Water relation | CEE Academy

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PLANT PHYSIOLOGY / PHYTOPHYSIOLOGY

▢ Father: Stephen Hales

▢ Definition: Science of life processes + functioning of plant cells, tissues, organs and whole plant

▢ Includes:

Table 1: Processes in plant physiology

Category	Processes
Physical processes	Diffusion, osmosis, plasmolysis, imbibition, absorption, ascent of sap, transpiration, guttation
Physico-chemical processes	Respiration, photosynthesis, photorespiration
Special processes	Hormone role, movement, seed germination, vernalization

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DIFFUSION

▢ Definition: Movement of ions/free atoms/molecules/particles from higher concentration to lower concentration along concentration gradient until uniform distribution

▢ Nature:

•
Passive process
•
Particle movement due to kinetic energy

▢ Regions:

Table 1: Diffusion regions

Component	Type
Diffusing particles	Solid / liquid / gas
Diffusing medium	Liquid / gas

▢ Diffusion Pressure:

•
Hypothetical term
•
Potential ability of solid/liquid/gas to diffuse
•
Pure solvent DP > solution DP
•
Water DP \(\approx 1236\) atm
•
Sugar solution DP < pure water DP

▢ Diffusion Pressure Deficit / DPD / Suction Pressure:

•
DPD = water absorbing capacity
•
•
DPD = decrease in diffusion pressure of solution compared with pure solvent
•
DPD = 0 → no water absorption by cell / turgid cell

▢ Water Potential:

Table 1: Water potential

Point	Data
Meaning	Free energy per mole of water molecule
Symbol	\(\Psi\) / psi
Pure water	\(\Psi = 0\)
After solute addition	\(\Psi\) decreases → negative value
Relation	\(\Psi = -DPD\)
Unit	Bars
Lowest \(\Psi\)	Xylem cells of leaves

▢ Rate of Diffusion:

Table 1: Factors affecting diffusion rate

Factor	Relation
Diffusion pressure gradient	Directly proportional
Temperature	Directly proportional; stops at \(0K\)
Humidity	Inversely proportional
Distance between diffusing particles	Inversely proportional
Size of diffusing particle	Inversely proportional
Density of diffusing particle	\(\propto \frac{1}{\sqrt{density}}\)
Density of medium

Graham’s law: diffusion of gas > liquid > solid

▢ Q₁₀: Temperature coefficient of diffusion = 1.2–1.3; most chemical reactions = 2–3

▢ Examples:

•
•
Aroma of flowers → diffusion of volatile aromatic compounds
•
Particle movement in protoplasm
•
Passive mineral uptake
•
Mineral movement through semipermeable membrane = diffusion, not osmosis
•
Water movement from higher concentration to lower concentration without semipermeable membrane
•
Independent diffusion → simultaneous diffusion of two/more substances
•
Respiration + photosynthesis gaseous exchange; transpiration water vapour loss
•
Facilitated diffusion → dissolved substances through semipermeable membrane with carrier protein; e.g., fructose transport

▢ Note: Opening and closing of stomata involve osmosis, not diffusion

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OSMOSIS

▢ Types of Membrane:

Table 1: Membrane types

Membrane	Permeability	Examples
Permeable membrane	Allows all solutes + solvents	Cellulosic cell wall, lignified cell wall
Selectively / differentially permeable membrane	Allows solvent + selected solutes	Living biological membranes, plasma membrane, tonoplast, organelle membranes
Semipermeable membrane	Allows solvent only; no solute	Copper ferrocyanide membrane, collodion, parchment membrane
Impermeable membrane	Allows neither solute nor solvent	Cutinized cell wall, suberinized cell wall

▢ Definition:

•
Solvent movement from lower solute concentration to higher solute concentration through semipermeable membrane
•
Water diffusion from higher water concentration to lower water concentration through semipermeable membrane
•
Special type of diffusion; requires semipermeable membrane

▢ Continues Until: Hydrostatic pressure = osmotic pressure

▢ Requirements:

Concentration difference
Semipermeable membrane

▢ Direction of Osmosis:

•
Dilute solution → concentrated solution
•
Hypotonic → hypertonic
•
Low OP → high OP
•
Low DPD → high DPD
•
Higher water potential → lower water potential
•
Higher free energy → lower free energy
•
Turgid cell → flaccid cell from vacuole
•
Osmotically inactive solution → osmotically active solution

