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why do organisms need to respire

Produces ATP as energy currency for:
a)active transport against concentration gradients e.g. to absorb nutrients from small intestine/soil.

b) metabolic reactions e.g. to form peptide bonds in protein synthesis.

C) muscle contraction.

Releases heat energy for thermoregulation.

textbook: respiration is the process that occurs in living cells and releases the energy stored in organic molecules such as glucose.The energy is immediately used to synthesise molecules of ATP from ADP and inorganic phosphate. ATP in cells can be hydrolysed to release energy needed to drive biological processes.

textbook: why do living organisms need energy: energy is the capacity to do work. The energy that is stored in complex organic molecules e.g. fats is potential energy. when this energy is released from organic molecules, via respiration, it can be used to make ATP to drive biological processes such as active transport, endocytosis, exocytosis, synthesis of large molecules such as proteins, DNA replication, cell division, movement such as the movement of bacterial flagella, activation of chemicals (glucose is phosphorylated at the beginning of respiration so that it becomes more reactive and able to be broken down to release more energy)


describe the structure of a mitochondrion

surrounded by double membrane.

folded inner membrane forms cristae: site of electron transport chain.

fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.

textbook: mitochondria maybe rod shaped, thread like also very cool.

All mitochondria have an inner and an outer phospholipid membrane making up the envelope.

The outer membrane is smooth and the inner membrane is folded into crusty giving it a larger surface area.

Embedded in the inner membrane of proteins that transport electrons and protein channels associated with ATP synthase enzyme that allow protons to diffuse through them.

Between the inner and outer mitochondrial membranes of the envelope is an inter-membrane space.

The mitochondrial matrix enclosed by the inner membrane is semi rigid and gel like, it contains mitochondria ribosomes, lived mitochondrial DNA and enzymes for the link reaction and Krebs cycle.

The matrix is where the link reaction and the Krebs cycle takes place it contains enzymes that catalyse the stages of these reactions, molecules of the coenzymes NAD and FRAD, oxaloacetate, mitochondrial DNA and ribosomes

The outer membrane – the phospholipid composition of the outer membrane is similar to that of membranes around other organelles in eukaryotic cells, it contains some proteins some of which form channels or carriers that allow the passages of molecules such as pyruvate into the mitochondrion.

The inner membrane – the lipid composition of the inner membrane differs from that of the outer membrane, this lipid bilayer is less permeable to small ions such as hydrogen ions that is the outer membrane.

The folds aka the cristae in the inner membrane give a large surface area for the electron carriers and ATP synthase enzymes embedded in them.

The electron carriers of protein complexes are arranged in electron transport chain. Electron transport chain is are involved in the final stage of aerobic respiration, oxidative phosphorylation.

The inter-membrane space between the outer and inner layers of the mitochondrial envelope is also involved in oxidative phosphorylation.

The inner membrane is in close contact with the mitochondrial matrix so the molecules of reduced NAD and FRD can easily deliver hydrogen to the electron transport chain


name the 4 main stages in aerobic respiration and where they occur

glycolysis: cytoplasm
link reaction : mitochondrial matrix
kerbs cycle: mitochondrial matrix
oxidative phosphorylation: via electron transfer train: membrane of cristae

The last three stages only take place on the aerobic conditions. in aerobic conditions the pyruvate molecules from glycolysis actively transported into the mitochondria for the link reaction. In the absence of oxygen i.e. anaerobic conditions pyruvate is converted in the cytoplasm to lactate or ethanol.
In the process the reduced NAD molecules are reoxidised so that glycolysis can continue to run, generating two molecules of ATP for every glucose molecule metabolised


outline the stages of glycolysis

1Glucose is phosphorylated to hexose
bisphosphate by 2x ATP.

