Plants Flashcards
(23 cards)
How do rolled leaves help/ hairy leaves xerophytes to reduce water loss
Reduce the surface area for evaporation at the stomata
They trap a layer of water vapour close to stomata which creates a high water vapour potential outside the stomata
This reduces the water vapour potential gradient
Therefore less evaporation of water vapour from leave via stomata
How does a sunken stomata help xerophytes reduce water loss
Traps a layer of water vapour as it isn’t taken away by the wind as easily
Creates a high water vapour potential outside of the stomata
This reduces water vapour potential gradient
So reduces evaporation of water vapour from the leaves
How do needle like hairs reduce water loss in xerophytes
Creates a smaller surface area
So less evaporation of water vapour
How does a dense sponge mesohpyll reduce water loss
Reduces the surface area for evaporation of the water from the vascular bundle into spongy mesophyll
Other adaptions of xerophytes
Thicker waxy cuticle
Less stomata which are closed in the day and found on lower surface of leaves
Long deep roots
How does air spaces in plant tissues help hydrophytes
Allows for buoyancy in water
To allow it to float
Why do hydrophytes have large leaves
To increase the surface area which will increase the rate of photosynthesis as water is not a limiting factor
Why do hydrophytes have roots that grow out of the water
To aid with gas exchange to increase the rate of photosynthesis
Other adaptations of hydrophytes
Lots of stomata and will be open all day, will be found on top surface of leaves
Thinner waxy cuticle
Short root systems to prevent damage by water currents
What are the two components of a vascular bundle
Xylem- inner side
Phloem- outer side
Role of xylem
To transport water and mineral ions up the plant (transpiration stream)
Supports the plant due to lignified walls
Dead hollow tubes as no organelles in tube allowing smooth flow of water
Structure of the xylem
Cell walls are completely broken down to form a hollow tubes
Spirals/rings of lignin in cell wall- provides mechanical strength
Not lignified pits-allows water and mineral ions to move out to surrounding cells if needed
Xylem parenchyma- stores food and tannins (bitter chemicals that prevent herbivores)
Function of phloem
Transports sugars (sucrose) up and down the plant from the source to the sink by translocation
Alive- can do active transport for translocation
Structure of phloem
Sieve tube elements- involved in translocation
Companion cells- life support system that keeps phloem alive
Lots of mitochondria
Involved in translocation
Plasmodesmata- links sieve tube elements to companion cell
Definition of transpiration
The loss of water vapour by evaporation through the stomata
What is the transpiration stream
The continuous movement of water and mineral ions from the roots up the xylem to the leaves
What is cohesion
Hydrogen bonding between water molecules, so when one molecule is pulled up it also pulls another water molecule with it
Allows for cohesion tension theory
What is adhesion
Hydrogen bonding between water and the xylem walls
Allows for capillary action
Transpiration steps
- Due to water loss in leaves they have a low water potential and the roots have a high water potential
- Water moves from the roots to the leaves by osmosis down a water potential gradient
- Caspian strip is made out of starch and blocks water
It converts to glucose which is then used in the active transport of mineral ions from soil - This lowers the xylem’s water potential so more water moves in which creates a high hydrostatic pressure
- Due to evaporation at the leaf there is low hydrostatic pressure so water moves from the xylem to the leaf by mass flow
5 factors that affect transpiration
Light intensity
Temperature
Humidity
Air movement
Water availability
How does an increase in humidity affect transpiration
Decreases transpiration
As there is a lower water vapour concentration gradient so less water will diffuse from stomata
How does an increase in light intensity affect transpiration
It increases rate of transpiration
As there is more photosynthesis so more gas exchange will occur, resulting in more stomata opening
Describe potometre
Estimates the transpiration rate
- Cut a leafy shoot from the plant and remove the ends underwater
- Lower potometre into sink of water to fill it and loose any air bubbles
- Place shoot in bung ensuring a tight seal
- Lift potometre and let one air bubble enter at the free end and then place free end back into water
- Allow plant to equilibriate
- Then measure the movement of the air bubbles during a set period of time