▢ Special Rules:

•
Osmosis absent in isotonic pressure
•
•
Free energy of pure water = 0
•
Free energy of solution = negative
•
Osmotically inactive solution due to insoluble solute; e.g., starch in water
•
Only living tissue shows osmosis
•
Dead/boiled/alcohol-treated cells lose semipermeability

▢ Significance in Plants:

•
Water absorption
•
Turgidity of plant organs
•
Cell-to-cell water movement
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Drought + frost resistance
•
Opening + closing of stomata

▢ Types of Solution:

Table 1: Hypotonic, isotonic and hypertonic solutions

Solution	Outer solution concentration	Effect on cell
Hypotonic	Lower than cell sap	Water enters cell
Isotonic	Equal to cell sap	No net water gain/loss
Hypertonic	Higher than cell sap	Water leaves cell

▢ Types of Osmosis:

Table 1: Endosmosis vs exosmosis

Feature	Endosmosis	Exosmosis
Solvent movement	Surrounding solution → cell	Cell → surrounding solution
Result	Turgidity	Flaccidity

▢ Special Points:

•
Turgidity maintained by osmotic pressure
•
Cell growth maintained by turgor pressure

▢ Osmosis Involved In:

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Absorption of water
•
Cell-to-cell water movement
•
Stomatal movement
•
Turgid guard cell → stomata open
•
Flaccid guard cell → stomata close
•
Growth of plumule + radicle during germination
•
Maintenance of form + structure of organs
•
Leaf movement in Mimosa pudica / seismonastic movement

▢ Osmotic Pressure:

Table 1: Osmotic pressure

Point	Data
Definition	Pressure required in opposite direction to stop solvent entry through semipermeable membrane
Cause	Presence of solute particles
Relation
Pure solvent	OP = 0
Solution	OP positive

▢ Turgor Pressure:

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Pressure developed due to osmotic entry of water against rigid cell wall
•
Hydrostatic pressure
•
Keeps leaves + floral parts stretched
•
Cause of stomatal opening
•
Turgor movement → Mimosa pudica, Desmodium

▢ Wall Pressure:

•
Pressure exerted by rigid cell wall against expanding protoplasm
•
WP = inward pressure
•
\(WP = -TP\)
•
Fully turgid cell → \(OP = TP\)

▢ DPD, OP and TP Relationship:

Table 1: DPD relationships

Condition	Formula
Normal cell	\(DPD = OP - TP\)
Using wall pressure	\(DPD = OP - WP\)
Fully turgid cell	\(DPD = 0\); because \(OP = TP\)
Plasmolysed cell	\(DPD = OP\); because \(TP = 0\)
Pure water	\(DPD = 0\)

❖ Notes:

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DPD = resultant force for water movement
•
Water enters root from soil due to suction pressure / DPD
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DPD = driving force of water absorption in roots
•
Normal cell → DPD positive
•
DPD never negative
•
Cell-to-cell water movement mainly depends on DPD / suction pressure

▢ RBC and Plant Cell MCQ Points:

Table 1: Pure water effects

Cell	Placed in pure water	Result
Human RBC isotonic to 5% glucose	Pure \(H_2O\)	Burst → ghost RBC
Cabbage stem cell isotonic to 1% NaCl	Pure water	Does not burst due to rigid cell wall

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PLASMOLYSIS

▢ Definition: Shrinkage of protoplast due to exosmosis when cell is placed in hypertonic solution

▢ Types:

Table 1: Types of plasmolysis

Type	Meaning
Incipient plasmolysis	Protoplast just leaves cell wall
Full plasmolysis	Complete shrinkage of protoplast

▢ Helps Determine:

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Permeable nature of cell wall
•
Semipermeable nature of cell membrane
•
OP of cell
•
Living/dead nature of unknown cell
•
Quickest physiological test for living/dead cell

▢ Special Points:

•
Plasmolysis not possible in dead cell
•
In plasmolysed/flaccid cell, space between wall and membrane filled by outer solution
•
No wrinkling of cell wall during plasmolysis because hypertonic solution fills the space

▢ Applications:

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Plants cannot survive in excessive fertilizer area
•
Bacteria cannot survive in salted pickles
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Salt spread in tennis court kills weeds

▢ Deplasmolysis: Plasmolysed cell regains normal condition in hypotonic solution

▢ Plasmoptysis: Bursting of cell in pure solvent/dilute medium

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IMBIBITION

▢ Definition: Surface phenomenon: solvent adsorbed on particle surface without solution formation → swelling

