Plant Biology
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | Photosynthesis | Process in chloroplasts where CO₂ + H₂O → glucose + O₂ using sunlight; produces food for plant & oxygen for us. |
| 2 | Respiration in Plants | Breakdown of glucose in mitochondria to release energy; occurs day & night; opposite of photosynthesis. |
| 3 | Transpiration | Loss of water vapour through stomata; creates suction pull for upward water transport (xylem). |
| 4 | Plant Hormones | Auxin (apical dominance), Gibberellin (stem elongation), Cytokinin (cell division), Abscisic acid (dormancy). |
| 5 | Phototropism & Geotropism | Growth towards light (+ve phototropism); roots grow downwards (+ve geotropism) due to auxin redistribution. |
| 6 | Nitrogen Fixation | Conversion of atmospheric N₂ to NH₃ by Rhizobium bacteria in root nodules of legumes; essential for protein synthesis. |
| 7 | Pollination vs Fertilisation | Transfer of pollen (pollination) → pollen tube → male gamete fuses with egg (fertilisation) → zygote → seed. |
| 8 | Economic Botany | Cotton (fiber), Jute (bast fiber), Sugarcane (stem sugar), Turmeric (rhizome), Groundnut (oilseed). |
15 Practice MCQs
1. Which pigment is essential for photosynthesis?
Options:A. Chlorophyll
B. Haemoglobin
C. Anthocyanin
D. Carotene
Answer: A. Chlorophyll
Solution: Chlorophyll traps solar energy in chloroplast thylakoids.
Shortcut: Remember “Chloro-phyll → Chloro-plast → Photo-synthesis”.
Tag: Photosynthesis
2. The site of respiration in plant cells is:
Options:A. Chloroplast
B. Mitochondria
C. Ribosome
D. Peroxisome
Answer: B. Mitochondria
Solution: Mitochondria are the “powerhouse” where glucose is broken to ATP.
Shortcut: “Mito = Might = Energy”.
Tag: Respiration
3. Stomata open due to:
Options:A. Decrease in turgidity of guard cells
B. Increase in turgidity of guard cells
C. Death of guard cells
D. Deposition of lignin
Answer: B. Increase in turgidity of guard cells
Solution: K⁺ ions enter guard cells → water follows → cells swell → stomatal pore opens.
Shortcut: “Turgor = Open, Flaccid = Closed”.
Tag: Transpiration
4. Which hormone causes bolting in cabbage?
Options:A. Auxin
B. Gibberellin
C. Cytokinin
D. Ethylene
Answer: B. Gibberellin
Solution: Gibberellin induces sudden stem elongation (bolting) before flowering.
Shortcut: “Gibberellin = Growth spurts”.
Tag: Plant hormones
5. Root nodules contain which bacteria?
Options:A. Azotobacter
B. Rhizobium
C. Clostridium
D. Nitrobacter
Answer: B. Rhizobium
Solution: Symbiotic Rhizobium fixes N₂ in legume roots.
Shortcut: “Rhizo = Root”.
Tag: Nitrogen fixation
6. Water moves upward in plants via:
Options:A. Phloem
B. Xylem
C. Cambium
D. Cortex
Answer: B. Xylem
Solution: Xylem vessels form continuous pipes; transpiration pull lifts water.
Shortcut: “Xylem = Upward pipeline; Phloem = Food downward”.
Tag: Transport
7. Which part of the flower develops into fruit?
Options:A. Ovule
B. Ovary
C. Style
D. Stigma
Answer: B. Ovary
Solution: After fertilisation ovary → fruit; ovule → seed.
Shortcut: “Ovary = Overcoat for seeds = Fruit”.
Tag: Reproduction
8. The opening and closing of stomata is controlled by:
Options:A. CO₂ concentration only
B. Light & internal CO₂
C. O₂ concentration
D. Gravity
Answer: B. Light & internal CO₂
Solution: Low internal CO₂ & light trigger K⁺ influx → stomata open.
Shortcut: “Light ON → Stomata ON”.
