Transport processes

Question 1

Over evolutionary time of plants, there has been a decreasing dependence on what?

Answer 1

Water

Question 2

How did algal ancestors of land plants absorb water, minerals & CO2?

How did early nonvascular land plants absorb water?

Answer 2

Directly from surrounding water

Lived in shallow water & had aerial shoots

Question 3

What are the 2 types of transport?

Answer 3

Short & long distance

Question 4

What is transported short distances?

Answer 4

Basic nutrients from cells w/ access to nutrient to those w/out

Question 5

What are the features of short distance transport?

Answer 5

Doesn’t require special tissue organisation

Occurs in vascular & non-vascular plants

Intercellular

Question 6

What is transported long distances?

Answer 6

Nutrients around whole plant

Question 7

What are the features of long distance transport?

Answer 7

Requires vascular tissue

Occurs only in vascular plants

Question 8

What are the 2 major pathways through plants?

Answer 8

Apoplast

Symplast

Question 9

What does the apoplast consist of?

Answer 9

Everything external to plasma membrane

- cell walls, extracellular spaces & interior of vessel elements + tracheids

Question 10

What does the symplast consist of?

Answer 10

The cytosol of living cells in a plant

& plasmodesmata

Question 11

How is membrane potential established in plants?

Answer 11

Pumping H+ out of cytoplasm via ATP-dependent proton pumps

Question 12

What does pumping H+ out of cells establish?

What can these be used for?

Answer 12

Membrane potential
pH gradient

= 2 forms of potential energy that can drive the transport of solutes

Question 13

What can be co-transported into plant cells with protons?

Answer 13

Neutral solutes e.g. sucrose loaded into phloem

Ions e.g. nitrate uptake in plant roots

Question 14

How do ion channels in plant cells work?

Answer 14

Open & close in response to: voltage, membrane stretching & chemical factors

e.g. K+ ion channel involved in release of K+ from guard cells when stomata close

Question 15

What 2 components affect water potential?

Answer 15

Solute conc

Pressure

Question 16

Which way does water flow?

Answer 16

Higher water potential to lower

Question 17

What does ‘potential’ refer to?

Answer 17

The capacity of water to do work

Question 18

What is solute potential directly proportional to?

Answer 18

Molarity (no. of particles present in solution)

Question 19

Why is water potential always -ve?

Answer 19

Pure water = 0
When solute added –> bind to water
–> reduces capacity to do work

so solute potential = always -ve

Question 20

Give examples of when pressure potential is +ve or -ve relative to atmospheric pressure

Answer 20

+ve = in cells –> produces turgor pressure

-ve = in xylem vessels

Question 21

What is plasmolysis?

Answer 21

When a cell shrinks & pulls away from cell wall

Question 22

What is the role of aquaporins?

Answer 22

Facilitate water diffusion across membranes

- affect rate at which water moves osmotically across membrane

Question 23

What causes the action of aquaporins to decrease?

Answer 23

Increases in cycstolic Ca2+
or
Decrease in pH

Question 24

By what process does long-distance transport occur?

Answer 24

Bulk flow
via pressure gradient (high–>low)

(independent of solute conc)

Question 25

What is the Casparian strip?

Answer 25

A belt of waxy material that blocks the passage of water & minerals

Question 26

How can water by-pass the Casparian strip?

Answer 26

Only minerals already in symplast (or entering that pathway by crossing the plasma membrane of an endodermal cell) can detour the Casparian strip

Question 27

How is xylem sap pushed up?

Answer 27

Root pressure

Question 28

Describe the process that creates root pressure

Answer 28

At night - low transpiration 
1.Accumulation of minerals in xylem 
(Casparian strip prevents leaking back)
2. Lowers water potential 
3. Water flows in from root cortex
4. Generates root pressure = positive pressure on xylem sap 
(Can cause guttation)

Question 29

How is xylem sap pulled up?

Answer 29

Cohesion-Tension

Question 30

Describe the process of transpirational pull

Answer 30

1. water vapour in airspaces diffuse down WP gradient & exit via stomata
2. Water evaporates
   - -> air-water interface retreats further into mesophyll cell walls
3. Surface tension creates -ve pressure potential
4. pulls water in xylem into leaf
5. pull on xylem sap transmitted from leaves to roots

Question 31

What type of bonds cause adhesion & cohesion?

Answer 31

H bonds

Question 32

What is adhesion?

Answer 32

Strong adhesion of water molecules to hydrophilic walls of xylem cells

Question 33

What is cohesion?

Answer 33

H bonds between water molecules

Question 34

What is phloem sap?

Answer 34

Aqueous solution high in sucrose

can also contain amino acids, hormones & minerals

Question 35

What must happen before sugar can be exported to sinks?

Answer 35

Sugar must be loaded into sieve-tube elements via symplastic or both symplastic & apoplastic pathways

Question 36

How is sugar loaded into sieve-tube elements at the source?

Answer 36

Active transport

- uses proton pumping & H+/sucrose co-transport

Question 37

How is sugar unloaded from sieve-tube elements at the sink?

Answer 37

Diffusion

Question 38

What causes bulk flow of phloem sap?

Answer 38

+ve pressure

= pressure flow

Question 39

Describe bulk flow of phloem sap

Answer 39

1. Higher sucrose conc at source than sink
2. Water moves in from xylem –> increases pressure
3. Higher pressure at source
4. Sap flows down pressure gradient to sink
5. Water moves back into xylem

Question 40

What is self-thinning?

Answer 40

When sinks demand more than sources can provide