Mass transport in plants

Question 1

If it is not a causal relationship it may be a….

Answer 1

correlation

Question 2

Describe the first stage of mass flow

Answer 2

-Co transport (by protein) of sucrose ( converted from glucose ) with H + ions ( active transport ) into companion cell
-diffusion of sucrose from companion cell into sieve tube element
-lowers water potential in sieve tube element so H2O enters tubes by osmosis from xylem / companion cells
-creates high pressure in sieve tubes, at source of phloem

Question 3

Describe the second stage of mass flow

Answer 3

-At the sink end, solutes are removed from the phloem to be used up
-This increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis
-this lowers the pressure inside the sieve tubes

Question 4

Describe the third stage of mass flow

Answer 4

-pressure gradient from the source to sink end of the sieve tube
-this gradient pushes solutes along the sieve tubes, toward the sink
-when they reached the sink the solutes will be used ( e.g. in respiration ) or stored ( e.g. as starch \0

Question 5

What tissue is adapted to transport solutes in plants, name the proces/ two organelles it contains.

Answer 5

Phloem-translocation:
-sieve tube element
-companion cell

Question 6

Describe the sieve tube elements and companion cells.

Answer 6

-Sieve tube elements: living cells that form a tube for transporting solutes, have no nucleus and few organelles so…
-Companion cell: carry out the living functions for sieve cells e.g. providing energy needed for A. transp. of solutes

Question 7

What tissue is adapted to transport water and mineral ions in the stem and leaves of plants, name the proces?

Answer 7

Xylem vessel, transpiration

Question 8

Describe how the xylem is adapted for transpiration

Answer 8

-Xylem vessels are hollow and have no end walls, so there is a long, uninterrupted flow of water

Question 9

Describe translocation, and what tissue is involved?

Answer 9

Translocation, phloem:
-movement of assimilates (solutes) from source to sink ( where it is made to where it is used up)
-Enzymes maintain a conc. gradient from source to sink by changing solutes at sink (e.g. hydrol. them) so always lower conc. at sink than source

Question 10

What are examples of a source in translocation

Answer 10

-source of sucrose is in leaves ( where it is made)

Question 11

Cohesion tension theory is a model for which process?

Answer 11

Transpiration

Question 12

Describe transpiration

Answer 12

-water evaporates from the moist walls and accumulates in the spaces between cells in leaf
-When stomata open, it moves out of the leaf down the conc. gradient ( there is more H2O inside leaf than out )

Question 13

How does light intensity affect transpiration rate?

Answer 13

• more light = higher transpiration rate transpiration rate, as stomata open to let in CO2 when it is light for photosynthesis

Question 14

How does humidity affect transpiration rate?

Answer 14

-lower humidity = higher transpiration rate ( negative correlation)
-if air around plant is dry, conc. gradient between H2O vapour in leaf and air increased, so water will diffuse out of leaf faster

Question 15

How does temp. affect transpiration rate?

Answer 15

-Temp:
1 ) higher temp. means faster rate of transpiration as as warmer H2O molecules so they evaporate from cells inside the leaf faster
2 ) This increases the conc. gradient between the inside/ outside of leaf

Question 16

How does wind affect transpiration rate?

Answer 16

-the windier it is, the faster the transpiration rate
-lots of air blows away the water molecules from around the stomata, increases conc. gradient, increases rate of transpiration

Question 17

What is cohesion tension theory?

Answer 17

-water evaporates from leaves at top of plant, creating suction/ tension which pulls up more water into leaf
-water molecules are cohesive due to H bonding / being polar molecules so when water some are pulled into the leaf others follow
-therefore, whole column of water in the xylem from the leaves down to the roots moves upwards
-water enters plant from the root

Question 18

What can be used to stain xylem in celerly

Answer 18

toluidine blue stains walls of xylem blue/green