Plant Physiology – B.Sc. Nursing Entrance Notes
(IIT‑JEE / Competitive Exam Focus)
Why Plant Physiology Matters in Nursing?
- Pharmacognosy – many drugs are plant‑derived; understanding plant metabolism helps trace biosynthetic pathways.
- Clinical Nutrition – herbal supplements and micronutrients (e.g., vitamin‑C, iron) originate from plant tissues.
- Environmental Health – plant–human interactions (air purification, oxygen production) require knowledge of plant processes.
1. Introduction
- Definition – The branch of biology that deals with the internal functions and processes of plants.
- Scope – Cellular structure → whole‑plant physiology → environmental interactions.
2. Plant Cell & Tissue Basics
| Feature | Details | Relevance |
|---|---|---|
| Cell Wall | Primarily cellulose + hemicellulose + pectin. | Determines cell rigidity, influences osmotic balance. |
| Plasmodesmata | Cytoplasmic channels between cells. | Facilitates inter‑cellular communication. |
| Large Central Vacuole | Stores water, ions, pigments. | Maintains turgor pressure; crucial for water relations. |
| Cell Types | Parenchyma (storage), Collenchyma (flexible support), Sclerenchyma (rigid). | Different functions in growth and stress response. |
3. Water Relations
3.1 Water Potential (Ψ)
[ \boxed{\Psi = \Psi_s + \Psi_p} ]
- Ψs – Solute (osmotic) potential.
- Ψp – Pressure potential (positive in turgid cells, negative in plasmolysed cells).
Derivation
Water moves from higher Ψ to lower Ψ; the total potential is the sum of all contributing potentials (osmotic, pressure, matric, gravitational). For most plant physiology exams, Ψ = Ψs + Ψp suffices.
Key Formulae
| Symbol | Unit | Typical Value in Turgid Cell |
|---|---|---|
| Ψs | MPa | –1 to –0.5 |
| Ψp | MPa | +0.5 to +1 |
| Ψ | MPa | –0.5 to 0 (net) |
Tricky Point – Negative pressure potential (tension) is possible in xylem during transpiration; it is not a “negative pressure” but a negative potential.
3.2 Transpiration
- Process – Evaporation of water from leaf surface.
- Driving Force – Vapor pressure deficit (VPD).
[ \text{VPD} = \text{Saturation Vapor Pressure (SVP)} - \text{Actual Vapor Pressure (AVP)} ]
- Stomatal Conductance (gs) – Determines water loss & CO₂ influx.
[ E = gs \times VPD ]
- Transpiration Rate (E) – Often expressed in mmol m⁻² s⁻¹.
Important Relationship –
[
E \propto \frac{gs \times VPD}{1 + gs \times R_s}
]
where (R_s) is leaf boundary layer resistance.
4. Photosynthesis
4.1 Overview
- Light Reactions – Occur in thylakoid membranes; produce ATP & NADPH.
- Calvin Cycle (Dark Reactions) – Uses ATP + NADPH to fix CO₂ → G3P.
4.2 Key Enzymes
| Enzyme | Reaction | Important Note |
|---|---|---|
| Rubisco | CO₂ + RuBP → 2 × 3‑PGA | Dual role: carboxylation & oxygenation (photorespiration). |
| PEP Carboxylase | (C₄) CO₂ + PEP → OAA | Bypasses Rubisco to concentrate CO₂. |
4.3 Photorespiration
- Occurs when Rubisco oxygenates RuBP.
- Energy Cost – consumes 3 ATP and 1 NADPH per CO₂ released.
- Mitigation – C₄ & CAM pathways.
4.4 C₃, C₄, CAM Pathways
| Pathway | Key Adaptation | Typical Environment |
|---|---|---|
| C₃ | Direct Rubisco fixation | Temperate, well‑watered |
| C₄ | CO₂ concentration via PEP carboxylase | Hot, dry, high light |
| CAM | Stomata open at night | Arid, nocturnal CO₂ uptake |
Derivation of Net CO₂ Uptake
[ A_n = V_c - 0.5 \times V_o - R_d ]
- (V_c) – Carboxylation rate.
- (V_o) – Oxygenation rate.
- (R_d) – Day respiration.
5. Plant Hormones & Growth Regulation
| Hormone | Major Effects | Key Receptors |
|---|---|---|
| Auxin (IAA) | Cell elong |