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AP-Biology-Reading-Guide-Chapter-36

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					  Chapter 36: Resource Acquisition and Transport in Vascular Plants

  Concept 36.1 Land plants acquire resources both above and below ground

  1. Competition for light, water, and nutrients is intense among the land
     plants. Let’s look first at adaptations to increase light capture. How
     do plants reduce self-shading?
  •Stems serve as conduits for water and nutrients, and as supporting
     structures for leaves
  •Phyllotaxy, the arrangement of leaves on a stem, is specific to each
     species
  •Light absorption is affected by the leaf area index, the ratio of total
     upper leaf surface of a plant divided by the surface area of land on
     which it grows
  •Leaf orientation affects light absorption

  2. What triggers self-pruning?
  Adding more leaves increases shading and the nonproductive leaves
     undergo cell death.

  3.There are different leaf orientations, and each orientation affects
     light capture. Compare the following as to the type of plant that has
     each orientation, and describe the advantage.
  •Light absorption is affected by the leaf area index, the ratio of total
     upper leaf surface of a plant divided by the surface area of land on
     which it grows
   Leaf orientation affects light absorption
  Orientation                  Type of Plant        Advantage
  Vertical leaf orientation    Grasses        Better in sunny
                                              conditions
H Horizontal leaf orientation                 Low-light conditions:
                                              Capture sunlight
4. What are mycorrhizae, and what is their role in resource acquisition?
Root Architecture and Acquisition of Water and Minerals
•Soil is a resource mined by the root system
•Taproot systems anchor plants and are characteristic of most trees
•Roots and the hyphae of soil fungi form symbiotic associations called
   mycorrhizae
•Mutualisms with fungi helped plants colonize land

Concept 36.2 Transport occurs by short distance diffusion or active
transport and long bulk flow

This section gives you a good relational review of the transport
mechanisms from Chapter 7. The next group of questions should be
familiar from AP Biology Laboratory 1, Diffusion and Osmosis, as well.
It covers the concept of water potential, so it might be a good time to
review that lab.

5. What is passive transport?
Diffusion and Active Transport of Solutes
•Diffusion across a membrane is passive, while the pumping of solutes
across a membrane is active and requires energy

6. What is active transport?
•Most solutes pass through transport proteins embedded in the cell
membrane

7. What is the role of transport proteins?
•Most solutes pass through transport proteins embedded in the cell
membrane

8. What are the most important plant cell transport proteins? How do
they work?
•The most important transport protein for active transport is the proton
pump

9. What is membrane potential? How can it be established?
•Proton pumps in plant cells create a hydrogen ion gradient that is a
form of potential energy that can be harnessed to do work
•They contribute to a voltage known as a membrane potential
•Plant cells use energy stored in the proton gradient and membrane
potential to drive the transport of many different solutes

10. Explain co-transport?
•Plant cells use energy stored in the proton gradient and membrane
potential to drive the transport of many different solutes

•In the mechanism called cotransport, a transport protein couples the
diffusion of one solute to the active transport of another
•The “coattail” effect of cotransport is also responsible for the uptake
of the sugar sucrose by plant cells
11. What is osmosis?
•To survive, plants must balance water uptake and loss
•Osmosis determines the net uptake or water loss by a cell and is
affected by solute concentration and pressure

12. Plant cells have a rigid cell all, which adds another factor that
affects osmosis: pressure. Define water potential?
•Water potential is a measurement that combines the effects of solute
concentration and pressure
•Water potential determines the direction of movement of water
•Water flows from regions of higher water potential to regions of lower
water potential
The equation for water potential is  = s + p, where  is water
potential, s is solute potential, and p is the pressure potential. The
understanding of this formula is an objective form Laboratory 1.
•Water potential is abbreviated as Ψ and measured in units of pressure
called megapascals (MPa)
•Ψ = 0 MPa for pure water at sea level and room temperature

13. By definition what the s of pure water? 0 or negative
•The solute potential (ΨS) of a solution is proportional to the number of
dissolved molecules
•Solute potential is also called osmotic potential

14. How does the adding of solutes to pure water affect water
potential?
•The solute potential (ΨS) of a solution is proportional to the number of
dissolved molecules
•The addition of solutes reduces water potential

15. The solute potential of a solution is therefore always 0 or negative.

16. What is pressure potential ? Under what conditions will it decrease?
•Pressure potential (ΨP) is the physical pressure on a solution
•Physical pressure increases water potential
•Negative pressure decreases water potential

Measuring Water Potential
•Consider a U-shaped tube where the two arms are separated by a
membrane permeable only to water
17. What is the water potential on the left side of tube A? Why?
0 Mpa, it is pure water, and •Ψ = 0 MPa for pure water at sea level
and room temperature

18. Is the water potential on the right side of tube A positive or
negative?
Negative

19. Explain in terms of water potential, why the level of the liquid is
higher on the right side of tube A.
•The addition of solutes reduces water potential

20. In tube B pressure is being applied on the right side. This is much
like the pressure exerted by the cell wall when a plant cell takes up
water. Explain in terms of water potential why the level of liquid is the
same on both sides even though the two solutions are not isotonic to
each other.
•Physical pressure increases water potential

