5 Respiration

Question 1

aerobic respiration

Answer 1

requires oxygen and produces carbon dioxide, water and much ATP

Question 2

anaerobic respiration

Answer 2

takes place in the absence of oxygen and produces lactate (in animals) or ethanol (in plants and fungi) but only as little ATP in both cases

Question 3

four stages of aerobic respiration

Answer 3

glycolysis
link reaction
krebs cycle
oxidative phosphorlyation

Question 4

glycolysis brief description

Answer 4

the splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules

Question 5

link reaction brief description

Answer 5

the 3-carbon pyruvate molecules enter onto a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule

Question 6

krebs cycle brief description

Answer 6

the introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD

Question 7

oxidative phosphorylation brief description

Answer 7

the use of the electrons, associated with reduced NAD and FAD, released from the krebs cycle to synthesise ATP with water produced as a by-product

Question 8

four stages of glycolysis

Answer 8

• phosphorylation of glucose to glucose phosphate
• splitting of the phosphorylated glucose
• oxidation of triose phosphate
• the production of ATP

Question 9

phosphorylation of glucose to glucose phosphate in glycolysis

Answer 9

glucose is made more reactive by the addition of two phosphate molecules (phosphorylation)
the phosphate molecules come from the hydrolysis of two ATP molecules to ADP.
this provides the energy to activate glucose and lowers the activation energy for the enzyme-controlled reactions that follow

Question 10

splitting of the phosphorylated glucose in glycolysis

Answer 10

each glucose molecule is split into two 3-carbon molecules known as triose phosphate

Question 11

oxidation of triose phosphate in glycolysis

Answer 11

hydrogen is removed from each of the two TP molecules and transferred to a hydrogen-carrier molecule known as NAD to form NADH

Question 12

the production of ATP in glycolysis

Answer 12

enzyme-controlled reactions convert each TP into another 3-carbon molecule called pyruvate
in the process, two molecules of ATP are regenerated from ADP

Question 13

the overall yield from one glucose molecule undergoing glycolysis is..

Answer 13

• 2 molecules of ATP (4 molecules are produced but 2 were used up in the initial phosphorylation of glucose and so the net increase is 2 molecules)
• 2 molecules of NADH
• 2 molecules of pyruvate

Question 14

where does glycolysis take place?

Answer 14

cytoplasm
the enzymes for the glycolytic pathway are found in the cytoplasm of cells and so glycolysis does not require any organelle or membrane for it to take place
it doesn’t require oxygen and therefore it can take place whether or not it is present

Question 15

how is glycolysis indirect evidence for evolution?

Answer 15

glycolysis is an universal feature of every living organism

Question 16

link reaction

Answer 16

the pyruvate molecules produced in the cytoplasm during glycolysis are actively transported into the matrix of mitochondria

• the pyruvate is oxidised to acetate. the 3-C pyruvate loses a CO2 molecule and two hydrogens. these Hs are accepted by NAD to form NADH, which is later used to produce ATP
• the 2-carbon acetate combines with a molecule called coenzyme A (CoA) to produce acetylcoenzyme A

Question 17

link reaction equation

Answer 17

pyruvate + NAD + CoA –> acetyl CoA + NADH + CO2

Question 18

where does the link reaction occur?

Answer 18

matrix of mitochondria

Question 19

krebs cycle

Answer 19

• the 2-C acetylcoenzyme A from LR combines a 4-C molecule to produce a 6-C molecule
• in a series of reactions this 6-C molecule loses CO2 and H (NAD is reduced) to give a 5-C molecule
• then 5-C molecule loses CO2 and H (NAD is reduced) to give a 4-C molecule and a single ATP molecule as a result of substrate-level phosphorylation
• another NAD molecule and a FAD molecule is reduced
• the 4-C molecule can now combine with a new molecule of acetylCoA to begin the cycle again

Question 20

for each pyruvate molecule, the link reaction and krebs cycle produces…

Answer 20

• reduced coenzymes such as NAD and FAD. these have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and are therefore the important products of krebs cycle
• one molecule of ATP
• 3 molecules of CO2

as 2 pyruvate molecules are produced from each original glucose molecule, the yield from a single glucose molecule is double the quantities above

Question 21

coenzymes

Answer 21

molecule that some enzymes require in order to function
they play a major role in PS and resp where they carry H atoms from one molecule to another
e.g. NAD, FAD and NADP

Question 22

significance of the krebs cycle

Answer 22

• breaks down macromolecules into smaller ones- pyruvate to CO2
• produced H atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. his leads to the production of ATP that provides metabolic energy for the cell
• it regenerates the 4-C molecule that combines with acetyl CoA, which would otherwise accumulate.
• it is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, AAs and chlorophyll

Question 23

mitochondria

Answer 23

organelles found in eukaryotic cells
each is bounded by a smooth outer membrane and an inner one that is folded into extensions called cristae
the matrix contains proteins, lipids and traces of DNA

Question 24

chemiosmotic theory of oxidative phosphorylation

Answer 24

• hydrogen atoms produced during glycolysis and Krebs cycle combine with coenzymes NAD and FAD
• the NADH and FADH donate the electrons of the hydrogen atoms they are carrying to the first molecule in the elec trans chain
• the elecs pass along a chain of elec trans carrier molecules in a series of oxidation-reduction reactions. as the electrons flow along the chain, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into inter-membranal space
• the protons accumulate in the inter-membranal space before they diffuse back into the mitochondrial matrix through ATP synthase channel embedded in the inner mitochondrial membrane
• at the end of the chain the elecs combine with these protons and oxygen to form water. oxygen is therefore the final acceptor of elecs in the elec trans chain

