Osmosis Flashcards
What is the definition of osmosis?
The movement of WATER molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane
Describe what a cell would look like if it was turgid
The cell would be filled with water which pushes the membrane against the cell wall
What is the role of the plant cell wall?
Prevents too much water from entering stops the cell from bursting. This ensures the plant stays upright giving the plant support
Explain why a plant cell would become turgid
- This occurs if there is a higher concentration of water outside the cell than inside the cell
-Water moves into the cell
What does plasmolysed mean?
When the cell loses too much water and causes it to shrink in size
What would a plasmolysed cell look like?
The cell membrane would pull away from the cell wall and the vacuole would shrink in size
Why can red blood cells burst if too much water enters them?
As they do not have a cell wall and cannot limit the volume of water that enters
What is the key word when a red blood cell fills with water and eventually bursts?
Cell lysis
What piece of equipment measures the rate of water uptake?
A potometer
Describe how you would set up a bubble potometer
- Water is taken up by the shoot and it evaporates from the leaves
-As water evaporates the bubble will moves towards the shoot - This allows us to calculate the rate of water uptake (distance the bubbles moves / time)
-The reservoir (or syringe) allows us to rest the practical and repeat it again
What is water used for in a plant?
photosynthesis, support (turgor) or transport
What is the definition of transpiration?
The evaporation of water from the mesophyll cells, followed by the diffusion through the air spaces and out of the stomata
What factors increase transpiration?
increased wind speed, increased temperature and decreased humidity
Explain why plants close their stomata in the dark
To reduce water lost from the plant by transpiration
Why does a warmer temperature speed up transpiration?
The water molecules have more kinetic energy so they evaporate faster
Why does a higher wind speed, speed up transpiration?
The wind moves the evaporating water away from the stomata faster. This creates a steeper concentration gradient of moisture.
Why does transpiration slow in periods of darkness?
Plants close their stomata in the darkness which reduces water loss
What will happen to the number of stomata as the surface area of the leave increases? How does that affect transpiration?
The number of stomata will increase and therefore the rate of transpiration will be higher
Explain why higher levels of humidity slows down the rate of transpiration.
Humid conditions slow down the evaporation of water molecules. Therefore, there is a decrease in the moisture concentration gradient between the leaf and the air.
How do you calculate the rate of transpiration in the mass potometer?
Distance bubble moves / time
How do you calculate % change in mass in the osmosis potato cylinder practical
Change / initial mass x 100
How could you work out the concentration of the potato cylinder?
This is the concentration which causes 0% change in mass. There is no net movement of water
Why does increased humidity slow the rate of transpiration?
There is a less steep concentration gradient
What is the term for a plant cell that has lost lots of water?
Plasmolysed
What is the term for a plant cell that has gained lots of water?
Turgid
Where does water diffuse out of the leaf?
Stomata
What happens to the stomata at night and why?
Stomata close to stop water being lost by transpiration
