Water absorption in plants

Views:
 
Category: Education
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

PowerPoint Presentation:

ABSORPTION OF WATER KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Soil Water : Hollard : Total soil water Chesard : Available to plants Echard : Non available to plants Types of soil water: KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Stages of Water Holding KIRTIVARDHAN, ACHF, NAU, Gujarat

Water Moves through soil by bulk flow:

Water Moves through soil by bulk flow As water moves from soil into root the spaces fill with air This reduces the flow of water Permanent wilting point At this point the water potential ( y w ) in soil is so low that plants cannot regain turgor pressure There is not enough of a pressure gradient for water to flow to the roots from the soil This varies with plant species KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Root : Absorbing organ KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Notice how the growing zone has no root hairs or lateral roots! Zone of Maturation - cell differentiation Protoderm Ground Meristem Provascular Zone of Cell Elongation - cell expansion Zone of Cell Division - new cells by mitosis Root Cap - penetration, padding Structure involved in water absorption KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

From the epidermis there are two pathways in which water can flow : 1: Apoplast pathway: Water moves exclusively through cell walls without crossing any membranes The apoplast is a continuous system of cell walls and intercellular air spaces in plant tissue 2: Transmembrane and symplast pathway: Water sequentially enters a cell on one side, exits the cell on the other side, enters the next cell, and so on. The symplast consist of the entire network of cell cytoplasm interconnected by plasmodesmata KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Water moves in root Apoplast Symplast Transmembrane Mechanism of movement KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Active absorption Water absorption Passive absorption:- KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Osmotic absorption Epidermis Cortex Casparian Strip Pericycle Endodermis Phloem Xylem Passage cell Imbibition of soil water by hydrophilic cell wall O.P Cell sap > O.P soil water DPD in root hair becomes higher Water from cell wall enter into them thro’ membrane by osmotic diffusion As a result, O.P, DPD of root becomes lower and T.P increased Now the cortical cell adjacent to root hair have higher O.P, DPD in comparison to root hair by osmotic diffusion Steps involved KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Osmotic absorption Epidermis Cortex Casparian Strip Pericycle Endodermis Phloem Xylem Passage cell Likewise, water moves by osmotic diffusion and reaches endodermis Endodermis water moves thro’ passage cell (because casparian cell) Now water reaches pericycle, pericylce becomes turgid and their DPD is decreased Last step, water is drawn into xylem from turgid pericycle cells (protoxylem in contact) Pressure is developed in the xylem of root by water entry – Root pressure KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Active non-osmotic absorption O.P of soil water > O.P of cell sap Non-osmotic – against conc. Gradient – energy is required Evidence Factors reducing respiration also decreases water absorption Poisons –metabolic activity –retard water absorption Auxin –increase metabolic activity of cell stimulate absorption of water II. Passive absorption of water Transpiration creates tension in water in the xylem of the leaves Tension is transmitted to water in xylem of root thro’ xylem of stem and water rises upward to reach transpiring surface Hence soil water enters cortical cells thro’ root hairs to reach xylem of roots to maintain the supply of water. The force for entry of water in leaves is due to rapid transpiration and root cells remain passive KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Root pressure serve as best evidence for active absorption. ? Root pressure not present in Gymnosperms Root pressure Not observed in fast transpiring plants Amount of water exuded from cut ends not equal to water lost due to transpiration. KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

