transport-translocation and transpiration

Question 1

what does the mass flow theory suggest

Answer 1

suggests there is a passive mass flow of sugars from source to sink

Question 2

name 7 features of a sieve tube

Answer 2

-alive
-end walls of eavh cell is perforated forming a sieve plate.
-have enlarged plasmodesmata.
-produces a tube.
-walls also have perforations
-as they mature they lose their nucleus, vacuole mitochondria and ribosomes for space.

Question 3

what is the role of the companion cell

Answer 3

are very active and control metabolism of sieve tube elements via plasmodesmata.

Question 4

name 4 bits of evidence for metabolic activity in companion cells.

Answer 4

-large nucleus.
-dense cytoplasm.
-large quantities of rough ER
-many mitochondria.

Question 5

what evidence is there to suggest translocation is an active process.

Answer 5

translocation is slowed by low temperatures and respiratory inhibitors.

Question 6

what is cytoplasmic streaming-

Answer 6

cytoplasm movement means solutes can be moved in different directions at the same time

Question 7

whta is the role of protein filaments in solute transport.

Answer 7

pass through pores in sieve plates transporting different solutes through the same sieve plates.

Question 8

what are the problems with mass flow.

Answer 8

rate of transport in phloem is 10000x faster than diffusion.
-does not take into account sieve plates.
-sucrose and amino acids move at different rates and directions at the same time.
-phloem has high 02consuption and translocation is slowed or stopped at low tamps or with cyanide.

Question 9

in ringing experiments to provide evidence for phloem transport- what is below the ring.

Answer 9

no sucrose
-suggesting it has been used by plant tissues and had not been replaced as ring blocks movement.

Question 10

how is radioactive tracers and autoradiography used as evidence?

Answer 10

plant photosynthesises in presence of c02.
-stem section placed on photoautographic film which is exposed if there is radiation producing an autoradiograph.
-position of exposure and radioactivity coincides with the position of the phloem . indicating that it is the phloem that translocated sucrose made from the radioactive carbon.

Question 11

what are mesophytes

Answer 11

-live in temperate regions so-
-shed leaves before winter
-annual mesophytes flower and produce seeds in one year
-underground corn and bulbs survive.

Question 12

xerophytes live in what conditions

Answer 12

arid

Question 13

what are adaptations of marram grass

Answer 13

-stiff parenchyma fibres maintain rolled shape to trap water vapour and prevents water loss.
-stomata in pits to trap humide air.
-thick waxy cuticle
-stiff inerlocking hairs on surface reduce air movement

Question 14

what are adaptation of water lilies

Answer 14

-has thin/no waxy cuticle
-stomata on upper surface
-air space continuous down to roots provides 02 and c02 and buoyancy.

Question 15

how does water enter the roots

Answer 15

soil water contains a dilute solution of mineral salts and has a high water potential. The vacuole and cytoplasm of root hair cell contain a concentrated soluion of these solutes and has a lower water potential. water passes into roots by osmosis down a conc gradient.

Question 16

how is water moved from root to cortex

Answer 16

either apoplast -cellulose fibres in cell wall are seperated by spaces through which water moves.
-symplast pathway-through cytoplasm and plasmodesmata which provides a continuous pathway to cortex.

Question 17

which is faster apoplast or symplast

Answer 17

apoplast

Question 18

why cant water enter the xylem from apoplast

Answer 18

lignin makes xylem cell water proof.

Question 19

where is the casparian strip located

Answer 19

endodermis

Question 20

what is the role of the imparrmeable casparian strip

Answer 20

water prevented moving along the apoplast pathway so reach xylem via symplast pathway through endodermis cells.

Question 21

how are mineral salts transported

Answer 21

-taken from root hairs into cytoplasm of epidermal cells -active transport.transported by apoplast and symplast pathway.

Question 22

describe the process of selective uptake in plants

Answer 22

ions blocked by casparian strip in apoplast.
-active and selective uptake ooccurs in endodermal cells.
ions enter xylem by active trasnport and diffusion.

Question 23

what is the xylem made up of

Answer 23

either elongated cells called tracheids or vessels

Question 24

what are the adaptations of xylem

Answer 24

-has primary wall of cellulose and thickened by wall of lignin.
-lignin waterproofs and strenthens the walls.
-stops cell collapsing if cell contents are unter pressure.
-can be pitted to allow water to pass from one cell to another.

Question 25

what is the transpiration stream

Answer 25

the movement of water from root to leaf

Question 26

name the three ways water moves through xylem

Answer 26

cohesian tension theory
-capillarity action
-root pressure

Question 27

how does the cohesian tension theory work

Answer 27

loss of water by transpiration from the top of the leaf creates tension of the column of water and pulls water up the xylem and because of cohesian water molecules are polar so are attracted o one another so as one molecule leaves other are pulled u after it. Water molecules are also attracted to the hydrophilic lining of xylem vessles contributing to upwards movement of water.

Question 28

how does capillarity action work

Answer 28

movement up narrow vessels. this only operates over short distances so does not explain full movement.

Question 29

how does root pressure work in upwards movement of water

Answer 29

active transport of mineral ions into base of xylem in roots decreases water potential. water flows in via osmosis pushing water upwards-this only operates over short distances.

Question 30

how do you measure water loss

Answer 30

enclose the pot of a potted plant in a plastic bag and put plant on a top pan balance- mass gradually falls as water evaporates.

Question 31

describe the experiment for measuring transpiration

Answer 31

1. a cut plant stem is sealed into potometer using a rubbber bung. An air bubble is then introduced to capillary tube. The distance the bubble travels shows how much water the stem as taken up giving an indirect measurement of transpiration rate.

Question 32

what are some issues with potometers

Answer 32

not all water taken up is lost as some is used in photosynthesis.
-the effects of photosynthesis and respiration is usually ignored as the volume of water involved in metabolic processes are insignificant compared to water in transpiration stream.