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30 Cards in this Set
- Front
- Back
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List the five properties of water. |
1) Water is metabolite 2) Solvent 3) High heat capacity 4) Large latent heat of vaporisation 5) Strong cohesion between molecules |
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What is a metabolite? |
chemicals involved in chemical reactions. Water can either be the reactant or product |
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Why is water a solvent? |
- Polar so it will attract other charge particles - Allows chemicals to dissolve in water to be easily transported |
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Why does water have a high heat capacity? |
Because of the large amount of hydrogen bonds |
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How does the high heat capacity of water relate to cells? |
Any large changes in external temperature will be minimised within cells |
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What does large latent heat of vapourisation mean? |
A lot of heat energy is required to evaporate it |
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Describe briefly how water enters the plant. |
1) Water enters through the root hair cells in the epidermis 2) It passes across the cells of the cortex, across the endodermis and into the xylem. 3) The xylem then transports water up the plant to the leaves |
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Describe and explain the structure of the roots. |
1) Have extensions that increase their surface area to increase the uptake of water 2) Thin cell wall for a short diffusion pathway 3) Maintain a conc. gradient |
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What two pathways can water follow in a plant? |
1) Apoplastic pathway 2) Symplastic pathway |
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Describe the symplastic pathway. |
1) Water passes through the cytoplasm of the cells 2) Moves across the cell membranes and through the plasmodesma from one cell to another 3) Water moves by osmosis |
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Describe the apoplastic pathway. |
1) Water passes through the adjoining cell walls 2) Water moves by diffusion 3) Once is reached the casparian strip water is forced to pass through the cytoplasm of the enodermis |
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Why does the casparian strip force the water to change course? |
It is a waterproof strip and stops water from flowing in the wrong direction |
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How does the water pass from the endodermis to the xylem? |
1) The endodermis cells actively transport ions to the roots 2)This lower the water potential allowing water to diffuse via osmosis into the xylem |
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What are the differences between the apoplastic pathway and the symplastic pathway? |
1) SYM uses osmosis 2) APO uses diffusion 3) SYM is slower because of resistance 4) APO is faster |
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What is transpiration? |
The evaporation of water from a plants surface |
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Describe two ways in which water is lost in a plant. |
1) Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf 2) The stomata open |
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Explain how cohesion and tension relate to the movement of water. |
1) Water evaporates from the leaves 2) This creates tension, which pulls water into the leaf due to a lower water potential 3) Water molecules are cohesive, and create a column of water in the xylem 4) Water enters the stem through the roots |
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What four main factors affect the rate of transpiration? |
1) Light 2) Temperature 3) Humidity 4) Wind |
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Why does light affect the transpiration rate? |
- More light = more transpiration - The stomata open to let in CO2 |
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How does temperature affect the transpiration rate? |
Warmer water molecules have more eenrgy and evaporate from cells faster |
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How does humidity affect transpiration? |
The drier the air the faster the transpiration rate because the conc. gradient is increased |
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How does wind affect the transpiration rate? |
The more wind there is the faster the transpiration rate as the conc. gradient is increased |
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What is the phloem tissue adapted for? |
Transporting solutes |
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What are sieve tube elements? |
Living cells that form the tube for transporting solutes |
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What are companion cells? |
They carry out the living functions of sieve cells which don't have a nucleus |
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What are sinks? |
The area where the solutes are used up |
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What are the sources? |
The area where solutes are made up |
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How do enzymes maintain a concentration gradient from the source to the sink? |
They change the solutes at the sink into something else, lowering the concentration |
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What is the best supported theory about how solutes are transported? |
Mass flow hypothesis |
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Describe Mass Flow hypothesis. |
1) Sugars are made by photosynthesising tissue 2) Sugars are actively transported into the phloem by companion cells 3) This lowers the water potential of the sieve cells, therefore water enters via osmosis 4) The pressure in the phloem increases causing mass movement to the sink (root) 5) Sugars are used for respiration or converted into starch |