▢ Mechanism: Water movement into imbibant by diffusion + capillary action

▢ Terms:

Table 1: Imbibition terms

Term	Meaning
Imbibate	Solvent adsorbed
Imbibant	Substance adsorbing solvent

▢ Good Imbibants:

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Solid substances with hydrophilic colloids
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Seed coat
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Cell wall
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Wood / woody tissue
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Velamen tissue

▢ Examples:

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Dry seeds swell in water
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First physiological process during seed germination
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Water absorption by root hairs starts with imbibition
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Seed germination accompanied by heat evolution
•
Wooden doors swell in rainy season
•
Wooden pieces in rock crevices can rupture rock by imbibition pressure
•
•
Rubber does not imbibe water; imbibes ether/kerosene/organic solvents

▢ Effects:

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Volume of imbibant increases
•
Pressure exerted
•
Heat released → exothermic
•
Temperature increase → imbibition increases

▢ Formula: \(DPD = Imbibition\ pressure - TP\)

▢ Special Points:

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Affinity between imbibant and liquid is necessary
•
Wood + water → swelling; wood + ether → no swelling
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Rubber + water → no imbibition; rubber + ether → imbibition
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First step = adsorption
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Adsorption = colloid property
•
Wood is good imbibant due to proteins + cellulose + starch
•
Capacity: Agar > Pectin > Protein > Starch > Cellulose
•
No imbibition in waxy substances e.g., cutin

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ABSORPTION OF WATER

▢ Definition: Movement of water from soil to xylem of roots

▢ Processes Involved:

Imbibition
Osmosis
Diffusion
Capillary action

▢ Site:

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Root hair zone / maturation zone
•
Root cap has no role → no root hairs
•
Water absorbed by root hairs when external medium is hypotonic

▢ Root Hair vs Lateral Root:

Table 1: Root hair vs lateral root

Feature	Root hair	Lateral root
Origin	Exogenous	Endogenous
Cellularity	Unicellular	Multicellular
Arises from	Epiblema / epidermis	Pericycle

▢ Water Sources in Soil:

Table 1: Soil water types

Term	Meaning
Main source	Rain water
Most easily available	Capillary water
Hardly available	Gravitational water
Completely unavailable	Hygroscopic water
Holard	Total water content in soil
Chesard	Water available to plants
Echard	Water unavailable to plants

▢ Root Hair Special Points:

•
Acts as osmotic system
•
More developed in herbs than shrubs/trees
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More developed in angiosperms than gymnosperms
•
Gymnosperms often have mycorrhiza
•
Cell wall permeable
•
Outer layer → pectin for soil-particle attachment
•
Inner layer → cellulose

▢ Absorption in Different Plants:

Table 1: Water absorption organs

Plant group	Absorbing structure
Thallophytes / algae + fungi	General body surface
Hydrophytes	General body surface
Lichens	Rhizines
Marchantia	Unicellular rhizoids
Moss / Funaria	Multicellular rhizoids
Fern gametophyte / prothallus	Unicellular rhizoids
Fern sporophyte	Fibrous/adventitious roots
Pinus	Mycorrhizal roots
Higher plants	Root hairs
Parasitic plants	Haustorial roots

Root hairs absent in mycorrhizic, parasitic and hydrophytic roots

▢ Pathway: Soil → root hair → cortex → endodermis/passage cell → pericycle → protoxylem → metaxylem

▢ Mechanism:

Table 1: Passive vs active water absorption

Feature	Passive absorption	Active absorption
Driving force	Transpiration; through DPD gradient	Root pressure; against DPD gradient / non-osmotic
ATP	Not required	Required
Respiration	Unaffected	Increases
Oxygen	Not affected by oxygen level	Oxygen needed
Gradient	Along osmotic/concentration gradient	Against concentration gradient
Time	Day; transpiration active	Usually night; transpiration stopped
Associated with	Transpiration	Bleeding + guttation
Role	Root passive; shoot active	Root active; shoot passive
Contribution	>90%	<10%
Path	Apoplast + symplast	Symplast
Speed	Rapid	Slower
Phrase	Water absorption through roots	Water absorption by roots

▢ Active Absorption Types:

Table 1: Active absorption types

Type	Mechanism
Osmotic active absorption	According to osmotic gradient without ATP
Non-osmotic active absorption	Against osmotic gradient using ATP

