Unit 5 - Energy transfers in and between organisms
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Summary AQA A LEVEL BIOLOGY CHAPTER 11 PHOTOSYNTHESIS NOTES
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Unit 5 - Energy transfers in and between organisms
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AQA
I created these notes throughout y12&13 and used them for my A level 2022 exams. I got a grade 9 in GCSE and am awaiting for my a level biology result. These notes were made using the CGP revision guide, AQA Biology textbook and class notes in order to cover everything in the course. I have also ad...
Unit 5 - Energy transfers in and between organisms
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11.1 OVERVIEW OF PHOTOSYNTHESIS
01 October 2021
18:31
Photosynthesis takes place in the chloroplasts of leaves.
Photosynthesis is the process in which energy from light is used to make glucose
from H2O and CO2 by a series of reactions.
● 6CO2 + 6H2O ---> C6H12O6 + 6O2
Energy is stored in glucose, until released in respiration.
There are 3 main stages to photosynthesis:
● Capturing of light energy by chlorophyll.
● Light-dependent reaction.
● Light independent reaction.
In the LDR, an electron flow is created by the effect of light on chlorophyll.
● Causes water to split into protons (H+ ions), electrons and oxygen - Photolysis.
● Products are reduced NADP, ATP and a waste product of oxygen.
In the LIR, H+ ions are used to produce sugars and other organic molecules.
● Products are glucose, ADP and Pi, NADP.
Grana - Stacks of thylakoid discs.
● Chlorophyll is located here and LDR takes place here.
Stroma - Fluid filled matrix where LIR occurs.
● Contains enzymes, sugars and amino acids.
, 11.2 THE LIGHT-DEPENDENT REACTION
01 October 2021
19:43
The absorption of light by chlorophyll provides energy for:
● Adding Pi to ADP to form ATP.
● Photolysis of water to H+ ions and oxygen.
As chlorophyll absorbs light, the electrons in the chlorophyll become excited and are
released from the molecule, resulting in the chlorophyll molecule being ionised.
● Photoionisation.
● Electrons are taken up by an electron carrier.
The electrons move down the electron transport chain, releasing energy.
● This energy and energy released from photolysis is used to actively transport
H+ ions into the thylakoid via proton pumps.
Due to photolysis and the transport of H+ ions, there is a higher concentration of H+
ion than in the stroma.
● H2O ---> 2H+ + 1/2O2 + 2e-
● These e- replace the lost electrons in the chlorophyll.
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