mass transport in plants

Question 1

autotrophs

Answer 1

taking in organic molecules and use the energy from light to convert the inorganic molecules into organic molecules in the process of photosynthesis

Question 2

what are the two tissues involved in plant transport?

Answer 2

xylem
phloem

Question 3

xylem

Answer 3

transports water and dissolved ions from the soil to the leaf

Question 4

phloem

Answer 4

transports assimilates (organic molecules made by the plant)from source to soil

Question 5

what system do the xylem and phloem make up?

Answer 5

these make up the vascular system in plants

Question 6

what is transpiration?

Answer 6

the evaporation of water from the leaf

Question 7

the process of the movement of water across a leaf?

Answer 7

1)there is a high water potential in air spaces in the leaf
2)there is a lower water potential in the air
3)water vapour from the air spaces leaves via the stomata down diffusion gradient
4)this reduces the water potential in the air space
5)water evaporates/transpires into airspace
6)water potential of cells is lowered
7)this causes a water potential/osmotic gradient across cells
8)water is drawn out of xylem into cells
9)this causes tension/ a negative pressure at the top of the xylem
10)water moves up (down a pressure gradient)
11)due to cohesion between water molecules, water moves up in one continuous column
12)this is called the cohesion-tension theory of water through xylem

Question 8

adaptions of the xylem

Answer 8

-long cells/tubes with no end walls
-continous tubes
-no cytoplasm/ no organelles to obstruct water flow
-spirals of lignin provides support to withstand tension
-pits in walls allow lateral movement/water can get blacked vessels

Question 9

cohesion-tension theory

Answer 9

-evaporation creates tension (negative pressure) in the xylem
-water molecules joined by hydrogen bonds/cohesion between water molecules
-water pulled up as a continuous column

Question 10

factors affecting transpiration

Answer 10

light intensity
temperature
air movement
humidity

Question 11

the higher the light intensity

Answer 11

the higher the rate of transpiration, as this increases photosynthesis meaning more stomata are open so increased diffusion of water vapour out of the leaf

Question 12

the higher the temperature

Answer 12

the higher the rate of transpiration. this is due to the increased evaporation of water fro cells due to increased kinetic energy

Question 13

the higher the air movement

Answer 13

the higher the rate of transpiration. this is due to increased movement of water vapour away from leaves

Question 14

the lower the humidity level in the air

Answer 14

the higher the rate of transpiration, the water potential gradient between airspaces and the environment so more diffusion of water vapour away from the leaf

Question 15

evidence of the cohesion-tension theory

Answer 15

tree trunks change diameter according to the rate of transpiration. during the day when transpiration is at its greatest, there is more tension (more negative pressure) in the xylem and the trunk reduces in diameter. this reverses at night

Question 16

what device do you use to measure the rate of transpiration

Answer 16

a potometer

Question 17

rate of transpiration

Answer 17

need to measure the distance the bubble has moved

Question 18

how to calculate the rate of transpiration

Answer 18

area of capillary tube x distance moved divided by time

Question 19

what do the phloem transport?

Answer 19

plant vascular that transports assimilates eg sucrose

Question 20

what are the phloem made up of?

Answer 20

living cells called sieve tube elements

Question 21

phloem structure

Answer 21

perforations in the end walls creating sieve plates. associated with a companion cell which provides ATP. companion cells have many mitochondria. Sieve element has few organelles for unrestricted flow of assimilates

Question 22

what is translocation?

Answer 22

movement of assimilates eg sucrose from source to sink by the process of mass flow

Question 23

what is the source?

Answer 23

photosynthesising tissue by leaves

Question 24

what is the sink?

Answer 24

growing tips and storage tissues that use of sucrose (or convert it to starch)

Question 25

how does movement occur?

Answer 25

assimilates move by mass flow down a hydrostatic pressure gradient

Question 26

mass flow hypothesis

Answer 26

movement of sucrose from source to phloem

Question 27

movement of sucrose from source to phloem

Answer 27

hydrogen pumped out of companion cell by active transport, hydrogen concentration gradient is produced and hydrogen moves down the concentration gradient into companion cell. sucrose co-transported into companion cell. sucrose moves via facilitated diffusion from companion cell into sieve tube element and enters the phloem.

Question 28

evidence the mass flow hypothesis

Answer 28

-using ringing experiments
-tree ringing
-using aphids
-using radioactive tracers

Question 29

using ringing experiments

Answer 29

-cut away the bar and the phloem in one section of the tree trunk (a ring)
-leave for a week
-a bulge develops above the ring as sap collects there
-the roots die showing sugars cannot move down the stem

Question 30

tree ringing

Answer 30

ring of bark containing phloem is removed. xylem are in the wood below the bark so they remain intact. sucrose collect in issues above the ring of removed phloem. this area becomes the sink. metabolism in the tree below the ring ceases (no sucrose for respiration)

Question 31

using aphids

Answer 31

aphids feed on plant sucrose by penetrating the phloem with their mouth peice. we can use their mouth pieces to collect samples of solution from the phloem to test it. if radioactive carbon dioxide is supplied to the leaves, we can collect samples from the phloem and it has been found that the radioactive sucrose soon enters the phloem and moves from source to sink

Question 32

using radioactive tracers

Answer 32

leaves are provided with an atmosphere containing radioactive isotope of carbon in carbon dioxide. this will make radioactive glucose and sucrose. x-ray film will develop when exposed to radiation so we can see where radioactive substances are present in the phloem and track its journey.

Question 33

using metabolic inhibitors

Answer 33

metabolic inhibitors eg cyanide inhibit mass flow. this shows an active process as required ATP

Question 34

evidence abasing the mass flow hypothesis

Answer 34

-sucrose is moved to all parts of the plant at the same rate rather than going to areas with low sucrose concentration more quickly. the role of sieve plates is unclear, surely they restrict flow

Question 35

how to use a potometer

Answer 35

1)seal joints/ ensure airtight/ ensure water tight or this will effect bubble position
2)cut shoot under water to avoid introducing air into the xylem
3)cut shoot at a slant to increase the surface area in contact with the water
4)dry off leaves to remove water which would decrease the diffusion gradient for water vapour
5)insert plant stem into the apparatus under water to avoid introducing air bubbles;e
6)ensure no air bubbles are present
7)ensure the tap is closed
8)note where the bubble is at the start/ move bubble start position using the tap
9)reset the bubble to the start using the tap and water from research