Transport in plants

  • Created by: Esme.B
  • Created on: 31-03-18 15:36
'Xylem tissue'?
Moves water and minerals from the roots to the leaves.
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'Phloem tissue'?
Moves assimilates up and down the plant from sources to sinks.
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Function of 'xylem vessels'?
Adapted to enable the free flow of water along the vessels.
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List x3 adaptations of 'xylem vessels'.
1). End walls are removed to form long tubes 2). no cytoplasm/ organelles are present 3). Cell walls impregnated with lignin(lignified) to make vessel wall waterproof and strengthen the vessel to prevent collapsing.
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List x2 adaptations of 'xylem vessels'?
4). Spiral, annular and reticulate thickening strengthens the wall to prevent collapse 5). Bordered pits between the vessels allow the movement of water between vessels.
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What are the X2 cell types involved in the 'pholem'?
Sieve tube elements + Companion cells
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'Sieve tube elements'?
Long sieve tube that transport the assimilates
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'Companion cells'?
Support cells that provide all the metabolic functions for the sieve tube elements and are involved in actively loading the sieve tubes.
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List x5 features of 'sieve tube elements' ?
1) Form long tubes 2) End walls are retained 3) End walls contain many sieve pores, called sieve plates. 4) Thin layer of cytoplasm 5) Very few organelles + No nucleus
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List x4 features of 'Companion cells'?
1) Closely associated with sieve tube elements 2). Connected to sieve tube elements by many plasmodesmata 3). Dense cytoplasm with many mitochondria. 4). Large nucleus
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'Transpiration'?
The loss of water vapour from aerial parts of the plant.
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'Transpiration'- x3 main stages?
1). Water moves by osmosis from the xylem to the mesophyll cells in the leaf. 2). Water evaporates from the surfaces of the spongy mesophyll cells into air spaces inside the leaves. 3). Water vapour diffuses out of leaf via stomata.
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What happens when the Stomata is open during the day?
1). Allow gaseous exchange -Co2 enters the leaf + o2 is released (enabling photosynthesis) 2). As it's open water vapour is lost.
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What must be present to make water vapour leave the plant?
Water potential gradient between air spaces in the leaf + surrounding air to make water vapour leave the leaf.
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What effect does the water potential gradient have on the water vapour leaving the plant?
The steeper this gradient, more rapid the loss of water vapour (Transpiration)
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Factors increasing Transpiration?
1). High temperatures: increases evaporation so there will be higher water potential in the leaf. 2). More wind- blows water vapour away from the leaf, reducing water potential in the surrounding area.
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Factors increasing Transpiration?
1). Lower relative humidity: increases the water potential gradient between the air inside the leaf and outside. 2). Higher light intensity - causes the stomata to open wider
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How can 'Transpiration' be measured?
Using a bubble potometer
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What does a 'potometer' actually measure?
Water uptake by the stem, but can assume that water uptake equals water loss from the leaves in most cases.
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Water: A cell wall of a plant cell?
A cell wall of a plant cell is permeable to water
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Water: cell- surface membrane?
Is selectively permeable
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What reduces 'Water potential' inside the cell?
Mineral ions in the solution reduces 'water potential'.
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How does water move with in the cell?
By osmosis from a cell with high water potential to a cell with lower potential. (water molecules move down a water potential gradient)
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What x3 ways can water move across a tissue (i.e- root cortex)?
1). Apoplast pathway 2). Symplast pathway 3). Vacuolar pathway
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'Apoplast pathway'?
Carries water between the cells through the cell walls (Water does NOT enter the cytoplasm or pass through cell-surface membranes)
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'Symplast pathway'?
Takes water from cell to cell through the cytoplasm of each cell. Water often passes through plasmodesmata linking the cytoplasm of adjacent cells.
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'Vacuolar pathway'?
Carries water through the cytoplasm and vacuole of each cell.
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How does water enter the' Root hair cells'?
Via osmosis- pass across the root by apoplast pathway or symplast pathway.
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'Transpiration stream'?
The flow of water from the roots to the leaves.
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What are the x3 mechanisms to move water up the stem?
1). Root pressure 2). Adhesion or capillary action 3). Transpirational pull
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what occurs when 'Root pressure' and 'capillary action is combined?
Raises water by a few metres - Transpiration and the pull it creates are essential to move water all the way up a tall stem.
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'Root pressure' ?
The pressure created by the action of the endodermis in the roots.
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How does the 'endodermis' use metabolic energy ?
1). To pump mineral ions into the root medulla. 2). Reduces the water potential in the medulla + xylem, making it more negative than in the cortex. 3). Water moves across the endodermis into the medulla by osmosis.
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Why can't water return to the cortex through the apoplast pathway?
As this is blocked by the Casparian *****. (causes pressure build up in the cortex, pushing the water up the xylem)
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'Adhesion'?
The attraction between the water molecules and the walls of the xylem vessel.
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What does 'Adhesion' result in?
Capillary action , the results in water creeping up the xylem.
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'Transpirational pull'?
'The cohesion-tension theory'
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'The cohesion-tension theory'?
The water is cohesive (molecules attract one another), the column of water is put under tension and pulled up the stem- this accounts for the movement of water up the xylem.
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'Xerophytes'?
Plants adapted to living in dry places.
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Adaptations of 'Xerophytes' to help them reduce loss of water vapour?
1). Thick waxy cuticle on the leaves 2). Smaller leaf area 3). Stomata in pits 4). Hairy leaves 5). Rolled leaves
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'Hydrophytes'?
Plants adapted to live in water (i.e- water lilies)
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X3 Adaptations of 'Hydrophytes'?
1). Leaves and leaf stems have large air spaces (to help them float) 2). Stomata may be on the upper surface of the leaf (to gain Co2 from the air) 3). The stem may be hollow ( to allow gases to move to the roots easily)
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'Translocation'?
An energy requiring process for transporting assimilates around a plant (mostly sucrose)
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Where does 'Translocation' occur?
1). The sieve tubes. 2). Companion cells are important in actively loading assimilates into the sieve tubes.
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How does 'Translocation' work?
1). Mass Flow 2). caused by creating a high hydrostatic pressure at the source and lower hydrostatic pressure at the sink. 3). Fluid in the phloem sieve tube then moves from high to low pressure (down its pressure gradient)
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A 'source'?
Part of the plant that has supply of assimilates that are loaded into the phloem.
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List x3 examples of a 'source'?
1). Leaf that has made sucrose from the products of photosynthesis during the spring and summer 2). Root that has stored starch + cannot convert this to sucrose, happening in spring. 3). Any other storage organ where plants have stored starch.
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A 'Sink'?
Part of the plant that removes sucrose from the phloem and uses or stores it.
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List x4 examples of a 'sink'?
1). buds or stem tips where growth occurs+energy is needed 2). leaves in spring as they grow +unfold 3). roots in summer and autumn when plants is storing sugars as starch 4). Any other organ where the plant may store starch.
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Process of Translocation?
Active loading - sucrose is moved into the sieve tube by a complex process involving active transport.
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Other cards in this set

Card 2

Front

'Phloem tissue'?

Back

Moves assimilates up and down the plant from sources to sinks.

Card 3

Front

Function of 'xylem vessels'?

Back

Preview of the front of card 3

Card 4

Front

List x3 adaptations of 'xylem vessels'.

Back

Preview of the front of card 4

Card 5

Front

List x2 adaptations of 'xylem vessels'?

Back

Preview of the front of card 5
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