Topic2.1 - Osmosis + Plant Transport Flashcards
Definition of osmosis
Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution, across a selectively permeable membrane.
What is a selectively permeable membrane?
Has holes in it that permit water molecules through but are too small to allow larger molecules through
Example of selectively permeable membrane
Visking tubing
Plant and animal cell membranes
Dilute solutions have a … concentration of water molecules.
High
Concentrated solutions have a … concentration of water molecules.
Low
Function of plant cell wall
Offers support and protection
Plant cells in high concentration
Water has left the cell by osmosis bc the solution surrounding the cell is more concentrated than the cytoplasm inside the cell.
The cytoplasm has pulled away from the cell wall: the cell is plasmolysed.
Sugar solution fills space between membrane and wall.
Plants cells in a medium concentration
The cell cytoplasm is at the same concentration as the solution surrounding the cell.
There is no net movement of water.
Plant cells in low concentration
Water has entered the cell by osmosis. The cytoplasm is more concentrated than the very dilute surrounding solution.
The cytoplasm is pushing against the cell wall: the cell is turgid.
Animal cells in high concentration
Water has left the cell by osmosis bc the solution concentration outside the cell is more than the concentration in the cell.
The cell becomes crenated (crenation) as the cytoplasm pulls away from the cell membrane.
Animal cells in a medium concentration
The cell cytoplasm is at the same concentration as the solution surrounding the cell.
There is no net movement of water.
Animal cells in low concentration
Water has entered the cell by osmosis, pushing the cytoplasm against the cell membrane. Bc the cell has no cell wall, it bursts as it becomes turgid.
The cell is destroyed. This is called lysis.
Plants need water for…
- support: when plant cells absorb water they become turgid
- transport: water is a solvent, many substances dissolve into water - this allows easy transport from one part of the plant to another
- photosynthesis: water is a reactant
- transpiration: a process that results from the evaporation of water from the surface of the leaf - important as it keeps the water moving through the plant
Definition of transpiration
Transpiration is the evaporation of water from mesophyll cells followed by diffusion through air spaces and the stomata.
Four stages of transpiration
(i) Water diffuses from the soil into the roots. Plants are covered in tiny projections called root hair cells. These structures increase the SA.
(ii) Water travels up the stem in the xylem. It diffuses from an area of higher water concentration to an area of lower water concentration.
(iii) Water travels through veins into the leaves. It then diffused out of the veins into cells and air spaces. From these spaces water evaporates through the stomata, into the air.
(iv) The loss of water through transpiration in the leaves sets up a concentration gradient, continuously pulling water from the soil into all parts of the plant.
