Unit 2: Photosynthesis Flashcards
(19 cards)
What are chloroplasts?
Convert light energy into glucose (sugar)
Photosynthesis reaction equation…
6CO2+12H2O—) C6H12O6+6O2+6H2O
What stages do photosynthesis occur in?
- Light reactions (thylakoid of chloroplast)
- Calvin cycle
(stroma of chloroplast)
Where is the thylakoid?
Is the membrane system
Where is the stroma?
Surrounding system
What are photosynthetic pigments?
Photosynthetic pigments capture energy from photons of sunlight
What are photons?
They are packets of energy that have properties of particles and waves (have characteristic wavelength; distance covered in one cycle of wave); most energetic photons travel at shorter wavelengths
What type of wavelength does red light have?
Long wavelength; less energy
What type of wavelength does blue light have?
Short wavelength; more waves per unit of time for blue light; more energy
Why are leaves green?
Because chlorophylls are the most abundant pigments; but other pigments are hidden beneath this overpowering green colour
Why do leaves turn red in autumn
Chlorophylls breakdown revealing the presence of other pigments
What light do chlorophyll a and b absorb?
They absorb both blue and red light wavelengths while reflecting and transmitting wavelengths in the middle of the visible spectrum (green and yellow)
What wavelengths do carotenoids absorb and what colours do they give off?
Absorb some blue and green wavelengths turn orange
What wavelengths do phycobilins absorb and give off?
They absorb most of the green, yellow, and orange wavelengths they give up purple light
Where do light reactions take place?
In the thylakoid of chloroplast (location in chloroplasts)
What are the 3 steps of light reactions?
- Pigments embedded in thylakoid membrane absorb energy from sunlight and give up electrons to membrane proteins; pigments are organized into 2 photosystems (take light get excited and move electrons and H+ ions
- Movement of electrons and H+ ions leads to the production of NADPH and ATP
- Electrons released by pigments are replaced by the splitting of H20, (photolysis) producing O2
The overall result is the formation of ATP + NADPH used in the Calvin cycle to construct glucose
What is the process of light reactions?
- Light energy of a wavelength excites chlorophyll a in photsystem II causing release of electrons
- photolysis (splitting of water by light) provides electrons to replace those lost by chlorophyll a and oxygen gas
- electrons released by chlorophyll a transferred through series of proteins in the thylakoid membrane until they reach photosystem 1
- just as with the etc, the movement of electrons through the thylakoid membrane results in the build of H+ ions within the thylakoid space
- H+ ion concentration used to power the synthesis of ATP
- Coenzyme NADP+ is the final electron acceptor; it is reduced to form NADPH
- ATP and NADPH are used in Calvin Cycle to build organic molecules like glucose
What did Melvin Calvin work out?
- Worked out the biochemical pathways of the light-independent reaction in experiments that used green algae called Chlorella
How does the Calvin Cycle begin?
- The first step in carbon fixation is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO)
- Rubisco attaches to carbon to RuBP
- NADPH and ATP convert 3-PGA to G3P
- 5 G3P and 3 ATP regenerates 3 RuBP
Phase 1:
- Rusbisco cataylses the reaction of 3 CO2 with 3 RuBP to form 6 PGA
Phase 2:
- 6 PGA are “reduced” to form 6 1,3-BPG which is the “reduced” to 6 G3P
- These reactions require 6 ATP and 6 NADPH
Phase 3:
- 5 G3P molecules are used to regenerate the 3 RuBP we began with
- 3 ATP are required
- 1 G3P can go towards making glucose
