Chapter 3

Question 1

Water potential

Answer 1

a measure of water’s potential energy; affects the movement of water in soil from one location to another.

Question 2

Matric (or matrix) potential

Answer 2

the potential energy generated by the attractive forces between water molecules and soil particles; occurs because water molecules and soil particles have electrical charges.

Question 3

saturated soil

Answer 3

most water does not contact soil particles and is not strongly held by the soil; matric potential is 0 MPa.

Question 4

field capacity

Answer 4

When gravity drains the water in soil, the matric potential drops to –0.01 MPa. The maximum amount of water held by soil

Question 5

wilting point

Answer 5

Matric potential decreases as plants extract more water from the soil. Past ~–1.5 MPa, known as the wilting point, most plants cannot extract more water.

Question 6

For a given volume of soil, the ____ surface area that soil has, the ____ water it can hold.

Answer 6

more; more

Question 7

Soil particle sizes small to large

Answer 7

clay, silt, sand

Question 8

Why can smaller particles hold more water?

Answer 8

Smaller particles (e.g., clay) have a larger surface area relative to their volume. As a result, they can hold more water, but that water is held very tightly.

Question 9

Loam soils

Answer 9

are some of the best for growing plants, contain 40% sand, 40% silt, and 20% clay.

Question 10

Salinization

Answer 10

the process of repeated irrigation (with salty water) that causes increased soil salinity; creates a challenge for crop plants.

Question 11

Cohesion

Answer 11

the mutual attraction of water molecules; allows water to move up through empty remains of xylem cells.

Question 12

Root pressure

Answer 12

when osmotic potential in the roots of a plant draws in water from the soil and forces it into xylem; can raise water to ~20 m.

Question 13

Transpiration

Answer 13

the process by which leaves can generate water potential as water evaporates from the surfaces of leaf cells.

Question 14

Cohesion-tension theory

Answer 14

the mechanism of water movement from roots to leaves due to water cohesion and water tension.

Question 15

Stomata

Answer 15

small openings on leaf surfaces that are points of entry for CO2 and exit points for water vapor; bordered by guard cells that open and close each stoma.

Stomata stop excess transpiration so plants do not wilt.

Question 16

Photon energy is ___________ related to frequency and ___________ related to wavelength.

Answer 16

Positively; inversely

Question 17

Chloroplasts

Answer 17

specialized cell organelles found in eukaryotic photosynthetic organisms.

Chloroplasts contain stacks of membranes (i.e., thylakoids) surrounded by a fluid-filled space (i.e., stroma).

Chlorophylls and carotenoids are pigments inside the thylakoids absorb light.

Question 18

Cartenoids (carrots)

Answer 18

reflect orange and red light; allow plants to absorb a wider range of solar energy.

Question 19

Photosynthesis

Answer 19

Photosynthesis is the process of combining CO2, H2O, and solar energy to produce glucose (C6H12O6)

Question 20

Light reactions

Answer 20

1. Chlorophyll in thylakoids absorbs photon energy.
2. Chlorophyll releases electrons to a chain of reactions.
3. In the process, H2O molecules are split into H+ and O2– ions.
4. O2– ions join to form molecular
   oxygen.
5. Energy is collected from released
   electrons and the split of H2O.
6. Energy + H+ + ADP–>ATP
7. Energy + H+ + NADP+–>NADPH

Question 21

Calvin cycle

Answer 21

Takes place in the stroma of the chloroplast.

The energy in ATP and NADPH is used to convert CO2 into glucose.

Several different types of Calvin cycles have evolved: C3 (most plants), C4 (grasses, sedges), and CAM (family Crassulaceae).

Question 22

C3 Photosynthesis

Answer 22

CO2 + RuBP–>2G3P

Question 23

Disadvantages of C3 photosynthesis

Answer 23

Rubisco has a low affinity for CO2, so C3 plants must pack their cells with large amounts of Rubisco.

Rubisco also preferentially binds to O2.

When conditions are hot and dry, leaf stomata close to prevent transpiration, which also prevents O2 from leaving the leaf.

Question 24

Photorespiration

Answer 24

the oxidation of carbohydrates to CO2 and H2O by Rubisco, which reverses the light reactions of photosynthesis.

Question 25

C4 photosynthesis

Answer 25

a photosynthetic pathway in which CO2 is initially assimilated into a four-carbon compound, oxaloacetic acid (OAA); provides an advantage in hot and dry conditions.

Calvin cycle occurs in internal bundle sheath cells; after OAA is converted to malic acid.

CO2 concentrations in sheath cells are 3–8 times higher than is available in C3 photosynthesis.

Question 26

Disadvantages of C4 photosynthesis

Answer 26

less tissue is used for photosynthesis; energy is used to produce OAA.

Question 27

PEP

Answer 27

phosphoenol pyruvate; has higher CO2 affinity than Rubisco.

Question 28

CAM (crassulacean acid metabolism) photosynthesis

Answer 28

a pathway in which the initial assimilation of carbon into OAA occurs at night.

During days, stomata close to reduce transpiration rates.

Stomata open to exchange gases during the night, when cool temperatures slow transpiration.

Question 29

C3 plants are adapted to _____________ whereas C4 and CAM plants are better adapted to______________ conditions.

Answer 29

cool, wet conditions; warm and arid

Question 30

embolisms

Answer 30

Small leaves with a high density of veins prevent loss of leaf tissue via embolisms, or air bubbles in veins, which are common in water-stressed environments.

Question 31

Negative feedbacks

Answer 31

The action of internal response mechanisms that restores a system to a desired state, or set point, when the system deviates from that state.

Example:
In mammals, the hypothalamus triggers increased metabolism when body temperature is below 37°C, and sweating when body temperature is above 37°C.

Question 32

Radiation

Answer 32

the emission of electromagnetic energy by a surface. Increases with the fourth power of absolute temperature.

Question 33

Conduction

Answer 33

the transfer of the kinetic energy of heat between substances that are in contact with one another.

Question 34

Convection

Answer 34

the transfer of heat by movement of liquids and gases; molecules next to a warm surface gain energy and move away.

Question 35

Evaporation

Answer 35

the transformation of water from a liquid to a gaseous state with the input of energy; removes heat from a surface

Question 36

Thermal inertia

Answer 36

the resistance to a change in temperature due to a large body volume.

Question 37

Poikilotherms

Answer 37

organisms that do not have constant body temperatures.

Question 38

Ectotherms

Answer 38

organisms with body temperatures determined by their external environment; not necessarily poikilotherms.

Question 39

Endotherms

Answer 39

organisms that can generate metabolic heat to raise body temperature higher than the external environment.

Question 40

How do endotherms replace lost heat?

Answer 40

by generating metabolic heat (which requires consuming resources) or by gaining heat through other means (e.g., solar radiation, convection).

Question 41

Blood shunting

Answer 41

when specific blood vessels shut off so less of an animal’s warm blood flows to cold extremities where heat would be lost.

Question 42

Countercurrent circulation

Answer 42

helps to conserve heat by positioning arteries that carry warm blood away from the heart alongside veins that carry chilled blood from the extremities back to the heart.