Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
Biology (9700) notes A-Level - Energy and Respiration (CIE)
Energy
● Need for energy: Synthesise large molecules from smaller ones
such as replicating DNA molecules or synthesising proteins.
● Features of ATP: The hydrolysis of one molecule of ATP can be
done quickly and easily, in whichever part of the cell energy is
required. Energy released is enough to fuel an energy requiring
A2
process in a cell (not so much that it’ll be wasted). ATP is a
relatively stable molecule in range of pH that normally occurs
in cells (does not break down until enzyme - ATPase is present)
● Synthesis of ATP: Transfer of phosphate in substrate linked
s
reactions (using energy directly by another chemical reaction)
am
and chemiosmosis in membranes of mitochondria and
chloroplasts (using energy released by movement of Hydrogen
ions down their concentration gradient.
Ex
● Relatively energy values of Carbohydrates is 1.0, lipids is 0.7
and proteins is 0.9
● Respiratory Quotient (RQ): It is the ratio of the number of
ck
molecules of carbon dioxide produced to the number of
molecules of oxygen taken in, as a result of respiration.
● The energy values of respiratory substrates depend on the
ra
number of Hydrogen atoms per molecule.
● RQ = CO2/O2
C
● Make sure the respiration equation is fully balanced before you
start doing any calculation to find RQ values.
● Simple respirometer investigations ( Paper 5)
Respiration
CRACK EXAMS A2 1
, Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
● Four stages of respiration in eukaryotic cells: Glycolysis in
cytoplasm, link reaction and Krebs Cycle in mitochondrial
matrix, Oxidative Phosphorylation on the inner membrane of
mitochondria.
● Glycolysis: Phosphorylation of glucose and the subsequent
splitting of fructose 1-6 bisphosphate (6C) into two triose
phosphate molecules (3C), which are then further oxidised to
pyruvate (3C), with the production of ATP and Reduced NADP.
A2
s
am
Ex
Picture from Biology A-Level CourseBook
ck
● When oxygen is available, pyruvate enters mitochondria to take
part in link reaction ( pyruvate moves through the 2 membranes
that makeup the envelope of mitochondria, is moved by active
ra
transport so small amount of ATP required)
● When pyruvate arrives in the matrix of mitochondria, enzymes
C
remove carbon dioxide (decarboxylation) and hydrogen
(dehydrogenation) from it. The remainder of the molecule
combines with coenzyme A (CoA) to produce acetyl coenzyme
A. This process is called link reaction because it links glycolysis
with Krebs cycle.
CRACK EXAMS A2 2
Biology (9700) notes A-Level - Energy and Respiration (CIE)
Energy
● Need for energy: Synthesise large molecules from smaller ones
such as replicating DNA molecules or synthesising proteins.
● Features of ATP: The hydrolysis of one molecule of ATP can be
done quickly and easily, in whichever part of the cell energy is
required. Energy released is enough to fuel an energy requiring
A2
process in a cell (not so much that it’ll be wasted). ATP is a
relatively stable molecule in range of pH that normally occurs
in cells (does not break down until enzyme - ATPase is present)
● Synthesis of ATP: Transfer of phosphate in substrate linked
s
reactions (using energy directly by another chemical reaction)
am
and chemiosmosis in membranes of mitochondria and
chloroplasts (using energy released by movement of Hydrogen
ions down their concentration gradient.
Ex
● Relatively energy values of Carbohydrates is 1.0, lipids is 0.7
and proteins is 0.9
● Respiratory Quotient (RQ): It is the ratio of the number of
ck
molecules of carbon dioxide produced to the number of
molecules of oxygen taken in, as a result of respiration.
● The energy values of respiratory substrates depend on the
ra
number of Hydrogen atoms per molecule.
● RQ = CO2/O2
C
● Make sure the respiration equation is fully balanced before you
start doing any calculation to find RQ values.
● Simple respirometer investigations ( Paper 5)
Respiration
CRACK EXAMS A2 1
, Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
● Four stages of respiration in eukaryotic cells: Glycolysis in
cytoplasm, link reaction and Krebs Cycle in mitochondrial
matrix, Oxidative Phosphorylation on the inner membrane of
mitochondria.
● Glycolysis: Phosphorylation of glucose and the subsequent
splitting of fructose 1-6 bisphosphate (6C) into two triose
phosphate molecules (3C), which are then further oxidised to
pyruvate (3C), with the production of ATP and Reduced NADP.
A2
s
am
Ex
Picture from Biology A-Level CourseBook
ck
● When oxygen is available, pyruvate enters mitochondria to take
part in link reaction ( pyruvate moves through the 2 membranes
that makeup the envelope of mitochondria, is moved by active
ra
transport so small amount of ATP required)
● When pyruvate arrives in the matrix of mitochondria, enzymes
C
remove carbon dioxide (decarboxylation) and hydrogen
(dehydrogenation) from it. The remainder of the molecule
combines with coenzyme A (CoA) to produce acetyl coenzyme
A. This process is called link reaction because it links glycolysis
with Krebs cycle.
CRACK EXAMS A2 2
