transport in plants

Question 1

stem

Answer 1

phloem and xylem are grouped together (vascular bundles)
ring arrangement around the pith

Question 2

root

Answer 2

xylem and phloem not bundled together
positioned in the centre of the root with xylem and phloem alternating (xylem is the cross)

Question 3

leaf

Answer 3

xylem and phloem grouped together (vascular bundles)
xylem on top, phloem below

Question 4

root pressure

Answer 4

pushing force caused by water entering the xylem at the roots
due to continual absorption of water by root hair cells
force is too weak to overcome gravitational force (minor contributor)

Question 5

capillary action

Answer 5

spontaneous movement of a liquid through a narrow tube (eg. capillary) and is independent of gravity
cohesion forces among water molecules
adhesion forces between water molecules and cellulose cell wall of xylem

Question 6

transpiration pull

Answer 6

main suction force to draw water and ions up xylem vessels from roots to all other parts of the plant

Question 7

transpiration

Answer 7

the loss of water vapour by diffusion through the stomata in leaves (result of gaseous exchange in plants)
creates suction force called transpiration pull
responsible for transporting water and mineral salts to all parts of the plant

Question 8

benefits of transpiration

Answer 8

cools down the plant by removing latent heat of vapourisation when water vapour evaporates, prevents plant from overheating

Question 9

factors affecting rate of transpiration

Answer 9

1. air temperature
2. air humidity
3. wind/air movement
4. light intensity

Question 10

wilting

Answer 10

when cells plasmolyse and lose their turgor pressure, causing the leaf to fold up and the plant to become limp

Question 11

advantages of wilting

Answer 11

SA of leaf exposed to atmospheric air is reduced, reduction of water vapour lost

Question 12

disadvantages of wilting

Answer 12

closure of stomata –> reduces volume of co2 entering leaf, decreases rate of photosynthesis
decreases surface area of leaf exposed to sunlight, decreases rate of photosynthesis

Question 13

translocation

Answer 13

transport of sucrose and amino acids using the phloem, from source to the sink

Question 14

mass flow hypothesis

Answer 14

states that translocation of glucose and other sugars within the phloem is caused by never-ending flow of water and dissolved nutrients between the source and sink

Question 15

translocation step 1

Answer 15

1. at source, sucrose produced in the mesophyll cells are actively transported into sieve tube cell
2. water potential of the sieve tube cell decreases and becomes more negative than the adjacent xylem and cells
3. water molecules from the xylem enter the sieve tube cells by osmosis (high hydrostatic pressure)

Question 16

translocation step 2

Answer 16

1. at the sink, sucrose is unloaded
2. water potential of the sieve tube cell increases and becomes less negative than the adjacent xylem and cells
3. water molecules from the sieve tube cell enter the xylem by osmosis (low hydrostatic pressure)

Question 17

translocation step 3

Answer 17

difference in hydrostatic pressures between source and sink cause mass flow of water, sucrose and amino acids to move from a region of high hydrostatic pressure to a region of low hydrostatic pressure

Question 18

xylem

Answer 18

continuous lumen with no cross walls and protoplasm
cellulose cell walls are further lignified

Question 19

phloem

Answer 19

thin layer of cytoplasm, no vacuole, nucleus and mitochondrion
sieve plates with pores
companion cells of phloem have numerous mitochondria