Membrane that contains chlorophyll
What's inside a chloroplast?
- Double membrane (outer/inner)
- Inermembrane space
- Thylakoid space
- 6 Water + 6 carbon dioxide + sunlight ->
- Glucose + 6 oxygen
History of photosynthesis formula
- O2 originally thought to come from the CO2
- van Niel first proposed that O2 came from H2O in 1930s
- Confirmed in 1950s
How is photosynthesis a redox reaction
- Water becomes oxidized to become oxygen
- Carbon dioxide is reduced to become sugar
Is photosynthesis endergonic or exergonic?
Electrons increase in potential energy so the reaction is endergonic
What form of energy is light?
A form of electromagnetic radiation
discrete particles with a fixed amount of energy (no mass!)
Why is the sky blue? Why does something appear white? black?
- This deals with how much wavelengths are making it to your eyes
- Black absorbs all visible light
- White reflects all visible light
- Substance that absorbs visible light
- Different pigments absorb different wavelengths of light
Why do chlorophyll a & b appear green?
They do not absorb wavelengths in that part of the spectrum
Why do leaves change colors?
Leaves stop producing chlorophyll so the other chemicals start showing through
Why do carotenoids exist?
To protect the plant. The pigments pick up the extra energy from the sun
Why does chlorophyll appear green
It reflects green wavelengths
Two parts of photosynthesis
- Light reactions
- Calvin cycle
- Converts light energy into chemical energy
- Located in the thylakoid membrane.
- Light + H2O -> NADPH + ATP + O2
- H2O is split to provide e- and H+
- NADP+ is reduced to NADPH
- ATP is produced
- O2 is given off
Contain pigment molecules which absorb light and transfer the energy to reaction-center complex (i.e light harvesting complex)
Contains a special pair of chlorophyll a molecules which can reduce the primary electron acceptor
What helps direct energy to the center in the antenna complex?
- Resonance energy transfer
- Energy in electron is transferred to nearby pigment
In the thylakoid membranes, what is the main role of the pigment molecules in a light-harvesting complex
Transfer light energy
As electron pass through the system of electron carriers after leaving photosystem II, they lose energy. What happens to the energy?
It is used to establish and maintain a protein gradient for the generation of ATP
The process of making ATP from ATP synthase. This is because the energy is coming from photons
When oxygen is released as a result of photosynthesis, it is a direct by product of?
Splitting water molecules
Cyclic electron flow
- Electrons from photosystem I transferred back to ETC
- Produces ATP instead of NAPDH
How are the light reactions and the Calvin Cycle connected?
The light reactions provide ATP and NADPH to the Calvin Cycle, and the Calvin cycle returns ADP, Pi and NADP+ to the light reactions
Uses the chemical energy stored in ATP and NADPH to reduce CO2 to sugar (G3P)
3 Phases of Calvin Cycle
- Carbon fixation
- Regeneration of CO2 acceptor
- First phase in Calvin Cycle
- Rubisco (RuBP carboxylase) attatches to CO2 molecule to RuBP
- Taking CO2 and fixing it to become an organic molecule
- Second phase in Calvin Cycle
- Carbon intermediate phosphorylated by ATP
- Reduction by NADPH and loses the phosphate = G3P
Regeneration of CO2 acceptor
- Series of steps which utilize ATP to rearrange 5 molecules of G3P to regenerate 3 molecules of RuBP
- Majority of sugar produced is turned into RuBP
What process is most directly driven by light energy
Removal of electrons from chlorophyll molecules
What does it mean when CO2 becomes fixed during photosynthesis?
CO2 becomes bonded to an organic compound
How many times must the Calvin Cycle occur to produce 1 net G3P
- 3 times
- For 1 G3p, cycle uses 9 ATP and 6 NADPH
Which doesn't happen in Calvin Cycle?
Oxidation of NADPH
Regeneration of CO2 acceptor
Consumption of ATP
Release of oxygen
Release of oxygen
- When Rubisco fixes oxygen in place of carbon dioxide.
- This causes plants to release carbon dioxide
- It also consumes ATP and decreases photosynthesis by siphoning off material from the Calvin Cycle
When is trouble with Rubisco most prevalent and why?
- Hot, dry climates
- Plants close stomata to minimize water loss but this reduces the amount of carbon dioxide available
- Concentration of oxygen released from light reactions increases favoring oxygen fixation
Plants that use rubisco for initial carbon fixation
Plants that have alternative modes of carbon fixation to minimize photorespiration
- C4 Plants
- CAM (crassulacean acid metabolism)
What happens in C4 plants?
- Carbon fixation is in a different location from the Calvin Cycle
- CO2 is initially fixed by PEP carboxylase in mesophyll cells to form a 4-carbon product
- Product is transported into bundle sheath cells where the CO2 is released and can be added to the Calvin Cycle by rubisco
- This process uses some energy but it helps ensure that the rubisco fixes only CO2
- Carbon fixation is separated from the Calvin Cycle at a different time
- Plants close their stomata during the day to conserve water and open at night
- Plants take in CO2 and fix it into organic acids which are stored in vacuoles
- During the day, when light can supply ATP and NADPH, CO2 is released from the organic acids and enters the cycle
- This also uses some energy
The alternative pathways of photosynthesis using the C4 or CAM systems are said to be compromises why?
Both minimize photorespiration but expend more ATP during carbon fixation
What happens to the sugar produced?
- 50% is used for cellular respiration
- Linked together to form cellulose -> build up the cell wall
- Excess stored as starch in the winter for trees
If you plant a maple seed in your backyard and over the course of many years it grows into a tall tree, where did the increase in mass come from?
- Carbon is pulled out of the air which gets bonded to organic molecules and turned into cellulose