Plant Biology
Subject: General Science — Biology | Topic: Plant Biology Exam: AP Group 2 (APPSC) | Sources: NCERT Class IX-X, Lucent's GS
Introduction
Plant biology covers classification, photosynthesis, reproduction, transport, and hormones. APPSC typically asks 1-2 questions — photosynthesis equation, monocot vs dicot differences, and plant hormone functions are the most tested.
Plant Kingdom Classification
| Division | Features | Examples |
|---|---|---|
| Thallophyta | No true roots/stems/leaves | Algae (Spirogyra), Fungi |
| Bryophyta | No vascular tissue; "amphibians of plant kingdom" | Moss, Liverwort |
| Pteridophyta | First with vascular tissue; no seeds | Fern, Horsetail |
| Gymnosperms | Naked seeds (not in fruit) | Pine, Deodar, Cycas |
| Angiosperms | Seeds enclosed in fruit; flowering plants | Most diverse group |
Monocots vs Dicots
| Feature | Monocots | Dicots |
|---|---|---|
| Cotyledons | One | Two |
| Leaf veins | Parallel | Reticulate (network) |
| Roots | Fibrous | Tap root |
| Examples | Rice, wheat, maize, banana | Pea, mango, neem, sunflower |
Photosynthesis
6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂
- Occurs in chloroplasts (chlorophyll captures sunlight).
- Light reaction: In thylakoid membranes. Water split, O₂ released, ATP and NADPH produced.
- Dark reaction (Calvin cycle): In stroma. CO₂ fixed into glucose.
- Factors: light intensity, CO₂, temperature, water.
- Day: plants release O₂ (photosynthesis > respiration). Night: release CO₂ only.
Transportation in Plants
| Tissue | Transports | Direction | Living/Dead |
|---|---|---|---|
| Xylem | Water and minerals | Upward only (unidirectional) | Dead (mature) |
| Phloem | Food (sucrose) — translocation | Bidirectional | Living |
- Transpiration: Water vapour loss from stomata. Creates suction pull; cools plant.
- Stomata: Open during day (CO₂ intake), close at night or under water stress. Surrounded by guard cells.
Plant Reproduction
Asexual (Vegetative)
- Stem cutting: Rose, Sugarcane. Grafting: Mango, Apple.
- Tuber: Potato. Bulb: Onion. Rhizome: Ginger.
- Leaf: Bryophyllum (buds on margins). Budding: Yeast. Fragmentation: Spirogyra.
Sexual (Flowering Plants)
- Pollination: Transfer of pollen from anther to stigma.
- Self-pollination: Same flower/plant.
- Cross-pollination: Different plant. Agents: wind, water, insects, birds.
- Double fertilisation (unique to angiosperms): One male gamete + egg → zygote. Another + polar nuclei → endosperm.
- Ovule → seed. Ovary → fruit.
Plant Hormones
| Hormone | Function |
|---|---|
| Auxins | Cell elongation, phototropism, apical dominance |
| Gibberellins | Stem elongation, seed germination, flowering |
| Cytokinins | Cell division, delay ageing |
| Abscisic acid (ABA) | Growth inhibitor, stomatal closure — "stress hormone" |
| Ethylene | Fruit ripening, leaf fall (abscission) |
Plant Responses (Tropisms)
| Response | Stimulus | Example |
|---|---|---|
| Phototropism | Light | Shoots grow toward light |
| Geotropism | Gravity | Roots grow toward gravity |
| Hydrotropism | Water | Roots grow toward water |
| Thigmotropism | Touch | Tendrils of climbing plants |
| Nastic movement | Non-directional | Mimosa pudica folds when touched |
Likely Exam Questions
-
The equation for photosynthesis is: Ans: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (with light energy)
-
Bryophyta are called: Ans: Amphibians of the plant kingdom
-
The plant hormone responsible for fruit ripening is: Ans: Ethylene
-
Double fertilisation is unique to: Ans: Angiosperms (flowering plants)
-
Xylem transports: Ans: Water and dissolved minerals (upward)
-
An example of a plant that reproduces through leaf buds is: Ans: Bryophyllum
-
The first group of plants with vascular tissue is: Ans: Pteridophyta (ferns)
-
Abscisic acid is known as: Ans: The stress hormone of plants
-
Monocots have ___ veins: Ans: Parallel veins
-
Transpiration occurs through: Ans: Stomata