photosynthesis Flashcards
photoautotrophs purpose
use light Energy to make organic molecules
what are the main producers of the biosphere?
plants and other autotrophs
heterotrophs purpose
consume organic molecules from other organisms for Energy and carbon
photoautotrophs examples
plants
cyanobacteria
purple sulfur bacteria
unicellular protists
multicellular algae
photosynthesis converts
light energy to chemical energy of food
chloroplasts are the site of
photosynthesis in plants
3 sites of photosynthesis
mesophyll
stomata
chlorophyll
where are chloroplasts mainly found in leaves
mesophyll cells
stomata
pores in leaf
what chemical process happens in stomata
CO2 enter
O2 exits
chlorophyll definition
green pigment in thylakoid membranes of chloroplasts
photosynthesis chemical reaction
6CO2 + 6H2O + Light Energy 🡪 C6H12O6 + 6O2
redox reaction defintion
reactions that involve the transfer of electrons from one species to another
redox reaction in photosynthesis
water is split 🡪
e- transferred with H+ to CO2 🡪
sugar
oxidation
loses electrons
reduction
gains electrons
what evidence enabled researchers to track atoms through photosynthesis?
Evidence that chloroplasts split water molecules
photosynthesis =
light reactions (photo) + Calvin cycle (synthesis)
light reactions convert
solar Energy to chemical Energy of ATP and NADPH
light = energy =
electromagnetic radiation
wavelength and energy relation
inversely related
shorter wavelength, higher energy
visible light can be detected by
the human eye
how is light seen? 3 ways
reflected
transmitted
absorbed
electromagnetic spectrum (low to high energy)
radio waves
micro-waves
infrared
visible light
uv
x-rays
gamma rays
how are pigments absorbed in photosynthesis?
they absorb different wavelengths of light
how does chlorophyll absorb light
absorb violet-blue/red light, reflect green
chlorophyll a
(blue-green): light reaction, converts solar to chemical Energy
chlorophyll b
(yellow-green): converts Energy to chlorophyll a
carotenoids
(yellow, orange): photoprotection, broaden color spectrum for photosynthesis
Absorption Spectrum determines
effectiveness of different wavelengths for photosynthesis
action spectrum
plots rate of photosynthesis vs. wavelength
(absorption of chlorophylls a, b, & carotenoids combined)
what did Engelmann do
used bacteria to measure rate of photosynthesis in algae
established action spectrum
Electrons in chlorophyll molecules are _ by absorption of light
excited
Photosystem defintion
reaction center & light-harvesting complexes (pigment + protein)
Two routes for electron flow:
Linear (noncyclic) electron flow
Cyclic electron flow
Light Reaction - Linear electron flow process (9 steps)
Chlorophyll excited by light absorption, picked up by pigment molecules in Photosystem II
E passed to reaction center of Photosystem II (protein + chlorophyll a)
e- captured by primary electron acceptor
Redox reaction 🡪 e- transfer
e- prevented from losing E (drop to ground state)
H2O is split to replace e- 🡪 O2 formed
e- passed to Photosystem I via ETC
E transfer pumps H+ to thylakoid space
ATP produced by photophosphorylation
e- moves from PS I’s primary electron acceptor to 2nd ETC
NADP+ reduced to NADPH
Light Reaction - Linear electron flow
main idea
Use solar E to generate ATP & NADPH to provide E for Calvin cycle
Cyclic Electron Flow uses
PS I only; produces ATP for Calvin Cycle (no O2 or NADPH produced)
granum
stack of thylakoids
chemiosmosis
generates ATP in respiration and photosynthesis
Proton motive force generated by:
H+ from water
H+ pumped across by cytochrome
Removal of H+ from stroma when NADP+ is reduced
Calvin Cycle
Uses ATP, NADPH, CO2
Produces 3-C sugar G3P (glyceraldehyde-3-phosphate)
3 phases of Calvin cycle
Carbon fixation
Reduction
Regeneration of RuBP (CO2 acceptor)
Calvin cycle process
3 CO2 + RuBP (5-C sugar ribulose bisphosphate)
Catalyzed by enzyme rubisco (RuBP)
Use 6 ATP and 6 NADPH to produce 1 net G3P
Use 3 ATP to regenerate RuBP
Alternative mechanisms of carbon fixation have evolved in what climates?
hot and arid
photo respiration definition
Metabolic pathway which:
Uses O2 & produces CO2
Uses ATP
No sugar production (rubisco binds O2 🡪 breakdown of RuBP)
when does photo respiration occur? why?
on hot, dry bright days when stomata close (conserve H2O)
Problem with C3 Plants
CO2 fixed to 3-C compound in Calvin cycle
Hot, dry days:
partially close stomata, less CO2
Photorespiration
less photosynthetic output (no sugars made)
C4 Plants
CO2 fixed to 4-C compound
less photorespiration, more sugar production
2 types of C4 plants
mesophyll and bundle sheath cells
mesophyll cells
PEP carboxylase fixes CO2 (4-C), pump CO2 to bundle sheath
bundle sheath cells
CO2 used in Calvin cycle
what happens to C4 plants on hot, dry days
stomata close
CAM (Crassulacean acid metabolism) Plants during night
stomata open 🡪 CO2 enters 🡪 converts to organic acid, stored in mesophyll cells
CAM (Crassulacean acid metabolism) Plants during day
stomata closed 🡪 light reactions supply ATP, NADPH; CO2 released from organic acids for Calvin cycle
plant photosynthesis importance
Glucose for respiration
Cellulose
global photosynthesis importance
O2 Production
Food source