Lecture 23: Plant Transport I

Question 1

What function is central to the integrated functioning of the whole plant

Answer 1

transport of materials

Question 2

What evolution made possible long-distance transport of material from “way down –> way up”

Answer 2

xylem & phloem

Question 3

What compromise do adaptations in land plants represent?

Answer 3

enhancing photosynthesis & minimizing water loss

Question 4

Light Capture is determined by

Answer 4

• canopy structure
• phyllotaxy (arrangement of leaves)
• quantified by leaf area index

Question 5

Leaf Area Index

Answer 5

• formula: m^2 leaf/m^2 ground
• if small, not many leaves; if large capturing more light

Question 6

What is nutrient acquisition in plants determined by

Answer 6

• root structure
• proliferation in high nutrient zones
• symbiotic associations w/ mycorrhizal fungi

Question 7

Two types of transport of material

Answer 7

1. short-distance diffusion or active transport
2. long-distance bulk flow

Question 8

how does transport begin?

Answer 8

with the absorption of resources by plant cells

Question 9

what regulates movement of substance into or out of cells

Answer 9

selective permeability

Question 10

explain passive vs active transport

Answer 10

1. passive transport is diffusion across a membrane
2. active transport is pumping of solutes across a membrane - requires energy (ATP)

Question 11

how do solutes pass through the cell membrane

Answer 11

transport proteins

Question 12

what do aquaporins do

Answer 12

channel water in/out of cells

Question 13

What is the most important transport protein for active transport

Answer 13

proton pump

Question 14

what do proton pumps in plant cells do?

Answer 14

• create a H+ ion gradient in a form of a potential energy
• contribute to voltage known as membrane potential

Question 15

How are cations driven into the plant cell

Answer 15

by the membrane potential

Question 16

the membrane potential generated by proton pumps contributes to absorption of _______ by _______

Answer 16

K+; root cells

Question 17

What is cotransport of an anion?

Answer 17

• a transport protein couples diffusion of one solute H+ with active transport of another NO-

Question 18

How does cotransport of a neutral solute occur?

Answer 18

• A sucrose-H+ cotransporter couples movement of sucrose against concentration gradient w/ movement of H+ down its electrochemical gradient

Question 19

What is osmosis and why do plants need it?

Answer 19

• Plants must **balance water uptake & loss **
• Osmosis determines net absorption or loss of water by a cell

Question 20

Plant cells have what type of cell wall and how does it work?

Answer 20

rigid cell walls; physical pressure of cell wall pushes back on expanding protoplast

Question 21

what is water potential and how does it work

Answer 21

• measurement that combines the effects of **solute concentration & pressure **
• determines direction of movement of water
• water flows from high water potential –> lower water potential

Question 22

units of water potential

Answer 22

psi; measured in megapascals (MPa)
psi = 0 for pure H2O at sea level & room temp

Question 23

Water potential & relation to solute

Answer 23

-** both pressure & solute** concentration affect water potential
- expressed by psi = psi(solute) + psi(physical pressure)
- solute potential: proportional to the number of dissolved molecules; more solutes = more -
- solute potential = osmotic potential

Question 24

pressure potential

Answer 24

physical pressure on a solution; cell walls pushing back on the membrane

Question 25

Turgor pressure

Answer 25

pressure exerted by the plasma membrane against the cell wall, and cell wall against the protoplast

Question 26

Explain what happens if a flaccid cell is placed in an environment w/ a higher solute concentration?

Answer 26

• cell will lose water & undergo plasmolysis
• plasmolysis occurs when protoplast shrinks & pulls away from the cell wall

Question 27

Explain what happens if a flaccid cell is placed in an environment w/ a lower solute concentration?

Answer 27

the cell will gain water & become **turgid **

Question 28

what does turgor loss in plants cause, and how can this be fixed?

Answer 28

wilting; plant is watered

Question 29

The three major pathways of transport for water & minerals

Answer 29

1. transmembrane route
2. symplastic route
3. apoplastic route

Question 30

transmembrane route

Answer 30

water and minerals out of one cell, across a cell wall, into another cell

Question 31

symplastic route:

Answer 31

via continuum of cytosol

Question 32

apoplastic route

Answer 32

via the cell walls & extracellular spaces; movement of water w/o going into the cells aka around

Question 33

Since ____ is only efficient for short-distance transport, the efficient long distance transport of fluid requires

Answer 33

diffusion; bulk flow, movement of a fluid driven by pressure ( low –> high p )

Question 34

what is transpiration

Answer 34

drives the transport of water & minerals from the roots to shoots

Question 35

where does most water & mineral absorption occur

Answer 35

near root tips, where epidermis is permeable to water

Question 36

root hairs make up

Answer 36

much of the surface area of roots

Question 37

what happens when soil solution enters the roots

Answer 37

extensive s.a. of cortical cell membranes enhances uptake of H2O & minerals

Question 38

why is concentration of essential minerals greater in roots than soil

Answer 38

active transport

Question 39

how can water cross from roots to shoots

Answer 39

via symplast or apoplast

Question 40

What blocks apoplastic transfer of minerals from the cortex to the vascular cylinder and it is located where

Answer 40

the waxy casparian strip of the **endodermal well **

Question 41

does apoplastic transfer of anything occur in the xylem?

Answer 41

no; cell walls are blocked off

Question 42

what regulates & transports needed minerals from the soil into the xylem

Answer 42

endodermis

Question 43

how do water & minerals move in roots

Answer 43

from protoplasts of endodermal cells into their cell walls

Question 44

what processes are involved in the movement from symplast to apoplast; and where do water & minerals go

Answer 44

diffusion and active transport; tracheids & vessel elements