Plant Kingdom
Plants are divided into five major groups based on plant body, vascular system, and reproductive structures.
Algae
- Simple thalloid plants, no differentiation into root, stem, leaf.
- Mostly aquatic (freshwater and marine).
- Chlorophyll present, autotrophic.
- Cell wall of cellulose.
Major Groups:
- Chlorophyceae (Green algae): Chlorophyll a, b. Stored food: starch. Examples: Chlamydomonas, Spirogyra, Ulva.
- Phaeophyceae (Brown algae): Chlorophyll a, c, fucoxanthin. Stored food: laminarin. Examples: Sargassum, Laminaria.
- Rhodophyceae (Red algae): Chlorophyll a, d, phycoerythrin. Stored food: floridean starch. Examples: Polysiphonia, Gracilaria.
Bryophytes
- 'Amphibians of plant kingdom' (need water for fertilisation).
- No true vascular tissue (xylem, phloem).
- Gametophyte is the dominant, independent phase.
- Sporophyte is dependent on gametophyte.
Examples: Marchantia (liverwort), Funaria (moss), Anthoceros (hornwort).
Role: Pioneer species in ecological succession, prevent soil erosion, indicator of pollution.
Pteridophytes
- First true vascular plants (xylem and phloem present).
- Sporophyte dominant.
- Reproduce by spores (produced in sporangia on sporophylls).
- Found in cool, damp, shady places.
Examples: Pteris (fern), Selaginella, Equisetum (horsetail), Adiantum.
Heterospory: Some produce two types of spores (microspores and megaspores). Precursor to seed habit.
Gymnosperms
- 'Naked seed' plants (seeds not enclosed in fruits).
- Vascular tissue present (xylem lacks vessels, phloem lacks companion cells).
- Sporophyte dominant.
- Heterosporous.
Examples: Pinus (pine), Cycas, Ginkgo, Cedrus (deodar).
Economic importance: Timber, paper, resins, medicines.
Angiosperms
- Flowering plants with seeds enclosed in fruits.
- Highly developed vascular tissue with vessels and companion cells.
- Sporophyte dominant.
- Heterosporous.
Two classes:
- Monocotyledons: One cotyledon, parallel venation, fibrous roots, floral parts in multiples of 3. Examples: Wheat, Rice, Maize, Lily.
- Dicotyledons: Two cotyledons, reticulate venation, taproot, floral parts in multiples of 4 or 5. Examples: Mango, Rose, Pea, Sunflower.
Morphology of Flowering Plants
The Root
- Typically underground, non-green, positively geotropic.
- Taproot system: Dicots. Primary root grows vertically (radicle).
- Fibrous root system: Monocots. Adventitious roots from stem base.
- Adventitious roots: From other plant parts (ivy, Banyan prop roots).
Modifications:
- Storage: Carrot, Radish (taproot), Sweet potato (adventitious).
- Support: Prop roots (Banyan), Stilt roots (Maize).
- Respiration: Pneumatophores (mangroves).
The Stem
- Aerial, positively phototropic, bears nodes and internodes.
- Functions: Support, conduction, storage, propagation.
Modifications:
- Storage: Potato (tuber), Ginger (rhizome), Onion (bulb).
- Support: Tendrils (grapevine), Thorns (citrus).
- Protection: Cactus (phylloclade for photosynthesis).
The Leaf
- Lateral, flattened outgrowth. Site of photosynthesis.
- Parts: Leaf base, petiole, lamina (blade).
- Venation: Reticulate (dicots), Parallel (monocots).
Types:
- Simple: Single lamina (Mango, Guava).
- Compound: Multiple leaflets (Rose, Neem - pinnate; Silk cotton - palmate).
Phyllotaxy: Arrangement of leaves on stem. Types: Alternate (sunflower), Opposite (Calotropis), Whorled (Alstonia).
Modifications:
- Spine: Cactus (protection, reduce transpiration).
- Tendril: Pea (support).
- Pitcher: Pitcher plant (insectivorous).
The Flower
Reproductive structure, modified shoot.
Parts: Calyx (sepals), Corolla (petals), Androecium (stamens), Gynoecium (pistils).
Floral symmetry: Actinomorphic (radial, e.g., Mustard), Zygomorphic (bilateral, e.g., Pea).
Inflorescence: Arrangement of flowers.
- Racemose: Indefinite growth (Radish).
- Cymose: Definite growth (Cotton).
The Fruit
Developed from ovary after fertilisation.
Types:
- True fruit: From ovary (Mango).
- False fruit: From other floral parts too (Apple, Strawberry).
- Parthenocarpic: Without fertilisation, seedless (Banana).
Worked Examples
Example 1: Differentiate between bryophytes and pteridophytes. Solution: Bryophytes: no vascular tissue, gametophyte dominant. Pteridophytes: vascular tissue present, sporophyte dominant.
Example 2: Give one modification each of root and stem. Solution: Root modification: Carrot (storage). Stem modification: Potato (storage, tuber).
Common Mistakes
- Alternation of generations: Understand which generation is dominant in which group.
- True fruit vs false fruit: Apple is false fruit (thalamus), Mango is true fruit (ovary).
- Monocot vs Dicot: Check cotyledons, venation, root type, flower parts.
- Phyllotaxy vs venation: Phyllotaxy is arrangement of leaves. Venation is vein pattern on lamina.
ISC Exam Focus
- Theory (70%): Plant kingdom characteristics, alternation of generations, morphology.
- Application (30%): Identifying modifications, distinguishing between groups.
- ISC frequently asks: "Write the difference between monocot and dicot" and "Explain modification of ...".
- Economic importance of different plant groups.
Self-Test Questions
Q1: Write three differences between monocots and dicots. Answer: Monocots: 1 cotyledon, parallel venation, fibrous roots. Dicots: 2 cotyledons, reticulate venation, taproot.
Q2: Give two examples each of bryophytes and pteridophytes. Answer: Bryophytes: Funaria, Marchantia. Pteridophytes: Pteris (fern), Selaginella.
Q3: What is the difference between taproot and fibrous root? Answer: Taproot: primary root from radicle, deep. Fibrous root: many roots from stem base, shallow.
Q4: What is a tendril? Give an example. Answer: A slender thread-like structure for support. Stem tendril: grape. Leaf tendril: pea.
Q5: Define phyllotaxy. Write its types. Answer: Arrangement of leaves on stem. Types: alternate, opposite, whorled.
Q6: Differentiate between racemose and cymose inflorescence. Answer: Racemose: indefinite growth (older flowers at base). Cymose: definite growth (older flowers at top).