▢ Apoplast and Symplast:

Table 1: Water movement systems

System	Path	Nature
Apoplast	Cell walls + intercellular spaces	Non-living
Symplast	Protoplasm + plasmodesmata	Living

▢ Rate of Water Absorption:

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Decreases at very low and very high temperature
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Maximum at \(20^\circ C-30^\circ C\)
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Decreases in saline soil / physiologically dry soil
•
Decreases in poorly aerated soil
•
Decreases in waterlogged soil
•
Directly proportional to transpiration

▢ Physiologically Dry Soil: Water present but plant cannot absorb due to dissolved salts

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ABSORPTION OF MINERALS

▢ Basic Points:

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Independent of water absorption
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Mostly through zone of elongation, not root hair zone
•
Mineral salt absorption directly by epiblema cells, not root hairs
•
Minerals absorbed as ions: cations/anions in soil solution
•
First step → ion exchange
•
Transport path → xylem

▢ Methods:

Table 1: Passive vs active mineral absorption

Feature	Passive absorption	Active absorption
Gradient	Along concentration gradient	Against concentration gradient
ATP	Not used	Used
Nature	Spontaneous; towards equilibrium	Non-spontaneous
Main concepts	Donnan equilibrium, ion exchange, mass/bulk flow	Carrier concept, Landegardh cytochrome pump theory

▢ Passive Concepts:

Table 1: Passive mineral absorption concepts

Concept	Scientist	Meaning
Donnan equilibrium		Entry of anions + cations across membrane to maintain electrochemical equilibrium
Ion exchange	Jenny and Overstreet	Exchange of ions adsorbed on root surface with similarly charged ions in soil solution
Contact exchange		Ion exchange type
Carbonic acid exchange		Ion exchange type
Mass flow / bulk flow	Kramer	Mineral absorption with mass flow of water under transpiration pull

If root surface has \(H^+\), anions absorbed; vice versa to maintain electrochemical balance. Ion exchange occurs when oscillation volumes overlap.

▢ Active Concepts:

Table 1: Active mineral absorption concepts

Concept	Scientist	Meaning
Carrier concept	Van den Honert	Carrier molecules form carrier-ion complexes
Carrier molecules		Proteinaceous; located on plasma membrane
Landegardh cytochrome pump theory	Landegardh	Anions actively absorbed through cytochrome; cations passively absorbed to maintain electrochemical balance

▢ Factors Affecting Mineral Salt Absorption:

Table 1: Factors

Factor	Effect
Temperature	Increase → absorption increases; very high temperature → decreases due to protein carrier denaturation
pH	Low pH → anion absorption increases; high pH → cation absorption increases
\(O_2\)	Low oxygen → active absorption decreases
Ageing	Older roots → absorption decreases due to suberization

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ASCENT OF SAP

▢ Definition: Upward movement of water with dissolved minerals through xylem vessel lumen against gravity

▢ Path in Gymnosperms: Tracheids

▢ Best Experiment:

Table 1: Ringing / girdling experiment

Point	Data
Meaning	Removal of bark as complete ring
Shows	Path of ascent of sap
Not applicable in	Bicollateral, amphivasal and scattered vascular bundles

▢ Theories:

❖ Vital Theories:

Table 1: Vital theories

Theory	Scientist	Path / Concept
Relay pump theory	Godlewski	Through xylem parenchyma
Pulsation theory	J. C. Bose	Through innermost cortical cells
Discarded by	Strasburger	Living cells not responsible for ascent of sap

❖ Root Pressure Theory:

Table 1: Root pressure theory

Point	Data
Given by	Priestley
Concept	Hydrostatic pressure in root due to absorbed water accumulation → ascent of sap

❖ Physical Force Theories:

Table 1: Physical force theories

Theory	Scientist	Concept
Atmospheric pressure theory	Boehm	Atmospheric pressure raises water to fill vacuum from evaporation
Imbibition theory	Unger; supported by Sachs	Water moves upward through thick walls of xylem cells + sclerenchyma cells of phloem by imbibition
Transpiration pull / cohesion-tension theory	Dixon and Jolly	Most accepted; based on cohesion + adhesion of water

▢ Cohesion-Tension Theory:

•
Most convincing / most widely accepted
•
Operates only in passive water absorption
•
Based on cohesive + adhesive properties of water
•
Transpiration necessary for ascent of sap

