Chapter 8: Photosynthesis Flashcards
photosynthesis
the conversion of light energy into chemical energy stored in glucose. occurs in plants, algae, and some bacteria
photoautotrophs
organisms that use light to synthesize organic molecules (glucose)
chemoautotrophs
organisms that oxidize inorganic substances like H2S and NH3 to produce energy in the form of glucose
photosynthesis takes place in the ______ which is found in _____
- chloroplast
- leaves
bundle sheath cells
type of photosynthetic cells arranged into tightly packed sheaths around the vein of the leaf
______ are the major sites of photosynthesis
leaves
chlorophyll is found in the _______
thylakoid membrane
chloroplasts are found mostly in the _____
palisade mesophyll layer
_____ enters the leaf and ______ exits through tiny pores called ______
- CO2
- O2
- stomata
_____ transports absorbed water to leaves and other parts of the plant
xylem
______ transports synthesized sugar from leaves to roots and nonphotosynthetic parts
ploem
sugar is transported in the form of ______
sucrose
cuticle
a thin waxy covering on the outer surface of the leaf
the primary function of the cuticle is to _______
prevent water loss within the leaf
epidermis
a layer of cells directly underneath the cuticle
xylem
upper layer of the bundle sheath cells that transports water
phloem
upper layer of the bundle sheath cells that transports glucose
mesophyll
layer of cells within the leaf which can be divided into two layers
palisade layer
column-like cells in the mesophyll that lie just under the epidermis
spongy layer
loosely packed cells in the mesophyll that lie between the palisade layer and the lower epidermis
the air spaces between the spongy cells allow for _________
gas exchange
mesophyll cells are packed with _______
chloroplasts
stomata
tiny holes in the leaf within the epidermis
guard cells
specialized cells that surround the stomata and are shaped like two cupped hands
___________ causes the stoma to open or close
changes within water pressure
if the guard cells are full of water, they _________
swell up and bend away from each other, which opens the stoma
if the guard cells have no water, _______
the guard cells close
photosynthesis takes place in two stages, __________ and __________
light reaction and dark reaction (calvin cycle)
light reaction takes place in the _________
thylakoid membrane
the purpose of the light reaction is to ______
use sunlight to produce ATP and NADPH, which are used in the Calvin Cycle to produce sugar
the dark reaction (calvin cycle) takes place in the ________
stroma
the dark reaction (calvin cycle) uses _________ to make sugar
CO2, ATP, and NADPH
light is a form of energy known as ________
electromagnetic energy
electromagnetic spectrum is ________
the entire range of radiation
all radiation travels as _______
waves
wave length
the distance from one wave peak to the next wave peak
visible light spectrum
the portion of the electromagnetic spectrum from 380 nm to 760 nm
the visible light spectrum is the radiation that __________
drives photosynthesis because it can be absorbed by pigments
each pigment has a ________
characteristic absorption spectrum, which is the wavelength of light that is best absorbed
light also behaves as particles called ______
photons
the energy of photon is __________
inversely proportional to its wavelength
pigments are ______
molecules that are good absorbers of light in the visible range
two types of pigments used in green plant photosynthesis are _________
chlorophyll and carotenoids
chlorophyll is made up of ______
a porphyrin head with magnesium in the center and a hydrocarbon tail
chlorophyll a & b absorb _______
violet, blue, and red light
chlorophyll a & b reflect _______
green light, which is why plants are green
_______ are accessory pigments
carotenoids
carotenoids
capture energy from the light of wavelengths that are not efficiently absorbed by either chlorophyll
carotenoids absorb _______
blue and green light
carotenoids reflect _______
orange and yellow light
another accessory pigment is _____
phycobiliproteins, found in cyanobacteria and some algae
photosystem organization
the light harvesting unit in photosynthesis located on the thylakoid membrane of the chloroplast
the 3 parts of photosystem organization are:
- antenna complex
- reaction center chlorophyll a
- primary electron acceptor
the antenna complex consists of ______
chlorophyll, accessory pigments, proteins, and other small molecules
the two types of photosystems are:
