Transport in plants | 8 Flashcards
Describe the transport system
Made up of xylem and phloem vessels , which transports nutrients from roots to stem and leaves.
Describe the Xylem
Used to transport water throughout the plant from the roots (Transpiration)
Made from hollowed out dead cells with ends removed to make a tube for water to pass through
Describe the Phloem
Made of living cells
Used to transport sugars and food nutrients
(translocation)
How does Water uptake occur
Water is taken up by root hair cells via osmosis
Water moves into root cortex cells by osmosis and then enters the xylem vessel where it goes to the stem and leaves
At the leaf it diffuses into mesophyll cells where it is used in metabolic reactions like photosynthesis
How are root hair cells adapted for efficient water intake
Large Surface area - increases the rate of osmosis into the root, as well as increasing the rate of ion uptake by active transport.
Thin wall - so the diffusion distance is shortened.
Transpiration
Transpiration is the loss of water vapour from the mesophyll cell surface due to evaporation.
The water vapour then exits the plant via the stomata.
Water helps maintain plant structure by keeping cells turgid , If the plant loses too much water which is not replaced, it begins to wilt as water moves out of cells and turgor pressure decreases.
To limit water loss, the plant closes the stomata to prevent water vapour diffusing out.
Transpiration pull
Water molecules are drawn up the xylem by transpiration pull (not osmosis).
Water molecules are cohesive, meaning they stick together. This means that as the water evaporates at the leaf and diffuses out of the stomata, more water is drawn up the plant from the roots.
Rate of transpiration
Temp high = rate high
Humidity high = rate low
Why do the factors of transpiration affect it the way they do
The rate of transpiration depends on the temperature and humidity.
On warm days the temperature is higher, so water evaporates more easily, therefore there is more diffusion of water vapour out of the plant, so the rate of transpiration is high.
A high humidity, however, decreases the rate of transpiration as the concentration gradient of water vapour between the inside and outside of the plant is comparatively low, so diffusion out of the plant is slower.
Translocation
Translocation occurs in the phloem vessels and involves the transport of amino acids and sucrose
Sources in translocation
Area where ammino acids and sucrose are produced is called sources
Sinks in translocation
Regions where ammino acids and sucrose are stored or used for respiration and growth are called sinks
Materials go from source to sink
How does sucrose and amino acids get produced , transported and used
Sucrose and amino acids are produced in the leaves.
Then they get transported to the roots for storage.
They are later transported to regions where they are used in respiration and for growth.
Some parts of the plant, such as the leaves, can act as both source and sink within a plant’s life as they synthesize molecules and use them in metabolic reactions.
