7.2 Transpiration & Translocation (Cambridge (CIE) O Level Biology): Flashcards
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Define transpiration.
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Define transpiration.
The loss of water vapour from the leaves of plants.
From where does water evaporate during transpiration?
From the surface of the leaf mesophyll cells, into the air spaces in the leaf.
Through which structures does water vapour leave the leaf?
Through the stomata.
By which process does water vapour leave the leaf through the stomata?
By diffusion.
State the functions of transpiration in a plant.
Transpiration:
transports mineral ions
provides water to keep cells turgid to support the plant
provides water for photosynthesis
keeps the leaves cool
In which vessels does water travel from the roots to the leaves?
In the xylem vessels.
During transpiration, water evaporates from the leaf mesophyll cells and out of the leaf through the stomata.
During transpiration, water evaporates from the leaf mesophyll cells and diffuses out of the leaf through the stomata.
Transpiration is the loss of from the leaves of plants.
Transpiration is the loss of water vapour from the leaves of plants.
True or False?
Transpiration helps to keep the leaves of a plant cool.
True.
The evaporation of water from the leaves during transpiration helps to keep the leaves cool.
True or False?
Water vapour leaves the leaf by osmosis through the stomata.
False.
Water vapour leaves the leaf by diffusion through the stomata.
Why does transpiration help to support the structure of a plant?
It provides water that keeps the cells turgid, which helps to support the structure of the plant.
Define a potometer.
A piece of apparatus used to investigate the effect of environmental factors on the rate of transpiration in a plant shoot.
What does a bubble potometer measure?
The uptake of water by the shoot, which indicates the volume of water lost by evaporation.
What does a mass potometer measure?
The change in mass of a plant, as a measure of the volume of water lost from the leaves and stem.
Why is a plant shoot cut underwater when setting up a potometer?
To prevent air entering the xylem, which could form blockages that affect water uptake.
How can the effect of wind speed on transpiration be investigated with a potometer?
By using an electric fan to generate air movement around the shoot.
How can the effect of temperature on transpiration be investigated with a potometer?
By setting up the potometer in rooms at different temperatures.
What does it mean if the air bubble travels further along the tube?
The further the bubble travels, the more water has been taken up, indicating a higher rate of transpiration.
Why should the leaves of the shoot be dried before starting?
Water on the leaves can block the stomata and reduce water loss from the shoot.
A is used to investigate the effect of environmental factors on the rate of transpiration.
A potometer is used to investigate the effect of environmental factors on the rate of transpiration.
When investigating the effect of one factor, all other must be kept constant.
When investigating the effect of one factor, all other variables must be kept constant.
True or False?
A bubble potometer measures the uptake of water by a plant shoot.
True.
A bubble potometer measures water uptake, which indicates the volume of water lost by transpiration.
True or False?
When investigating temperature, the wind speed can be allowed to change.
False.
All other variables, including wind speed, must be kept constant so they do not affect the results.
Define the transpiration stream.
The movement of water in the xylem from the roots to the leaves of a plant.
Define transpiration pull.
The upward force generated by transpiration in the leaves that draws water up the xylem.
What replaces the water lost from the leaves during transpiration?
More water is drawn up the xylem from the roots to replace it.
What holds the water molecules together in the transpiration stream?
Forces of attraction, known as cohesion, between the water molecules.
How do the forces of attraction move water up the xylem?
Moving water molecules 'pull' neighbouring molecules up the xylem, so a continuous column of water moves upwards.
By which process are more water molecules drawn into the leaf?
By osmosis.
Forces of attraction between water molecules, known as , maintain a continuous column of water in the xylem.
Forces of attraction between water molecules, known as cohesion, maintain a continuous column of water in the xylem.
The upward force generated by transpiration in the leaves is called .
The upward force generated by transpiration in the leaves is called transpiration pull.
True or False?
Water travels up the xylem as a continuous column.
True.
Forces of attraction between water molecules keep them in a continuous column as they move up the xylem.
True or False?
The transpiration stream moves water from the leaves down to the roots.
False.
The transpiration stream moves water upwards, from the roots to the leaves.
In which direction does water move in the transpiration stream?
Upwards, from the roots to the leaves.
How does an increase in wind speed affect transpiration rate, and why?
It increases transpiration; wind blows away water molecules from the leaf, creating a concentration gradient so more water vapour diffuses out.
