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29 Cards in this Set
- Front
- Back
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Which two gas exchange processes take place in a plant? |
Photosynthesis, where CO2 is removed and oxygen is released. Respiration, where oxygen is used and CO2 is released |
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How do plants reduce the need to exchange gases with the environment? |
They use the oxygen made in photosynthesis directly for respiration |
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Which occurs at a higher rate? |
The rate of photosynthesis is higher than the rate of respiration |
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What does this mean? |
CO2 has to be gained from the external environment |
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What is one difference between photosynthesis and respiration? |
Respiration continues at night, whilst photosynthesis can't |
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What is a dicotyledonous plant? |
A flowering plant which has a pair of leaves in the embryo of the seed |
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What is the structure of the leaf? |
On top is a waxy cuticle and below this are the upper epidermis cells. Then, there are palisade mesophyll cells, followed by spongy mesophyll cells. Then there's the sub stomatal air space, lower epidermis cells, guard cells and stoma. |
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What does the leaf structure mean? |
No living cell is far from the external air- there's a short diffusion pathway |
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Where is the rate of diffusion quicker? |
The rate of diffusion is quicker in the air than the water |
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How does gas exchange occur? |
There's no specialised system, so gases diffuse down diffusion gradients mostly through leaves |
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What do guard cells do? |
They can open and close the stomata |
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How do the guard cells open the stomata? |
They become swollen (as water moves into them) and as the cell wall is thicker on the inside, it creates an opening |
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How do they close the stomata? |
They become shrunken when the water's gone, closing the opening |
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What is the reason for controlling the stomata? |
They help control water loss via transpiration by closing |
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Wha are the stomata? |
They are lots of small pores, meaning no cell is far from the stomata-short diffusion distance. |
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Where are most stomata found? |
Under the leaf |
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What are two features of mesophyll cells? |
There are numerous interconnecting air spaces to connect the mesophyll cells. There's a large surface area of mesophyll cells for quick diffusion |
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What is a problem plants face? |
Increased water loss due to a large surface area (necessary for photosynthesis) |
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What do plants have to reduce water loss? |
Waterproof covering- waxy cuticle (not cellular) on the leaves' surface
Guard cells and stomata |
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Which plants are specialised to reduce water loss from transpiration? |
Xerophytes |
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What do xerophytic adaptations do? |
They reduce the water vapour potential gradient with the environment |
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What are the 5 xerophytic adaptations? |
Thicker waxy cuticle Rolled leaves Hairy leaves Stomata in sunken pits Leaves with a reduced surface area to volume ratio |
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What does a thicker waxy cuticle do? |
It reduces water loss via evaporation |
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What do rolled leaves do? |
They reduce air movement across the stomata and reduce the water vapour potential gradient. This is because the stomata are rolled on the inside, trapping water vapour. |
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What do hairs on leaves do? |
The hairs trap water vapour, reducing the water vapour potential gradient |
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How do stomata in sunken pits reduce water loss? |
They reduce air movement across the stomata and trap water vapour. This reduces the water vapour potential gradient |
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How does reducing the surface area to volume ratio of leaves reduce water loss? |
It reduces the surface area for less loss of water vapour |
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Define transpiration |
The loss of water vapour through the stomata of the leaf by diffusion |
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What is the structure of a plant leaf? |
Waxy cuticle Upper epidermis Palisade cells Spongy mesophyll cells Sub-stomatal air spaces Lower epidermis Guard cells Stomata |
