IB Biology HL II — Unit 34: Photosynthesis
State that NADPH is an electron carrier molecule
NADPH is an electron carrier molecule
Explain why plants are green
- Sunlight made up of different colors/wavelengths - Pigments absorb and reflect some wavelengths - Green is reflected
State the chemical equation for photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
Outline the process of separating pigments using chromatography
1. A mixture is dissolved in a fluid (mobile phase) and passed through a static material (like chromatography paper, stationary phase) 2. Different components of mixture travel at different speeds, separating them (based on adhesion, determined by molecular structure)
State that the 5-carbon molecule ribulose bisphosphate (RuBP) is carboxylated by CO2, forming 2 3-carbon molecules called glycerate-3-phosphate (G3P).
1. Carbon fixation: Ribulose bisphosphate (RuBP) is carboxylated (via a CO2 molecule) to turn into a six-carbon molecule (RuBP is a five-carbon molecule), which is immediately split into two molecules, called phosphoglycerate (PGA)
State that the light independent reactions of photosynthesis include: carbon fixation, carboxylation of RuBP, production of triose phosphate, ATP and NADPH as energy sources, ATP used to regenerate RuBP, ATP used to produce carbohydrates
1. Carbon fixation: Ribulose bisphosphate (RuBP) is carboxylated (via a CO2 molecule) to turn into a six-carbon molecule, which is immediately split into two molecules, called phosphoglycerate (PGA) 2. Production of trioesphosphate: PGA is reduced and phosphorylated to form trioesphosphate (G3P) with the use of NADPH and an ATP molecule (per PGA molecule) 3. 6 G3P molecules are made per round of the Calvin Cycle, but five of them are sent back through to regenerate RuBP via ATP 4. ATP is needed in the cycle, and six turns of the cycle is needed to make one glucose molecules
List mechanisms for measuring the rate of photosynthesis
1. Measuring uptake of CO2 2. Measuring production of O2 3. Measuring production of carbohydrates
Outline the process of photoactivation of the reaction center chlorophyll
1. Photoactivation: light enters Photosystem II (PSII) and excites the electrons of the pigment molecules, moving them through the light-harvesting complexes, where they'll land on P680 in the reaction-center complex
State that the light dependent reactions of photosynthesis include: photoactivation, photolysis, electron transport, chemiosmosis, ATP synthesis, and reduction of NADP to NADPH + H+
1. Photoactivation: light enters Photosystem II (PSII) and excites the electrons of the pigment molecules, moving them through the light-harvesting complexes, where they'll land on P680 in the reaction-center complex 2. Photolysis: At the same time as photoactivation, a water molecule is added. The light energy splits the water molecule, where the electrons will be replaced in the reaction center chlorophyll. The oxygen is waste, and the H+ ions are sent to ATP synthase later down the ETC 3. Electron transport: Just like in cellular respiration, the electrons go through a series of proteins (starting with PSII, then moving onto plastoquinone (PQ), a cytochrome, a plastocyanin, and then Photosystem I (PSI, e- land on P700). These electrons power H+ pumps, which pump H+ ions into the thylakoid lumen to create a protein gradient, which allows for chemiosmosis to occur. 4. ATP synthesis: The H+ ions produced from photolysis and pumped in the lumen from the ETC move back out into the stroma via ATP synthase, which produces an ATP molecule 5. Electrons that pass through PSI, along with H+ ions in the stroma, reduce NADP to NADPH + H+
State that to replace the electrons lost during photoactivation, the reaction center chlorophyll takes electrons by splitting water
2. Photolysis: At the same time as photoactivation, a water molecule is added. The light energy splits the water molecule, where the electrons will be replaced in the reaction center chlorophyll. The oxygen is waste, and the H+ ions are sent to ATP synthase later down the ETC
State that ATP is used to regenerate RuBP from triose phosphate
3. 6 G3P molecules are made per round of the Calvin Cycle, but five of them are sent back through to regenerate RuBP via ATP
State that in the Calvin cycle, triose phosphate is used to regenerate RuBP and create glucose
3. 6 G3P molecules are made per round of the Calvin Cycle, but five of them are sent back through to regenerate RuBP via ATP
State that the energy released by the movement of electrons is used to pump protons across the thylakoid membrane, from the stroma into the thylakoid lumen
3. Electron transport: Just like in cellular respiration, the electrons go through a series of proteins (starting with PSII, then moving onto plastoquinone (PQ), a cytochrome, a plastocyanin, and then Photosystem I (PSI, e- land on P700). These electrons power H+ pumps, which pump H+ ions into the thylakoid lumen to create a protein gradient, which allows for chemiosmosis to occur.
State that six turns of the Calvin Cycle are needed to produce one molecule of glucose
4. ATP is needed in the cycle, and six turns of the cycle is needed to make one glucose molecules
State the range of wavelengths that fall within the visible spectrum
400nm-700nm
State that ATP (from the light dependent reaction) provides the energy for NADPH (from the light dependent reaction) to reduce G3P, forming a three carbon carbohydrate, triose phosphate.