Tag: Transpiration
9. Which is a C₄ plant?
Options:A. Wheat
B. Rice
C. Maize
D. Barley
Answer: C. Maize
Solution: Maize has Kranz anatomy; tolerates high temperature & low CO₂.
Shortcut: “C₄ = Corn (Maize) & Sugarcane”.
Tag: Photosynthesis
10. Dormancy of seeds is broken by:
Options:A. Abscisic acid
B. Gibberellin
C. Cytokinin
D. Florigen
Answer: B. Gibberellin
Solution: Gibberellin stimulates enzyme synthesis in aleurone → germination.
Shortcut: “Gibberellin = Germination”.
Tag: Plant hormones
11. Which plant fibre comes from the stem?
Options:A. Cotton
B. Coir
C. Jute
D. Silk
Answer: C. Jute
Solution: Jute fibre is extracted from bast (phloem) of Corchorus capsularis stem.
Shortcut: “Jute = Stem; Cotton = Seed hair”.
Tag: Economic botany
12. Photoperiodic stimulus is perceived by:
Options:A. Leaves
B. Roots
C. Stem apex
D. Flowers
Answer: A. Leaves
Solution: Leaves detect day-length & produce florigen that moves to bud apex.
Shortcut: “Leaves = Light sensor”.
Tag: Flowering
13. Which equation represents photosynthesis?
Options:A. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
B. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
C. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
D. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Answer: B. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Solution: Carbon dioxide & water synthesise glucose in presence of light.
Shortcut: “CO₂ & H₂O on left = Photosynthesis; on right = Respiration”.
Tag: Photosynthesis
14. Edible part of turmeric is:
Options:A. Tuber
B. Rhizome
C. Bulb
D. Corm
Answer: B. Rhizome
Solution: Underground horizontal stem with nodes & internodes = rhizome.
Shortcut: “Turmeric & Ginger = Rhizome”.
Tag: Morphology
15. Groundnut is:
Options:A. Dicot, oilseed, hypogeal germination
B. Monocot, oilseed, epigeal
C. Dicot, pulse, epigeal
D. Monocot, fiber, hypogeal
Answer: A. Dicot, oilseed, hypogeal germination
Solution: Two cotyledons, stores oil, cotyledons remain below soil.
Shortcut: “Groundnut = Below ground nut → Hypogeal”.
Tag: Economic botany
Speed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| Remember photosynthesis vs respiration equation | “Left CO₂ = Photo, Right CO₂ = Respire” | 6CO₂ left in photosynthesis; 6CO₂ right in respiration |
| C₃ vs C₄ plants | C₄ = “Maize Sugarcane Sorghum” (MSS) | All are tropical grasses |
| Hormones & function | “ABC” – Auxin (Apical), Bolting (Gibberellin), Cell division (Cytokinin) | Quick recall list |
| Fibre source | “Seed-Cotton, Stem-Jute, Leaf-Sisal, Fruit-Coir” | Never mix again |
| Geotropism sign | “Root = +ve (down), Shoot = –ve (up)” | Plus & minus arrow trick |
Quick Revision
| Point | Detail |
|---|---|
| 1 | Chlorophyll a is primary pigment; b & carotenoids are accessory. |
| 2 | Light reaction in thylakoid produces ATP & NADPH; dark reaction in stroma uses them to fix CO₂. |
| 3 | Lenticels perform transpiration in woody stems; stomata in leaves. |
| 4 | Casparian strip forces water to cross cell membranes → controls mineral uptake. |
| 5 | Sieve tubes in phloem lack nucleus; companion cells supply ATP. |
| 6 | Vernalisation = cold treatment to induce flowering in winter cereals. |
| 7 | N₂ fixation → NH₃ (nitrogenase enzyme) → nitrite → nitrate (nitrifying bacteria). |
| 8 | Leguminous crop rotation enriches soil nitrogen—green manure. |
| 9 | Parthenocarpic fruit = without fertilisation; e.g., seedless banana, grapes (GA spray). |
| 10 | Botanical name: Potato = Solanum tuberosum; Pea = Pisum sativum; Mango = Mangifera indica. |
BETA