- photosystem l
- photosystem ll
photosystem l is composed of _______
chlorophyll a at the reaction center, which is called p700, meaning the wavelength of light that is best absorbed by this chlorophyll is 700nm
photosystem ll is composed of:
chlorophyll a at the reaction center, called p680, meaning the wavelength of light that is best absorbed by this chlorophyll is 680 nm
step 1 of light reaction
light is absorbed by pigments in photosystem ll until it reaches reaction center chlorophyll a. this excites 2 electrons to a higher level in the reaction center chlorophyll p680, where they are captured by the primary electron acceptor
step 2 of light reaction
an enzyme splits water to extract its electrons to supply it to p680, replacing the lost electrons when light energy was absorbed
step 3 of light reaction
excited electrons pass from the primary electron acceptor of photosystem ll to photosystem l through the electron transport chain
step 4 of light reaction
the energy released by the fall of electrons down the ETC is used to pump protons from the stroma into the interior of the thylakoid. protons diffuse back out to the stroma through ATP synthase, producing ATP (chemiosmosis)
step 5 of light reaction
when an electron reaches the bottom of the ETC, it fills an electron hole in p700. this hole is created when light energy drives 2 electrons from p700 to the primary electron acceptor of photosystem l
step 6 of light reaction
the primary electron acceptor of photosystem l passes the excited electrons to a second ETC, where NADP+ reductase produces NADPH
cyclic-photophosphorylation happens when ________
the cell needs extra ATP
dark reaction (calvin cycle) is also known as ________ and _________
carbon fixation & C3 pathway
carbon fixation/c3 pathway
incorporates CO2 into organic compound in the form of glucose. the first sugar produced in this cycle is PGA, which contains carbon
C3 plants are _______
plants that fix carbon using calvin cycle. ex: rice, wheat, and soybeans
to produce 1 molecule of glucose _______
2 molecules of G3P, 6 molecules of CO2, and 6 rounds of the calvin cycle are needed
the 3 stages of the calvin cycle:
- carbon fixation
- reduction
- regeneration
1st step of calvin cycle
6 molecules of CO2 combine with 6 molecules of RuBP, forming PGA
2nd step of calvin cycle
PGA is phosphorylated by 12 molecules of ATP, forming 12 molecules of 3C
3rd step of calvin cycle
3C is reduced by NADPH and undergoes dephosphorylation, forming 12 molecules of G3P
4th step of calvin cycle
2 of the G3P molecules leave the chloroplast and undergo reversal reactions in the cytoplasm to produce glucose
5th step of calvin cycle
the remaining 10 molecules of G3P are used to regenerate RuBP
photorespiration
on hot, dry days, plants close their stomata to conserve water. once the stomata closes, photosynthesis rapidly uses up the CO2 remaining in the leaf and produces O2, which accumulates in the chloroplast. rubisco can react with O2 which competes with CO2 for its active site. rubisco will catalyze the reaction of RuBP with O2 instead of with CO2, making some of the intermediates involved in the calvin cycle degrade into CO2 and H2O
photorespiration occurs in the presence of _______
light
photorespiration requires ______
O2
photorespiration produces ____________
CO2 and H2O, but does not yield ATP
2 photosynthetic adaptations that minimize photorespiration are:
- C4 photosynthesis (tropical)
- CAM plants (desert)
examples of C4 plants are _________
sugar cane, corn, some grasses
two distinct types of photosynthetic cells in C4 plants are:
- bundle sheath cells
- mesophyll cells
process of photosynthesis in C4 plants
CO2 is added to PEP through the stomata to form oxaloacetate through PEP carboxylase. oxaloacetate is reduced by NADPH to malate. mesophyll cells export malate to bundle sheath cells through plasmodesmata. malate releases CO2 in the bundle sheath cells which enters the calvin cycle. this keeps the concentration of CO2 high enough for rubisco
step 1 of photosynthesis in CAM plants
the plant will open the stomata during the night and close it during the day
step 2 of photosynthesis in CAM plants
during the night, the plant takes CO2 and incorporates it into organic acids like malate using C4 pathway
step 3 of photosynthesis in CAM plants
the mesophyll cells of CAM plants store malate in their vacuoles until daytime where the stomata closes
step 4 of photosynthesis in CAM plants
