Transport in Plants (Edexcel GCSE Biology)
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Define the term transpiration.
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Define the term transpiration.
Transpiration is the loss of water vapour from the leaves of plants by evaporation. This drives the upward movement of water and mineral ions through plants.
True or False?
Transpiration results in the upward movement of sucrose and amino acids.
False.
Transpiration drives the upward movement of water and mineral ions in the xylem vessels.
Sucrose and amino acids move in the phloem by translocation.
How are water and dissolved minerals transported through plants?
Water and dissolved minerals are transported upwards in the xylem. Water is drawn upwards in a continuous column to replace the water lost by evaporation in the leaves.
Describe the structure of stomata.
The stomata are pores in the leaf surface, surrounded by two guard cells.
What is the role of the stomata and guard cells in transpiration?
The stomata and guard cells allow plants to regulate the volume of water lost during transpiration. When water availability is low the guard cells can close, reducing transpiration.
By what process does water vapour exit the leaf air spaces?
Water vapour exits the leaf air spaces by the process of diffusion.
Which environmental factors can affect the rate of transpiration in plants?
Factors that affect the rate of transpiration include:
light intensity
wind speed / air movement
temperature
Transpiration rate can also be affected by humidity.
What happens to transpiration rate as light intensity increases?
As light intensity increases the transpiration rate increases.
True or False?
Transpiration rate increases at high light intensity because the stomata close.
False.
Transpiration rate increases with light intensity because the stomata open at high light intensities to enable gas exchange for photosynthesis.
True or False?
Transpiration rate increases as wind speed increases.
True.
As wind speed increases the transpiration rate increases.
Why does transpiration occur faster on a windy day?
Transpiration is faster on a windy day because wind blows water vapour away from the surface of leaves, maintaining a water vapour concentration gradient between the inside and the outside of leaves.
What happens to transpiration rate as temperature decreases?
As temperature decreases the transpiration rate decreases.
True or False?
Transpiration rate increases at higher temperatures due to the increased kinetic energy of molecules.
True.
At higher temperatures water molecules have more kinetic energy and are more likely to diffuse out via the stomata.
How can the piece of equipment below be used to measure transpiration rate?
A bubble potometer works to measure transpiration rate as follows:
a bubble is introduced into a tube containing a cut plant stem
as the plant transpires water is pulled up the stem, causing the bubble to move
the distance the bubble moves in a given time indicates the transpiration rate
How can the results of a potometer investigation be used to calculate transpiration rate in a plant shoot?
The results of a potometer investigation can be used to calculate transpiration rate as follows:
rate of transpiration = distance moved by bubble
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timeDefine the term translocation.
Translocation is the movement of dissolved sucrose through phloem tissue.
Why does phloem tissue contain living cells with many mitochondria?
The living cells in phloem tissue release energy from their mitochondria. This allows them to move sucrose into the phloem by active transport so that translocation can occur.