3.3 Transport in Plants

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  • Created by: elbungay1
  • Created on: 20-03-19 18:36
Why do plants need a transport system?
To move water and mineral from the roots up to the leaves. To move sugars from the leaves to the rest of the plant
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Transport system in plants consists of what two vascular tissues?
Water and soluble mineral ions travel upwards in the xylem tissue. Assimilates, such as sugars, travel up or down in the phloem tissue
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What impregnates the walls of cells, developing xylem vessels?
Lignin
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Incomplete lignification leads to what forming between cell walls
Bordered Pits
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What are the adaptations of Xylem Vessels?
They form a continuous column, thin tubes mean water column does not break easily, bordered pits allow water to move sideways from one vessel to another, lignin in spiral patterns allows bending and stretching of stem
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The flow of water in xylem is not impeded because...
there are no cross walls, there are no cell contents (nucleus or cytoplasm) and lignin thickening prevents the walls from collapsing
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Phloem tissues consists of what elements?
Sieve tube elements and companion cells
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What properties of sieve tube elements allows mass flow?
No nucleus and very little cytoplasm
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Name of perforated cross-walls that allow movement of sap from one element to the next
Sieve Plates
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Properties of companion cell
Dense cytoplasm, large nucleus, numerous mitochondria
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Name of gaps in cell wall containing cytoplasm that connects two cells
Plasmodesmata
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Three pathways of water through plants
Apoplast pathway, Symplast Pathway, Vacuolar Pathway
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Describe how water travels through the apoplast pathway
Water passes through the spaces in the cell walls and between cells. It does not pass through any plasma membrane into the cells. this meams the water moves by mass flow rather than by osmosis. dissolved mineral ions and salts can be carried.
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Describe Symplast Pathway
Water enters the cell cytoplasm through the plasma membrane. It can then pass through the plasmodesmata from one cell to the next.
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Describe the vacuolar pathway
Similar to symplast pathway, but water is not confined to the cytoplasm of cells. It is able to enter and pass through the vacuoles as well.
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What is water potential
The tendency of water molecules to move from one place to another. Water always moves from a region of higher water potential to a region of lower water potential.
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Cellulose prevents cells bursting, instead when full of water they become
Turgid
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Excessive water loss leads to the cell becoming flaccid and the plasma membrane pulled away from cell wall, what is this condition called?
Plasmolysis
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What is transpiration?
the loss of watervapour from the aerial parts of the plant, mostly through the stomata in the leaves
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What is the typical pathway taken by most water leaving the leaf?
1. Water enters the leaf through the xylem, moves by osmosis into cells of spongy mesophyll. 2. water evaporates from the cell wall of the spongy mesophyll. 3. water vapour moves out by diffusion out of leaf through open stomata.
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The diffusion of water vapour out of leaves is dependent on what?
water vapour potential gradient
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What is the importance of transpiration?
Transports useful minerals up the plant, maintains cell turgidity, supplies water for growth, cell elongation and photosynthesis, supplies water that, as it evaporates, can keep the plant cool on a hot day.
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What environmental factors affect transpiration?
Light intensity (stomata open in light for photosynthesis). Temperature (more KE, more evaporation, decrease relative water vapour potential), Relative humidity, air movement (carry away water vapour, maintain gradient), water availability
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What is the role of root hair cells?
Increase surface area of the root and absorb mineral ions and water from soil
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The apoplast pathway in roots is blocked at the endodermis of the vascular bundle by what?
Casparian *****
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What is the role of the endodermis?
Casparian ***** blocks apoplast pathway ensuring all water and dissolved mineral ions have to pass into teh cell cytoplasm through the plasma membranes. Plasma membranes contain transporter proteins which actively pump mineral ions into medulla/xylem
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What three process moves water up the stem
Root Pressure (water cannot move back to endodermis, so water pushed up) Transpiration pull (water attracted to each other by cohesion, loss of water must be replaced) Capillary action (water attracted to sides of xylem by adhesion)
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How does water leave the leaf?
Water evaporates from the cells lining the cavity immediately above the guard cells. This lowers water potential of cells, causing water to enter by osmosis from xylem or neighbouring cells
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What is the difference between a hydrophyte and a xerophye
Hydrophytes are plants adapted to living in water or where the ground is very wet. Xerophytes are plants adapted to living in dry conditions
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What is Translocation?
The movement of assimilates throughout the plant. From source to sink
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Why are H+ ions actively pumped out of companion cells in Active Loading?
This creates a concentration gradient, allowing H+ to diffuse back in carrying sucrose molecules. Example of cotransport
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in active loading, the high concentration of sucrose in companion cells due to cotransport results in what?
As the concentration of sucrose increases, it can diffuse through the plasmodesmata into the sieve tube
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How does sucrose move along the Phloem
Sap is a solution of sucrose, amino acids and other assimilates and it moves along by mass flow. the flow is caused by a hydrostatic pressure gradient. Water enters phloem at source, increasing pressure and leaves at sink, decreasing pressure
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What is a Sink?
Anywhere that removes sucrose from the phloem
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What is a source
Any part of the plant that loads sucrose into the sieve tube
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How do roots act as a source and a sink
Roots recieve sugars and store them as starch, at another time of the year, the starch may be converted back to sugars and transported to a growing stem
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What are the typical adaptations of a hydrophyte?
Many large air spaces in leaf, keeping leaf afloat. Stomata are on upper epidermis so exposed to air to allow gaseous exchange. Leaf stem has many large air spaces, helps with buoyancy and allows oxygen to diffuse to roots for aerobic respiration
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What are the features of xerophytes
waxy cuticle will reduce water loss due to evaporation. Stomata are on under-surface of leaves reduces evaporation due to direct heating, stomata are closed at night, lose leaves in winter when temp too low for photosynthesis
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What are the adaptations of Cacti?
Cacti are succulents-store water in stem, can expand when water is avaliable, leaves reduced to spines reduced total surface area less water lost by transpiration, stem is green for photosynthesis, widespread roots
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Other cards in this set

Card 2

Front

Transport system in plants consists of what two vascular tissues?

Back

Water and soluble mineral ions travel upwards in the xylem tissue. Assimilates, such as sugars, travel up or down in the phloem tissue

Card 3

Front

What impregnates the walls of cells, developing xylem vessels?

Back

Preview of the front of card 3

Card 4

Front

Incomplete lignification leads to what forming between cell walls

Back

Preview of the front of card 4

Card 5

Front

What are the adaptations of Xylem Vessels?

Back

Preview of the front of card 5
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