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TRANSPIRATION

▢ Definition: Loss of water vapour in pure form from aerial parts of plants

▢ Conditions:

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Occurs when outer atmosphere has less moisture than substomatal cavities
•
Most rapid: low humidity + high temperature + turgid guard cells/open stomata + moist soil
•
Increases in hot, dry and windy conditions
•
Reduced by cutin deposition
•
Reduced when light intensity decreases
•
Does not occur from roots
•
Controlled phenomenon

▢ Importance:

•
Necessary for water + mineral absorption
•
Ascent of sap
•
Body temperature regulation / cooling effect
•
Curtis → transpiration is a necessary evil
•

▢ Sites:

Table 1: Sites of transpiration

Site	Contribution	Note
Stomata	\(90\%\)	Maximum
Cuticle	\(9\%\)	General body surface
Lenticel	\(1\%\)	Bark of woody trees

▢ Leaf Surface:

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Dorsiventral leaf → lower surface transpiration higher due to more stomata
•
Cobalt chloride test compares transpiration from two leaf surfaces
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Dry \(CoCl_2\) paper → blue
•
Moist \(CoCl_2\) paper → pink
•
Lower surface changes blue → pink faster

▢ Experiments / Instruments:

Table 1: Transpiration tests

Test / Instrument	Use
Bell jar experiment	Shows water vapour loss from aerial plant parts
Ganong’s potometer	Measures rate of transpiration
Cobalt chloride paper	Shows unequal transpiration in dorsiventral leaf

▢ Mechanism:

•
Stomatal transpiration regulated by stomatal opening/closing
•
Opening/closing due to guard cell turgor pressure change
•
Transpiration through leaves → foliar transpiration
•
Transpiration through corky covering of stem → bark transpiration

▢ Transpiration vs Evaporation:

Table 1: Transpiration vs evaporation

Feature	Transpiration	Evaporation
Nature	Physiological process	Physical process
Surface	Living cells only	Living + non-living surfaces
Path	Epidermis; mainly stomata	Free surface
Forces	VP, TP, OP involved	No such forces
Surface effect	Prevents drying / keeps surface wet	Causes dryness
Temperature	Regulates plant body temperature	No regulation

▢ Factors Affecting Transpiration:

❖ Internal / Plant Factors:

Table 1: Internal factors

Factor	Effect
Root/shoot ratio	Higher ratio → higher transpiration
Leaf area	More area → more transpiration
Plant size per unit area	Smaller plants transpire more than larger plants
Removal of leaves	Transpiration per unit area increases
Cuticle	Thin cuticle → higher cuticular transpiration
Stomatal number	More stomata/unit area → higher transpiration
Sunken stomata	Reduce transpiration
Leaf maturity	Maximum rate in mature leaf

❖ External / Environmental Factors:

Table 1: External factors

Factor	Effect
Light	Controls stomatal opening/closing; generally open in day, closed in dark
Red light \(660\ nm\)	Maximum stomatal opening
Blue light \(445\ nm\)	Opening after red light
Green / UV / far-red light	No stomatal opening
Temperature	Rate increases up to \(35^\circ C\)
Relative humidity	Inversely proportional
Low humidity	Increases transpiration
Gentle wind	Increases transpiration by removing saturated air
Violent wind	Decreases transpiration
Soil condition	Affects transpiration through water absorption

▢ Anti-transpirants:

•
Phenyl mercuric acetate / PMA
•
Abscisic acid / ABA
•
Salicylic acid
•
Aspirin
•
Waxy substances e.g., silicon emulsion
•
High \(CO_2\) concentration

▢ Significance:

•
Removes excess absorbed water
•
Maintains plant temperature
•
Produces suction force in leaves → ascent of sap
•
Ash + sugar content of fruits increases with transpiration

▢ Disadvantages:

•
High rate → wilting
•
Photosynthesis reduced
•
Growth stopped
•
Flower/fruit/seed production inhibited

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GUTTATION

▢ Cause: Root pressure

▢ Definition: Loss of liquid water droplets from leaf margin and tip; mainly margin

▢ Water Nature: Impure; contains dissolved minerals

▢ Function: Removal of excess water

▢ Structure:

Table 1: Hydathode

Point	Data
Structure	Hydathodes / water stomata
Position	Leaf margin + tip; mainly margin
Epithem	Loosely arranged parenchyma in hydathode
State	Always open

