They usually bear cones, have a dominant sporophyte and reduced gametophytes; most are woody and many have needle-like leaves.
5. Bryophytes vs Pteridophytes vs Gymnosperms
- Bryophytes: non-vascular, no true roots, gametophyte dominant, reproduce by spores.
- Pteridophytes: vascular, true roots, stems and leaves, no seeds, sporophyte dominant.
- Gymnosperms: vascular, naked seeds, usually borne in cones.
6. Gametophyte and Sporophyte
The gametophyte is the haploid generation that produces gametes. After fertilisation, the diploid zygote develops into a sporophyte, which produces haploid spores by meiosis. Bryophytes have dominant gametophytes; vascular plants have dominant sporophytes.
7. Root Morphology and Functions
The root usually develops from the radicle and grows downward. The root cap protects the tip; the meristematic region divides; the elongation region increases length; the maturation region bears root hairs. Roots anchor plants, absorb water and minerals, and may store food.
8. Stem Morphology and Functions
The stem develops from the plumule and bears nodes, internodes, leaves, buds, flowers and fruits. It supports aerial parts, transports water, minerals and food, and may store food, photosynthesise or aid vegetative propagation.
9. Leaf Morphology and Functions
A typical leaf has a leaf base, petiole and lamina with veins. Leaves arise at nodes and bear axillary buds. They perform photosynthesis, gas exchange and transpiration; some are modified for storage, support or protection.
10. Phyllotaxy
Phyllotaxy is the arrangement of leaves on a stem. Alternate: one leaf per node (China rose). Opposite: two leaves per node (guava). Whorled: three or more leaves per node (Alstonia).
11. Inflorescence: Racemose and Cymose
- Racemose: the main axis continues growing; flowers are arranged in acropetal order.
- Cymose: the main axis ends in a flower; flowers develop in basipetal order.
12. Types of Inflorescence
Racemose types include raceme, spike, catkin, spadix, corymb, umbel, capitulum (head) and panicle. Cymose types include monochasial, dichasial and polychasial cymes.
13. Flower: Parts and Functions
A flower is the reproductive part of an angiosperm. It has four whorls: the calyx (sepals protect the bud), corolla (petals attract pollinators), androecium (stamens produce pollen) and gynoecium (carpels contain ovules; after fertilisation, ovules become seeds and the ovary becomes the fruit). The thalamus bears the floral parts, and the pedicel supports the flower.
14. Floral Diagram of a Typical Flower
Draw and label the calyx, corolla, androecium and gynoecium; include the bract and mother axis where shown.
15. Aestivation
Aestivation is the arrangement of sepals or petals in a floral bud.
- Valvate: margins touch without overlapping (Calotropis).
- Twisted: each member overlaps the next and is overlapped by the previous (China rose).
- Imbricate: irregular overlapping (Cassia).
- Vexillary: the standard overlaps the wings, which overlap the keel (pea).
16. Fruit: Morphology and Functions
A fruit is the mature ovary, usually formed after fertilisation. The fruit wall is the pericarp, often differentiated into epicarp, mesocarp and endocarp. Fruits protect seeds and aid dispersal; they may be simple, aggregate or multiple. Fruits formed without fertilisation are parthenocarpic.
17. Typical Seed Structure
A seed contains a seed coat, an embryo and stored food. The seed coat has a testa and tegmen; the embryo has a radicle, plumule and one or two cotyledons. The hilum marks the attachment scar, and the micropyle is a small pore. Seeds may be albuminous or non-albuminous.
18. Maize Seed
The maize grain has an outer aleurone layer. The embryo lies on one side; the plumule is protected by the coleoptile and the radicle by the coleorhiza. The seed coat is fused with the fruit wall. Diagram labels: endosperm, aleurone layer, scutellum, embryo, plumule, coleoptile, radicle, coleorhiza.
19. Dicot Seed
A bean seed has a testa and tegmen, two food-storing cotyledons and an embryo with a plumule, radicle and embryonal axis. The hilum is the attachment scar; the micropyle is a small pore. Diagram labels: seed coat, cotyledons, plumule, radicle, hilum, micropyle.
20. Solanaceae: Floral Formula and Diagram
Members of Solanaceae are herbs, shrubs or small trees with alternate, simple leaves. Flowers are bisexual, actinomorphic, pentamerous and hypogynous. The calyx and corolla each have five united members, there are five epipetalous stamens, and the gynoecium is bicarpellary and syncarpous with a superior ovary. The fruit is a berry or capsule. Floral formula: ⊕ K(5) C(5) A5 G(2). Draw and label the five united sepals, five united petals, five stamens and superior bicarpellary ovary.
21. Diagnostic Characters of Solanaceae
Leaves are alternate and exstipulate; flowers are bisexual, actinomorphic, pentamerous and hypogynous. The formula is K(5), C(5), A5, G(2); the ovary is superior, bicarpellary, syncarpous and usually bilocular with axile placentation. The fruit is a berry or capsule, and seeds are numerous.
22. Floral Characters of Solanaceae
- Calyx: five united, persistent sepals.
- Corolla: five united petals, usually funnel-shaped.
- Androecium: five epipetalous stamens alternating with the petals.
- Gynoecium: two fused carpels; a superior, usually bilocular ovary with axile placentation and many ovules.
23. Solanaceae: Examples and Economic Importance
Examples include potato, tomato, brinjal, chilli, tobacco and Datura. Potato is a food crop; tomato and brinjal are vegetables; chilli is a spice; tobacco is a commercial crop; Datura contains medicinal compounds but is poisonous.