during daytime, CO2 will be released from malate and will be used in calvin cycle to produce sugar
photosynthesis is different in cyanobacteria because ________
there is no chloroplast, so light reaction will take place in the plasma membrane where pigments exist. dark reaction takes place in the cytoplasm
equation for photosynthesis
6CO2 + 12H2O ———> C6H12O6 + 6H2O + 6O2
the role of chlorophyll is to _______
absorb light
equation for photosynthesis in sulfur bacteria
CO2 + 2H2S ———> CH2O + H2O + 2S^
in sulfur bacteria, only _______ photosystem is used
one
sulfur bacteria uses an electron donor such as _____ rather than water, so _______ is not released
H2S & O2
electrons from H2S are used to _______
reduce NADP+
in sulfur bacteria, the calvin cycle happens in the ________
cytoplasm
light affects rate of photosynthesis because _______
increasing light intensity will increase the rate of photosynthesis until the light reactions are saturated with light energy
CO2 concentration affects rate of photosynthesis because __________
increasing CO2 concentration increases rate of photosynthesis until it reaches the CO2 saturation point, where any more increase has no effect
temperature affects rate of photosynthesis because ________
increasing temp will increase rate of photosynthesis until a certain point, 35°C. beyond this point, rate of photosynthesis will decrease because enzymes in the reaction will denature AND stomata will close to limit water loss
_________ can be used to measure the absorption spectrum of a substance
spectrophotometer
water affects rate of photosynthesis because _________
lack of water will slow rate of photosynthesis stomata will close from water loss
the metabolic reaction in photosynthesis is ______
anabolic
the raw material in photosynthesis is _______
CO2, H2O, & O2
ATP production process in photosynthesis is ________
ETC
the location of the ETC is _______
thylakoid membrane
electron acceptor in photosynthesis is _______
NADP+
transpiration is __________
water continuously evaporating from the surface of leaf cells exposed to air
plants transpire for _________
evaporative cooling
evaporative cooling
as water converts from a liquid to gas at the leaf cell, energy is released. this process uses energy to break the strong H bonds between H2O molecules. the gas molecules will release into the atmosphere, which cools the plant
explain how the stomata opens
when stomata is signaled to open, K+ enters the guard cells, creating a hydrostatic pressure that changes the shape of the stomata. the guard cells expand on the outer edges of the stomata, but not on the inner side, resulting in kidney-shaped cells & an opening between 2 guard cells for has exchange
explain how the stomata closes
guard cells lose water & become flaccid. K+ moves back out of the guard cells, followed by H2O, which lowers pressure in the guard cell
the stomata is signaled to close by:
- lack of water
- internal CO2 concentration is high
- temperature is too higher
the equation for how factors affect transpiration is _______
[water potential(leaf)] - [water potential(atmosphere)] / resistance
the factors affecting rates of transpiration are:
- stomata
- boundary layer
- cuticle
- relative humidity
- temperature
- soil water
- light
- wind
stomata affects rate of transpiration because __________
when stomata is open, transpiration rates increase
boundary layer affects rate of transpiration because __________
the larger the boundary layer, the slower the rates of transpiration
cuticle affects rate of transpiration because __________
the thicker the cuticle, the slower the rate of transpiration
relative humidity affects rate of transpiration because __________
the higher the relative humidity, the lower the rate of transpiration
temperature affects rate of transpiration because __________
the higher the temperature, the higher the rate of transpiration because there is less water in the air, so water can always move from leaf to air
soil water affects rate of transpiration because __________
the more moisture, the higher the rate of transpiration because there is enough water to move through the plant
light affects rate of transpiration because __________
in the light, stomata is open, so transpiration rates will increase
wind affects rate of transpiration because __________
the windier it is, the higher the rate of transpiration because the leaf’s boundary layer is smaller
the boundary layer is _______
a thin layer of still-air hugging the surface of the leaf, which is not moving
