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21 Cards in this Set
- Front
- Back
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Describe the transpiration stream. |
Water enters the root hair cells by osmosis and mineral ions by active transport. The xylem vessels transport them up through the plant to the leaves where water leaves the plant through the open stomata by evaporation. |
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How are root hair cells adapted for their purpose? |
They have a large surface area for increased volume of water and mineral uptake and have lots of mitochondria to provide energy needed for active transport. |
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How do you measure the rate of transpiration? |
Use a potometer. As water moves up through the plant the air bubble moves along the scale giving a measure of water absorbed by the plant over time and thus the transpiration rate. Vaseline is applied around the rubber bungs to ensure an airtight seal to prevent water loss by evaporation. The reservoir allows you to move the bubble back to the zero to reset it. |
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What factors affect the rate of transpiration in a plant? |
Light intensity: Bright light = increased uptake as the stomata open wider (to allow more CO2 in for photosynthesis) Temperature: Increased temperature = increase in thermal and kinetic energy = more evaporation and diffusion Wind speed: More wind = water vapour removed quickly = quicker diffusion of water vapour Humidity: Humid air = reduced diffusion gradient = slower evaporation |
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What other factors affect water uptake in a plant? |
The stomata must be open - at night they're not.
They require CO2. |
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What happens to the rate of water uptake if the lower surface of the leaves are covered in vaseline? |
The rate decreases as it blocks the majority of stomata which allow water vapour to diffuse out. However some will still be able to diffuse out of the upper surface. |
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What happens to the rate of water uptake if the upper surface of the leaves are covered in vaseline? |
There are less stomata than the upper surface so only a slight reduction in rate of transpiration and therefore a slight reduction in water uptake. |
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How can you decrease light intensity around a plant? How does this affect the rate of transpiration and why? |
Move a lamp closer and further away. A decrease in light intensity means a decrease in rate of transpiration as the plant can't photosynthesise due to their being no light. This means the stomata don't need to open to absorb carbon dioxide and so water can't be lost. |
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How can you increase air temperature around a plant? How does this affect the rate of transpiration and why? |
Have a heater on different settings next to it. An increase in air temperature means an increase in transpiration as at higher temperatures more evaporation can occur as the water molecules have more kinetic energy. |
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How can you decrease air movement around a plant? How does this affect the rate of transpiration and why? |
Use a fan at different distances. Windier conditions mean an increase in transpiration as the moving air removes any water vapour which might remain near the stomata. This moist air would otherwise decrease the concentration gradient and slow down the diffusion and evaporation rate. |
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How can you decrease humidity around a plant? How does this affect the rate of transpiration and why? |
Place different sized bags over the plant. A decrease in humidity means an increase in transpiration. Humid air reduces the diffusion gradient between the stomata and the external air. This causes evaporation to occur more slowly and therefore there's a decrease in water loss. |
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What do the xylem transport? |
Water and mineral ions. |
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Where does the water need to reach in a plant? |
All cells, particularly the photosynthetic cells in the leaves. |
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Describe the structure of xylem cells |
They are made of dead cells joined end to end. They are hollow spaces (like the lumen of blood vessels) They are reinforced by lignin which is strong and impermeable to water. |
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What do phloem vessels transport? |
Sugars and amino acids. |
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What is glucose converted into and why? |
Glucose is converted into sucrose as it is less reactive so won't affect the osmotic potential of the surrounding cells, |
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Describe the structure of the phloem. |
The cells which form the phloem are living so retain their cytoplasm and have cellulose cell walls. They are controlled by nearby companion cells. The cell ends have walls with perforations called sieve plates. |
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Does water flow one or two-way in the xylem? |
One-way. |
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Does water flow one or two-way in the phloem? |
Two-way. |
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Similarities between the xylem and phloem. |
Both have cells arranged end to end. Both transport substances from one place to another. Neither contain a nucleus. Both are made from cells. Both found in the stem/veins. |
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Differences between the xylem and phloem. |
Xylem is made of dead cells, phloem is made of livving cells. Xylem transports water and mineral ions, phloem transport sucrose and amino acids. Xylem reinforced by lignin, phloem have cellulose cell walls. Xylem walls are impermeable to water, phloem walls are permeable. Xylem vessels are hollow, phloem vessels are filled with cytoplasm. |
