Photosynthesis Flashcards
What does photosynthesis do?
- Uses energy from light to convert carbon dioxide into sugar.
What is the major source of chemical energy for most organisms?
- Carbohydrate in the form of glucose.
What is Light?
- A form of electromagnetic radiation.
- Travels as a wave
- Behaves as particles (photons).
What are Pigments?
- Molecules that absorb wavelengths in the visible
spectrum.
Read
- The electromagnetic spectrum shows the wide range of wavelengths / energy levels that photons can have.
- Spectrum ranges from short
wavelength/high energy gamma
rays to long wavelength/low
energy radio waves
What happens when a photon meets a molecule? (B.P.A)
- 1: The photon can BOUNCE of the molecule.
- 2: The photon may PASS through the molecule.
- 3: The photon may be ABSORBED by the molecule.
: 1+2 no changes made to molecule
: 3: Photon disappears but not its energy, because energy is
neither created nor destroyed.
What do photons do a molecule?
- Add energy to the molecule.
Read
- The molecule moves from
ground state to an excited state and possess more energy.
What is Chlorophyll? (green pigment)
- Absorbs red + blue light but reflects Green light, making plants appear green.
What are the 2 Chlorophylls that absorb light energy?
- Chlorophyll a
- Chlorophyll b
What are Carotenoids also called?
- Accessory Pigments
What are Carotenoids?
- Absorb wavelengths between red + blue and transfer some of that energy to the chlorophylls
Where does Photosynthesis occur?
- In Chloroplasts
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- Chlorophyll was once free-living bacteria that got swallowed up by ENDOSYMBIOSIS.
- In other parts of the plant, chloroplasts get used for storage of food or other pigments.
What are Chromoplasts?
- Have many pigments e.g. yellow, orange +red (like in flowers &
fruits) .
Look at structure of Chloroplast.
- Double membrane (inner + outer)
- Stroma (a semifluid interior)m’nd
- Grana (made of thylakoids)
- Thylakoids ( membranous disks interconnected w/ each other + inner membrane).
What photosynthetic pigments do thylakoids contain?
- Chlorophyll a + b
What is the Photosynthesis equation?
6 CO2 + 6 H2O → C6 H12 O6 + 6 O2
What are the 2 stages/parts of Photosynthesis?
- Light Reactions/
- Calvin cycle/
Describe the light reaction stage.
- occurs ONLY in light.
- location Thylakoid Membrane.
- Light energy is captured by chlorophyll + used to extract electrons from water, which converts it to oxygen.
- Solar energy is converted to chemical energy:
solar energy → chemical energy (ATP, NADPH)
What are the 2 photosystems utilized by the Light Reactions stage?
-Photosystem I (PS I)→ P700(molecules of chlorophyll a)
• absorbs light energy @ 7oonm
• non cyclic pathway produces NADPH
• cyclic pathway is N.B to produce ATP
-Photosystem II (PS II) )→ P680 (molecules of chlorophyll b)
• only participates in the non cyclic pathway
• produces ATP
• hydrolysis of water → O2
organized in the way they were discovered.
What do are the photosystems composed of?
- a Pigment Complex ( PS 1 + PS 11)
- Electron acceptor molecule.
the pigment complexes act as antenna to gather solar energy.
Describe the non - cyclic pathway of the light reactions. (part 1+2)
1 - Begins w/ PS II. The pigment complex (P680) absorbs solar energy, which gets passed from one pigment to the other until it is concentrated in a particular pair of chlorophyll b molecules, called the RXN CENTRE.
2 - Electrons (e-) in the RXN CENTRE become so energized that they ESCAPE from the rxn center and move to nearby electron acceptor molecules.
Describe the non - cyclic pathway of the light reactions. (part 3+4)
3 - W/ out replacement electrons PS II would disintegrate, and these are removed from water, which splits, releasing oxygen (O2) to the
atmosphere.
4 - An electron acceptor sends energized electrons down the E.T.C, a series of carriers that pass electrons from one to the other. As the electrons pass from one carrier to the next, energy is captured & ATP is produced. ATP will be used in the Calvin cycle.
Describe the non - cyclic pathway of the light reactions. (part 5+6)
5 - When the PS I pigment complex (P700) absorbs solar energy, energized electrons leave the rxn centre + are captured by electron acceptors. Low-energy electrons from the ETC replace those lost by PS I.
6 - The electron acceptors in PS I pass their electrons to NADP+ molecules to become a reduced to NADPH. This NADPH will be used by the Calvin cycle reactions in the stroma.
Describe the cyclic pathway of Light Reactions.
- Electrons leave P700 & then return back to it, instead of reacting with NADP+.
- Before they return to P700 they pass ETC and ATP
is produced.
Read
- Cyclic electron flow common in cell with especially high ATP needs (such as the sugar-synthesizing)
- Cyclic electron flow may play a photoprotective role, preventing excess light from damaging photosystem.
Where does the Calvin cycle occur?
- The stroma of the chloroplast.
How does the Calvin cycle produce sugars?
- By using CO2 from the atmosphere.
What 3 portions is the calvin cycle divided into?
1) CO2 fixation
2) CO2 reduction
3) regeneration of ribulose-1,5-bisphosphate (RuBP)
What happens in the fixation of CO2?
- CO2 + ribulose-1,5-bisphosphate (5 carbon sugar)
- = 6 carbon molecule, that splits into two 3-carbon molecules.
What happens during the reduction of CO2?
- The two 3-carbon molecules are called 3PG (3-phosphoglycerate).
- The two 3PG molecules undergo reduction
- Turning to G3P (glyceraldehyde 3-phosphate)
This rxn uses the ATP and NADPH from the light rxn.
What happens during the regeneration of RuBP?
- 5 molecules of G3P become 3 moles of RuBP.
- Only after 3 turns of the Calvin cycle can 1 G3P exit.
This rxn uses ATP produced by light.
What is the end product of photosynthesis?
- It is considered to be Glucose
Two G3Ps are needed to form
glucose phosphate;
What role does sucrose have in plants?
- The transport sugar in plants.
what role does starch have in plants?
- The storage form of glucose.
What role does cellulose play in plants?
- Helps structurally to the plant cell wall
Read
• Plants capture solar energy and store it in carbon-based organic nutrients that are passed to other organisms when they feed on plants and/or on other organisms.
– Plants are called autotrophs because they make their own
organic food.
– Heterotrophs are organisms that take in preformed organic
food.
• Therefore all life is dependent on the ability of plants to capture solar energy and produce carbohydrate molecules.
