Topic 6: Photosynthesis - Light-Dependent and Light-Independent Reactions

Flashcards covering the mechanics of photosynthesis, including the light-dependent reactions, photophosphorylation, electron transport, and the Calvin cycle.

What is the overall chemical equation for photosynthesis as presented in the notes?

$$6 CO_2 + 6 H_2O \rightarrow C_6H_{12}O_6 + 6 O_2$$

According to the notes, where does most biomass (carbon) in plants come from?

$$CO_2$$

What are the components of the chloroplast's triple membrane system?

Outer membrane, inner membrane, and the thylakoid membrane.

Distinguish between the light-dependent reactions and the Calvin cycle regarding their location within the chloroplast.

Light-dependent reactions occur in the thylakoids (light absorption, electron transport, ATP synthesis), while the Calvin cycle occurs in the stroma.

What is the relationship between wavelength and energy in the electromagnetic spectrum?

Short wavelengths have high energy, and long wavelengths have low energy.

What is the specific wavelength range of visible light mentioned in the notes?

$400\,nm$ to $700\,nm$

What are the three possible outcomes when a photon strikes an object?

1. Reflected (bounce away), 2. Transmitted (flow through), or 3. Absorbed (photons are absorbed by energy).

What must occur for a pigment to absorb a photon and raise an electron to a higher energy level?

The wavelength of the photon must exactly match the energy needed to raise the electron to that specific level.

What is the role of carotenoids in photosynthesis?

They act as accessory pigments to extend the range of visible light a plant can use and protect the plant from sunburn.

What is Inductive Resonance?

The transfer of energy from one electron to another in antenna pigments, where the electron drops back down to ground state as it passes energy to a neighbor.

What is the specific name of the reaction center pigment in Photosystem II?

P680

How does P680 replace its electrons after donating them to the primary electron acceptor?

By splitting $H_2O$ into $H^+$ and $O_2$.

Describe the function of Plastoquinone (PQ) as an electron taxi.

PQ is a hydrophobic electron taxi that grabs an $H^+$ from the stroma when reduced and passes electrons to the cytochrome $b_6f$ complex.

What is the name of the reaction center pigment in Photosystem I?

P700

What are the three factors that produce the strong proton electrochemical gradient ($PMF$) across the thylakoid membrane?

1. $H^+$ released into the thylakoid lumen when $H_2O$ is oxidized at PSII; 2. $H^+$ moved from stroma to lumen by PQ; 3. $H^+$ removed from stroma when $NADP^+$ is reduced at PSI.

On which side of the thylakoid membrane is ATP generated by ATP synthase?

The stroma side.

What are the typical pH values for the stroma and the thylakoid lumen during active photosynthesis?

Stroma $pH = 8$, thylakoid lumen $pH = 5$, making the gradient 1000 times stronger.

What are the three major stages of the Calvin Cycle?

1. Carboxylation (Fixation), 2. Reduction Phase, and 3. Regeneration.

What enzyme is responsible for the fixation of carbon in Phase 1 of the Calvin Cycle?

Rubisco

What is the role of cyclic electron transport in photosynthesis?

It allows Ferredoxin to reduce PQ instead of NADP reductase, creating extra $PMF$ to generate the additional ATP required by the Calvin cycle.

What happens to the Glyceraldehyde-3-phosphate (G3P) produced in the Calvin Cycle?

It can be converted to glucose for use in glycolysis/aerobic respiration, linked into starch for storage, cellulose for cell walls, or used to synthesize amino acids, nucleic acids, and lipids.

How does anoxygenic photosynthesis differ from oxygenic photosynthesis?

It occurs only in prokaryotes, uses only cyclic electron flow, does not split $H_2O$, and does not produce $O_2$.

Whats photosynthesis

process by which autotrophs use energy to convert carbon dioxide (inorganic) into organic molecules

equation : 6CO2 + 6H2O >> C6H{12}O6 + 6O2

Which bonds in photosynthesis are broken and fromed

Polar covalent c-o, o-h bonds in reactants broken

Non polar covalent bonds c-c , c-h, o-o in products formed

whats reduced and whats oxidized in photosynthesis

co2 is reduced to glucose (gain) and water is oxidized to oxygen (lose)

what are chloroplasts

Organelles in plant cells where photosynthesis occurs, containing chlorophyll. triple membrane system conatining the outer membrane, inner membrane, and thylakoid membranes.

how does the chroloplasts membranes look

cytosol

Outer membrane

IMS

Inner membrane

Stroma

Thylokoid membrane

Thylakoids stacked in granum, interconnected by stroma lamella.

whats the electromagentic spectrum

• visible light range

• properties

A range of all types of electromagnetic radiation, including visible light, ultraviolet light, and infrared radiation, categorized by wavelength.

