Chapter 3 Flashcards
(42 cards)
Water potential
a measure of water’s potential energy; affects the movement of water in soil from one location to another.
Matric (or matrix) potential
the potential energy generated by the attractive forces between water molecules and soil particles; occurs because water molecules and soil particles have electrical charges.
saturated soil
most water does not contact soil particles and is not strongly held by the soil; matric potential is 0 MPa.
field capacity
When gravity drains the water in soil, the matric potential drops to –0.01 MPa. The maximum amount of water held by soil
wilting point
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.
For a given volume of soil, the ____ surface area that soil has, the ____ water it can hold.
more; more
Soil particle sizes small to large
clay, silt, sand
Why can smaller particles hold more water?
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.
Loam soils
are some of the best for growing plants, contain 40% sand, 40% silt, and 20% clay.
Salinization
the process of repeated irrigation (with salty water) that causes increased soil salinity; creates a challenge for crop plants.
Cohesion
the mutual attraction of water molecules; allows water to move up through empty remains of xylem cells.
Root pressure
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.
Transpiration
the process by which leaves can generate water potential as water evaporates from the surfaces of leaf cells.
Cohesion-tension theory
the mechanism of water movement from roots to leaves due to water cohesion and water tension.
Stomata
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.
Photon energy is ___________ related to frequency and ___________ related to wavelength.
Positively; inversely
Chloroplasts
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.
Cartenoids (carrots)
reflect orange and red light; allow plants to absorb a wider range of solar energy.
Photosynthesis
Photosynthesis is the process of combining CO2, H2O, and solar energy to produce glucose (C6H12O6)
Light reactions
- Chlorophyll in thylakoids absorbs photon energy.
- Chlorophyll releases electrons to a chain of reactions.
- In the process, H2O molecules are split into H+ and O2– ions.
- O2– ions join to form molecular
oxygen. - Energy is collected from released
electrons and the split of H2O. - Energy + H+ + ADP–>ATP
- Energy + H+ + NADP+–>NADPH
Calvin cycle
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).
C3 Photosynthesis
CO2 + RuBP–>2G3P
Disadvantages of C3 photosynthesis
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.
Photorespiration
the oxidation of carbohydrates to CO2 and H2O by Rubisco, which reverses the light reactions of photosynthesis.
