Download AP Biology, Chapter 36 Resource Acquisition and Transport in

AP Biology, Chapter 36
Resource Acquisition and Transport in Vascular Plants
Underground Plants
36.1 Adaptations for acquiring resources were key steps in the evolution of vascular plants
Intro
Shoot Architecture and Light Capture
Root Architecture and Acquisition of Water and Minerals
36.2 Different mechanisms transport substances over short or long distances
Intro
1. Compare the processes of passive and active transport. Distinguish between the two
main categories of transport proteins.
Passive
Does not require the use of cellular energy; higher  lower
Ex.: osmosis, CO2 into parenchyma
Active
Requires the use of cellular energy; lower  higher
Ex.: sugar into phloem, protons out of the cell
Transport protein mechanisms
Undergo a conformational change; ex.: ??
Form a selective channel; ex.: K+ channels, aquaporins
The Apoplast and Symplast: Transport Continuums
2. Describe the three major compartments in vacuolated plant cells, noting their
interrelationships.
Cell wall: soaked in extramembraneous fluid; continuous with neighbors
Cytoplasm: modified by transport through membranes and plamsodesmata
Vacuole: contents = cell sap; not continuous from cell-to-cell
3. Describe the three routes available for lateral transport in plants.
Apoplast: transport through extramembraneous fluid
Symplast: cytoplasms are continuous by plasmodesmata
Cell-to-cell across cell membranes
Short-Distance Transport of Solutes Across Plasma Membranes
4. Describe the role and importance of proton pumps in transport across plant
membranes.
ATP is used to pump H+ out
Chemical gradient since H+ is higher outside
Voltage or potential positive outside
Uses
Positive ions like K+ are attracted into the cell
Diffusion of H+ can power transport of other materials
Short-Distance Transport of Water Across Plasma Membranes
Intro
5. Define osmosis and water potential. Explain how water potential is measured.
Osmosis = diffusion of water through a selectively permeable membrane
Water potential
Tendency of water to move taking into account concentration and
pressure
Measured in megapascals (MPa), a unit of pressure
How Solutes and Pressure Affect Water Potential
6. Explain how solutes and pressure affect water potential.
Water pressure (Ψ) = solute potential (ΨS) + pressure potential (ΨP)
Adding solutes makes ΨS negative, lowering water potential
Increasing the pressure increases water potential
Water Movement Across Plant cell membranes
7. Explain how the physical properties of plant cells are changed when the plant
is placed into solutions that have higher, lower, or the same solute
concentrations. Define flaccid, plasmolyze, turgor pressure, and turgid.
Solution effects: hypo, bigger; hyper, smaller; iso, the same
Definitions
Flaccid: not exerting outward pressure
Plasmolyze: lose water, membrane shrinks away from cell wall
Turgor pressure: pressure of the cell against the cell wall
Turgid: solute potential balances pressure potential, stiff with
water
Aquaporins: Facilitating Diffusion of Water
Long-Distance Transport: The Role of Bulk Flow
8. Relate the structure of sieve-tube cells, vessel cells, and tracheids to their functions
in bulk flow.
Sieve-tube members are cells
Must maintain sugar concentration
Simplified for lower resistance
Vessel elements and tracheids are dead and empty for lower resistance
36.3 Transpiration drives the transport of water and minerals from roots to shoots via the
xylem
Intro
Absorption of Water and Minerals by Root Cells
Transport of Water and Minerals into the Xylem
9. Explain how the endodermis functions as a selective barrier between the root cortex
and vascular tissue.
Apoplast is blocked by suberin in the Casparian strip around each endodermal
cell
Water and minerals must pass through the symplast to enter stele
Minerals are pumped out of the endodermal cells into the stele apoplast
Endodermis especially prevents leakage back out of the stele
Bulk Flow Transport via the Xylem
Intro
Pushing Xylem Sap: Root Pressure
10. Describe the potential and limits of root pressure to move xylem sap. Define
root pressure, transpiration, and guttation.
Root pressure
At night, transpiration stops
Roots are still absorbing water
Xylem in the stele has higher solutes
Pressure builds up in root xylem, pushing the water up
Transpiration is the evaporation of water out of the leaves
If the root pressure is high enough drops of water come out the leaves
= guttation.
Pulling Xylem Sap: The Cohesion-Transpiration Hypothesis
Intro
Transpirational Pull
11. Explain how transpirational pull moves xylem sap up from the root
tips to the leaves.
Water evaporates from spaces in spongy parenchyma
Water film forms strong menisci in the corners of the spaces
Surface tension of the menisci pulls water through apoplast
Cohesion of water molecules pulls on the entire water column
Adhesion and Cohesion in the Ascent of Xylem Sap
Xylem Sap Ascent by Bulk Flow: A Review
36.4 The rate of transpiration is regulated by stomata
Intro
Stomata: Major Pathways for Water Loss
12. Describe the role of guard cells in photosynthesis-transpiration.
Plant must balance needs to exchange gases and save water
Guard cells can open and close stomata
13. Explain the advantages and disadvantages of the extensive inner surface area of a
leaf.
Advantages
Increases surface area for absorption of CO2
Most photosynthetic cells are close to air
Disadvantages
Increases surface area for water loss
90% of water loss is through stomata
14. Explain how the transpiration-to-photosynthesis ratio is calculated and what it
indicates about a plant.
Calculation: water lost per gram of fixed CO2
Indicates efficiency of water usage: C 4 plants use half the water
Mechanisms of Stomatal Opening and Closing
15. Explain how and when stomata open and close.
During the day: guard cells are turgid, more curved, stomata open
Proton pumps export H+
K+ flows in, water follows by osmosis
At night: guard cells are flaccid, less curved, stomata closed
At dawn
Light receptors turn on proton pumps
Photosynthesis begins, CO2 in mesophyll goes down
Circadian rhythm
Close in the daytime in response to stress
Stimuli for Stomatal Opening and Closing
Effects of Transpiration on Wilting and Leaf Temperature
16. Explain how transpiration changes the temperatures of leaves and why this is
adaptive. Explain how plants with low transpiration rates compensate for higher
temperatures.
Transpiration is evaporative cooling
Keeps photosynthetic enzymes from denaturing
Desert plant enzymes are adapted to be stable at higher temperatures
Adaptations That Reduce Evaporative Water Loss
17. Explain how xerophytes reduce transpiration.
Small thick leaves with a thick cuticle
Stomata in depressions with trichomes
CAM plants store CO2 at night; close stomata in the day
36.5 Sugars are transported from sources to sinks via the phloem
Intro
Movement of Sugar Sources to Sugar Sinks
Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms
18. Define and describe the process of translocation. Trace the path of phloem sap from
the primary sugar source to common sugar sinks.
Translocation is the transport of food
Phloem sap
Flows through sieve tube members
As much as 30% sucrose; also minerals, amino acids, hormones
Translocation mechanism = pressure flow
Sugar is actively transported into sieve tube members
Water follows by osmosis
Increased pressure pushes sap through sieve plates
Pathway
Sources: leaves, storage tissues
Through sieve tube members
Sinks: growing tissues, storage tissues, any living tissue
19. Describe the process of sugar loading and unloading.
Various combinations of symplast and apoplast
Into sieve tube members by cotransport with protons
36.6 The symplast is highly dynamic
Intro
Changes in Plasmodesmata
Phloem: An Information Superhighway