Photosynthesis Flashcards
Purpose of photosynthesis
to convert solar energy into glucose (chemical energy)
What does photosynthesis occur in?
plants, algae & other protists, cyanobacteria and some prokaryotes
Photosynthesis chemical equation
6CO2+6H2O+Light energy–> C6H12O6+6O2
List the level of organiztion in plants:
Leaf-Mesophyll-Chloroplast-Thylakoid-Chlorophyll
Define the cuticle
waxy covering that protects the leaf from excess water loss
Define the upper epidermis
outer layer of cells for protection
Define the palisade mesophyll
light collection by closely packed rows of palisade mesophyl (2 rows may be in present in plants adapted to low light)
Define the spongy mesophyll
adapted gas exchange–> loosely packed fewer chloroplasts than palisade cels, and have intercellular air spaces where gases collect & mix - they do less photosynthesis
define the function of guard cells
controls the amount of water and air entering and exiting the leaf , when guard cell fills with water stoma closes
Define stoma
small openings in the underside of the leaf that allow entry of gases–> when guard cells fill with water= stoma closes
Define stomata
complex of guard cell and stoma
What of the chloroplast is analogous to the inner membrane?
thylakoid
what of the chloroplast is analogous to the matrix?
stroma
what of the chloroplast is analogous to the mitochondrial intermembrane space?
thylakoid lumen
What type of light drive photosynthesis? (absorbed, transmitted or reflected)
absorbed
What type of light is the most useful for photosynthesis?
visible light
What types of light do leaves absorb and which one does it reflect?
absorb: violet, blue, and red
reflect: green
most important wavelength is blue and red regions
Do shorter wavelengths have lower or higher energy?
Higher
Do longer wavelengths have lower or higher energy?
lower energy
what are the 3 types of pigment in the thylakoid?
chlorophyll a
chlorophyll b
carotenoids
What is the structure chlorophyll a?
-complex ring structure- porphyrin ring
has 8 smaller rings
- long hydrocarbon side chain (non polar and anchors chlorophyll in the thylakoi)
What atoms do the ring structure of chlorophyll are composed of and what is the central atom?
carbons and nitrogens
central- magnesium
What reactions do chlorophyll a initiate? What lights does it reflect or absorb?
reactions- light-dependent reactions
reflect- green
absorb- blue and red
Describe structure of chlorophyll b
same as chlorophyl but has a carbonyl group instead of carboxyl
What is another difference between chlorophyll and b
b absorbs different wavelengths- appears yellow-green
What lights does carotenoids reflect and absorb?
absorbs: violet and blue-green light
reflects- yellow and orange
What is the function of carotenoids?
accessory pigment
can transfer energy to chlorophyll a
serve as antioxidants
Absorption spectra of chlorophyll a
400-500
650-700
Absorption spectra of chlorophyll b
400-500
580-700
Absorption spectra of carotenoids
400-510
Action spectrum of rate of photosynthesis
decreases during green light
Describe Engelmann’s experiment
most photosynthetically active regions will have highest concentrations of bacteria which was mainly in the regions of red and violet light showing they had the most photosynthetic activity. Green light did not have any
Where does the light dependent reactions take place?
thylakoid membrane
beginning molecules of light-dependent reactions
Light, CO2, NADP+, ADP and H2O
enzymes of light-dependent reactions
NADP+ reductase - reduces NADP+ to NADPH
magnese containing enzyme splits water
End products of light dependent reactions
NADPH and ATP and O2
Photosystem II
1st absorbs wavelength at 680 nm
photosystem I
absorb wavelength at 700 nm
What is the first step of light dependent reactions
light strikes PSII in teh ligth harvesting complex and passes through each pigment to reach chlorophyll a in P680 causing the electron to get excited & reach a higher energy level. Then, the electron is accepted by primary electron acceptor.
What happens to PSII when the electron is lost?
water is split into 2 e-, 2H+, and 1/2O2. Those electrons replace the ones that left
What happens to the electrons that went off to the primary electron acceptor?
Excited electrons move from primary electron acceptor of PSII through ETC to PSI
What happens to the electrons in PSI?
light hits pSI and energy is transferred to reaction enter and joins the p700 pair of chlorophyll which excites them. Lost electron get replaced by electron from PSII. The PSI electrons go to ETX
What happens to the electrons after PSI
They move through the ETC and to the outside into the stroma and get accepted by NADP+ reducing it to NADPH by enzyme NADP+ reductase
Describe the process of chemiosmosis in light dependent reactions?
electrons passing (exergonic) powers the active transport of H+ from the stroma to the thylakoid lumen (endergonic). pH of lumen decreases. H+ diffuse through ATP synthase (exergonic) powers the making of ATP (ADP+P0
What are the 2 parts photosystems have?
reaction center and light harvesting complex
define reaction center
made of chlorophyll a and primary electron acceptor
define light harvesting complex
protein and chlorophyll
What’s the basic difference between the mitochondrial etc chain and the chloroplast?
there are 2 in chloroplast
where does the calvin cycle take place?
stroma of chloroplast
beginning molecules of calvin cycle
ATP, NADPH, and CO2
End products of calvin cycle
G3P
What are the 3 steps of the calvin cycle?
carbon fixation
reduction
regenertaion
describe carbon fixation
CO2 molecule combines with RuBP (5 carbon acceptor molecules) –> split into 2 molecules of 3-PGA . reaction is catalyzed by rubisco
define reduction
NADPH donates electrons (reduced) a 3 carbon intermediate to make G3P (3 carbons sugar)
define regeneration
some G3P molecules go onto make glucose and while other must be recycled to regenerate RuBP acceptor. ATP is necessary
How many turns of the calvin cycle is necessary to make 1 G3P?
3 turns
How many turns of the calvin cycle is necessary to make glucose?
6 turns
What are the names of the plants (general class name) that use the normal Calvin cycle?
C3 plants
What the two problems plants face?
- plants risk losing CO2 and water bc of the open stoma
2, rubisco is fickle will bind to CO2 and O2 depending on the abundance of either
define photorespiration
wasteful process for plants because Rubisco binds with O2 instead of CO2, which prevents glucose production–> carbon fixation won’t occur
what are the 2 plants that deal with this problem?
C4 plants and CAM plants
How do C4 deal with the problem?
structured solution- incorporates CO2 into 4 carbon compound in mesophyll cells and those 4 carbon compounds are exported to bundle sheath cells and release CO2 for usage in calvin cycle –> PEP carboxylase is used
How do CAM plants deal with this issue?
stomata opens at night to load CO2 and closes during day to perform calvin cycles
define photons
a tiny particle that comprises waves of electromagnetic radiation. It causes an electron to get excited
difference between absorption of ligth and transmitted
absorption: when light strikes and its energy is absorbed by the material
transmitted- passing of light w/o absorption
At which measure does PSII absorb the best?
680 nm
At which measure does PSI absorb the best?
700 nm
Light intensity effect on photosynthesis
increase until chlorophyll get damaged
light-dependent reactions doesn’t depend on temperature
CO2 effect on photosynthesis
increase CO2 = increased rate of photosyntheiss, plateus until max fixation is reached
Temperature effect on photosynthesis
light independent reactions depend on heat because of enzymes
increases until optimal temperature is met; denatures when temperature exceeds that
