Transport in plants

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  • Created by: sophiee96
  • Created on: 02-04-13 18:15
What are the two main types of tissue vascular bundles are made up of?
Xylem and phloem
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How are the xylem arranged in roots?
Centrally
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What is the advantage of the xylem being arranged centrally in roots?
Resistance to vertical stresses (pull) and so helps the anchorage of the plant
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In stems xylem are arranged in vascular bundles which are placed in a ring where?
at the periphery
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Whatis the benefit of xylem being arranged in vascular bundles that are placed in a ring at the periphery in the stem?
Gives flexible support but also resists to bending strain
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What gives flexible strength and resists tearing strains in the leaves?
The arrangement of vascular tissues in the midrib and network of veins
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What are the two main types of cells in xylem?
Vessels and tracheids
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What do vessels and tracheids form?
A system of tubes through which water can travel
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What happens as cells mature and differentiate?
Their cellulose cell walls incorporate lignin
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What is lignin?
A very hard, strong substance
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What happens when lignin builds up?
The cell contents dies leaving behind an empty space. The end walls break down so the cells form a continuous tube
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What two things does the deposition of lignin do?
Strengthens the wall and makes the walls impermeable to water and solutes
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What are the two functions of xylem?
Transport and providing mechanical strength and support to the plant
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What is transpiration?
The evaporation of water from inside the leaves,through the stomata to the atmosphere
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What is water needed for in plants?
Photosynthesis
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Where does photosynthesis take place?
In the leaves of plants
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Water is drawn up from the soil through the what?
Roots
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Some water is used in photosynthesis, what happens to the rest of it?
It's lost through the stoma of the leaves by a process of transpiration
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What is the advantage of root hairs?
Increased surface area
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Whydoessoil water have a high water potential?
Because it contains a weak solution of mineral salts
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The vacuoles of the root hair contains a strong solution of dissolved substances, what does this mean?
It has a low water potential
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Water passes down a water potential gradient, form a high water potential to a low water potential by which process?
Osmosis
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Name the three pathways water can travel across the cells of the cortex of the root?
Apoplast, symplast and vacuolar pathway
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What is the apoplast?
Through the cell wall
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What is the symplast?
Through the cytoplasm and plasmodesmata
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What is the vacuolar pathway?
From vacuole to vacuole
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Which are the two main pathways water takes across the root?
The symplast and apoplast
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Which is the fastest pathway water can take across the root?
The apoplast
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What is the endodermis?
A ring of cells surrounding the xylem tissue having an impermeable waterproof barrier through their cell walls
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The cell walls of the endodermis are impregnated with a waxy material cuticle called what?
Suberin
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Suberin forms a distinct band known as what?
The Casparian *****
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What does the Casparian ***** prevent?
The use of the apoplast pathway
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What is the only way water can pass across the endodermis to the xylem?
Along the symplast pathway
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What is root pressure?
A force created at the base of the xylem vessel by the influx of water along a water potential gradient
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What is cohesion?
The tendency for water molecules to stick together
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What is adhesion?
When water molecules stick to the walls of the xylem
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What is capillarity?
The tendency for water to rise in narrow tubes
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What is the most likely way water enters the xylem from endodermis cells?
Active transport of salts
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What does the active transport of mineral ions into the xylem by the endodermal cells do?
Lowers the water potential in the xylem
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What happens when the water potential in the xylem is lowered?
Water enters, by osmosis, along a water potential gradient
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How are minerals taken up by the root hairs from the soil solution?
By active transport
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What happens to mineral ions once they are absorbed?
They are moved along the apoplast pathway carried in a solution by water being pulled up the plant in the transpiration stream
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What happens when mineral ions reach the endodermis?
The Casparian ***** prevents further movement along the cell walls
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What happens to ions that enter the cytoplasm of the cell?
They diffuse or are actively transported into the xylem
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Nitrogen usually enters the plant as what ions?
Nitrate ions or ammonium ions
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How do nitrate/ammonium ions enter the apoplast stream?
By diffusing along the concentration stream
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How do nitrate/ammonium ions enter the symplast?
By active transport against the concentration gradient
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Nitrate/ammonium ions flow via the plasmodesmata in which stream?
The cytoplasmic stream
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When is the plant able to selectively take up ions?
At the endodermis, ions are actively taken up to by-pass the Casparian band
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What is the main force that pulls water up the stem?
Transpiration
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Is transpiration an active or passive process? Why?
Passive - it doesn't require energy to take place
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What does water travel in up through the stem to the leaves?
The xylem
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What happens to water once it reaches the leaves?
Most evaporates from the internal leaf surface and passes out, as water vapour in the atmosphere
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What does the transpiration of water from the leaves do?
Draws water across the leaf from the xylem tissue along the same three pathways as in the root
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What happens as water molecules leave the xylem?
They pull up other water molecules
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What makes the transpiration pull possible?
The large cohesive forces between water molecules and adhesive forces which exist between the water molecules and the hydrophilic lining of the vessels
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What is the theory of the mechanism by which water moves up the xylem?
Cohesion-Tension theory
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What force other than cohesion and adhesion may contribute to the rise of water in the xylem?
Capillarity
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Is capillarity more relevant in small plants or large trees?
Small plants
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What happens if a plant loses an excessive quantity of water?
It reaches a point where it cannot regain its turbot and dies (wilts!)
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Why do plant stoma need to be open during the day?
To allow the exchange of gases between the tissue of the leaf and the atmosphere
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How is the loss of water vapour through the leaf epidermis reduced?
By the presence of the waxy cuticle on the surface of the leaves
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What is the rate at which water is lost from plants called?
The transpiration rate
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What increases the rate of transpiration?
An increase in water potential gradient between the water vapour in the leaf and the surrounding atmosphere
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Name 4 external factors which effects transpiration rate?
Temperature, humidity, air movementand light intensity
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How does the increase in temperature speed up the rate of diffusion of water vapour into the surrounding atmosphere?
By providing kinetic energy for water molecules, the water potential of the atmosphere also becomes lower and it can hold more moisture
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Transpiration in still air results in what?
The accumulation of a layer of saturated air at the surfaces of leaves
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What does the movement of air do?
Reduces the thickness of the layer of saturated air so results in increased transpiration
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How does light intensity affect transpiration?
It controls the degree of stomatal opening
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Does the substomal chamber have a high or low water potential?
High
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Other cards in this set

Card 2

Front

How are the xylem arranged in roots?

Back

Centrally

Card 3

Front

What is the advantage of the xylem being arranged centrally in roots?

Back

Preview of the front of card 3

Card 4

Front

In stems xylem are arranged in vascular bundles which are placed in a ring where?

Back

Preview of the front of card 4

Card 5

Front

Whatis the benefit of xylem being arranged in vascular bundles that are placed in a ring at the periphery in the stem?

Back

Preview of the front of card 5
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Ahmed Ahnaf

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Thank you Sir/Madam whoever has created this. You actually save time for students by spending yours. Thank you Thank you

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