Photosynthesis Flashcards
What wavelengths of light does chlorophyll A absorb
Blue and red regions of the visible spectrum
List three accessory pigments and state their role
Chlorophyll B, Carotenoids, Xanthophyll. They increase the range of wavelengths of light that can be absorbed so increase the rate of photosynthesis
What is a photosystem
A light harvesting complex embedded in a thylakoid membrane
What is photolysis?
Water molecules spilt in photolysis To produce H+, e- and O2. H+ are used in ATP synthesis. Electrons are fed back into Chlorophyll A to reduce it. Oxygen in used in aerobic respiration or will diffuse out of stomata.
Outline the importance of photosynthetic pigments in photosynthesis
Primary pigments (chlorophyll A) absorb photons and excite electrons.
Accessory pigments channel light towards the primary pigment and increase the range of wavelengths of light that can be absorbed. This produces ATP and NADP which are then used in light independent reaction
What is chemiosmosis
The flow of protons down their concentration / electrochemical gradient across thylakoid membrane, through a channel associate with ATP synthase which results in the formation of ATP
What is photophosphorylation
The formation of ATP from ADP + Pi in the presence of light. There are both cyclic and non-cyclic photophosphorylation that occur in light dependent stage of photosynthesis. v
Describe cyclic photophosphorylation
Electrons from PS1 are unable to be accepted by NADP so they return to PS1 via a chain of electron carriers. A steed proton gradient is maintained so ATP continues to be made. Only involve PS1. Only product is ATP
Describe stages of Light independent Reaction (Calvin Cycle)
RUBP is converted into GP by enzyme RUBISCO with carbon dioxide. This forms unstabe 6C Gp molecule which splits into 2 X 3C GP molecule. GP is converted into TP by ATP (which is hydrolysed) and NADP (which is oxidised). 1/6 TP leaves Calvin cycle to be converted into glucose, etc, the other 5/6 are returned to RuBP as ATP is converted into ADP + Pi.
How does light intensity affect photosynthesis?
As light intensity inreases, there are more photons, so more electrons are excited so more ATP is formed and more NADP is formed . When LI no longer limiting CO2 conc / temperature may be limiting.
How does Carbon dioxide concentration affect photosynthesis?
As CO2 conc. increases, rate of P/S increases as more carbon fixation by RUBISCO (more RuBp -> GP). CO2 becomes no longer limiting
How does temperature affect rate of photosynthesis?
At lower temperatures, enzymes and substrates have limited KE so are unlikely to form ESC. As temp increases, enzymes and substrates gain KE so more frequent successful collisions. Above optimum temperature, active site changes shape so enzymes denatured.
What happens during water stress?
Occurs when insufficient water in the soil. ABA that is synthesised in roots is transported up the xylem in transpiration stream. ABA acts on receptors in guard cell plasma membranes so ions actively pumped out of guard cells, water flows in by osmosis down water potential gradient and so guard cells become flaccid and close