▢ Time:

•
Early morning or night
•
Transpiration low + absorption high → root pressure increases
•
Not due to hydathode activity; due to root pressure

▢ Examples:

•
Water drops on leaf margins of Tropaeolum
•
Balsam
•
Grasses
•
Moist mesophytic herbs → tomato, balsam, cucurbita, Colocasia

▢ Nature: Uncontrolled phenomenon

▢ Transpiration vs Guttation:

Table 1: Transpiration vs guttation

Feature	Transpiration	Guttation
Water form	Vapour	Liquid droplets
Time	Daytime	Night / early morning
Water type	Pure water	Impure water with minerals
Path	Stomata, epidermis, cuticle, lenticels	Hydathodes
Control	Controlled	Uncontrolled
Temperature regulation	Present	Absent
Water absorption	Helps	No role

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EXUDATION / BLEEDING

▢ Exudation: Loss of water sap from incision of plant body parts

▢ Bleeding: Exudation of water from leaf incision

▢ Guttation: Exudation of water from leaf margin

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WILTING

▢ Definition: Loosening of plant part due to loss of turgidity

▢ Cause:

•
Transpiration > water absorption
•
Xylem blocked
•
Xylem removed

▢ PWC / PWP: Percentage of water left in soil when plant wilts = permanent wilting coefficient / permanent wilting percentage

▢ Sequence: Exosmosis → plasmolysis → temporary wilting → permanent wilting

▢ Types:

Table 1: Types of wilting

Type	Feature
Incipient wilting	Not visible; partial loss of turgidity
Temporary wilting	Hot days; transpiration high + absorption low; recovers at night; reversible
Permanent wilting	Plant fails to recover; xylem vessels blocked; irreversible

▢ Note: During wilting, cell wall wrinkles because water is lost without replacement

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STOMATA

▢ Definition: Minute pores on epidermis

▢ Number: About 1000 per \(cm^2\) of common leaf

▢ Structure:

Table 1: Stomatal structure

Part	Feature
Guard cells	Kidney-shaped in dicots; dumb-bell-shaped in monocots
Thickest guard cell wall	Inner wall
Subsidiary cells	Surrounding cells; support guard cell movement

▢ Guard Cell Notes:

•
Specialized epidermal cells
•
Contain chloroplasts
•
Other epidermal cells usually lack chloroplasts
•
Guard cell chloroplasts show poor photosynthesis due to absence of RuBP carboxylase
•
PS-I and PS-II present
•
Crucifer type stomata → 3 subsidiary cells
•
Sunken stomata reduce transpiration

▢ Types Based on Distribution:

Table 1: Stomatal types by distribution

Type	Distribution	Example
Apple / mulberry type	Only lower/dorsal surface	Trees
Potato type	More on lower than upper surface	Most common; dorsiventral leaf
Oat type	Equally on both surfaces	Isobilateral leaf, grasses
Water lily type	Only upper surface	Free-floating hydrophytes
Potamogeton type	Absent / vestigial	Submerged hydrophytes

▢ Stomatal Behaviour Types:

Table 1: Stomatal behaviour

Type	Behaviour	Example
Alfalfa type	Open during day; close at night	Thin-leaved mesophytes
Barley type	Close at night; open for few hours in day	Most cereals
Photoactive	Open in daytime	Usual plants
Scotoactive	Open at night	Succulent xerophytes / CAM plants e.g., Opuntia, Bryophyllum

▢ Opening and Closing:

Table 1: Stomatal state

State	Guard cell condition
Stomata open	Guard cells turgid; OP + TP increase
Stomata close	Guard cells flaccid

▢ Starch-Sugar Hypothesis:

•
Proposed by Lloyd
•
Elaborated by Sayre and Steward
•
Depends on starch phosphorylase activity at different pH
•
High pH: starch → sugar → stomata open
•
Low pH: sugar → starch → stomata close
•
Starch to organic acid conversion required for stomatal opening

▢ Potassium Malate Theory / Active \(K^+\) Exchange:

▢ Status: Most accepted theory

▢ Given by: Fujino; modified by Levitt

▢ Day / Opening: Light → \(CO_2\) decreases → pH increases → insoluble starch converted to soluble sugar → \(K^+\) influx → OP increases → endosmosis → guard cell turgid → stomata open

