Transport in Plants

1
Chapter 36

• Transport in Plants

2
Transport Important Adaptation

• Algal ancestors were bathed in water and
  dissolved minerals
• No need for transport
• Land required a way to get those substances into
  the plant
• Three levels of transport
• Uptake and loss of water and solutes by cells
• Short distance transport, from cell to cell
• Long distance transport, sap within xylem and
  phloem

3
(No Transcript)
4
Transport at the cellular level

• Work much the same way we discussed in chapter 8
• Selectively permeable membrane
• Transport proteins
• Passive transport
• Active transport

5
Proton Pumps
6
Water Potential

• In animal cells we can determine the flow of
  water simply by figuring out where the highest
  concentration of water is (solute concentration)
• Plant cells have a cell wall
• So we must also consider the pressure

7
Water Potential Examples
8
Turgor Pressure
9
Absorption of Water and Minerals by Roots

• Water and minerals from soil enter plant through
  the epidermis, cross the root cortex, pass into
  the steele, and then flow up xylem vessels to the
  shoot

10
Endodermis

• Inner most layer of cells in the root cortex
• Checkpoint for the selective passage of minerals
  and water
• Waxy covering of the cells insures that only
  minerals the plant wants in gets in

11
Water Uptake
12
Transport of Xylem Sap

• Xylem transports water and minerals from the
  roots up the stem into the leaf branches
• Water is lost by leaves at an astonishing rate
• Maple tree loses 200 L of water every hour in the
  summer
• Guttation at night roots are still absorbing
  water and forcing it into the xylem
• In the morning droplets of water can be seen
  exuding from the leaf because the water has
  nowhere else to go

13
(No Transcript)
14
Pulling Xylem Sap

• Guttation is a form of pushing sap from the roots
• This is not the main way a plant gets water
• Water is pulled from the leaves up the stem from
  the roots
• Transpiration of water and the cohesive nature of
  water is responsible for this

15
(No Transcript)
16
(No Transcript)
17
Control of Transpiration

• Leaves must have CO2 to do photosynthesis
• Stomata are openings on the leaf to allow the
  passage of CO2
• These openings also allow water to escape

18
Stomata

• Stomata are flanked by guard cells
• Three cues for opening and closing stomata
• Light causes guard cells to accumulate
  potassium and the guard cells open
• Depletion of CO2
• Internal clock open when the day should be and
  close at night

19
(No Transcript)
20
Translocation of Phloem

• Travel is variable
• Xylem is unidirectional
• Flows through source and sink type flow
• Source leaves making sugar
• Sink fruits and storage cells of sugar

21
(No Transcript)