ATP provides the energy for NADPH to reduce PGA into G3P
Distinguish between an action spectrum and an absorption spectrum
Absorption spectrum: wavelengths of light absorbed by each pigment Action spectrum: Overall rate of photosynthesis at each wavelength
State that in chemiososis, ATP is generated as protons move down their concentration gradient through ATP synthase
Already in set twice lol
State that the oxygen produced in photolysis is a waste product of photosynthesis
Bruh you just said that too
State that carbon fixation occurs in the chloroplast stroma
Carbon fixation occurs in the chloroplast stroma
Define carbon fixation and carboxylation
Carbon fixation: inorganic carbon incorporated into organic compounds Carboxylation: A carboxyl group is produced when a substrate is treated with CO2
Define photosynthesis
Conversion fo light energy into chemical energy
Describe the shape of the curve for an absorption spectrum
Different peaks from different pigments at either side of the center
State the function of the following chloroplast structures: double membrane, thylakoids, pigment molecules, thylakoid lumen, stroma
Double membrane: Evidence for endosymbiosis Thylakoid: Has electron transport chain and ATP synthase for photophosphorylation, stacks of which make up grana, and the stacks are connected by lamella Pigment molecules: Absorbs light, which excites electrons and catalyzes light dependent reactions Thylakoid lumen: Internal thylakoid space is very small, allowing for the proton motive force to be built up faster Stroma: Has appropriate enzymes and a suitable pH for the Calvin Cycle
State evidence that suggests chloroplasts were once free living prokaryotes
Endosymbiosis Evidence: 1. Double membrane 2. Naked DNA and 70s ribosomes 3. Metabolic processes susceptible to antibiotics
State the equation for photolysis
H20 --> 2H+ + 2e- + 1/2O2
State that the discovery of the radioactive 14C isotope allowed Calvin to determine the pathway of the light independent reactions of photosynthesis
He used an x-ray for his experiment, and he therefore needed radioactive C. the discovery of the radioactive 14C isotope allowed Calvin to determine the pathway of the light independent reactions of photosynthesis
State that the electrons from the Photosystem II electron transport chain are used to replace the electrons lost during photoactivation of Photosystem I
Instead of going through PSI, the electrons from PSII replace the ones form PSI, which left because of photoactivation
State the energy conversion that occurs during photosynthesis
Light dependent reactions: converts sunlight to ATP Light independent reactions: Use ATP to make glucose
Explain how the following factors limit the rate of photosynthesis: temp, light intensity, CO2 concentration
Light intensity: If low, ATP and NADPH production will slow (rarely limiting factor) Temp: Low temp slows all enzyme-catalyzed reactions in Calvin cycle, high temps denature rubisco (more commonly low temp than high temp) CO2 Concentration: Carbon fixing = limited --> less G3P, RuBP and NADPH built up (often limiting factor because atmospheric CO2 is low)
State that the light dependent reactions convert light energy into chemical energy in the form of ATP and NADH
Light produces ATP/NADPH and splits water Light energy absorbed by Photosystem I and II (each one has a light-harvesting complex (e- excited) and a reaction center complex (e- acceptor)
Define pigment
Light-absorbing molecule
Define limiting factor
Limiting factor: The factor that reduces the rate of production of a metabolic pathway the most
State the relationship between wavelength and energy
Longer wavelength = less energy Vice versa
State that photoactivation of the reaction center chlorophyll in photosystem I excites electrons which pass through a different electron transport chain
PSII, ETC, PSI, ETC
Define photolysis
Photolysis: Splitting of water molecules by sunlight
Define photosystem and reaction center
Photosystem: groups of photosynthetic pigments (including chlorophyll) embedded within the thylakoid membrane Reaction center: Absorbs light and promotes e- to higher energy level
State the primary and accessory pigments found in chloroplasts
Primary: Chlorophyll a - absorbs sunlight and releases electrons to main reaction center Accessory: Chlorophyll b, cartenoids, xanthophylls, anthocyanins - absorbs broader spectrum of light, transfer electrons to main reaction center
Define visible light
Range of wavelengths from violet (400nm) to red (700nm)
Calculate the Rf value for pigments using pigment chromatography
Retardation factor = distance component travels ÷ distance solvent travels
State that the enzyme that catalyzes the carboxylation of RuBP is called ribulose bisphosphate carboxylase (rubisco)
Ribulose bisphosphate carboxylase (rubisco) catalyzes the carboxylation of RuBP
State the location of the light dependent reactions of photosynthesis
Thylakoid membrane
Describe the shape of the curve for an action spectrum
Two peaks at either side of the center
State that the light dependent reactions of photosynthesis begin at Photosystem II
Uhmmmm you just said that
Define independent variable, controlled variable, and responding variable
We can do these
Outline how chloroplast structure could evolve through natural selection
Whichever ones produced glucose the most efficiently most likely had a higher chance of having healthy offspring because they had a larger supply of energy
State that electrons pass through a chain of electron carrier molecules
e- pass through a chain of electron carrier molecules
State that the result of the electron transport chain is a proton gradient, with a high concentration of protons in the thylakoid lumen
electrons power H+ pumps, which pump H+ ions into the thylakoid lumen to create a protein gradient, which allows for chemiosmosis to occur.
State that the electrons of Photosystem I are used to reduce NADP+ to form NADPH
electrons that pass through PSI are only used to reduce NADP+ to form NADPH
State the location of the light independent reactions of photosynthesis
stroma