Olive Defence

Biology · AFCAT

BA03 — Botany — Plant Biology

BA03 · AFCAT General Awareness — Biology ★ Moderate Yield

Plants sustain every ecosystem. AFCAT tests the photosynthesis equation, which gas comes from which source, plant hormones, and the xylem-phloem distinction. The key trap: oxygen comes from water, not CO₂.

AFCAT Focus: 6CO₂+6H₂O+light→C₆H₁₂O₆+6O₂; O₂ released comes from WATER; chlorophyll absorbs red+blue light; ethylene = fruit ripening; ABA = stress/drought; auxin = phototropism; xylem = water upward (dead cells); phloem = food bidirectional (living cells).

Part 1 — Photosynthesis

1. Photosynthesis

Overall Equation: 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂

●Light Reactions (thylakoid): Water + Light + Chlorophyll → ATP + NADPH + O₂

●Water is split (photolysis): 2H₂O → 4H⁺ + 4e⁻ + O₂ — O₂ comes from WATER not CO₂

●Dark Reactions / Calvin Cycle (stroma): CO₂ + ATP + NADPH → Glucose

AFCAT Trap: "The oxygen released in photosynthesis comes from ___?" → Always Water. CO₂ provides only carbon atoms. Appears in multiple AFCAT papers.

Part 2 — Transport & Hormones

2. Transport in Plants

What it transports

Xylem

Water + dissolved minerals from roots upward

Phloem

Food (sugars/sucrose) made in leaves

Direction

Xylem

Unidirectional (upward only)

Phloem

Bidirectional (up and down)

Cell type

Xylem

Dead cells; thick lignified walls

Phloem

Living cells; sieve tubes + companion cells

Driving force

Xylem

Transpiration pull (suction from leaf water loss)

Phloem

Pressure flow (source to sink)

Process name

Xylem

Ascent of sap

Phloem

Translocation

3. Plant Hormones

Auxin (IAA)

Produced in

Shoot apex

Primary Function

Cell elongation; phototropism (bending toward light)

AFCAT Fact

Plant bends toward light

Gibberellin

Produced in

Young leaves, seeds

Primary Function

Stem elongation; seed germination; fruit growth

AFCAT Fact

Dwarf plants grow tall

Cytokinin

Produced in

Root apex

Primary Function

Cell division; delays leaf senescence (ageing)

AFCAT Fact

Keeps leaves green longer

ABA

Produced in

Leaves, seeds

Primary Function

Stomatal closure (water stress); seed dormancy

AFCAT Fact

Stress hormone; only inhibitor

Ethylene

Produced in

Ripening fruits

Primary Function

Fruit ripening; leaf and flower drop

AFCAT Fact

Only gaseous hormone

AFCAT PYQs — Botany

Q1. Oxygen released during photosynthesis comes from:AFCAT PYQ

(a) CO₂

(b) Glucose

(d) Chlorophyll

✓ Answer: (c) Water

Water is split by photolysis: 2H₂O → O₂ + 4H⁺ + 4e⁻. CO₂ provides only carbon atoms for glucose. Proven by ¹⁸O isotope experiments.

Q2. Which plant hormone causes bending toward light?AFCAT PYQ

(a) Gibberellin

(b) Cytokinin

(d) ABA

✓ Answer: (c) Auxin

Auxin migrates to the shaded side, causing more elongation there → shoot bends toward light (phototropism). ABA is the inhibitory stress hormone.

Quick Memory Chart — BA03

Photosynthesis

6CO₂+6H₂O+light → glucose+6O₂
O₂ from WATER (photolysis)
Chlorophyll: absorbs red + blue
Light rxn: thylakoid → ATP+NADPH+O₂
Dark rxn: stroma → glucose

Plant Hormones

Auxin: phototropism (bends to light)
Gibberellin: stem elongation
Cytokinin: cell division, anti-ageing
ABA: stomata close; stress; inhibitor
Ethylene: fruit ripening (only gas)

Transport

Xylem: water+minerals upward (dead)
Phloem: food bidirectional (living)
Transpiration: water loss via stomata
Transpiration pull drives xylem flow

📝 Mocks 🎯 Quizzes