21. To summarize water moves from regions of higher water potential to
regions of lower water potential.
Water moves in the direction from higher water potential to lower water
potential

22. Define these terms:•Water potential affects uptake and loss of
water by plant cells
   1. Flaccid•If a flaccid cell is placed in an environment with a higher
      solute concentration, the cell will lose water and undergo
      plasmolysis
   2. Turgid •If the same flaccid cell is placed in a solution with a
      lower solute concentration, the cell will gain water and become
      turgid •Turgor loss in plants causes wilting, which can be reversed
      when the plant is watered

23. In the figure below a plant cell that has an initial water potential of
-0.7 MPa is placed into two different conditions. Explain in terms of
water potential what is happening in each case?




a. Cellular water potential has greater environmental water potential;
and
b. Cellular water potential has lesser environmental water potential.

24. What are aquaporins?
Aquaporins: Facilitating Diffusion of Water
•Aquaporins are transport proteins in the cell membrane that allow the
passage of water
•The rate of water movement is likely regulated by phosphorylation of
the aquaporin proteins

25. There are three major pathways of transport between plant cells.
On the sketch label and explain:
Three Major Pathways of Transport
•Transport is also regulated by the compartmental structure of plant
cells
•The plasma membrane directly controls the traffic of molecules into
and out of the protoplast
•The plasma membrane is a barrier between two major compartments,
the cell wall and the cytosol
•The third major compartment in most mature plant cells is the vacuole,
a large organelle that occupies as much as 90% or more of the
protoplast’s volume
•The vacuolar membrane regulates transport between the cytosol and
the vacuole
    1. Transmembrane route: –Transmembrane route: out of one cell,
       across a cell wall, and into another cell
•The cytoplasm of neighboring cells is connected by channels called
plasmodesmata
    2. Apoplast: –Apoplastic route: via the cell walls and extracellular
       spaces
•The apoplast is the continuum of cell walls and extracellular spaces
    3. Symplast: - Symplastic route: via the continuum of cytosol
•The cytoplasmic continuum is called the symplast–
26. What is bulk flow?
•Efficient long distance transport of fluid requires bulk flow, the
movement of a fluid driven by pressure
•Water and solutes move together through tracheids and vessel
elements of xylem, and sieve-tube elements of phloem
•Efficient movement is possible because mature tracheids and vessel
elements have no cytoplasm, and sieve-tube elements have few
organelles in their cytoplasm

Concept 36.3 Water and minerals are transported from roots to shoots

27. On the sketch use colored pencils to trace the uptake of water and
minerals from root hairs to the xylem and phloem in a root. Following a
symplasitc route and an apoplastic route. Then label each of the
following elements: Root hair, plasma membrane, plasmodesmata, stele,
endodermis, Casparian strip, symplastic route, and apoplastic route.
28. What is the role of the Casparian strip?
•The waxy Casparian strip of the endodermal wall blocks apoplastic
transfer of minerals from the cortex to the vascular cylinder

29. Write a short essay to explain the movement of water from the soil
into the stele of the root using all the terms in question 27: Following a
symplasitc route and an apoplastic route. Then label each of the
following elements: Root hair, plasma membrane, plasmodesmata, stele,
endodermis, Casparian strip, symplastic route, and apoplastic route.
Absorption of Water and Minerals by Root Cells
•Most water and mineral absorption occurs near root tips, where the
epidermis is permeable to water and root hairs are located. They
account for much of the surface area of roots. After soil solution
enters the roots, the extensive surface area of cortical cell membranes
enhances uptake of water and selected minerals. The endodermis is the
innermost layer of cells in the root cortex. It surrounds the vascular
cylinder and is the last checkpoint for selective passage of minerals
from the cortex into the vascular tissue. Water can cross the cortex
via the symplast or apoplast.
The waxy Casparian strip of the endodermal wall blocks apoplastic
transfer of minerals from the cortex to the vascular cylinder.

30. What is transpiration?
•Plants lose a large volume of water from transpiration, the evaporation
of water from a plant’s surface
•Water is replaced by the bulk flow of water and minerals, called xylem
sap, from the steles of roots to the stems and leaves

31. There are two mechanisms that pull water up through the plant
from roots to leaves. Explain root pressure.
•At night, when transpiration is very low, root cells continue pumping
mineral ions into the xylem of the vascular cylinder, lowering the water
potential
•Water flows in from the root cortex, generating root pressure

