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LGS A-Level OCR Biology - Unit 3 - Transport in Plants Part 2

Biology25 CardsCreated about 1 month ago

This deck covers key concepts related to the transport of water in plants, focusing on pathways, mechanisms, and the structure of plant vascular systems.

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What is the apoplast pathway?

Water travels through the cellulose cell wall
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Key Terms

Term
Definition
What is the apoplast pathway?
Water travels through the cellulose cell wall
What is the symplast pathway?
Water travels through the cytoplasm and from cell to cell via plasmodesmata
What is the advantage of travelling through the cellulose cell wall?
It offers the path of least resistance
What is the Casparian strip made of?
Suberin
What is the key property of the Casparian strip?
It is impermeable to water
What happens to water travelling via the apoplast pathway when it reaches the Casparian strip?
It cannot continue and so is diverted to the symplast pathway
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LGS A-Level OCR Biology - Unit 3 - Transport in Plants Part 2
TermDefinition
What is the apoplast pathway?
Water travels through the cellulose cell wall
What is the symplast pathway?
Water travels through the cytoplasm and from cell to cell via plasmodesmata
What is the advantage of travelling through the cellulose cell wall?
It offers the path of least resistance
What is the Casparian strip made of?
Suberin
What is the key property of the Casparian strip?
It is impermeable to water
What happens to water travelling via the apoplast pathway when it reaches the Casparian strip?
It cannot continue and so is diverted to the symplast pathway
What is the advantage of water being diverted into the symplast pathway?
It allows the plant to control the movement of water into the root via osmosis
How does water enter the xylem from the endoderm?
Endodermal cells actively pump salts into the xylem this makes the water potential of the xylem more negative than the endodermal cells this means water enters the xylem via osmosis ensures a large water potential gradient is maintained
Where is the Casparian strip located?
In the endodermal cells
How do endodermal cells move ions into the xylem?
Active transport
Once water has entered the xylem how does it move?
As a continuous stream
What force is created by the bonds between water molecules?
Cohesion
What are force is created by the interaction between water molecules and the vessel holding the water?
Adhesion
How is the continuous stream of water created?
Cohesion and adhesion
What 3 processes are involved in the movement of water up the stem and through the leaf?
Root pressure, capillarity, cohesion-tension theory
What causes root pressure?
Endodermal cells actively pump ions into the xylem vessels A water potential gradient is generated so water enters the xylem vessel by osmosis, as the water potential in the xylem is more negative than the water potential in endodermal cells Pressure in the xylem increases, forcing water upwards
What is the evidence for root pressure?
If cyanide is added to the root sap is no longer exuded root pressure relies on the active pumping of ions which requires ATP If there is no ATP no ions are pumped actively and no water potential gradient is created therefore water cannot enter the xylem by osmosis so there is no root pressure
What causes capillarity?
The adhesive forces between xylem vessels and the water molecules This pulls a water molecule up due to the cohesive forces between water molecules other water molecules are pulled up with it
Why is xylem a bundle of very narrow vessels rather than one wide vessel?
Greater heights of liquid are achieved in thinner tubes due to capillarity with a smaller tube there is a greater contact with the vessel wall compared with the volume of water in the centre so greater cohesive forces
What is transpiration?
The loss of WATER VAPOUR from leaves and stems as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata
Why is transpiration pull referred to as the Cohesion-tension theory?
The cohesive force between water molecules pulls other molecules upwards as it is a continuous stream this puts pressure on the column of water this inward pressure is called tension
What effect does tension have on the column of water?
It produces a narrower column of water
What happens if a xylem vessel is broken?
The continuous stream of water is broken so no water can be taken up
If a xylem vessel becomes blocked can water still reach the leaves?
Yes
Why can water still reach the leaves if a xylem vessel becomes blocked?
The pits in the xylem allows for the movement of water