mass transport in plants

Question 1

what is the xylem

Answer 1

xylem is a tissue which transports water

Question 2

what is the phloem

Answer 2

tissue that transports solutes/ sugars

Question 3

what is the cohesion theory

Answer 3

it is the movement of water up the xylem tissues against gravity VIA TRANSPIRATION STREAM

Question 4

cohesion theory in points

Answer 4

• water is evaporated from the leaves
• this reduces water potential and increases water potential gradient
• water is drawn out from the xylem
• this creates tension
• the cohesive forces between the water molecule
  draws up the water up the xylem against gravity
• water lost enters roots by osmosis

Question 5

mass flow hypothesis: in translocation

Answer 5

the movement of solutes from the source to the sink ( from one place to another)

Question 6

mass flow hypothesis: at the source

Answer 6

• high concentration of solute
• the solute enters the sieve tube in the phloem from companion cell by active transport
• lowers water potential
• water enters sieve tubes from companion cell
• increases pressure

Question 7

mass flow hypothesis: at the sink

Answer 7

• low concentration of solute
• solute used up
• higher water potential
• water leaves the tubes via osmosis
• this reduces the pressure in the tubes

Question 8

mass flow hypothesis: mass flow

Answer 8

solute stored at the sink

Question 9

adaptions of the phloem

Answer 9

they have no nucleus and less organelles (creates more space)

Question 10

what is the use of tracers

Answer 10

to supply the plant with radioactive substances eg 14c from co2
- the autoradiography - kills plants and uses photographic film if film turns black radioactive substance is present