SBI4U - Chapter 3: Photosynthesis
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What two parts make up chlorophyll? Describe it
Porphyrin - Mg atom surrounded by hydrocarbon ring with alternating single and double bonds. The electrons in these bonds absorb light energy and begin the photosynthetic process
Phytol tail - hydrophobic, anchors molecule to membrane
Significance of cyanobacteria?
One of the firsdt cells to produce oxygn on a large scale and use sunlight in production of organic compounds from water and carbon dioxide
True or false: in plants only leaves can photosynthesize
STRUCTURE AND FUNCTION: CUTICLE
- Protect the leaf from excessive absoprtion of light and evaporation of water
STRUCTURE AND FUNCTION: EPIDERMIS
Allows light to pass through mesophyll cells
STRUCTURE AND FUNCTION: MESOPHYLL
Spongy and palisade
Photosynthetic cells that form the bulk of a leaf
STRUCTURE AND FUNCTION: GUARD CELL
Bean shaped around stoma
Photosynthetic epidermal cells of a leaf or stem that GUARDS the size of an opening
STRUCTURE AND FUNCTION: STOMATA
Openings on surface of leaf that allow the exchange of gas
How much water will the average tree lose through stomata by transpiration?
How does transpiration help photosynthesis? (2)
- Creates transpiration pull that helps move water, minerals, and other substances from roots to leaves
- Produces an evaporative cooling system that prevents leaves from heating to temperatures that could inhibit or denature enzymes that catalyze the reactions of photosynthesis
When would a leaf close their stomata?
To maximize CO2 intake and limit water loss, any weather that promotes transpiration like sunny, warm, dry weather, will have guard cells reduce the size of stomata
When guard cells are turgid (swollen), will stomata be open or closed?
When guard cells are flaccid (limp), will stomata be open or closed?
How does the size of a guard cell change?
When water moves in and out of cell; follows diffusion of potassium ions.
Basically when K moves into guard cells, water follows, and guard cells swell, stoma open
How does light affect the opening and closing of stomata?
Sun come out, blue light activates blue receptors, making proton pumps pump protons out of cell = gradient
Gradient makes K ions move, making water move, making guard cells swell, makinjg stomata open
Simultaneously, mesophyll cells photosynthesize thus using CO2, making stomata open
STRUCTURE AND FUNCTION: STROMA
Protein rich semiliquid material
Synthesis of photosynthesis
STRUCTURE AND FUNCTION: THYLAKOIDS
Interconnected flattened membrane sacs
Separate compartment in stroma
STRUCTURE AND FUNCTION: GRANA
Stack of thylakoids
STRUCTURE AND FUNCTION: LAMELLAE
Contains light-gathering pigment molecules and ETC
Break down photosynthesis into three parts
- Capture light energy
- Use energy to make ATP and NADPH
- Use free energy of ATP and NADPH to synthesize organic compounds from CO2
Why is it wrong to call the Calvin cycle a dark reaction
Enzymes that catalyze these reactions are activated by light and inactive in dark. Calvin Cycle also requires ATP and NADPH from light reactions
What is a photosystem?
Clusters of photosynthetic pigments embedded in thylakoid membranes of chloroplasts that absorb light energy.
Absorbed light energy goes in ADP, Pi, and NADP+ to make ATP and NADPH. The H shit is from water
What is the difference between action spectrum and the absorption spectrum?
