2101 - Water Movement in Plants Flashcards
Diffusion - Definition
Liquid or Gas
The movement of one substance from a region of High Concentration to one of Lower Concentration
Ink drop in beaker
Osmosis - Definition
Liquid
The movement of water from a solution of low concentration to one of higher concentration across a semi-permeable membrane.
(or high concentration of water to Low concentration of water)
Capillary Action - Definition
The movement of water within the spaces of a porous material due to forces of adhesion, cohesion and surface tension
Diffusion
Physical process (no energy expenditure).
The movement of a substance from an area of High concentration to an area of low concentration.
The movement of solute DOWN a concentration gradient to a point where solute molecules are equally distributed.
Can occur in the plant:
Liquid - Cell walls
Gaseous - From Cell walls to the Stomatal air space. And then from there to the outside air.
Osmosis
Net movement of water molecules through a semi-permeable membrane.
From Low Solute to High Solute. Water moves in the direction that tends to equalise the solute concentrations between the two sides of the Semi Permeable Membrane.
Solute molecules are too big for SPM, only water can travel across.
Osmosis - Plasmolysis
An excess of fertiliser in the soil will change the concentration Gradient, so the soil becomes an area of Higher Solute than the Plant cell cytoplasm.
Therefore Osmosis will occur, drawing water out of the plant cells into the soil.
This is called PLASMOLYSIS. Resulting in temporary wilting and potential death of plant cells and eventually the plant.
Osmosis cont…
Osmosis - occurs across the membranes of Root Hairs.
Water is passively drawn by osmosis into the plant cells because their Cytoplasm is more concentrated than the plant soil.
Osmotic pressure - is the main cause of support in non-woody plants. Raises the Turgor pressure exerted against the cell walls, which will become balanced.
Osmotic pressure = Cell Wall Resistance
Also responsible for plant growth. As sugars are more present in growing points, thereby causing water to move there by Osmosis and driving cell expansion and growth.
Semi-Permeable
Permeable to some molecules but not others. Water not Solutes. Passive Process, no energy expenditure.
Selevtively-Permeable
Membrane can choose which molecules pass and which do not cross. Active process controlled by the plant, expends energy, allows plant to control which nutrients and other solutes are absorbed.
Semi/Selectively Permeable
Plant Membranes can be both semi-permeable and selectively-permeable
Capillary Action
Movement of water within the pores of a porous material due to forces of:
Adhesion - Hydrogen bonding between unlike molecules (water and cell walls)
Cohesion - Hydrogen Bonding between like molecules. (Water)
Surface Tension - Less adhesion to air than to cohesion together
Where do these forces take place?
Osmosis - Cell Membrane
Diffusion - Into and from Cell Wall
Capillary Action - Xylem
Transpirational Pull
Process where water is drawn up the roots into the stem and up into the leaves by the force created by Transpiration.
Creates a continuous ‘pipeline’ of water in Xylem vessels.
Transpiration
The loss of water vapour from the leaves of the plant. Greatest loss is through the stomata, though some loss from the Leaf Lamina (limited by Waxy Cuticle).
Water Enters Root by…
Diffusion - through the (permeable) cells walls in the root epidermis and cortex parenchyma tissue.
Cell Walls are permeable allowing water and solutes to pass as far as the Caparian Strip.
Osmosis - across the (semi permeable) cell membranes of epidermal root hairs and cortex parenchyma cells. Once inside Water and Solutes travel intercellularly via the Plasmodesmata.
