Transport in plants

Question 1

What is transpiration?

Answer 1

• the loss of water from the leaves of a stem

Question 2

How is water moved from the roots to the xylem?

Answer 2

• water enters through the root hair cells due from a high water potential to a low water potential
• it can then take the symplast pathway where water moves from the cytoplasm of one cell to the next through the plasmodesmata
• the other way is the apoplast pathway where water moves through spaces between cellulose molecules in the cell wall
• they then move into the xylem vessel through the endodermis

Question 3

How is water moved up the xylem?

Answer 3

• water is evapourated from the surface of the leaves from the stomata, creating a water potential gradient
• water molecules then form hydrogen bonds and stick together, this is known as cohesion
• the water then forms a continuous, unbroken column across cells and up the xylem
• this creates tension in the xylem so water forms a transpiration stream
• this is known as the cohesion - tension theory

Question 4

What factors affect transpiration

Answer 4

• light
• temperature
• humidity
• wind

Question 5

What is the structure of the xylem?

Answer 5

• long, tube like structure formed from dead cells joined end to end
• no end walls, water can therefore pass up the middle very easily
• supported by rings of lignin

Question 6

What is translocation?

Answer 6

• the movement of solutes to where they are needed in a plant

Question 7

What is the structure of the phloem

Answer 7

• companion cells adjacent to sieve cells which contain mitochondira to pump sucrose into sieve cells using atp and protein channels
• Sieve cells which from the lining and transport solutes

Question 8

What is step one in transport of plants?

Answer 8

• Source
• companion cells pump sucrose into sieve cells using co transport proteins and ATP (active transport)
• this decreases the osmotic potential of the sieve cells so water osmoses from the xylem to the sieve cells
• this increases the hydrostatic pressure in the sieve cells

Question 9

What is the theory of translocation

Answer 9

• mass flow

Question 10

What is step two of translocation

Answer 10

• the sinks
• in the sinks of the sieve cells, sucrose is being used up
• this increases its osmotic pressure and causes water to osmose from the sinks back to the xylem
• this reduces their osmotic pressure

Question 11

What is step three?

Answer 11

• mass flow occurs down the concentration gradient and from a high hydrostatic pressure to one of a lower hydrostatic pressure

Question 12

What is the supporting evidence?

Answer 12

-there is pressure in the sieve cells, when they are cut, sap is released
- the concentration of sucrose is higher in the leaves than the roots
- metabolic posions inhibit translocation of sucrose
- companion cells contain mitochrondria to form ATP
- an increase in sucrose in the leaves, leads to the increase of sucrose in the pholem

Question 13

What are the objections?

Answer 13

• the functions of the sieve plates is unclear, they seem to hinder mass flow
• not all solutes move at the same speeds
• sucrose is delivered at similar rates at all areas instead of fastest to areas with the lowest concentration of sucrose

Question 14

What are the ways to prove the pholem transports sucrose?

Answer 14

• ringing = removing a outer layer of a woody stem, after a while sucrose accumulates above and the cells below die
• tracer = growing plants in environments of radioactive carbon dioxide
• this means it is incorparated in the sugars of the phoem
• these sugars can then be traced
• when x rayed, the areas with sugars are blackened and these match the areas the phloems in