• visible light ranges 400-700

• wave and particle properties

short wavelength properties

• High energy and frequency

• 400nm wavelenths

• blue or violet colour

long wavelength properties

• low energy

• 700nm wavelengths

• red colour

how do we see colour

light eneters earth as a photon; particles w diffrent wavelengths and it strikes an object, then either absorbed transmitted or reflected

if absorbed by pigment, it is converted to energy and we perceive the color of the light that is reflected. The specific wavelengths that are not absorbed determine the color we see.

whasts a pigment

molecules that absorb photons of specific wavelengths, enabling photosynthesis by capturing light energy.

wavelegth ofphoton must match energy needed in order to be absorbed and excite electrons to higher lvl

Blue green and red pigments wavelengths

blue 450nm

red 700nm

green 550nm

red and blue are absorbved by plants and green is reflected which is why we see them as green

what are photosynthetic pigements

• whats the main one in photoautotrophs

• other pigement

Photosynthetic pigments are those embaded in the tylokoid membrane that capture light energy for photosynthesis. The main pigment in photoautotrophs is chlorophyll, primarily chlorophyll a, while other pigments include carotenoids and chlorophyll b.

what are carotenoids

acessory pigments that absorb whatever light chrorophylls dont absorb and protect the plant from light dmg

what parts is photosynthesis split into

1. light dependent rxn

2. and light independent rxn (Calvin cycle)

how are pigments organized

Organized into photosystems that are light harvesting complexies which contain hudreds of antenna pigments grouped around reaction center to capture and transfer light energy efficiently.

light pathway trnasfering energy from one electron to another

light hits first electron within antenna pigment and excites it to a higher energy state, allowing it to be transferred to next electron on next antenna pigment and so on until it reahces the reaction center. only energy reaches not the electron

WHats the simplified pathway of light for photosyntheis once the elctron reaches the reaction center

Light

↓

PSII (P680)

↓

Water split > H+ ions on thylokoid lumen side > ATP

ETC

↓

PSI (P700)

↓

NADPH + ATP

↓

Calvin cycle or if not enough ATP for kelvin cycle > Cyclic Electron Transport

↓

PSI

↓

Fd

↓

PQ

↓

b6f

↓

PC

↓

PSI making more ATP only

As light is recived, whats the pathway for photosynthesis to occur the light dependent rxn part

1. Reaction center reduces a primary electron acceptor, Photosystem 2

2. Here P680 (rxn ceneter) is excited by inductive resonance of lighttransfers its electron to a primary electron acceptor , P680 is oxidized

3. PEA takes electron to PQ (hydrophobic e taxi) that graps H+ ions from stroma when reduced and trnsports electron to cytochrom b6f releasing H+ into thylokoid lumen when oxidized

4. b6f transport the electron to plastocyanin (electron taxi) reducing it , which passes electron to P700 Photosystem 1

5. Again P700 is reduced by light and passes electron to ferrodexin (electron taxi) that carries the electron to NADP+ reductase, converting NADP+ into NADPH.

6. The NADPH and ATP made by ATP synthase using H+ gradient on the inside thylokoid lumen side make the calvin cycle occur

the calvin cycle photosynthesis pathway

• ATP and NADPH made by light dependent rxn are used to build organic oxygen from inorganic carbon dioxide in athmosphere

• Carboxylation od RuBP ( C5 compound) by attaching CO2, 2 x 3-PGA (C6 total)

• 3PGA reduced to G3P using ATP and NADPH from light dependent rxn

• Sometimes some G3P leaves to be stores as glucose or other carbohydrates

• the rest is used to regenerate RuBP with energy from ATP , allowing the cycle to continue.

whats cylic electron transport and why and when does it occur

Cyclic electron transport is a process when calvin cycle requires more atp than nadph because it uses more of it, so it uses only photosystem 1 to generate additional ATP through PSI without producing NADPH.

• light excites photosystem 1 p700

• electron transffered transffered to primary electron acceptor ferredoxin

• ferredoxin reduced PQ instead of NADP+

• electron flows from PQ to cytochrome b6f complex which pumps H+ ions into the thylakoid lumen

• electron goes to plastocyanin then back to charge p700 and proton gradient H+ gets used to make only ATP at the synthase

whats the product of phtosynthesis

G3P is the main product, which can be used to form glucose and other carbohydrates.

whats the made glucose by photosynthesis used for

glycolysis or aerobic respiration in mitochondria

linked into polumers of starch or cellulose

used to synthesize aa, nucleic acid or lipids

how does oxygenic photosynthesis occur in prokaryotes

all metabolism occurs in cytosol and cell membrane

similar mechanism using ps1 and ps2 and calvin cycle

how does anoxygenic photosynthesis occur

only in prokaryotes

eveolved before oxygen in athmosphere

Only uses ETC and cyclic electron flow not linear and does not produce oxygen as a byproduct by splitting water