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25 Cards in this Set
- Front
- Back
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What two types of tissue are involved in transport in plants? |
Xylem and phloem |
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What does the xylem transport? |
Water and soluble mineral ions travel upwards in xylem tissue. |
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What does phloem transport. |
Assimilates, such as sugars, travel up or down in phloem tissue. |
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Location of xylem and phloem in a root |
They are in the centre to provide support for the root as it pushes through the soil. The xylem is in a X shape, whilst the phloem are found in between the arms of the X-shaped xylem tissue. |
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Location of xylem and phloem in the stems
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They are near the outside to provide a sort of 'scaffolding' that reduces bending |
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Location of xylem and phloem in a leaf
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They make up a network of veins which support the thin leaves |
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How are xylem vessels adapted for transporting water and mineral ions? |
Long, tube-like structures formed from cells joined end to end No end walls - uninterrupted tube that allows water to pass up through the middle easily The cells are dead, so they contain no cytoplasm Their walls are thickened with a woody substance called lignin - support and stops from collapsing inwards Lignin amount increases as the plant ages Water and ions move into and out of the vessels through small pits in the walls (no lignin) |
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How is phloem tissue adapted for transporting solutes? |
Formed from cells arranged in tubes Purely a transport tissue Phloem tissue contains phloem fibres, phloem parenchyma, sieve tube elements and companion cells |
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Sieve tube elements |
These are living cells that form the tube for transporting solutes through the plant They are joined end to end to form sieve tubes The sieve parts are the end walls, which have lots of holes in them to allow solutes to pass through Unusually for living cells, these have no nucleus, a very thin layer of cytoplasm and few organelles The cytoplasm of adjacent cells is connected through the holes in the sieve plates |
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Companion cells |
The lack of nucleus and organelles in sieve tube elements - can't survive alone A companion cell for each one Companion cells carry out the living functions for both themselves and their sieve tube elements |
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How does water enter a plant? |
Through root hair cells, then it passes through the root cortex, including the endodermis, to reach the xylem Water is drawn into the roots down a concentration gradient |
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Symplast pathway |
Goes through the living parts of cells (cytoplasm) |
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Apoplast pathway |
Goes through the non-living parts of cells (cell wall) |
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Casparian strip |
This is a waxy strip in the cell walls, which means that when water in the apoplast pathway gets to the endodermis cells in the root, its path is blocked So the water has to take the symplast pathway This is useful because it has to go through a plasma membrane, and plasma membranes are able to control whether or not substances in the water get through Once the water is past this barrier it moves into the xylem |
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How is water transported up the xylem and out at the leaves? |
Xylem vessels transport the water all around the plant At the leaves, water leaves the xylem and moves into the cells mainly by the the apoplast pathway Water evaporates from the cell walls into the spaces between cells in the leaf When the stomata open, the water moves out of the leaf into the surrounding air |
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How does cohesion and tension help water move up plants? |
Water evaporates from the leaves at the top of the xylem This creates tension which pulls more water into the leaf Water molecules are cohesive so when some are pulled into the leaf, others follow This means the whole column of water in the xylem moves upwards Water enters the stem through the root cortex cells |
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How is adhesion partly responsible for the movement of water? |
Water molecules are attracted to the walls of the xylem vessels This helps water to rise up through the xylem vessels |
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Transpiration |
The evaporation of water from a plant's surface as a result of gas exchange |
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How does gas exchange cause the evaporation of water? |
A plant needs to open its stomata to let in carbon dioxide so that it can produce glucose This also lets water out - there's a higher concentration of water inside the leaf than in the air so water moves out down the water potential gradient So transpiration is really a side effect of gas exhange needed for photosynthesis |
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Four factors that affect the rate of transpiration |
1. Light - the lighter it is, the faster the rate 2. Temperature - the higher it is, the faster the rate 3. Humidity - the lowere it is, the faster the rate 4. Wind - the windier it is, the faster the rate |
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How are xerophytic plants adapted to reduce water loss? |
Stomata that are sunk in pits - sheltered from wind Reduced number of stomata Thick, waxy layer on epidermis - reduces water loss by evaporation because the layer is waterproof 'Hairs' - traps moist air Curled leaves - traps moist air Spines instead of leaves - reduces the surface area for water loss |
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Translocation |
The movement of dissolved substances to where they're needed in a plant It's an energy-requiring process that happens in the phloem Translocation moves substances from 'sources' to 'sinks' |
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Source |
The source of a substance is where it's made (so it's at a high concentration there) |
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Sink |
The sink is the area where it's used up (so it's at a lower concentration there) |
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Mass Flow Hypothesis |
Active transport is used to actively load the dissolved solutes into the sives tubes of the phloem at the source This lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis This creates a high pressure inside the sieve tubes at the source end of the phloem At the sink end, solutes are removed from the phloem to be used up This increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis This lowers the pressure inside the sieve tubes The result is a pressure gradient from the source end to the sink end - this gradient pushes solutes along the sieve tubes to where they're needed |
