Gas exchange in insects and plants

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  • Created by: zoolouise
  • Created on: 02-05-16 18:37
What are most adult insects?
Terrestrial, meaning that they live on land.
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What do insects risk?
They risk dehydration as the water evaporates from their bodies.
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What does efficient gas exchange require?
A thin, permeable surface with a large surface area, conflicting with the need to converse water.
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Why can't insects use their body for gas exchange?
They have a small surface area to volume ratio
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Where does gas exchange take place?
In paired holes called spiracles. They run along the side of the body, leading into tubes called tracheae which are lined with chitin, they branch into smaller tubes called tracheoles.
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What are spiracles able to do?
Open and close so gas exchange can take place and also water loss can be reduced.
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What do some insects have?
Hairs covering the spiracles which prevent solid particles from getting in.
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Where does diffusion take place when the insect is resting and moving?
When it's resting diffusion takes place through spiracles, tracheae and tracheoles. During activity the movements of the abdomen ventilate the tracheae.
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Where does gas exchange take place in insects?
The ends of the tracheoles, they're close to muscle fibres and filled with fluid. Oxygen dissolves into the fluid and diffuses directly into muscle cells. No respiratory pigment or blood circulation is required. CO2 diffuses out by reverse process.
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What happens in the day in plants?
Plants respire and photosynthesise during the day. Some of the carbon dioxide needed for photosynthesis is provided by respiration, the rest diffuses from the atmosphere into the leaves.
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What happens in the night in plants?
Plants respire but there's no photosynthesis so oxygen is needed from the atmosphere. Gas exchange takes place at the leaves and a small amount enters the stems and roots by diffusion.
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What do gases diffuse through in leafs?
They diffuse through the stomata down a concentration gradient. They diffuse from the sub-stomatal air chambers into the intercullular spaces and into cells. Direction of diffusion depends on the concentration of gases in the atmosphere.
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Why do leaves have a large surface area?
There's room for many stomata for gas exchange and they capture as much light as possible for photosynthesis
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Why are leaves thin?
The diffusion pathway for gases is short in gas exchange and light penetrates through the leaf in photosynthesis.
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Why are the cuticle and epidermis transparent in leaves?
The light penetrates to the mesophyll in photosynthesis.
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Why are palisade cells elongated and packed with chloroplasts?
So they can accommodate a large number and capture as much light as possible
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Why do chloroplasts rotate and move within mesophyll cells?
They move into the best position for maximum absorption of light
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Why are their air spaces in the spongy mesophyll?
To allow oxygen and carbon dioixide to diffuse between the stomata and cells in gas exchange and to allow carob dioxide to diffuse to the pthosynthesising cells in photosynthesis.
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Why are their stomatal pores?
So gas exchanges in and out of the leaf would be made
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What are stomata?
Small pores found on the above-ground part of plants. Occur on the lower surface of leave. Each pore is bounded by 2 guard cells. They're epidermal cells with chloroplasts and unevenly thickened walls.
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What can the width of the stomata do?
The inner wall, next to the pore is thicker than the outer wall. The width of the stomata can change so stomata control the exchange of gases between the atmosphere and the internal tissue of the leaf.
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What happens if water enters or leaves guard cells?
During the day if water enters they become turgid and swell, the pore opens. If water leaves, they become flaccid and the pore closes.
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What's the process that leads to changes in the stomata?
Chloroplasts in guard cells photosynthesise, producing ATP. Provides energy for active transport of K- into guard cells. Stored starch is converted into malate. K- and malate lower the WP in guard cells, making it more -, water enters by osmosis
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Guard cells expand as they absorb water, less in areas where the cell wall is thick. As the guard cells stretch, a pore appears due to the inner walls stretching.
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What happens at night?
Reverse process, pore closes. Plant loses water by evaporation, transpiration. Plants wilt if they lose too much water. Sunlight on upper surface increases transpiration, this is why stomata are on lower epidermis. Waxy cuticle reduces water loss.
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When do the stomata close?
At night to prevent water loss when there's insufficient light for photosynthesis. In bright light and intense heat which would increase evaporation. If there's excessive water loss
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Card 2


What do insects risk?


They risk dehydration as the water evaporates from their bodies.

Card 3


What does efficient gas exchange require?


Preview of the front of card 3

Card 4


Why can't insects use their body for gas exchange?


Preview of the front of card 4

Card 5


Where does gas exchange take place?


Preview of the front of card 5
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