Topic 8.3 Photosynthesis Flashcards
Limiting factors
CO₂, temperature, and light intensity. Not water as if water was so scarce that it was a limiting factor, there would be many other problems already in the plants such as its inability to remain turgid.
Two steps in photosynthesis
The light-dependent, light-independent reaction.
Light dependent reaction occurs in the thylakoid.
Light independent reaction occurs in the stroma.
Light-dependent reaction involving photosystem 2
Light enters the plant, hits photosystem 2, this makes 2e⁻ leave the photosystem which is then taken by plastoquinone and moved to photosystem 1.
Light-dependent reaction involving photosystem 1
More light that entered the plant hits photosystem 1, this makes 2e⁻ leave this photosystem which then reduces ferredoxin which reacts with NAPD reductase to form reduced NADP.
Chemiosmosis during the light-dependent stage
As electrons are transferred to photosystem 1 and from photosystem 1, they release energy which is used to create a concentration gradient of protons on one side of the thylakoid membrane which moves through the membrane to the stroma, producing ATP by ATP synthase.
This production of ATP from ADP + P is called photophosphorylation.
Effect of light-dependent reactions on light-independent reactions
In the darkness, photosynthesis can continue for around a few seconds as the light-independent reaction is dependent on the light-dependent reaction.
Light-dependent reactions produce reduced NADP and ATP which are needed in the independent reaction. These resources run out quickly without resupply.
Electron transport chain in plants
Begins with plastoquinone and involves electrons being passed from carrier to carrier, ending with a water-soluble electron acceptor (reduced plastocyanin).
Cyclic phosphorylation
The process of phosphorylation of ADP which is caused by the electron transport chain.
Carbon fixation
Carbon is fixed from the atmosphere to react with ribulose bisphosphate to form two molecules of glycerate phosphate.
The action of inorganic carbon dioxide reacting with the organic ribulose bisphosphate to form organic products is carbon fixation.
Role of reduced NADP and ATP
NADPH and ATP both react with glycerate phosphate to form trios phosphate.
Triose phosphate
Trios phosphate can react with other trios phosphates to form either ribulose bisphosphate by reacting with NADP or can also form carbon compounds like glucose.
RuBP regeneration
6 carbon dioxides are used to create one glucose. This means that 6 carbon dioxide are used in the Calvin cycle. Therefore, 6 CO₂ reacts with 6 ribulose bisphosphates to form 12 glycerate phosphates which form 12 trios phosphates.
Two triose phosphates are used to form a glucose molecule. The remaining 10 triose phosphates (containing 30 carbons in total) are used to create 6 molecules of ribulose bisphosphate (each has 5 carbons, 30/5 = 6).
Since the same amount of RuBP that is used is also formed from cycles, RuBP is regenerated and allows the cycle to continue until there is not sufficient light.
Chloroplast structure
Thylakoids - internal membranes where the light-dependent reactions occur
Stroma - fluid around the thylakoids which contain enzymes, this is where the LIR occur
Chloroplast envelope - double membrane around the chloroplast.
Grana - stacks of thylakoids. If rapid photosynthesis has occurred, starch grains or lipid droplets may form in the stroma.
Photolysis
The charge in photosystem 2 is returned to normal charge as H₂O is split into 2H⁺ and 0.5O₂ which gives 2e⁻ to the photosystem. Waste oxygen is produced which is released.
Electrons transferring to photosystem 1
This is returned to normal charge as plastoquinone passes electrons through the electron transport chain (causing the phosphorylation of ADP) and passes them to plastocyanin which gives the electrons to photosystem 1.
