ecology quiz 2! Flashcards
6.1 what is photosynthesis?
process by which energy from the sun (shortwave radiation) drives a series of chemicals rxns that result in fixation of CO2 into carbs and the release of O2 as the byproduct
6.1 what is photosynthetically active radiation?
amount of light available for photosynthesis
6.1 what is the rxn for photosynthesis?
6CO2 + 6H2O –> C6H12O6 +6O2
6.1 what are the two metabolic rxns?
light dependent and light independent
6.1 light dependent rxn begins with…? and ends with?
- chlorophyll molecules within the chloroplast absorb light energy (chlorophyll is a light-absorbing pigment)
- absorption of photon of light raises energy level of chlorophyll molecules - excited molecule is not stable and electrons rapidly move to ground state, thus releasing absorbed proton energy
- energy is transferred to another acceptor molecule - resulting in photosynthetic electron transport, which then results in synthesis of ATP and NADPH
6.1 ATP & NADPH ARE ____ energy substance and ___ reductant essential for ______?
high, strong, light-independent
6.1 what happens in light-independent rxns?
- CO2 is incorporated into simple sugars
- the rxn does not require sunlight but is dependent on the product of light dependent rxn
6.1 steps of light-independent rxn?
- RuBP combines with CO2 to form two molecules of a three-carbon compound called PGA (3-PGA) (phosphoglycerate)
- plant converts the 3-PGA into energy rich sugar molecule = G3P
- some of the G3P is used to produce simple sugars while the other is used to synthesize new RuBP to continue process
6.1 Synthesis of G3P from 3-PGA requires what?
ATP & NADPH
6.1 availability of light energy can ____ light-independent rxn but why?
limit - because solar radiation is used to make the product of light-dependent rxn in which is used in light-independent rxn for the making of simply sugars and the synthesis of G3P and regeneration of RuBP
6.1 Photosynthetic pathway involving inital fixation of CO2 into 3-PGA is called?
calvin cycle / C3 cycle
6.1 what is the rxn called when co2 and RuBP combine to make 3-PGA?
carboxylation and is catalyzed by rubisco
6.1 what is the drawback of the C3 cycle?
rubisco can also act as an oxygenase - so as a catalyst, the oxygenation of RuBP results in the release of CO2, referred to as photorespiration - in all it reduces efficiency of C3 photosynthesis
6.1 where does cellular respiration happen and involves what?
mitochondria and involves oxidation of carbs to generate energy
6.1 rxn of cellular respiration?
C6H12O6 + 6O2 —> 6CO2 + 6H2O + ATP
6.1 leaves use both ____ during photosynthesis and produce ___ during respiration - difference is what?
CO2, O2, rates of net gain in carbon
6.1 what is net photosynthesis?
difference between rate of carbon intake in photosynthesis and carbon loss in respiration
6.1 process of photosynthesis occurs in _____ within ______ ?
chloroplast within mesophyll cells
6.2 availability of light to the leaf = ?
influences rate of photosynthesis
6.2 what happens at night in abscence of PAR? and then what?
only respiration occurs and net uptake of CO2 is negative
but as sun rise, value of PAR increases, meaning rate of photosynthesis increases and eventually reaches level where rate of CO2 uptake in photosynthesis = rate of CO2 loss in respiration
AT THIS POINT, RATE OF NET PHOTOSYNTHESIS = 0
6.2 What is light compensation point?
level of light where photosynthesis and respiration balance each other
6.2 as light levels ___ LCP, rate of net photosynthesis increases with PAR and eventually photosynthesis _________
exceed, becomes light saturated
6.2 what is the light saturation point?
amount of light at which plants achieve maximum rate of photosynthesis ; no further increase in photosynthesis occurs
6.2 plants that are adapted to shady environments, photosynthetic rates ____ as light levels exceed saturation
decline
6.2 negative effect of high light levels is called?
photoinhibition and it can result in “overloading” processes in light-dependent rxns
6.3 process of photosynthesis occurs in cells within the leaf called?
mesophyll cells and they are the specialized tissue between epidermal layers of leaf
6.3 CO2 must move from ____ into the leaf
outside atmosphere
6.3 in land plants, CO2 enters leaf through its ____ by ____.
stomata - pores on leaf
diffusion
6.3 what is diffusion
movement of substance from high to low concentration
6.3 what happens when concentration is equal?
equilibrium is reached and no more net exchange occurs
6.3 what two factors control diffusion of CO2 into leaf?
stomatal conductance and diffusion gradient
6.3 what is diffusion gradient
difference between concentration of CO2 in air adjacent to leaf and concentration of CO2 in leaf interior
6.3 what is stomatal conductance? and what are its 2 components?
flow rate of CO2 through stomata
1. stomatal density
2. size of stomatal opening (arpeture)
6.3 stomatal aperture is under _____, stomata open and close in response to _____
plant control, environment and biochemical factors
6.3 As long as concentration of CO2 in air outside leaf is ____ than that inside of leaf and stomata are open —>
greater, CO2 will continue to diffuse through the stomata into the leaf
6.3 why do concentration of CO2 inside and outside leaf not come to equilibrium?
concentration inside leaf declines as CO2 is transformed into sugars during photosynthesis - as long as photosynthesis occurs, gradient remains
6.3 what would happen if photosynthesis stopped?
if it stopped and stomata stayed open as well, CO2 would diffuse into leaf until internal CO2 = outside concentration
6.3 when photosynthesis and demand for CO2 are reduced, stomata….
closes which reduces flow into leaf
6.3 as CO2 diffuses in stomata, water vapor inside leaf _____ through same opening
diffuses
6.3 what is transpiration
water loss through stomata - loss of water vapor from plant to outside atmosphere
6.3 water vapor diffuses from?
high to low concentrations
6.3 Lower relative humidity of air means what to the diffusion gradient?
it will be larger and more rapidly the water inside the leaf will diffuse through stomata into surrounding air
6.3 does the leaf have to replace water lost to atmosphere?
yes otherwise it’ll wilt and die
6.4 what is turgor pressure?
forced exerted outward on a cell wall by water contained in the cell (osmosis)
6.4 growth rate of cells & efficiency of physiological processes are high____? but when water content declines ____
highest when their cells are at maximum turgor pressure
when it declines, turgor pressure drops and water stress occurs
6.4 what to do to maintain maximum turgor pressure?
water lost to atmosphere in transpiration must be replaced by water taken up from soil
6.4 what is water potential?
a measurement used to describe gibbs energy of water at any point along soil-plant-atmosphere continuum
6.4 water potential goes from?
areas of high water potential to low
6.4 when relative humidity of atmosphere is 100%, what is at 0atm?
atmospheric water potential
6.4 what happens as relative humidity of atmosphere drops?
atmospheric water potential becomes negative
6.4 as long as relative humidity of air is below 99%, gradient of water potential between lead and atmosphere will ____?
drive process of diffusion
6.4 water vapor moves from?
high water potential (interior of leaf) to low water potential (atmosphere) ; state of high to low gibbs energy
6.4 water being lost to atmosphere through stomata =?
water content of cell decreases - which increases concentration of solutes in cell
6.4 decrease of cell water content =?
decrease in water potential of cells
6.4 what factors determine water potential in plant?
- turgor pressure
- increasing solute concentration
- surfaces of larger molecules
6.4 how does turgor pressure affect cell water potential?
it increases water potential - represents hydrostatic pressure
