Mass transport in Plants Flashcards
What is transpiration?
The loss of water vapour from the stomata by evaporation.
How does light intensity affect the rate of transpiration?
More light intensity the faster the rate of transpiration. This is because the light stimulates stomata opening therefore a larger surface for evaporation.
What is the theory that explains water transport in the xylem?
The cohesion-tension theory.
What is cohesion in water molecules?
Water is a dipolar molecule therefore hydrogen bonds form between the slightly positive hydrogen and slightly negative oxygen. Therefore water can travel up the xylem in a continuous water column.
What is adhesion?
Adhesion of water is when water sticks to other molecules. Water adheres to the xylem walls.
What is root pressure?
As water moves into the roots through osmosis it increases the volume of liquid in the roots increasing the pressure. This creates a ‘push’ effect (positive pressure).
What is the first step in the cohesion tension theory?
As water evaporates through the stomata (transpiration) more molecules are drawn behind as a result of cohesion. This is called the transpiration pull.
What does a potometer do?
A potometer measures the uptake of water from a plant. The water uptake is proportional to transpiration so is used as a measure of the rate of transpiration.
Why is the plant cut underwater when using a potometer?
To prevent any air from entering and breaking the water column.
What two cells does the phloem tissue hold?
Sieve tube elements and companion cells (provides ATP for active transport of organic substances).
Where do organic substances move from and to in mass flow hypothesis?
The source to the sink.
Describe the translocation of sucrose from the source to the sieve tube element:
Photosynthesis creates sucroses. High concentration of sucrose, therefore, moves to companion cells through facilitated diffusion. Active transport of H+ ions from companion cells to spaces in the cell wall. Creates concentration gradient therefore H+ ions move into sieve tube element through carrier proteins. Co-transport with sucrose.
Describe the translocation of sucrose in the sieve tube element:
An increase of sucrose concentration in sieve tube element lowers water potential. Water enters from xylem through osmosis. Increases water volume so hydrostatic pressure increases causing liquid to move towards sink.