▢ Night / Closing: Dark → \(CO_2\) increases → pH decreases → soluble sugar converted to insoluble starch → \(K^+\) efflux → OP decreases → exosmosis → guard cell flaccid → stomata close

▢ Special Points:

•
\(K^+\) influx → stomata open
•
\(K^+\) outflux → stomata close
•
Opening = active process
•
Closing = passive process
•
Old stems + fruits transpire through lenticels
•
High altitude plants show xeromorphic adaptation

📚

MINERAL NUTRITION IN PLANTS

▢ Definition: Green plants take inorganic substances from soil as minerals/mineral nutrients to prepare organic food

▢ Ash Analysis:

•
About 92 mineral elements found in different plants
•
30 elements present in every plant
•
16 essential elements: C, H, O, N, P, S, K, Mg, Ca, Fe, Cu, B, Zn, Mn, Mo, Cl

▢ Essential Elements:

Table 1: Macro and micro elements

Type	Requirement	Elements
Macro / major elements	Large amount	H, C, N, O, P, S, K, Mg, Ca
Micro / minor / trace elements	Very small amount	Fe, Cu, B, Zn, Mn, Mo, Cl

Elements with atomic number >20 are microelements except boron and chlorine

▢ Special Element Groups:

Table 1: Element groups

Group	Elements / Note
Non-mineral elements	C, H, O
C source	Atmospheric \(CO_2\)
H source	Mainly \(H_2O\)
O source	Air or \(H_2O\)
Tracer elements
Critical elements	N, P, K; usually deficient in soil; supplied as fertilizers
Framework elements	C, H, O → carbohydrates → cell wall
Protoplasmic elements	N, P, S with C, H, O → protoplasm
Balancing elements	Ca, Mg, K → counteract toxicity by ion balancing

▢ Additional Essential Elements in Some Plants:

Table 1: Additional elements

Element	Found in
Silica	Grasses + diatoms
Sodium	Algae + microbes
Aluminium	Ferns + Lycopodium
Iodine	Marine algae

▢ Special Points:

•
Molybdenum = least required micronutrient
•
Nitrogen derived from mineral + non-mineral sources

▢ Roles of Elements:

Table 1: Specific roles and deficiency symptoms

Element	Absorbed as / Source	Role	Deficiency
Nitrogen / N	Chief source: nitrates of Ca and K	Proteins, nucleic acids, vitamins, hormones, coenzymes, ATP	Stunted growth, lower respiration, chlorosis of older leaves, premature leaf fall
Sulphur / S	Sulphates	Certain proteins, thiamine, biotin, CoA, ferredoxin	Chlorosis of younger leaves
Phosphorus / P	Phosphate	Nucleic acids, cell membrane, certain proteins, nucleotides, phosphorylation reactions	Premature leaf fall
Calcium / Ca	Nitrates + sulphates	Selective membrane permeability, enzyme activation, stem/root apex development, calcium pectate in middle lamella	Disintegration of growing meristem
Magnesium / Mg	\(Mg^{2+}\)	Chlorophyll constituent; ribosomal particle binding for protein synthesis	Chlorosis
Potassium / K	Nitrate + chloride	Photosynthesis, respiration, stomatal movement	Mottled chlorosis, growth inhibition
Iron / Fe	Mostly ferrous form	Cytochrome; ETS, photosynthesis, respiration; chlorophyll synthesis	Chlorosis
Boron / B	Borate	Food translocation	Death of shoot tip, suppressed flowering, stunted root growth, brown heart disease
Manganese / Mn	Oxide	Enzyme activator in Krebs cycle; photolysis of water; chlorophyll + IAA synthesis; ETS reactions	Grey spots in leaves
Zinc / Zn	Foliage absorption also	Tryptophan synthesis → IAA formation	Chlorosis of older leaves; Khaira disease of rice; white bud of maize
Copper / Cu		Enzyme-related functions	Necrosis of tip of new leaves
Molybdenum / Mo		Nodulation in legumes	Fruit formation inhibition; whiptail disease of cauliflower
Chlorine / Cl			Wilting of leaf tip → chlorosis → necrosis

▢ Liebig’s Law of Minimum: Crop yield determined by essential element present in minimum quantity relative to plant demand

