Photosynthesis Flashcards
First step of light dependent stage (non-cyclic photo phosphorylation)
- photons of light absorbed by chlorophyll in photosystem 2 (PS2)
Second step of light dependant stage (non-cyclic photo phosphorylation)
- increases kinetic energy in electrons and chlorophyll undergoes photoionisation
Third step of light dependant stage (non-cyclic photo phosphorylation)
- photosystems are linked by proteins called electron carriers and form electron transport chain. Electrons leave chlorophyll and move to photosystem 1 (PS1)
Forth step of light dependant stage (non-cyclic photo phosphorylation)
- light energy can split water by photolysis forming protons (H+), electrons and oxygen. Electrons can be used to replace those lost in photosystem 2 (PS2)
Fifth step of light dependant stage (non-cyclic photo phosphorylation)
- electrons lose energy as they move down the electron transport chain. This energy is used to actively pump protons against their electrochemical gradient from the stroma to the thylakoid space
Sixth step of light dependant stage (non-cyclic photo phosphorylation)
- hydrogen ions move down the concentration gradient back out into the stroma via the embedded enzyme ATP synthase. This allows ATP to form
Seventh step of light dependant stage (non-cyclic photo phosphorylation)
- steps 1 and 2 are repeated in photosystem 1 with electrons leaving the chlorophyll molecules of photosystem 1 (PS1)
Eighth step of light dependant stage (non-cyclic photo phosphorylation)
- Using enzyme NADP reductase, electrons from photosystem 1 (PS1) are transferred to NADP along with a proton from the stroma to form NADPH. Electrons from photosystem 2 (PS2) that moved along the electron transport chain replace those lost from photosystem 1 (PS1)
First step of light independent stage (cyclic photo phosphorylation/calvin cycle)
- carbon dioxide enters chloroplast by diffusion and passes into the stroma, combining with intermediate compound ribulose bisphosphate (RuBP) and catalysed by enzyme rubisco in carbon fixation producing 2 molecules of glycerate 3 phosphate (G3P)
Why are large quantities of enzyme rubisco required in calvin cycle
- slow process
Second step of light independent stage (cyclic photo phosphorylation/calvin cycle)
- Energy from ATP and hydrogen from reduced NADP (from light dependant stage) is used to reduce glycerate 3 phosphate (G3P) to form triose phosphate (TP)
Third step of light independent stage (cyclic photo phosphorylation/calvin cycle)
- 1/6 of triose phosphate (TP) is used to make glucose phosphate and in turn, glucose.
- condensation of many glucose molecules in the stroma forms starch
- glycerol is synthesised from triose phosphate (TP) and fatty and amino acids from glycerate 3 phosphate (G3P)
Forth step of light independent stage (cyclic photo phosphorylation/calvin cycle)
- 5/6 of triose phosphate must be used to regenerate ribulose bisphosphate (RuBP) using ATP
Limiting factors of photosynthesis
- Carbon dioxide concentration
- Light intensity
- Temperature
Limiting factor definition
- something present in the environment in such short supply that it restricts life processes, slowing rate of reaction
Rate limiting step
- step in a process proceeding most slowly at a given time
Carbon dioxide concentration
- low carbon dioxide concentration causes NADPH and RuBP to accumulate so the rate limiting step is carbon fixation stage of the Calvin cycle
Temperature
- low temperature causes the enzymes catalysing the whole of the Calvin cycle to slow down, especially the activity of rubisco
Light intensity
- low light intensity causes a shortage of products of light dependant reaction (NADPH and ATP) so rate limiting step is when glycerate 3 phosphate (G3P) is reduced in the light independent stage as those products are required
Explanation of curved graph section A
- as (x axis) increases, so does the rate of photosynthesis. (X axis) is limiting factor. … reaction occurs producing…
Explanation of curved graph section B
- graph starts to plateau as some other factor is starting to become limiting
Explanation of curved graph section C
- (x axis) is no longer a limiting factor; now (other 2 limiting factors). Rate of photosynthesis won’t increase more. … step has become rate limiting step overall
How to isolate a sample of chloroplasts from leaves?
- break open cells and filter
- in cold, isotonic, pH controlled solution
- centrifuge and remove cell debris
- spin at higher speeds until chloroplasts settle out
Photoionisation
- light energy absorbed by chlorophyll releasing electrons and causing them to pass to an electron acceptor at the start of the electron transport chain
Chemiosmosis
- movement of electrons along the electron transport chain creating a proton gradient across the membrane to drive ATP synthase
Photolysis
- process of splitting water molecules using light energy to reduce electrons, oxygen and hydrogen ions
Electrochemical gradient
- difference in charge and chemical concentration across a membrane
Explain how to use chromatography to separate photosynthetic pigments
- draw pencil line with ruler to mark origin
- using paint brush, apply pigment in origin mark and mark solvent front
- place solvent in tube and place chromatogram below the origin line
- measure the rf value
Why use propanone for chromatography?
- breaks down cells, chloroplasts and thylakoids to release pigment
- dissolves chlorophyll to isolate from plant tissues