2. Hexose bisphosphate splits into 2x triose phosphate (TP).

3. 2x TP is oxidised to 2x pyruvate.

net gain of 2x reduced NAD and 2x ATP per glucose

textbook: glycolysis is a biochemical pathway that occurs in the cytoplasm of all living organisms that respire, including many prokaryotes.
The pathway involves a sequence of 10 reactions, each catalysed by a different enzyme, some of the help of the coenzyme NAD.
The three main stages are 1 phosphorylation of glucose to hexose Bisphosphate 2 spitting each hexose bisphosphate molecule into to triose phosphate molecules 3. Oxidation of triose phosphate to pyruvate
The products of glycolysis – from each molecule of glucose, at the end of glycolysis there are two molecules of ATP four have been made but two were used to kickstart the process, so the net gain is two molecules of ATP, two molecules of reduced NAD and two molecules of pyruvate


how does pyruvate from glycolysis enter the mitochondria

via active transport


what happens during the link reaction

1. Oxidation of pyruvate to acetate.
per pyruvate molecule: net gain of 1xCO2 squared (decarboxylation) & 2H atoms (used to reduce 1xNAD).

2. Acetate combines with coenzyme A (CoA) to form Acetylcoenzyme A

The link reaction produces two reduced NAD and two carbon dioxide, zero ATP and zero reduced FAD


give a summary equation for the link reaction

series of redox reactions produces:
- ATP by substrate-level phosphorylation
- reduced coenzymes
- CO2 from decarboxylation

Begins when acetyl group from Acetyl COA (2C) reacts with oxaloacetate (4C). Cycle regenerates oxaloacetate.

textbook: The link reaction occurs in the mitochondrial matrix. Pyruvate is decarboxylated and dehydrogenated, catalysed by large multi enzyme complex, pyruvate dehydrogenase, which catalyses the sequence of reactions that occur during the link reaction. No ATP is produced during this reaction.

1. The carboxyl group is removed and is the origin of some of the carbon dioxide produced during respiration

2 this decarboxylation of pyruvate together with dehydrogenation produces an acetyl group

3 The acetyl group combines with CoA to become acetyl coenzyme A

4 The coenzyme NAD becomes reduced

coA accepts the acetyl group and in the form of acetyl-CoA, carries the acetyl group onto the Krebs cycle


what happens in the krebs cycle

series of redox reactions produces:
ATP by substrate-level phosphorylation
reduced coenzymes
• CO, from decarboxylation
Begins when acetyl group from Acetyl COA (2C)
reacts with oxaloacetate (4C). Cycle regenerates

textbook; like the link reaction the Krebs cycle takes place in the mitochondrial matrix.

The Krebs cycle is a series of enzyme catalysed reactions that oxidise the acetate from the link reaction to 2 molecules of carbon dioxide, while conserving the energy by reducing the coenzymes NAD and FRD.

These reduce coenzymes than carry the hydrogen atoms to the electron transport chain on the cristae, where they will be involved in the production of many more ATP molecules

The Krebs cycle makes six reduced NAD, two reduced FAD, for carbon dioxide and two ATP


what is the electron transfer chain

Series of carrier proteins embedded in
membrane of the cristae of mitochondria.

Produces ATP through oxidative
phosphorylation via chemiosmosis
during aerobic respiration


what happens in the electron transfer chain

Electrons released from reduced NAD & FAD undergo successive redox reactions.

The energy released is coupled to maintaining proton gradient or released as heat.

Oxygen acts as final electron acceptor.

textbook; each electron carrier protein contains a cofactor a non-protein Heem group that contains an iron ion.

The iron ion can accept and donate electrons because it can become reduced by gaining an electron and then become oxidised when donating the electron to the next electron carrier. Electron carrier proteins are oxidoreductase enzymes.

The electron carriers also have a coenzyme that, using energy released from the electrons, pumps protons from the matrix to the inter-membrane space.

Protons accumulate in the inter-membrane space and a proton gradient forms across the membrane.

The proton gradient can produce a flow of proteins through the channels in the ATP synthase enzymes to make ATP.


how does chemiosmosis produce atp during aerobic respiration

Some energy released from the ETC is coupled to active transport of H* ions (protons) from mitochondrial matrix
into intermembrane space.

