Biology Module 4 Photosynthesis

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Photosynthesis

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1. Endergonic redox process by which green plants, blue-green algae, and some bacteria transform sunlight into carbs, and create O2.
2. Where? Chloroplasts.
3. 2 stages: light reactions/dark reactions
4. Overview: Chlorophyll catches light, which is the energy for reducing CO2 to carb. Electrons for this come from Water.

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chloroplasts

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1. Organelles in plant cells.
2. 2x membrane
3. interior fluid = stroma
3. thylakoids -- grana/granum

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stroma

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1. interior fluid of a chloroplast.
2. contains the thylakoids and grana.
3. where dark reactions occur

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thylakoids

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1. the 3rd membranous region inside stroma of a chloroplast.
2. area inside thylakoids = thylakoid space.
3. Org. into granum, grana.
4. membranes of thylakoids contain chlorophyll
5. The membranes are where the light reactions occur.

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Light reactions

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1. Occur in thylakoid membranes
2. 1st steps of photosynthesis

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Dark reactions

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1. Where? Stroma
2. Also called Calvin cycle
3. Called dark bc don't directly need sunlight to occur.

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Steps of photosynthesis - big view

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1. Two stages - light/dark.
2. Light: on thylakoid membranes, light energy converts to ATP & NADPH, (where NADP+ is like NAD+) O2 is released as byproduct of splitting water.
3. Dark: Products of light (ATP & NADPH) drive reducing CO2 to carb.

3. Dark:

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Light reaction: big view

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During the light reactions, which occur on the thylakoid membranes of chloroplasts, light energy is converted to the chemical energy of ATP and NADPH—where NADP+ is similar to NAD+. The light energy absorbed from the sun energizes the splitting of water, and electrons from this water are transferred to NADP+ to yield NADPH. Oxygen is released as a byproduct of the water splitting event. ATP is generated by a process called photophosphorylation.

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Dark reaction: big view

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The Calvin cycle, which occurs in the chloroplast stroma, uses the products of the light reaction, ATP and NADPH, to drive the reduction of CO2 into carbohydrate. The Calvin cycle is also referred to as the dark reactions since it does not directly require sunlight.

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wavelength

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distance between the tops of waves of the measured light

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electromagnetic spectrum

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1. a method of org. solar wave energy in terms of wavelength.
2. short - gamma, long - radio

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visible light range

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from 380 to 750 nm.
Impt to photosynth

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photons

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1. light behaving as if it were discrete particles or quanta.
2. carries a fixed amount of energy that is inversely proportional to its corresponding wavelength. For example, photons in the UV range are of higher energy that those in the visible light range.

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absorption spectrum

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pertains to pigments that absorb light. can be shown graphically.

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action spectrum

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pertains to pigments and their ability to drive reactions as a result of absorbing light. For example, chlorophyll drives photosynthesis - blue/red lights good, green light ineffective.

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chlorophyll a

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1. main kind of chlorophyll in plants.
2. passes on the electron in reaction center complex to initiate the light reactions
3. behaves subtly differently depending if its in the reaction center of photosystem I or II.
a) If it's in I - absorbs best at 700nm (far red), & is called P700.
b) If it's in II - absorbs light best at 680nm as is called P680.

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chlorophyll b

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1. a yellow-green accessory pigment to chlorophyll a.
2. diff structure and absorption spectrum, too.

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carotenoids

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1. accessory pigment.
2. yellow orange - contributes to capturing light

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photosystem

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1. cluster of pigment molecules (all kinds) in the thylakoid membrane.
2. two kinds: I & II, dist. by diff in chloro a in the reactions centers

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reaction center complex

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where the chlorophyll a receives the light energy from the pigment molecules.

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How do the electrons captured by the pigments travel?

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Via cyclic flow or noncyclic flow.

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Cyclic flow

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1. one of the two routes for captured electrons to travel
2. simpler way to go, only photosystem I involved.
3. produces ATP, but not NADPH or O2.
4. chemiosmosis & proton motive force
5. cyclic phosphorylation

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Cyclic phosphorylation

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1. one of the two routes for electrons to travel
2. chemiosmosis & proton motive force
3. electrons flow down transport chain in thylakoid membrane.
4. carriers pick up H+ (protons) from stroma, and bring them into thylakoid space where pH is lower (i.e., H+ is higher!)
5. Protons flow down concentration gradient thru ATP synthase & make ATP.