Ch. 36 Transport in Plants

Question 1

what is the relationship between shoot height and light capture?

Answer 1

taller height = more light capture but
taller height = thicker stems to support height
-more branches give more access to light, but require more energy to grow

Question 2

what is phyllotaxy?

Answer 2

-arrangement of leaves on a stem
-leaves are usually organized to minimize self shading and maximize usable leaf area
-shaded leaves can be lost via self pruning

Question 3

how do roots capture minerals and water / increase their effective surface area?

Answer 3

-roots branch more towards nutrient rich areas, but will not overcrowd other roots of same species
-plants have evolved mutualistic relationships with fungi to capture nutrients and water better = MYCORRHIZAE

Question 4

how does water enter and exit a plant?

Answer 4

enters via roots
leaves via leaves [stomata]

Question 5

how does sugar enter a plant?

Answer 5

as CO2 from the atmosphere [photosynthesis]

Question 6

what is apoplasty?

Answer 6

transport of water/minerals OUTSIDE of cell membranes (cell walls are hydrophilic)

Question 7

what is symplasty?

Answer 7

transport INSIDE the cytosol of living cells (from cell-cell through the cytoplasm and plasmodesmata)

Question 8

what is transmembrane transport?

Answer 8

-substances moving out of one cell, through the cell wall, and into another cell
-requires multiple membrane proteins

Question 9

how do plant cells establish an electrochemical proton gradient?

Answer 9

-proton pump pumps H+ out of cell against concentration gradient
-this sets up an electrochemical gradient that can be used for many things

Question 10

how do cells use electrochemical gradients?

Answer 10

1. cotransporting neutral solutes - sucrose
2. cotransporting ions - NH3 in roots
3. creating gradients to affect cation movements - K+ to regulate stomata openings

Question 11

what is water potential?

Answer 11

water potential = psi = Ψ
-depends on solute concentration inside and outside cell wall
water moves from high Ψ -> low Ψ

Question 12

what is the equation for total water potential?

Answer 12

total water potential = pressure potential + solute potential
Ψ = Ψp + Ψs

Question 13

how is Ψ measured?

Answer 13

-measured in KPa
-Ψ = 0KPa in pure water
-Ψ = 0.5 KPa in most plant cells

Question 14

what is Ψs? how is it measured?

Answer 14

Ψs = solute potential
=0 for water
= <0 in all solutions

Question 15

what is Ψp? how is it measured?

Answer 15

Ψp = physical pressure on a solution
-can be positive or negative
= -2MPa in xylem, + in living cells
= 0MPa in standard conditions

Question 16

what is osmosis?

Answer 16

the movement of water molecules due to the presence of a solvent
-water moves from high concentration of water molecules to a lower concentration of water molecules

Question 17

what is bulk flow?

Answer 17

movement of fluid using pressure gradients
-faster way to move substances long distances

Question 18

how do xylem use bulk flow?

Answer 18

transpiration = negative pressure
negative pressure = xylem can pull up minerals and water

Question 19

how does phloem use bulk flow?

Answer 19

positive pressure = phloem can transport sap through sieve-tube member

Question 20

how do roots get water and minerals into them?

Answer 20

active transport pumps minerals from soil into root = decreased Ψs
-root cells are now hypertonic to soil
-water will flow into the root

Question 21

what is the casparian strip?

Answer 21

a thick layer of lipids right before the stele / vascular cylinder
-acts as a filter and holds xylem sap in place

Question 22

what is root pressure?

Answer 22

-occurs @ night when transpiration is low
-low Ψs and low Ψp = water moves into xyelm from root
-water is pushed up xylem and drips from leaves, creating guttation fluid

Question 23

how does water move up xylem?

Answer 23

-bulk flow of water is driven primarily by Ψp
-active transport of into root moves water into root
-cohesion pulls water up roots
-adhesion to cell walls overcomes force of gravity

-main force that lets water move up is transpiration due to low Ψp in atmosphere

Question 24

what is cavitation?

Answer 24

formation of a water vapour pocket = water cannot move up xylem

Question 25

what are the 5 steps to opening the stomata and letting water into the roots?

Answer 25

1. H+ is pumped out of cell
2. this creates -ve charge in guard cells
3. K+ flows into guard cell down its gradient
4. This decreases Ψs
5. Water flows into cell and cell becomes turgid

Question 26

What is the closing mechanism for stomata?

Answer 26

1. proton pump is turned off, H+ returns to cell
2. K+ diffuses out of cell
3. Ψs increases, and water flows out

Question 27

what stimuli control the opening of the stomata?

Answer 27

light: circadian rhythm
CO2 = stomata will open when levels are low
humidity: if high, stomata will be open
wind: if high, stomata will be closed

Question 28

how do environmental conditions [high temp, low h2o) affect the stomata?

Answer 28

dry conditions = closed stomata
high temperatures = closed stomata
this results in reduced CO2 intake = less photosynthesis = less growth

Question 29

what is sap composed of?

Answer 29

sugar, amino acids, regular acids, hormones, pigments, RNA, lots of other things

Question 30

what are “sinks”?

Answer 30

a location in the plant that uses or stores phloem sap, such as growing roots/shoots, stems and fruits

Question 31

what are sap “sources”?

Answer 31

where sap was made - is usually close to the sink

Question 32

what are the two methods of sap transport?

Answer 32

1. sap transported into sieve tube member via symplastic route - done when sugar can flow down its gradient
2. sap moves via apoplastic route, companion cells work to actively transport sap against its gradient into a sieve-tube member

Question 33

how does phloem translocation via pressure flow work?

Answer 33

1. loading of sugar into phloem cells creates a low Ψs, so water from xylem moves into phloem
2. pressure due to osmosis pushes phloem sap towards sink
3. some water will pass into sink, some into xylem to be recycled
4. solvent follows pressure gradient down into sink

Question 34

how does phloem unloading at the sink work?

Answer 34

-sink usually has lower sugar concentration than phloem, so passive transport is used