External factors affecting absorption of water Available soil water Amount of water Capillary water Soil aeration Concentration of Soil Solution High salt concentration O.P – Problematic soil Soil air Aeration in soil High CO 2 retard root respiration Growth of root hair Water logged soil – Physiologically dry Soil Temperature Up to 30% favours Above 30% and low temp Low temp – Viscosity of water and protoplasm is increased Permeability of cell membrane is decreased Metabolic activity is decreased KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Ascent of sap The phenomenon of ascending of absorbed water against gravitation through xylem is called ascent of sap. KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Mechanism of ascent of sap In small trees and herbaceous plants, the ascent of sap can be explained easily, but in tall trees like Eucalyptus and conifers reaching a height of 300- 400 feet), where water has to rise up to the height of several hundred feet, To explain the mechanism of Ascent of sap, a number of theories have been put forward 1. vital theory 2. root pressure theory 3. physical force theory 4. transpiration pull and cohesion of water theory KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Vital theories According to vital theories, the ascent of sap is under the control of vital activities in the stem 1. According to Godlewski (1884) – Ascent of sap takes place due to the pumping activity xylem tissues which are living 2. According to Bose (1923) – upward translocation of water takes place due to pulsatory activity of the living cells of the inner most cortical layer just outside the endodermis KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Root pressure theory root pressure which is developed in the xylem of the roots can raise water to a certain height but does not seem to be an effective force in ascent of sap due to the following reasons Magnitude of root pressure is very low (less than 0.1 Mpa) Even in the absence of root pressure, ascent of sap continues For example, when leafy twig is cut under water and placed in a beaker full of water it remains fresh and green for sufficient long time KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Water transport through Tracheids and Vessels Tracheids : Elongated spindle-shaped cells –arranged in overlapping vertical files. Water flows between them via pits – areas with no secondary walls and thin porous primary walls Vessel elements : Shorter & wider. The open end walls provide an efficient low-resistance pathway for water movement. Perforation plate forms at each end – allow stacking end on to form a larger conduit called a vessel At the end there are no plates- communicate with neighboring vessels via pits KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Why xylem suited to carry water from roots to the leaves? Water movement require less pressure in xylem than living cells. Xylem are adopted for the transport of water under tension. Air bubbles can form in xylem, air can be pulled through microscopic pores in the xylem cell wall Gas bubbles can not easily pass through the small pores of the pit membranes . Xylem are interconnected, so one gas bubble does not completely stop water flow Water can detour blocked point by moving through neighboring, connected vessels. KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Transpiration pull and cohesion theory (cohesion tension theory) The theory was originally proposed by Dixon and Jolly (1894) Water vapours diffuse out from the intercellular space to the atmosphere. Evaporation of water vapours from thin walled mesophyll cells (leaf) into the intercellular space. Reduced water content in the cell Increased osmotic potential in cell sap Movement of water from adjacent cell by osmosis Movement of water from xylem to adjacent cell KIRTIVARDHAN, ACHF, NAU, Gujarat

Water evaporation in the leaf affects the xylem:

Water evaporation in the leaf affects the xylem The tensions needed to pull water through the xylem are the result of evaporation of water from leaves. Water is brought to leaves via xylem of the leaf vascular bundle, which branches into veins in the leaf. From the xylem, water is drawn in to the cells of the leaf and along the cell wall. KIRTIVARDHAN, ACHF, NAU, Gujarat

Water evaporation in the leaf affects the xylem:

Water evaporation in the leaf affects the xylem Transpiration pull , which causes water to move up the xylem begins in the cell walls of leaf cells Water adheres to cellulose and other hydrophilic wall components. Mesophyll cells within leaf are in direct contact with atmosphere via all the air spaces in the leaf KIRTIVARDHAN, ACHF, NAU, Gujarat

Water evaporation in the leaf affects the xylem:

Water evaporation in the leaf affects the xylem So, negative pressure exists in leaves- cause surface tension on the water As more water is lost to the atmosphere – the remaining water is drawn into the cell wall As more water is removed from the wall the pressure of the water becomes more –ve This induces a motive force to pull water up the xylem KIRTIVARDHAN, ACHF, NAU, Gujarat

Water movement from leaf to atmosphere:

Water movement from leaf to atmosphere After water has evaporated from the cell surface of the intercellular air space diffusion takes over. So: the path of water Xylem Cell wall of mesophyll cells Evaporated into air spaces of leaf Diffusion occurs – water vapor then leaves via stomatal pore Goes down a concentration gradient . KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

PASSIVE ASCENT OF SAP Transpiration creates tension in water in the xylem of the leaves Tension is transmitted to water in xylem of root thro’ xylem of stem and water rises upward to reach transpiring surface Hence soil water enters cortical cells thro’ root hairs to reach xylem of roots to maintain the supply of water. The force for entry of water in leaves is due to rapid transpiration and root cells remain passive KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

In the intact plant, water is brought to the leaves via the xylem of the leaf vascular Bundle From the xylem, water is drawn into the cells of the leaf and along the cell walls negative pressure that causes water to move up through the xylem develops at the surface of the cell walls in the leaf. Initially water evaporates from a thin film lining these air spaces. As water is lost to the air, the surface of the remaining water is drawn into the interstices of the cell wall where it forms curved air–water interfaces As more water from the wall radius of curvature of the air–water interfaces decreases and the pressure of the water becomes more negative KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Transpirational Pull KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

KIRTIVARDHAN, ACHF, NAU, Gujarat

PowerPoint Presentation:

Thank You KIRTIVARDHAN, ACHF, NAU, Gujarat