Question 25

importance of oxygen in respiration

Answer 25

acts as final acceptor of the hydrogen atoms produced produced in glycolysis and the Krebs cycle
without its role in removing hydrogen atoms at the end of the chain, the hydrogen ions and elecs would ‘back up’ along the chain and the process of respiration would come to a halt

Question 26

releasing energy in stages

Answer 26

the greater the energy that is released in a single step, the more of it is released as heat and less there is available for more useful purposes
when energy is released a little at a time, more of it can be harvested for the benefit of the organism

Question 27

energy transfers in oxidative phosphorylation

Answer 27

elecs carried by NAD and FAD are not transferred in one explosive step
instead, they are passed along a series of electron trans chain molecules, each of which is at a slightly lower energy level
the elecs therefore move down an energy gradient
the transfer of elecs down this gradient allows their energy to be released gradually and therefore more usefully

Question 28

alternative respiratory substrates

Answer 28

sugars are not the only substances which can be oxidised by cells to release energy
both lipids and protein may, in certain circumstances, be used as respiratory substrates, without first being converted to carbohydrate

Question 29

what happens in absence of O2 - respiration

Answer 29

neither the krebs cycle nor the elec trans chain can continue because soon all the FAD and NAD will be reduced
no NAD or FAD will be available to take up the protons produced during the Krebs cycle and so the enzymes stop working
this leaves only the anaerobic process of glycolysis as a potential source of ATP

Question 30

glycolysis in absence of O2

Answer 30

its products of pyruvate and hydrogen must constantly be removed. the H must be released from the NADH in order to regenerate NAD.
without this, the already tiny supply of NAD in cells will be entirely converted to NADH, leaving no NAD to take up the hydrogen newly produced from glycolysis
glycolysis will then grind to a halt
the replenishment of NAD is achieved by the pyruvate molecule from glycolysis accepting the hydrogen from reduced NAD
the oxidised NAD produced can then be used in further glycolysis

Question 31

anaerobic respiration in plants and some microorganisms

Answer 31

produces ethanol
occurs in organisms such as certain bacteria and fungi (e.g. yeast) as well as in some cells of higher plants
the pyruvate molecule formed at the end of glycolysis loses a molecule of CO2 and accepts H from reduced NAD to produce ethanol

Question 32

equation of anaerobic respiration in plants and MO

Answer 32

pyruvate + NADH –> ethanol + CO2 + NAD

Question 33

anaerobic respiration in animals

Answer 33

produces lactate
occurs in animals as a means of overcoming a temporary shortage of oxygen
lactate production occurs most commonly in muscles as a result of strenuous exercise
in these conditions O2 may be used up more rapidly than it can be supplied and therefore an O2 debt occurs.
it is often essential, however, that the muscles continue to work despite the shortage of O2
when O2 is in short supply, ???NAD??? from glycolysis can accumulate and must be removed
to achieve this, each pyruvate molecule produced takes up the two hydrogen atoms from the NADH produced in glycolysis to form lactate
at some point the lactate produced is oxidised back to pyruvate
this can then be either further oxidised to release energy or converted into glycogen
this happens when O2 is once again available
lactate will cause cramp and muscle fatigue if ti is allowed to accumulate in the muscle tissue
as lactate is an acid it also causes pH changes which affects enzymes
its important that lactate is removed by the blood and taken to the liver to be converted to glycogen

Question 34

anaerobic respiration in animals equation

Answer 34

pyruvate + NADH –> lactate + NAD

Question 35

in what ways is energy derived from cellular respiration?

Answer 35

• substrate level phosphorylation in glycolysis and the krebs cycle. this is direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP
• oxidative phosphorylation in the elec trans chain. this is the indirect linking of energy from phosphate to ADP to produce ATP involving energy from the hydrogen atoms that are carried on NAD and FAD. cells produce most of their ATP this way

Question 36

where does each stage of respiration occur?

Answer 36

glycolysis- cytoplasm
link reaction- matrix of mitochondria
krebs cycle- matrix of mitochondria
oxidative phosphorylation- inner mitochondrial membrane

Question 37

how does aerobic respiration differ from anaerobic?

Answer 37

Water is produced.
More ATP is produced.
Glucose is fully broken down.
After glycolysis, there are more steps (the link reaction, the Krebs cycle and oxidative phosphorylation).

Question 38

Which enzyme catalyses the conversion of pyruvate to ethanal?

Answer 38

pyruvate decarboxylase

Question 39

Which enzyme catalyses the conversion of pyruvate to lactate?

Answer 39

lactate dehydrogenase

Question 40

Which enzyme catalyses the conversion of ethanal to ethanol?

Answer 40

ethanol dehydrogenase

Question 41

Why does anaerobic respiration produce far less ATP than aerobic respiration?

Answer 41

Anaerobic respiration relies on substrate level phosphorylation in the glycolytic pathway to produce a net 2 ATP per glucose.
Aerobic respiration produces 2 ATP from substrate-level phosphorylation in glycolysis, 2 ATP from substrate-level phosphorylation in the Krebs cycle and around 32 ATP from oxidative phosphorylation.