H* ions move down concentration gradient into mitochondrial matrix via channel protein ATP synthase

ATP synthase catalyses ADP + Pi -> ATP


state the role of oxygen in aerobic respiration

final electron acceptor in electron transfer chain

(produces water as a byproduct)


name the stages in respiration that produce atp by substrate level phosphorylation

glycolysis (anaerobic)
krebs cycle (aerobic)


what happens during anaerobic respiration in animals

only glycolysis continues

reduced NAD + pyruvate


oxidised NAD (for further glycolysis) + lactate


What happens during anaerobic respiration in some microorganisms e.g. yeast and some plant cells?

Only glycolysis continues, so much less ATP is produced compared to aerobic respiration.

Pyruvate is decarboxylated to form ethanal.

Ethanal is reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis.


what are the benefits of being able to respite anaerobically

ATP production for vital metabolic processes continues.

Production of ethanol/ lactate converts reduced NAD back into NAD so glycolysis can continue = maximum yield of ATP in the conditions.


Suggest how a student could investigate the effect of a named variable on the rate of respiration of a single-celled organism.

1. Use respirometer (pressure changes in boiling tube cause a drop of coloured liquid to move).

2. Use a dye as the terminal electron acceptor for the ETC.


What is the purpose of sodium hydroxide solution in a respirometer set up to measure the rate of aerobic

Absorbs CO, so that there is a net
decrease in pressure as O2 iS


How could a student calculate the rate of respiration using a respirometer?

Volume of O, produced or CO, consumed/ time x mass of sample.

Volume = distance moved by coloured
drop x (0.5 x capillary tube diameter) squared x TT.


Name 2 types of molecule that can be used as alternative respiratory substrates.

• (amino acids from) proteins
• (glycerol and fatty acids from) lipids


What is the respiratory quotient (RQ)?

RQ = carbon dioxide produced / oxygen consumed

Can be used to determine:
respiratory substrate being used (carbohydrates: 1.0, lipids: 0.8, proteins 0.9)

if organism is undergoing anaerobic respiration (anaerobic values are larger)


Why do different respiratory substrates have different relative energy values?

Depends on the number of hydrogens in
the structure which are oxidised to water
e.g. the number of hydrogens is greater
in fatty acids than carbohydrates.


ppq: why does aerobic respiration yield fewer molecules of atp than the theoretical maximum 2 marks

some ATP used to (actively) transport pyruvate (into the mitochondrion) ;

some ATP used to (actively) transport
H(+) from (reduced) NAD,
formed in glycolysis / into the mitochondrion;


ppq: explain why the incomplete breakdown of glucose in anaerobic respiration produces less atp than aerobic respiration

in anaerobic respiration
1 glycolysis / conversion of glucose into pyruvate occurs

produces 2 molecules of ATP (net) ;

(only) substrate level phosphorylation (occurs) ;

oxygen not available as final electron acceptor;


ppq: Respiration can be aerobic or anaerobic.
(i) Certain parasites live in the blood of mammals.

Suggest why, even though blood carries oxygen, these parasites are adapted to respire anaerobically. 2 marks

parasites have little access to oxygen

(inaccessible because) little oxygen dissolved in plasma / oxygen not very soluble (in plasma) ;


ppq: The anaerobic respiration pathway in animal cells can be reversed, but the anaerobic respiration pathway in yeast cells cannot be reversed.

Explain why, using your knowledge of the differences between the two pathways.
In your answer, you should use appropriate technical terms, spelled correctly.

in animals :
pyruvate is converted to lactate
can be reversed as so other product formed
lactate dehydrogenase available to reverse the reaction

in yeast
pyruvate converted to ethanol and carbon dioxide
cannot be reversed as carbon dioxide is lost
decarboxylase enzyme cannot reverse the reaction


ppq: state precisely where in the cell glycolysis occur

cytoplasm of cell


ppq: outline the process of glycolysis 3 marks

1 phosphorylation of glucose ;

2 so forming hexose (1,6) bisphosphate;

3 (then) splitting into / formation of
two /2 , triose phosphate(s) / TP ;

4 (for formation of pyruvate) dehydrogenation / oxidation / formation of reduced NAD ;

5 pyruvate produced (from , TP / (3C) intermediate) ;
total production 4 ATP / net production of 2 ATP ;


(a) State the product of the ornithine cycle in Pathway P and the organ to which this product is transported for removal from the body.

organ the product is transported to:

product : urea
organ transported to : kidney


(il) The lactate that enters pathway S is produced by cells, such as muscle cells, undergoing anaerobic respiration.

