concept 11 - BIO10008

what is photosynthesis

photosynthesis is the process where plants take water and carbon dioxide and generate oxygen and glucose from the help of sunlight

what is the chemical equation for photosynthesis

6CO2 (reduced) + 6H2O (oxidised) → (sunlight) C6H12O6 (oxidised)+ 6O2 (reduced)

oxygen (reduced state) in water molecules are oxidised to form oxygen gas

carbon (oxidised state) in CO2 are reduced to form glucose

where does cyanobacteria photosynthesise

thylakoid

green algae

chloroplast → thylakoid

what is chloroplast

chloroplast captures the sunlight and undergo photosynthesis, inside the chloroplast there is two membrane, it has a thylakoid stack (granum), inside the granum is the thylakoid lumen and chlorophyll. These are found in the mesophyll cells in plants.

light reactions

reactions that need the input of energy/sunlight to produce ATP and NADPH (reducing agent)

In the cell, where does the reduction of CO2 occur, and what is the reducing agent?

the reduction of CO2 occurs in the stroma of the chloroplast, the reducing agent is NADPH

what light is least effective in driving photosynthesis

green light as chloroplast reflect green light (giving them that green colour, thus the light will not get absorbed

which region of the chloroplast is associated with the capture of light energy

the chloroplast’s chlorophyll inside the thylakoid membranes

describe the function of a photosystem

photosystem 2 is first in the light reactions, the photosystem captures a photon which then drives the movement of electrons’ linear flow. the photon strikes the pigment molecule which then excites an electron (jumped an energy state), then as the electron goes back to its ground state. The energy from the electron’s released to another pigment molecule. This process repeats until, it reaches p680. the electron from p680+ is transferred to a primary electron acceptor via a redox reaction, the electrons come from H2O and is supplied to the p680, through enzyme catalysing the splitting to replace an electron that was transferred up to the primary electron acceptor. Then the H+ from H2O will release into the thylakoid space and O2 gas is diffused out of the chloroplast as a byproduct

photosystem 1

it does the same thing as photosystem 2 except the pair of the final chlorophyll molecule is the p700 and NADPH is produced through NADP+ reductase to provide a reducing power to synthesise carbohydrates in the calvin cycle. the p700 is supplied with electrons that flowed from photosystem 2.

what is the light independent reaction

the calvin cycle’s carbon fixation phase, it doesnt directly need light to proceed but it needs products that are made from the light reaction.

carbohydrates reduced from cabron dioxide through ATP and NADPH helping with this process to create RuBP in the stroma

what is RuBP

the CO2 acceptor, accepts the carbon from RuBP. then with catalyzation from rubisco, the reaction intermediate splits into 3PG.

what is the name of the enzyme that catalyses the reaction of CO2 with RuBC

rubisco, it has a higher affinity for CO2

what is the potential impact of this attractive force on photosynthesis

photosynthesis in plants is more favoured for the calvin cycle to make 3PG than photorespiration as it is less efficient

outputs and inputs of calvin cycle

input: CO2, NADPH, ATP

output: half a glucose from GA3P, RuBP and G3P,

photorespiration

rubisco can be used as a carboxylase or oxygenase, where photorespiration can be used to produce phosphoglycolate and 3PG and uses up energy and releases CO2, although this inhibits some reactions in the calvin cycle and has to be eliminated.

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What are the three steps of the Calvin cycle? How many ATP molecules are required for each cycle, and which steps use them?

The three steps are (1) the fixation of CO2, (2) the reduction of 3PG to form glyceraldehyde 3-phosphate (G3P), and (3) the regeneration of the CO2 acceptor RuBP. Altogether, 18 ATP molecules are used for each cycle: 12 for phosphorylation during the reduction step and 6 in the conversion of RuMP compound into RuBP during regeneration

what parts of photosynthesis are endergonic and exergonic

light reaction exergonic (releasing energy)

calvin cycle - light independent endergonic (using energy)

photorespiration

occurs on hot dry days, leaf stomatas close, and ig there is relatively high O2 and low CO2 within the life, the oxygenase activity is favoured although it reduces net carbon fixed.