Plant Water Relation — Class 12 Maharashtra HSC Biology revision notes
A 6-page visual revision sheet for Plant Water Relation, written for Class 12 Maharashtra HSC Biology. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Plant Water Relation in one look
a root hair's three-step pull, and the tension it hands all the way up to the topmost leaf
Water, the elixir of life
- water is 90 to 95% of most plant cells and tissues, and keeps cells turgid
- best solvent, a neutral pH, pure, inert compound; transport medium for minerals/food, and all biochemical reactions
- high specific heat, heat of vaporization/fusion make it a thermal buffer, via hydrogen bonding
- high adhesive/cohesive forces plus surface tension let it rise in capillaries: basis of sap's ascent
Root, the water absorbing organ
- terrestrial roots absorb liquid soil water; epiphytes (orchids) absorb air vapour via epiphytic roots' velamen
- the zone of absorption carries unicellular hair-like extensions of epidermal (epiblema) cells, the root hairs
- root hair: 1-10 mm, colourless, unbranched, ephemeral; large vacuole, thin cytoplasm, wall pectin outside/cellulose inside
- cell wall is freely permeable; plasma membrane is selectively permeable, enabling osmosis next
Imbibition, step one
- imbibition: swelling of hydrophilic colloids by adsorption of water, no solution forms
- imbibant: the adsorbing substance (root hair wall: pectic compounds, cellulose); imbibate: the water taken up
- water moves along a concentration gradient until equilibrium; visible in soaking seeds, swelling raisins, kneading flour
- explains why wooden doors swell and jam shut in the rainy season
Diffusion, step two
- movement of ions/atoms/molecules from higher to lower concentration, driven by kinetic energy, continuing until equilibrium
- diffusion pressure (DP) of pure solvent is always more than DP of solvent in a solution
- Diffusion Pressure Deficit (DPD) (B.S. Meyer, 1938): DP of pure solvent minus DP of solution
- colloquially a cell's "thirst"; DPD is now called water potential
- wall water's DP exceeds the cell sap's, so it diffuses in first, to the wall-membrane interface
Page 1 of 6. The full sheet, all 6 pages, opens free in the app.
What this Plant Water Relation sheet covers
- Water, the elixir of life
- Root, the water absorbing organ
- Imbibition, step one
- Soil water, four kinds
- Diffusion, step two
- Osmosis, step three
- The DPD relation
- Water potential (ψ)
- One root hair's three-step intake
- Imbibition
- Diffusion
- Osmosis
- Water potential falls inward
- Plasmolysis and deplasmolysis
- Path of water across the root
- Apoplast (non-living)
- Symplast (living)
- Passive vs Active absorption
- Passive absorption
- Active absorption
- Root pressure
- Three theories of ascent of sap
- Root Pressure (Vital) theory
- Capillarity (physical force) theory
- Cohesion-Tension theory
- Cohesion-tension in detail
- Transport of minerals
- Transport of food: source and sink
- Munch's Pressure Flow (Mass Flow) Hypothesis
- Vein loading
- Mass flow
- Vein unloading
- Transpiration, water lost as vapour
- Transpiration, three routes
- Leaves by stomatal distribution
- Epistomatic
- Hypostomatic
- Amphistomatic
- Stomatal apparatus and its opening
- A dicot stoma, open and closed
- Two theories of stomatal movement
- Starch-sugar interconversion (Steward, 1964)
- Proton transport theory (Levitt, 1974)
- Why transpiration matters
- Abbreviations
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Biology chapter by chapter against your real exam dates and free hours, and when the plan reaches Plant Water Relation the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.
More Biology Class 12 revision notes
- Biodiversity, Conservation and Environmental Issues
- Biotechnology
- Control and Co-ordination
- Ecosystems and Energy Flow
- Enhancement of Food Production
- Human Health and Diseases
- Inheritance and Variation
- Molecular Basis of Inheritance
- Organisms and Populations
- Origin and Evolution of Life
- Plant Growth and Mineral Nutrition
- Reproduction in Lower and Higher Animals
- Reproduction in Lower and Higher Plants
- Respiration and Circulation