💧 Transport in Plants – NEET Notes, Concepts, and PYQs (Botany Sir Himansu)

🌿 Introduction: The Movement That Keeps Plants Alive

Just like humans have blood circulation, plants have their own internal transport system!

This system moves water, minerals, and food to every part of the plant — from roots to leaves and back.

The chapter “Transport in Plants” forms the backbone of Plant Physiology, and NEET often asks 3–4 direct questions from it.

Let’s explore this vital topic step-by-step — in simple, NEET-focused language.

---

🌱 Section 1: What is Transport in Plants?

Transport in plants refers to the movement of materials like:

Water & minerals — from roots to leaves (through xylem)

Organic food (sucrose) — from leaves to other parts (through phloem)

Why it’s important:

To maintain turgidity

To transport nutrients for growth

To remove metabolic waste

---

💦 Section 2: Types of Transport

Plants use three main types of transport mechanisms depending on distance:

1️⃣ Short Distance Transport (Cell-to-cell):

Occurs through:

Diffusion

Facilitated diffusion

Active transport

2️⃣ Long Distance Transport:

Movement through xylem (water/minerals) and phloem (food).

Also called translocation.

---

🌬️ Section 3: Diffusion

Definition: The passive movement of molecules from a region of high concentration to low concentration.

Key Points:

No energy required.

Depends on concentration gradient.

Examples:

Movement of O₂ and CO₂ in leaves.

Water vapor diffusion during transpiration.

NEET Tip:

Diffusion is slow and random — effective only over short distances.

---

🔄 Section 4: Facilitated Diffusion

Some molecules (ions, sugars) cannot pass directly through the membrane, so they use carrier proteins or channel proteins.

Features:

Passive (no ATP required).

Highly selective.

Follows concentration gradient.

Example:

Transport of glucose into cells using carrier proteins.

NEET Trick:

Diffusion → No protein

Facilitated diffusion → Protein channel

Active transport → Requires ATP

---

⚡ Section 5: Active Transport

Definition: The energy-dependent movement of substances against the concentration gradient.

Key Features:

Requires ATP.

Involves carrier proteins (pumps).

Moves ions like K⁺, Na⁺, Ca²⁺.

Example:

Uptake of mineral ions from soil by root hairs.

---

🌿 Section 6: Osmosis

Definition: The movement of water molecules through a semipermeable membrane from a region of high water potential to low water potential.

Key Terms:

Water Potential (Ψ): The potential energy of water.

Pure water has Ψ = 0.

Solute Potential (Ψs): Always negative (adding solute decreases water potential).

Pressure Potential (Ψp): Positive pressure increases Ψ.

Equation:

Ψw = Ψs + Ψp

NEET Question Example:

If solute potential = -0.7 MPa and pressure potential = 0.5 MPa, then

Ψw = -0.2 MPa.

---

🌱 Section 7: Plasmolysis and Deplasmolysis

When a plant cell is placed in:

Hypertonic solution: Cell loses water → Plasmolysis

Hypotonic solution: Cell gains water → Deplasmolysis

Isotonic solution: No change

Example:

Soaking pickles in salt solution → cells shrink (plasmolysis).

---

💧 Section 8: Water Absorption by Roots

Water enters plants through root hairs by osmosis.

Then it travels via:

Apoplast pathway (through cell walls)

Symplast pathway (through cytoplasm via plasmodesmata)

Casparian Strip (Endodermis):

Blocks apoplastic flow, forcing water into symplast — ensures selective uptake.

---

🌿 Section 9: Ascent of Sap

Definition: Upward movement of water from roots to leaves through xylem.

Theories Explaining It:

🔹 (A) Root Pressure Theory:

Occurs due to osmotic pressure in roots.

Seen in small plants (guttation in morning).

Not sufficient for tall trees.

🔹 (B) Cohesion-Tension Theory (Dixon & Joly):

Major theory accepted for NEET.

Transpiration pulls water up via:

Cohesion (water molecules stick together)

Adhesion (stick to xylem walls)

Tension (created by evaporation at leaf surface)

NEET Tip:

Transpiration → creates suction force → pulls water upward.

---

🌬️ Section 10: Transpiration

Definition: The loss of water vapor from aerial parts of plants.

Types:

Stomatal (via stomata) — most common

Cuticular (via cuticle)

Lenticular (through lenticels)

Functions:

Maintains water movement

Cools the plant

Helps in mineral transport

Factors Affecting Transpiration:

Internal: Leaf area, stomatal number

External: Light, temperature, humidity, wind

NEET PYQ:

Opening and closing of stomata are controlled by — Guard cells (due to turgor pressure) ✅

---

🌾 Section 11: Translocation of Organic Solutes

Definition: Transport of food (mainly sucrose) through phloem from source (leaves) to sink (roots, fruits, seeds).

Mechanism — Pressure Flow Hypothesis (Münch, 1930):

1. Sugars are actively loaded into phloem (source).

2. Water enters → pressure builds up.

3. Sugars move to sink where they’re unloaded.

4. Pressure decreases and flow continues.

NEET Note:

Phloem transport is bidirectional, while xylem transport is unidirectional.

---

🌻 Section 12: Mineral Nutrition Transport

Minerals move as ions in xylem.

Can be passive or active transport.

Deficiency symptoms appear in older or younger leaves depending on nutrient mobility.

Example:

Nitrogen (mobile) deficiency → older leaves first.

Calcium (immobile) deficiency → younger leaves first.

---

🧠 Section 13: NEET PYQs from Transport in Plants

1️⃣ NEET 2023:

Which part of the plant is responsible for upward water movement?

✅ Xylem

2️⃣ NEET 2021:

Transpiration pull is mainly responsible for:

✅ Ascent of sap

3️⃣ NEET 2020:

Which theory explains phloem transport?

✅ Pressure Flow Hypothesis

4️⃣ NEET 2019:

Casparian strip is made up of:

✅ Suberin

5️⃣ NEET 2018:

Opening and closing of stomata is due to:

✅ Changes in turgor pressure of guard cells

---

🌸 Section 14: Summary Table (Quick Revision)

Process Tissue Direction Type Energy Use

Water transport Xylem Upward Physical Passive

Mineral transport Xylem Upward Active ATP required

Food transport Phloem Source → Sink Biological Active

Transpiration Stomata Upward water loss Physical Passive

---

🌳 Conclusion

The Transport in Plants system is a marvel of nature — no pumps, no heart, yet a perfectly coordinated movement of water and food through physics and biology.

For NEET aspirants, focus on xylem–phloem difference, transpiration mechanism, and pressure flow hypothesis, as these are frequent exam questions.