1. Chapter 29
Part 1

2. Phyllotaxy, the arrangement of leaves on a stem, is specific to each species
Most angiosperms have one leaf per node (alternate phyllotaxy) with leaves arranged in a spiral
The angle between leaves is 137.5° and likely minimizes shading of lower leaves
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3. The productivity of each plant is affected by the total area of the leafy portions of all the plants in the community
Self-pruning, the shedding of lower shaded leaves when they respire more than photosynthesize, occurs when the canopy is too thick
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4. These relationships help absorb water and nutrients more efficiently
Roots form mutually beneficial relationships with fungi, called mycorrhizae
These relationships help absorb water and nutrients more efficiently
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5. Three transport routes for water and solutes are
The apoplastic route, through cell walls and extracellular spaces
The symplastic route, through the cytosol (plasmodesmata)
The transmembrane route, across cell walls and plasma membranes
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6. © 2016 Pearson Education, Inc.
Figure 29.5
Cell wall
Apoplastic route
Cytosol
Symplastic route
Transmembrane route
Figure 29.4 Cell compartments and routes for short-distance transport
Plasmodesma
Apoplast
Plasma membrane
Symplast
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7. Short-Distance Transport of Solutes Across Plasma Membranes
Plasma membrane permeability controls the movement of substances into and out of cells
Both active and passive transport occur in plants
In plants, membrane potential is established through pumping H+ by proton pumps
In animals, membrane potential is established through pumping Na+ by sodium-potassium pumps
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8. The direction of water flow is determined by water potential, a quantity that includes the effects of solute concentration and pressure
Water flows from regions of higher water potential to regions of lower water potential
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9. Ψ = 0 MPa for pure water at sea level and at room temperature
Water potential is abbreviated as Ψ and measured in a unit of pressure called the megapascal (MPa)
Ψ = 0 MPa for pure water at sea level and at room temperature
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10. Pressure potential (ΨP) is the physical pressure on a solution
Turgor pressure is the pressure exerted by the protoplast against the cell wall
The protoplast is the living part of the cell, which also includes the plasma membrane
This pressure helps maintain the stiffness of plant tissues and drives cell elongation
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11. How Solutes and Pressure Affect Water Potential
Both pressure and solute concentration affect water potential
This is expressed by the water potential equation: Ψ = ΨS + ΨP
The solute potential (ΨS) of a solution is directly proportional to its molarity
Adding solute reduces water potential, so it has a negative effect. Because of this, solute potential is always negative.
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12. Water Movement Across Plant Cell Membranes
Water potential affects uptake and loss of water by plant cells
If a flaccid (limp) cell is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis
Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall
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13. If a flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid (firm)
Turgor loss in plants causes wilting, which can be reversed when the plant is watered
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14. © 2016 Pearson Education, Inc.
Figure
Environment
0.4 M sucrose solution:
Initial flaccid cell:
yP = 0
yP = 0
yS = -0.7
yS = -0.9
y = -0.7 MPa
y = -0.9 MPa
Final plasmolyzed cell
at osmotic equilibrium
with its surroundings:
Figure Water relations in plant cells (part 1: plasmolyzed cell)
yP = 0
yS = -0.9
y = -0.9 MPa
(a) Initial conditions: cellular y > environmental y
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15. © 2016 Pearson Education, Inc.
Figure
Environment
Pure water:
Initial flaccid cell:
yP = 0
yP = 0
yS = -0.7
yS = 0
y = -0.7 MPa
y = 0 MPa
Final turgid cell
at osmotic equilibrium
with its surroundings:
Figure Water relations in plant cells (part 2: turgid cell)
yP =
yS = -0.7
y =
0 MPa
(b) Initial conditions: cellular y < environmental y
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16. © 2016 Pearson Education, Inc.
Figure 29.6
Wilted
Turgid
Figure 29.6 A moderately wilted plant can regain its turgor when watered.
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17. Short-Distance Transport of Water Across Plasma Membranes
Osmosis, the diffusion of free water across a membrane, determines the net uptake or water loss by a cell
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18. Aquaporins: Facilitating Diffusion of Water
Aquaporins are transport proteins in the plasma membrane that allow the passage of water
Aquaporin channels can open or close to change the rate of water movement across the membrane
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19. Concept 29.3: Plants roots absorb essential elements from the soil
Water, air, and soil minerals contribute to plant growth
80–90% of a plant’s fresh mass is water
96% of a plant’s dry mass consists of carbohydrates from the CO2 assimilated during photosynthesis
4% of a plant’s dry mass is inorganic substances from soil
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20. Macronutrients and Micronutrients
More than 50 inorganic chemical elements are found in plants, but not all are essential
There are 17 essential elements, (essential nutrients) chemical elements required for a plant to complete its life cycle
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21. Nine of the essential elements are called macronutrients because plants require them in relatively large amounts
The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium
Nitrogen is the most important nutrient contributing to plant growth and crop yields
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22. Plants with C4 and CAM photosynthetic pathways also need sodium
The remaining eight are called micronutrients because plants need them in very small amounts
The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum
Plants with C4 and CAM photosynthetic pathways also need sodium
Micronutrients function as cofactors, nonprotein helpers in enzymatic reactions
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23. © 2016 Pearson Education, Inc.
Table
Table Macronutrients in plants (part 2)
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24. Symptoms of Mineral Deficiency
Symptoms of deficiency depend on the mineral’s function and mobility within the plant
The most common deficiencies are those of nitrogen, potassium, and phosphorus
Nitrogen is most limiting to plant growth on a global scale
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25. © 2016 Pearson Education, Inc.
Figure 29.8
Healthy
Nitrogen-
deficient
Phosphorus-
deficient
Figure 29.8 The most common mineral deficiencies, as seen in maize leaves
Potassium-deficient
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