Suggest why this lactate is converted into pyruvate by the hepatocytes (liver cells) rather than by the respiring cells in which it is produced.

hepatocytes can tolerate , lactate / low pH (which would otherwise be toxic) ;

hepatocytes have / (other) cells do not have , enzymes to metabolise lactate / catalyse this reaction ;

(conversion of lactate) requires oxygen and muscle cells do not have enough oxygen / O2 is not available during anaerobic respiration / O2 is sufficient in hepatocytes;


ppq: state precisely where in the liver cell the excess reduced NAD can be re-oxidised

cristae / inner mitochondrial membrane


ppq: how are the subunits joined in a molecule of atp

row of 3 phosphates joined to ribose and ribose joined to adenine ;

stated that phosphate(s) joined to carbon 5 and adenine joined to carbon 1 ;


ppq: suggest the type of reaction that removes a phosphate group from an ATP molecule



ppq: state the precise location of the electron transport chain in the cell



If oxygen is not present or is in short supply, respiration can take an anaerobic pathway after glycolysis. In plant cells, this pathway is the same as the one used in yeast cells

(i) Name the hydrogen acceptor in this pathway.

(ii) Name the intermediate compound in this pathway.

(iii) Name the products of this pathway.

(iv) Explain why this pathway is important for the plant cell.

(i) Name the hydrogen acceptor in this pathway. = ETHANAL

(ii) Name the intermediate compound in this pathway = ETHANAL

(iii) Name the products of this pathway. = ETHANOL AND CARBON DIOXIDE



ppq: state the stages of aerobic respiration during which:
(I) carbon dioxide is produce

(II) oxygen is used

(i) link reaction and krebs cycle

(ii) oxidative phosphorylation


ppq: suggest why respirometer B contained some glass beads

to make the volume of contents (the peas) the same in the respirometers

because the volume of peas in A is greater than the volume of peas in B



(1) name of hydrogen acceptor after glycolysis in mammals and yeast

(2) is co2 produces for mammals and yeast

(3) name of final product for mammals and yeast

1) mammal: pyruvate, yeast : ethanal

2) mammal: no yeast : yes

3) mammal: lactate, yeast : ethanol


ppq: suggest one benefit of anaerobic respiration to an organism

atp produced

recycles nad so can be used again

allows glycolysis to continue


ppq: Triose phosphate is a compound that is central to the metabolism of this cell.

Explain how the three reaction pathways (W, X and Y) are able to work independently each other in the same leaf cell.

take place in different organelles of the cell

compartmentalisation separates reactions

glycolysis (w) in cytoplasm
calvin cycle (x) in chlorplast, stroma
krebs cycle (y) in mitochondrion matrix.


ppq: which reaction pathway is associated with

1) photosynthesis

2) aerobic respiration

1) calvin cycle

2) glycolysis and krebs cycle


ppq) name the specific process that is carried out by cristae

chemiosmosis (oxidative phosphorylation)


ppq: (b) In anaerobic conditions, compound F does not proceed to the link reaction. Describe the fate of compound F during anaerobic respiration in an animal cell and explain
the importance of this reaction.

(pyruvate / F) converted to lactate ;

F/ pyruvate , accepts hydrogen (atoms) ;

hydrogen from, reduced NAD / reduced E;
(catalysed by) lactate dehydrogenase ;

no, oxygen / O2, to act as (final),
hydrogen / electron, acceptor ;
(so) link reaction / Krebs cycle / ETC, cannot take place ;

