Why do plants need a transport system?
They are too large for materials to simply diffuse in and out and meet the demand of the plant
Give three examples of a plant organ
Where is sucrose transported to?
The sinks e.g. roots
This is where the sucrose is converted to starch or other molecules for storage
What causes the stomata to open?
The guard cells absorb water
This causes the guard cells to become turgid
This causes the stomata to open and widen
What is the role/function of the palisade mesophyll layer in the leaf?
These cells are specialised to contain many chloroplasts
Hence they carry out photosynthesis
What is the role/function of the stoma in the leaf?
- Stomata can widen and narrow to control how much gas exchange occurs i.e. intake of carbon dioxide and loss of oxygen
- and to control how much water vapour is lost from the leaf during transpiration
Summary: Control gas exchange and water vapour loss
Which direction does xylem transport materials?
ONLY up the plant i.e. one way movement
From the roots to the stem and the leaves
What is the role/function of the air spaces in the leaf?
Site for gas exchange:
a) oxygen diffuses out of the mesophyll cells into the air spaces
b) carbon dioxide diffuses from the air spaces into the mesophyll cells
Which process of transport uses phloem tissue?
How does transpiration take place?
Hint: there are 3 key stages
1. Water vapour evaporates out of the leaf through the stomata
2. This generates a transpiration pull - which pulls water up through the plant in the xylem
3. The water that is lost from the base of the plant is then replaced as root hair cells absorb more water from the soil by osmosis
What is the role/function of the guard cell in the leaf?
Specialised cells that can take in water or lose water by osmosis
Depending on how much water they contain they can open and close pores (stomata)
Control gas exchange and water vapour loss
What assumption is made when using a potometer to measure the rate of transpiration?
That the rate of water vapour loss from the plant is the SAME as the rate of the water uptake by the plant
What causes transpiration?
Transpiration is a side effect of photosynthesis
When the plant is photosynthesising it opens its stomata to allow carbon dioxide to diffuse in
This then allows the water vapour in the air spaces of the leaf to diffuse out causing the transpiration stream
What materials does xylem transport?
Water and dissolved mineral ions
How does the water vapour exit the leaf?
Remember water vapour is a gas!
Describe and explain how root hair cells adapted for the uptake of mineral ions
Many mitochondria are present in each root hair cell
The mitochondria produce ATP
The ATP can then be used/broken down to release energy
Thsi energy is used for the active transport of mineral ions into the cell
What conditions cause the rate of transpiration to INCREASE?
Faster wind speed
Lower air humidity (dier air)
What materials does phloem transport?
Sucrose (a specialised carbohydrate made from glucose)
Where is the xylem and phloem located in plants?
In vascular bundles
What is the role/function of the phloem in the leaf?
Specialised cells forming a tissue responsible for transporting dissolved sugars up and down the plant
Located in the vascular bundles (veins)
What causes the stomata to close?
The guard cells lose water
This causes the guard cells to become plasmolysed
This causes the stomata to narrow and close
What is the main role of stomata?
To allow gas exchange between the leaf the atmosphere
How is the rate of transpiration usually investigated in a laboratory?
Using a potometer
Give 4 key features of xylem
- The cells are dead
- The cells are hollow (no cytoplasm)
- The cells have lignin around them (to make them waterproof and strengthen the cell)
- The cells are joined end to end to form continuous hollow columns
Where is sucrose transported from?
The source i.e. the leaves (where the sucrose is made)
What is the role/function of the upper epidermis in the leaf?
Specialised cells which are thin and flat It is transparent to enable light to pass through them easily to reach the palisade mesophyll tissue
What 3 gases diffuse in and out of the leaf? For each gas state which direction it diffuses.
Oxygen - diffuses out of the leaf
Carbon dioxide - diffuses in to the leaf
Water VAPOUR - diffuses out of the leaf
Why is it incorrect to say a potometer measures the rate of transpiration?
The potometer doesn't actually measure the amount of water vapour that is lost from the plant
Instead it actually measure the volume of water taken up by the plant
How do water molecules move through the xylem during transpiration?
As a continuous column of water molecules
What is the role/function of the chloroplast in the leaf?
Site where photosynthesis occurs
Chloroplast contain a special pigment called chlorophyll that is essential for photosynthesis