An action spectrum is a graph illustrating effectiveness of wavelengths promoting photosynthesis; which wavelength is good for a specific pigment
An absorption spectrum is a graph illustrating the wavelengths of light absorbed by pigments
Differentiate between chlorophyll a and chlorophyll b
- Chlorophyll A is the main bitch absorbing the energy of light to the carbon fixation reactions of photosynthesis, R group is CH3
- Chlorophyll B is a side bitch accessory pigment absorbing things chlorophyll A cant, R group is CHO
State other accessory pigments
- Cartenoids - absorb light that can damage chlorophyll and lose energy as heat, orange
- Xanthophylls - interspersed in thylakoid membranes, yellow
- Anthocyanins - in plant cell vacuoles, not chloroplasts, red, violet, and blue
Break down the light reactions into three parts
- Photoexcitation: absorption of a photon by an electron of chlorophyll
- Electron transport: transfer of excited electron thru series of membrane bound electron carriers = gradient = reduces an electron acceptor
- Chemiosmosis: movement of protons through ATPase complexes to drive the phosphorylation of ADP and ATP
STAGE ONE: CAPTURE LIGHT ENERGY
Occurs in thylakoid membrane
Light is absorbed by photosystems - first by PII then PI
What are photosystems composed of?
- Antenna complex
- several hundred pigment molecules
- absorb photons and transfers to rxn centre
- Reaction centre
- chlorophyll a molecule - energy trapped in here is sent to ETC
Photon -> pigment -> pigment -> pigment -> chlorophyll a -> energy
STAGE TWO: PRODUCING NADPH AND ATP
Noncyclic electron flow
TWO THINGS HAPPENING: ATP AND NADPH
Excited e for PII moves through primary electron acceptor (pheophytin), e carriers (PQ, b6f, PC) and then ETC to replace an electron lost by photosystem I. This occurs twice
Prior to, Z protein in PII splits water into H and G+ and electrons. One of these electrons are used to replace the missing e in PII. Oxygen is diffused out of cell, leaving protons in thylakoid space. These electrons will pass a proton pump called Q cycle to create an H+ gradient for chemiosmosis to photophosphorylate ADP to ATP. Four H+ per ATP per pair of e
- e in PI is energized by photon
- e goes to ferredoxin -> NADP reductase (to reduce to produce NADPH).
What reaction transfers the excited e from chlorophyll to a primary electron acceptor?
Why do isolated chlorophyll molecules fluoresce?
There is no primary electron acceptor to receive the photoexcited electron, so they are the primary light harvesting unit of the chloroplast
List the series of e carriers in noncyclic e flow in order
Plastoquinone, b6f-complex, and plastocyanin
What is the primary electron acceptor?
Which is which: PI, PII, P680, P700?
What does the Z protein do?
Z protein in PII splits water into H and G+ and electrons. One of these electrons are used to replace the missing e in PII
Where does Z protein split water?
What is Cyclic Electron flow? Why does it occur?
It is another way to produce energy using only PI. It makes ATP, but not NADPH, so it can be used when NADPH is high
- Photon ejects e from PI
- e -> Fd erredoxin -> Q cycle -> b6f-complex (cytochrome chain) -> PI
It creates the proton gradient for ATP
True or false: PI is only used in cyclic electron flow
True or false: PII is only used in cyclic electron flow
False, only PI
True or false: ATP and NADPH is produced in Cyclic Electron Flow
False; only ATP
True or false: ATP and NADPH is produced in Noncyclic Electron Flow
If NADPH high, will cyclic of noncyclic occur?
If NADP high, will cyclic of noncyclic occur?
STAGE 3: USING NADPH AND ATP TO SYNTHESIZE ORGANIC COMPOUNDS
let's make some coco in da stroma
dis all bout da CO2
CO2 will be synthesized into carbs using energy from NADPH and ATP.
1) Carbon Fixation
CO2 is being added to 5-carbon molecule RuBP to make a 6-carbon shit, producing two 3-carbon shit (3 PGA). These reactions are catalyzed by rubisco
Is Stage 3 cyclic or nah?
Where does each stage of photosynthesis occur?
- STAGE 1: Thylakoid membrane
- STAGE 2: Thylakoid lumen
- STAGE 3: Stroma of chloroplasts
Name the three Calvin Cycle stages
- Carbon fixation
- Reduction Reaction
What percentage of rubisco make up the leaf?
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