Studied by 2 people
What does the waxy cuticle do?
Prevents water from evaporating and acts as a protective layer
What does the upper epidermis do?
It's thin and transparent
↳ allows light to enter
What does the palisade mesophyll do?
Contains chloroplasts
↳ absorbs more light to maximise photosynthesis
What does the spongy mesophyll do?
Contains pockets of air
↳ Increases surface area to volume ratio for the diffusion of gases
What does the lower epidermis contain?
Guard cells
Stomata
What do guard cells do?
Absorbs or loses water to close and open the stomata
↳ controls gas exchange and water
What does the stomata do?
Where gas exchange takes place
Why is the stomata closed at night?
There's no sunlight for photosynthesis
No need for carbon dioxide
SO they're closed to prevent water loss
What is transpiration?
The movement of water in a plant
The loss of water from evaporation
Describe the process of transpiration
Water is absorbed by the roots from the soil by osmosis
Water travels through the xylem helped by:
↳ Cohesion (Water molecules sticking together) and adhesion (Water molecules sticking to the walls) this creates a pulling force which drags the water upwards (Transpiration pull)
Water on the surface of the spongy mesophyll and palisade mesophyll evaporates and diffuses out of the leaf
What are the factors affecting transpiration?
Light Intensity: More light causes stomata to open, increasing transpiration.
Temperature: Higher temperatures speed up evaporation and diffusion.
Wind speed : Wind removes water vapor from the leaf’s surface, maintaining the diffusion gradient.
Humidity: Lower humidity reduces the concentration of water molecules outside the leaf; diffusion of water from the leaf increases
What can we use to measure transpiration
Potometer- time taken for a bubble in the tube to move a set distance
What is translocation?
The movement of dissolved sugars and amino acids (cell sap)
Describe the process of translocation
Phloem cells are connected end to end by sieve plates which allow the flow of sugars
There are companion cells which contain mitochondria to provide energy for the active transport of sugars
Sugars can move in either direction depending on the plant's needs
Why are guard cells and stomata important?
They take in CO2 for photosynthesis
They prevent water loss