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IMPORTANT INSTRUMENTS

Table 1: Instruments and measurements

Instrument	Measures / Demonstrates
Osmoscope	Osmosis demonstration vessel; thistle funnel with egg membrane, potato osmoscope, egg osmoscope
Osmometer	Osmotic pressure / osmosis
Potometer	Rate of transpiration
Porometer	Size of stomata / pore area of stomata
Manometer	Root pressure
Hygrometer	Relative humidity
Psychrometer	Atmospheric humidity + amount of water transpired
Tensiometer	Amount of water in soil
Conductivity meter	Soil salinity
Respirometer	Respiration
Auxanometer	Plant growth
Crescograph	Growth per second
Clinostat	Inclination of curvature due to geotropism

📚

READ AND DIGEST

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Root hairs absorb water when solute concentration is higher in root hairs
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In osmosis, outermost protoplasm layer acts as membrane, not whole protoplast
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Fully turgid cell → suction pressure / DPD / water potential = 0
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Plant cell in water takes water until DPD equalizes inside and outside
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Cell wall permeability shown by movement of water + mineral salts from pericycle into tracheal elements
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Purple cabbage leaves release colour in hot water because heat kills plasmalemma and makes it permeable
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Excess chemical fertilizers kill crops due to exosmosis
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During root water absorption, cell sap water potential is lower than pure water and soil solution
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Mango in concentrated NaCl contracts
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Cotton fibres absorb water by capillarity
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Cut flowers dipped in dilute NaCl reduce transpiration
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Leaves mainly perform photosynthesis + transpiration
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Guard cells of land plants differ from other epidermal cells by having chloroplasts
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Plant cells in distilled water become turgid
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Water potential + osmotic potential of pure water = 0
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Osmotic potential is negative
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Water in plants moves from less negative to more negative gradient
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Solute addition to pure water creates negative water potential
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In girdled plant, root dies first
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Tree girdled up to xylem may survive briefly but dies because sugar cannot move downward
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Girdling not possible in sugarcane because vascular bundles scattered
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Ringing/girdling experiment first performed by Hartig
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Root pressure maximum when transpiration very low and absorption high
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Cohesive force of water due to H-bonds / OH-bonds
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Blotting paper absorbs water by capillary action
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Sunken stomata occur in xerophytes
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Frequency + position of stomata determined by porometer
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Actual atmospheric water vapour content = absolute humidity
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Cereal stomata opening for few hours in day = barley type
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Thin-leaved mesophyte stomata open day + close night = alfalfa type
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PMA reduces transpiration
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Potassium involved in stomatal regulation
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Leaf water potential near zero/positive during guttation
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Leafy twig of mesophyte in water demonstrates transpiration
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Twig in salty water remains fresh longer due to decreased transpiration
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Half leaves removed randomly → transpiration magnitude decreases but flux increases
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PEP carboxylase connected with stomatal opening/closing
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Transpiration highest when soil wet and air dry
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Stomata open during day for gas exchange
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Glycolate induces stomatal opening in presence of oxygen
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Hydroponics = soilless cultivation of plants

Table 1: Processes in plant physiology

Table 1: Diffusion regions

Table 1: Water potential

Table 1: Factors affecting diffusion rate

Table 1: Membrane types

Table 1: Hypotonic, isotonic and hypertonic solutions

Table 1: Endosmosis vs exosmosis

Table 1: Osmotic pressure

Table 1: DPD relationships

Table 1: Pure water effects

Table 1: Types of plasmolysis

Table 1: Imbibition terms

Table 1: Root hair vs lateral root

Table 1: Soil water types

Table 1: Water absorption organs

Table 1: Passive vs active water absorption

Table 1: Active absorption types

Table 1: Water movement systems

Table 1: Passive vs active mineral absorption

Table 1: Passive mineral absorption concepts

Table 1: Active mineral absorption concepts

Table 1: Factors

Table 1: Ringing / girdling experiment

Table 1: Vital theories

Table 1: Root pressure theory

Table 1: Physical force theories

Table 1: Sites of transpiration

Table 1: Transpiration tests

Table 1: Transpiration vs evaporation

Table 1: Internal factors

Table 1: External factors

Table 1: Hydathode

Table 1: Transpiration vs guttation

Table 1: Types of wilting

Table 1: Stomatal structure

Table 1: Stomatal types by distribution

Table 1: Stomatal behaviour

Table 1: Stomatal state

Table 1: Macro and micro elements

Table 1: Element groups

Table 1: Additional elements

Table 1: Specific roles and deficiency symptoms

Table 1: Instruments and measurements

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