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