RESPIRATION
(a) The need for cellular respiration.
● To include examples of why plants, animals and microorganisms need to respire (suitable
examples could include active transport and an outline of named metabolic reactions).
As energy is the capacity to do work, potential energy stored in organic molecules, such as
glucose, carbohydrates, and fats, respiration occurs in order to to release the organic energy in
glucose to synthesise ATP, from ADP and an inorganic phosphate ion (P i), an immediate source
of energy. ATP, the product of photosynthesis is needed to sustain energy-requiring processes;
hydrolysing the first and second inorganic phosphates liberates 30.5kJ mol -1. Eukaryotic and
prokaryotic microorganisms, plant, animals, fungi, and protoctists all respire to obtain energy.
Active transport, endo and exocytosis, the synthesis of large molecules, such as collagen,
enzymes and antibodies, DNA replication, cell division, intracellular transport, the actions of
motor proteins in the movement of flagella, cilia, and undulipodia, the phosphorylation of
apoenzymes, muscle contraction, all use ATP as an immediate source of energy.
(b) The structure of the mitochondrion.
● The components of a mitochondrion including inner and outer mitochondrial membranes,
cristae, matrix and mitochondrial DNA.
The mitochondria have a double phospholipid membrane. The outer mitochondrial membrane
separates the mitochondrial matrix and the reactions of the Kreb’s cycle and electron transport
chain from the cytoplasm, allowing high concentrations of enzymes, substrates, and products to
be maintain, increasing the rate of respiratory reactions. It is permeable to small molecules, such
as sugars, salts and nucleotides, the passage of some of which is facilitated by proteins in the
membrane, such as pyruvate. The isolated matrix contains 70S ribosomes, mitochondrial DNA
and enzymes e.g. decarboxylase. The DNA codes for proteins which are manufactured by the
ribosomes and are involved in the metabolic reactions, in this case, the Krebs cycle. It also
contains molecules of coenzymes NAD and FAD, which can be reduced, and pyruvate, which can
be decarboxylated and dehydrogenated. The inner mitochondrial membrane is less permeable to
hydrogen ions, and has an arrangement of electron carriers with binding sites for coenzymes
and sequentially lower electron affinities, allowing their energy to be harnessed to transport
protons across the membrane, establishing a gradient. It is folded to form cristae, increasing the
surface area for the attachment of enzymes and co-enzymes involved in the electron transfer
chain and allows the sequential attachment of electron carriers in the ETC and contains ATP
synthase, so the proton gradient used to synthesise ATP in chemiosmosis. The intermembrane
space between the two allows for a proton gradient to be quickly established.
(c) The process and site of glycolysis.
● To include the phosphorylation of glucose to hexose
bisphosphate, the splitting of hexose bisphosphate into
two triose phosphate molecules and further oxidation to
pyruvate
● the production of a small yield of ATP and reduced NAD.
Glycolysis is a biochemical pathway that occurs in the cytoplasm.
It is an anaerobic process, and is the first process in both aerobic
and anaerobic respiration. Glucose is the initial substrate and the
product is two pyruvate molecules. Additionally, there is a net
yield of two molecules of ATP and two molecules of NADH.