NAD / E, regenerated / recycled / able to be re-used;
allows glycolysis to continue / pyruvate continues to be made ;


ppq) suggest how the seal is adapted to respire for such a long time underwater

large nostrils open to take in air
when submerged nostrils close to keep air in
lungs have high vital capacity

seal has low metabolic rate, respiratory rate and use little atp so able to respire anaerobically for a long time for more glycolysis. also have large supply of nad which prevents build up of lactate


ppq) discuss the advantages and disadvantages of using yeast to make ethanol rather than using the chemical method

advantages of using yeast
A1 less energy required ;
does not need,
high temperature / 300°C / high pressure
A3 can use waste material (as a substrate) ;
A4 substrate is , sustainable / grown each year ;
A5 process does not use up , oil reserves / fossil fuels ;
A6 product is carbon neutral / no carbon footprint ;

disadvantages of using yeast
D1 time consuming / takes several days ;
D2 needs, downstream processing / purification of product ;
D3 is killed by product;
D4 can (only) use batch method;
D5 aseptic / sterile , conditions required;


CFS can affect every system in the body and is identified by symptoms that include fatigue, muscle weakness and aching muscles.
(i) It has been suggested that, in the cells of people with CFS, pyruvate may not be
transferred into the mitochondria efficiently.
Outline the consequences of an inefficient transfer of pyruvate into mitochondria and link
this to the symptoms of CFS stated above.

Expected Answer
less pyruvate for , link reaction / Krebs cycle
link reaction / Krebs cycle , cannot take place / reduced
only / mainly , glycolysis takes place ;
no / little , oxidative phosphorylation ;
less, energy / ATP ,
for muscle contraction /
resulting in muscle weakness /
for mental processes ;
anaerobic respiration takes place ;
lactate / decrease in pH, causing aching muscles ;


the role of atp

ATP is the standard intermediary between energy releasing and energy consuming metabolic reactions in both eukaryotic and prokaryotic cells. ATP is a phosphorylated nucleotide and each molecule of ATP consists of ad nauseam, which is the nitrogenous base adenine plus the five carbon sugar ribose and three phosphate groups.

ATP is relatively stable– it does not break down to ADP and PI, When in solution in cells, that is readily hydrolysed by enzyme catalysis.

well ATP is hydrolysed to ADP and P, a small quantity of energy is released for use in the cells.

Cells can therefore obtain the energy they need for a process in small manageable amounts that will not cause damage or be wasteful.



enzymes that catalyse oxidation and reduction reactions need the help of coenzymes that accepts the hydrogen atoms removed during oxidation.

NAD is a non-protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions.

NAD oxidising substrate molecules during glycolysis, the link reaction and the Krebs cycle.

NAD is synthesised in living cells.

Reduced NAD carries the protons and electrons to the Christe of mitochondria and delivers them to be used in oxidative phosphorylation for the generation of ATP from ADP and PI. When reduced NAD gives up the protons and electrons that are accepted during one of the first three stages of respiration, it becomes oxidised and can be reused to oxidise more substrate, in the process becoming reduced again


respiratory substrates ; carbohydrate

Besides carbohydrates, lipids and proteins can also provide respiratory substrate. They can be oxidised in the presence of oxygen to produce molecules of ATP, carbon dioxide and water and each of different relative energy values

carbohydrates – the monosaccharide glucose is the chief respiratory substrate.

Some mammalian cells, for example brain cells are red blood cells, can use only glucose for respiration.

Animals and some bacteria store carbohydrate as glycogen, which can be hydrolysed to glucose for respiration. Plant cells store carbohydrates starch and this can also be hydrolysed to glucose for respiration: disaccharides can be digested to monosaccharides for respiration and monosaccharides such as fructose and galactose can be changed, but Isomerase enzymes to glucose for respiration


respiratory substances : lipids

Lipids are important respiratory substrate for a number of types of tissue, including muscle.

Triglycerides are hydrolysed by lipase took us round fatty acids and glycerol can then be converted to trials phosphate and respired.

Lipids produce loads of ATP and are converted into aceto-groups and enter Krebs cycle to combine with Oxaloacetate


Respiratory substrate: protein

excess amino acids, released after the digestion of proteins, are denominated in the liver.

The rest of the amino acid molecule, a ketoacid, enters the respiratory pathway as pyruvate, acetyl-CoA or a Krebs cycle acid such as oxaloacetic acid.

During starvation when insufficient glucose or lipid are available for respiration protein from muscle can be hydrolysed to amino acids which are then respire and these amino acids may be converted to pyruvate or acetate and into the Krebs cycle