32. The second mechanism that pulls water up through the plant
transpiration-cohesion-tension. Refer to this sketch in your text. Note
that water is moving from a region of high water potential to a region of
lower water potential. The arrow on the left side of the figure shows
this gradient. Beginning where you stopped in question 29, write an
essay to explain the movement of water from the roots to the leaves.
Include some of these terms in your essay, and label them on the
figure: lower water potential, higher water potential, hydrogen bonding,
adhesion, cohesion, xylem tubes, and stomata.
•Positive root pressure is relatively weak and is a minor mechanism of
xylem bulk flow
Transpirational Pull
•Water vapor in the airspaces of a leaf diffuses down its water
potential gradient and exits the leaf via stomata
•Transpiration produces negative pressure (tension) in the leaf, which
exerts a pulling force on water in the xylem, pulling water into the leaf
Cohesion and Adhesion in the Ascent of Xylem Sap
•The transpirational pull on xylem sap is transmitted all the way from
the leaves to the root tips and even into the soil solution
Transpirational pull   is facilitated by cohesion of water molecules to each
other and adhesion     of water molecules to cell walls
•Drought stress or     freezing can cause cavitation, the formation of a
water vapor pocket     by a break in the chain of water molecules




Concept 36.4 Stomata help regulate the rate of transportation

33. Leaves generally have large surface areas and high surface to
volume ratios. Give an advantage and disadvantage of these traits.
   1. Advantage: Increase photosynthesis; and
   2. Disadvantage: Increase water loss through stomata.

34. Plants lose 95% of their water through stomata! What controls the
amount of the water loss?
•About 95% of the water a plant loses escapes through stomata
•Each stoma is flanked by a pair of guard cells, which control the
diameter of the stoma by changing shape

35. On the sketches label the guard cell, stomata, K+, and H2O.
Explain why the stoma opens when K+ accumulates in the guard cells.




36. 3 types of stimuli can cause guard cells to open. Name and explain.
Stimulus for Stomata        Explanation
Open / Close
•Generally, stomata open    •Changes in turgor pressure open and close
during the day and close    stomata
at night to minimize water
loss
•Stomatal opening at        •Transpiration also results in evaporative
dawn is triggered by         cooling, which can lower the temperature of
light, CO2 depletion, and    a leaf and prevent denaturation of various
an internal “clock” in       enzymes involved in photosynthesis and other
guard cells                  metabolic processes
are 24-hour cycles
•All eukaryotic organisms    •Plants lose a large amount of water by
have internal clocks;        transpiration
circadian rhythms

37. What plant hormone is produced in response to water deficiency?
Crassulacean acid metabolism (CAM)

•Xerophytes are plants adapted to arid climates
•They have leaf modifications that reduce the rate of transpiration
•Some plants use a specialized form of photosynthesis called
crassulacean acid metabolism (CAM) where stomatal gas exchange occurs
at night



38. List four different physiological or morphological adaptations of
xerophytes, and explain how each of them reduces water loss.
•Xerophytes are plants adapted to arid climates
   1. Plants lose a large amount of water by transpiration
   2. If the lost water is not replaced by sufficient transport of water,
      the plant will lose water and wilt
   3. Transpiration also results in evaporative cooling, which can lower
      the temperature of a leaf and prevent denaturation of various
      enzymes involved in photosynthesis and other metabolic processes
   4. Xerophytes have leaf modifications that reduce the rate of
      transpiration
   5. Xerophytes sometimes use a specialized form of photosynthesis
      called crassulacean acid metabolism (CAM) where stomatal gas
      exchange occurs at night

Concept 36.5 Sugars are transported from leaves and other sources to
sites of use or storage

39. What is translocation?
•The products of photosynthesis are transported through phloem by the
process of translocation

40. What is a sugar source, and what is a sugar sink? Give an example
of each.
Movement from Sugar Sources to Sugar Sinks
•Phloem sap is an aqueous solution that is high in sucrose
•It travels from a sugar source to a sugar sink
•A sugar source is an organ that is a net producer of sugar, such as
mature leaves
•A sugar sink is an organ that is a net consumer or storer of sugar,
such as a tuber or bulb
•A storage organ can be both a sugar sink in summer and sugar source
in winter

41. What cell types transport sugars?
•Transfer cells are modified companion cells that enhance solute
movement between the apoplast and symplast

42. Explain the process of pressure flow by annotating the figure below.
Refer to your text, and divide the process into four steps.
Do the ten Self Quiz questions.

43. Study Figure 36.21. How do aphids feed? When houseplants are
infested with aphids, why is there a sticky mess on the floor around
them? See diagram below.
Concept 36.6 The symplast is highly dynamic

44. Give two specific signals that move through the symplast, and
describe the function of each signal.
•The symplast is a living tissue and is responsible for dynamic changes in
plant transport processes
Plasmodesmata: Continuously Changing Structures
•Plasmodesmata can change in permeability in response to turgor
pressure, cytoplasmic calcium levels, or cytoplasmic pH
•Plant viruses can cause plasmodesmata to dilate
•Mutations that change communication within the symplast can lead to
changes in development
Electrical Signaling in the Phloem
•The phloem allows for rapid electrical communication between widely
separated organs
•Phloem is a “superhighway” for systemic transport of macromolecules
and viruses
•Systemic communication helps integrate functions of the whole plant
Testing Your Knowledge: Self-Quiz Answers
Now you should be ready to test your knowledge. Place your answers
    here:
1._________ 2._________ 3._________ 4.________ 5._________
6._________ 7._________ 8._________ 9.________10._________

				
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