How does an increase in temperature affect transpiration rate, and why?
It increases transpiration; water molecules gain more kinetic energy and move faster, so they diffuse out of the stomata more quickly.
How does an increase in humidity affect transpiration rate, and why?
It decreases transpiration; humid air reduces the diffusion gradient between the leaf and the air, so less water vapour diffuses out.
How does an increase in light intensity affect transpiration rate, and why?
It increases transpiration; the stomata open for photosynthesis, allowing more water vapour to diffuse out.
As humidity increases, the rate of transpiration .
As humidity increases, the rate of transpiration decreases.
As wind speed increases, the rate of transpiration .
As wind speed increases, the rate of transpiration increases.
True or False?
Increasing the humidity around a leaf increases the rate of transpiration.
False.
Increasing humidity decreases transpiration, because it reduces the diffusion gradient out of the leaf.
True or False?
In bright light the stomata open for photosynthesis, which increases transpiration.
True.
Higher light intensity opens the stomata for gas exchange, allowing more water vapour to diffuse out.
Define wilting.
The drooping of a plant that occurs when water is lost by transpiration faster than it can be replaced.
Why does a plant become floppy when it wilts?
The cells lose water and are no longer turgid, so they can no longer support the weight of the plant.
How can wilting benefit a plant?
Wilted leaves may fold, reducing the exposure of the stomata to the air and slowing further water loss.
True or False?
A plant wilts when it loses water faster than it can be replaced.
True.
When water loss by transpiration exceeds water uptake, the cells lose turgor and the plant wilts.
Define translocation.
The transport of sucrose and amino acids in the phloem, from a source to a sink.
Define a source in translocation.
The part of a plant that supplies sucrose and amino acids.
Define a sink in translocation.
The part of a plant that uses or stores sucrose and amino acids.
In which tissue does translocation occur?
In the phloem.
In what form are sugars transported in the phloem?
As sucrose.
What two substances are translocated in the phloem?
The phloem translocates:
sucrose
amino acids
Why can transport in the phloem occur in different directions?
Because the source and sink change with the stage of development or the time of year.
Translocation moves sucrose and amino acids from a to a .
Translocation moves sucrose and amino acids from a source to a sink.
The sugars and amino acids made in photosynthesis are transported in the .
The sugars and amino acids made in photosynthesis are transported in the phloem.
True or False?
Sugars are transported through the phloem in the form of sucrose.
True.
Sugars are carried in the phloem as sucrose during translocation.
True or False?
Translocation transports water and minerals through the plant.
False.
Translocation transports sucrose and amino acids; water and minerals travel in the xylem.
Give an example of a part of a plant acting as a source.
A photosynthesising leaf in summer, or a storage organ such as a potato tuber in early spring that breaks down starch into sugars.
Define xylem vessels.
Vascular tissue that transports water and mineral ions from the roots to the stem and leaves.
Define phloem vessels.
Vascular tissue that transports sucrose and amino acids from sources to sinks.
How are the vascular bundles arranged in a stem?
Around the outer edge, with the phloem closer to the outside and the xylem closer to the inside.
Where is the vascular bundle found in a root?
In the centre of the root, with the xylem forming an 'x' shape and the phloem arranged around the outside.
State two functions of the cortex in a plant.
The cortex is involved in:
transport of water towards the vascular tissue
storage of starch
Why are xylem vessel walls thickened with lignin?
Lignin strengthens the vessels, reducing breakages, and provides structural support to the plant.
How does a xylem vessel being dead and hollow help its function?
The hollow tube with no cell contents allows the free passage of water and minerals.
Why do xylem cells have no cross walls?
So they form a continuous tube through which water and dissolved minerals can flow.
The walls of xylem vessels are thickened with , which strengthens them and supports the plant.
The walls of xylem vessels are thickened with lignin, which strengthens them and supports the plant.
vessels transport sucrose and amino acids, while vessels transport water and minerals.
Phloem vessels transport sucrose and amino acids, while xylem vessels transport water and minerals.
True or False?
In the stem, the xylem is found closer to the inside of the vascular bundle than the phloem.
True.
In stems the xylem is always on the inside and the phloem on the outside of the vascular bundle.
True or False?
Xylem vessels are made of living cells full of cytoplasm.
False.
Xylem cells are dead and hollow, with no cell contents, allowing free passage of water.
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