B7 Mass Transport Flashcards
Relate the structure of arteries to their function.
Have thick muscular walls to handle high-pressure, and are elastic to control blood flow
Describe how the structure of veins relate them to their function
Thinner walls and wider lumen due to lower pressure. Less muscular and elastic fibres as they don’t have to control blood flow. Contain valves
Name the nodes involved in heart contraction
Sinoatrial Node (SAN)
Atrioventricular Node (AVN)
Where is the SAN located?
Wall of right atrium
Where is the Atrioventricular Node located?
Between the two atria.
Explain how the heart contracts
SAN initiates and spreads impulse across the atria, so the atria contract
- AVN receives, delays, and then conveys impulse down the Bundle of His
- Impulse travels into the Purkyne fibres which branch across the ventricles
Why does the impulse need to be delayed?
Needs time for all blood to pass through and for valves to close
How is the structure of capillaries related to their function?
One cell thick - short diffusion pathway
Very narrow - RBC lie flat
Numerous and highly branched, Large SA
How is water transported in plants?
Xylem: Long, continuous columns which also provide structural support
What is the xylem made out of?
Lignin - waterproof polymer
Explain the cohesion-tension theory.
Cohesion - water molecules form hydrogen bonds with each other, causing them to stick together
Tension - water molecules form Hydrogen bonds with the side of xylem vessel elements - draws water up the stem
Describe sieve tube elements.
Form a tube to transport sucrose in the dissolved form of sap
What are the sieve tube elements made from?
Cellulose
Describe companion cells.
- Connected to sieve tube elements via plasmodesmata
- Have a nucleus
What is plasmodesmata?
Allows the cytoplasm to be shared between companion cells and sieve tube elements.
What are sieve plates?
At either end of the sieve tube elements and contain large pores to allow sap to move through
How does sucrose in the leaf enter the phloem?
Sucrose enters companion cells via active transport. This involves the co-transport of hydrogen ions with sucrose. Sucrose then diffuses into the sieve tube elements via the plasmodesmata.
How do phloem vessels transport sucrose around the plant?
The water potential is reduced in the phloem - water diffuses into the phloem via osmosis due to the water potential gradient.
Unloading of sucrose - sink cells
What is the evidence for the mass flow theory?
- Sap is released when a stem is cut, therefore there must be pressure
- There is a higher concentration of sucrose in the leaves than in the roots
- Increasing sucrose levels in the leaves increases sucrose levels in the phloem
What is the evidence against the mass flow theory?
The structure of sieve tubes seem to hinder mass flow
