xylem and phloem

Question 1

define transpiration

Answer 1

evaporation of water from the leaves

Question 2

describe the theory of cohesion

Answer 2

water evaporates, leaving a low WP in the leaf. water will therefore move into the cell. because of the cohesive forces in the water there is a continuous column of water which is therefore pulled up through the xylem as a result of transpiration

Question 3

define cohesion

Answer 3

the tendency for water molecules to stick together
because of their hydrogen bonding

Question 4

describe tension in the xylem

Answer 4

• ## the transpiration pull puts the xylem under tension - there is a negative pressure that will pull the xylem in. it becomes narrower.

Question 5

what is the evidence for the cohesion tension theory

Answer 5

when you break a xylem vessel water does not leak out - air will be drawn in as their is tension in the tube

Question 6

what are factors that increase the rate of the transpiration stream

Answer 6

low humidity - water potential gradient- so that water can evaporate

• high temp
• high wind speeds - so water is blown in
• high light intensity

Question 7

which direction can sucrose move in

Answer 7

up and down

Question 8

define translocation

Answer 8

whereby organic molecules and some mineral ions are transported from one part of the plant to another.

Question 9

where does translocation happen between

Answer 9

sources ( where the sucrose is produced) to the sinks (litro anywhere in the plant)

Question 10

describe sucrose goes from the photosynthesising tissue to the sieve elements

Answer 10

• sucrose is manufactured in the cells with chloroplasts
• sucrose diffuses down the conc grad by facillitated diffusion into the companion cells
  -hydrogen ions diffuse down a conc grad through carrier proteins into sieve tube elements
  -sucrose is co-transported with the hydrogen ions