Chapter 6 Flashcards
What waves is used for photosynthesis?
shortwaves of 400-700 nm (visible light)
What is the equation for photosynthesis?
6CO2 + 12H2O > C6H12O6 + 6O2 +6H2O
What occurs during the light-dependent reaction?
chlorophyll absorbs light, excites and releases energy to another molecule (ETC)
What is synthesized in the light reaction?
ATP and NADPH
What occurs during the light-independent reaction?
Corboxylation through Rubisco
What is carboxylation?
CO2 is incorporated into simple sugars using RuBP to form 3-PGA
What occurs after carboxylation?
3-PGA into G3P using ATP and NADPH > some G3P is for sugars, others synthesize RuBP
How does light availability limit light-independent reactions?
controlling ATP and NADPH synthesis (seen in C3 plants)
What are drawbacks of c3 plants?
rubisco can fix O2 through photorespiration, which reduces efficiency by 25%
What is net photosynthesis?
photosynthesis- respiration
What is the light compensation point?
light level at which rate of net photosynthesis is 0
What is light saturation point?
value of PAR which no further increase in photosynthesis occurs
What is photoinhibition?
photosynthetic rates declining as light levels exceed saturation
What are mesophyll cells?
specialized cells where photosynthesis occurs
What do stomatas do?
controls opening in the leaf for diffusion of CO2
What controls CO2 diffusion?
diffusion gradient
stomatal conductance
What is a diffusion gradient?
difference between the concentration of CO2 in air adjacent to the lead and concentration of CO2 in the lead interior
What is stomatal conductance?
flow rate of CO2 through the stomata
What controls stomatal conductance?
1) number of stoma per unit leaf surface area
2) aperture/ size
What is transpiration?
water loss through the stomata
What does transpiration depend on?
depends on water gradient and stomatal conductance
What is turgor pressure?
force exerted outward on a cell wall by water in the cell
What occurs at max turgor?
plant is most efficient (fully hydrated)
What happens at low turgor pressure?
wilting due to dehydration
What is water potential?
difference in gibbs energy (energy available to do work) between the water of interest and pure water
How does water diffuse out of a leaf, and what does it lead to?
lower pressure in the atmosphere > increased solute concentration > reduced water potential
What is osmotic potential?
difference in solute content in and out the cell
What is matric potential?
tendency for water to adhere to surfaces, reducing gibbs energy and water potential
How does matric potential reduce gibbs energy and water potential?
the more water in the soil, the easier it is to extract > seen in larger particles
What is the total water potential?
turgor pressure + osmotic potential + matric potential
Water potential from greatest to least
soil
root
leaf
atomsphere
How does water loss occur through transpiration?
the amount of energy striking the leaf is enough to supply the necessary latent heat of evaporation
What is water-use efficiency?
ratio of carbon fixed per unit of water lost
What is the tradeoff of stomatas?
opening stomata for CO2 but lose water, or close stomata to stay hydrated by not photosynthesize
How does CO2 diffuse in aqautic organisms?
diffusing through their membrane
How can some aquatic organisms use bicarbonate? (3 steps)
1) must first convert it into CO2 using carbonic anhydrase
2) through active transport, bring bicarbonate into the cell followed by conversation to CO2
3) or excretion of enzyme into water and intaking converted CO2
Why can CO2 levels deplete in the water?
it diffuses slower in water
What happens as temperature rises above freezing, in terms of photosynthesis?
photosynthesis and respiration increases
How does temperature differ between photosynthesis and respiration?
photosynthesis has a quicker rise but has a maximum level
What controls rate of photosynthesis and respiration in the plant?
leaf temperature
What does leaf temperature depnd on?
exchange of thermal energy between lead and environment
What must plants do to maintain internal temperature?
plants must exchange thermal heat with environment
How do plants exchange thermal heat?
1) evapotranspiration
2) convection
When is evapotranspiration important?
in water-available regions
What is convetion?
transfer of heat energy through circulation of fluids (direct contact)
When is convection important?
drier areas
What does convection influence?
boundary layer (layer of air around the leaf)
What influences boundary layer?
leaf size and shape
What do 8 things plants require?
1) positive carbon balance
2) light
3) CO2
4) Water
5) minerals
6) proper temperature
7) proper Salinity
8) proper pH
What do plants in dry environments deal with, and how do they adapt?
water demand and low humidity
small leaves and more roots
What are trade-offs for plants?
allocating carbon to leaves and stem for more light and CO2 but less for roots (water and soil nutrients)
How does shade-tolerant plants differ from shade-intolerant plants? (6 ways)
1) lower light saturation point and lower maximum rate of photosynthesis
2) lower concentrations of rubisco
3) higher chlorophyll levels
4) lower light compensation point to offset respiration
5) lower net carbon gain and growth rate
6) produce leaf structures with higher surface areas
How does amount of water required differ with temperature?
amount of water required by plant to offset losses from transpiration will increase with temperature
How do plants acclimate to dry temperatures?
1) stomata is closed
2) can close stomata during the hottest time of day
How do plants acclimate to low water availability?
it can limit opening stomata during humid mornings
What 4 other acclimation methods do plants have for heat?
1) curling leaves/ wilting- reduce water loss and heat gain by reducing surface area
2) inhibition of chlorophyll- yellow leaves
3) leaf shedding
4) low soil water availability leads to more carbon allocation to roots
How do plants adapt to dry soil? (3)
1) lower stomatal conductance
2)more carbon for production of roots
3) smaller and thicker leaves
How do plants in moderate environments adapt? (3)
1) small, thick leaves with tiny stomata
2) hairs to scatter light
3) wax to reflect light
How do plants adapt to seasonal environments?
drop leaves during dry seasons
What do C4 plants possess?
bundle sheath cells that divide photosynthesis between those cells and mesophyll cells
How does CO2 react in C4 plants?
reacts CO2 with PEP in mesophyll > catalyzed by PEP carboxylase to produce OAA
What happens to organic acids afterwards in C4 plants?
organic acid is transported into bundle sheath cells to forming concentrated CO2
What is 1 pro and 1 con for C4 plants?
pro- PEP does not react with oxygen
con- more energy expenditure to produce PEP
What is the CAM pathway?
CO2 reacts with PEP, but all steps occur in mesophyll cells at separate times
What happens during the night for CAM plants?
stomata opens at night to intake CO2 and convert into malic acid
What happens during the day for CAM plants?
during day, stomata closes and acid is converted into CO2
What is the drawback for CAM plants?
slow and inefficient
How does photosynthesis temperature match with the environment?
temperature for minimum, optimum, and max photosynthesis matches prevailing environmental temperatures
How can plants adapt to shifting temperatures?
when individuals of same species are grown under different thermal conditions, range of temperatures where net photosynthesis is maximum shifts
How can plants adapt to extreme cold? (2)
1) frost hardening- cold-sensitive cells into hardy ones (uses antifreeze and other compounds)
2) shed (winter deciduous)
What are macronutrients, and what 9 nutrients do plants need?
elements needed in large amounts
1. carbon
2. hydrogen
3. oxygen
4. nitrogen
5. phosphorus
6. potassium
7. calcium
8. magnesium
9. sulfur
Where are macronutrients found?
found in air, soil, or water
What occurs when carbon levels are low?
carbon is allocated to root growth
How can plants adapt to low nutrients (5)?
1) low absorption rate to absorb more nutrients in low-availability
2) greater allocation of carbon to roots
3) lower rate of needed nutrients to grow
4) slower growth
5) leaf longevity (requires less energy to grow leaves)
