respiration Flashcards
Why is respiration important?
● Respiration produces ATP (to release energy)
● For active transport, protein synthesis etc.
structure of mitochondria
outer membrane
inner membrane - cristae folded
matrix - circ dna, 70 s ribsomes
Summarise the stages of aerobic & anaerobic respiration
areobic resp :
- glycolysis - cytoplasm
- link reaction - matrix
- krebs cycle - matrix
ox phos - inner mito mem
anaerobic resp:
- glycolysis - cytoplasm
- nad regeneration - cytoplasm
Describe the process of glycolysis
- Glucose phosphorylated to glucose phosphate
○ Using inorganic phosphates from 2 ATP - Hydrolysed to 2 x triose phosphate
- Oxidised to 2 pyruvate
○ 2 NAD reduced
○ 4 ATP regenerated (net gain of 2)
Explain what happens after glycolysis if respiration is anaerobic
- Pyruvate converted to lactate (animals &
some bacteria) or ethanol (plants & yeast) - Oxidising reduced NAD → NAD regenerated
- So glycolysis can continue (which needs
NAD) allowing continued production of ATP
Suggest why anaerobic respiration produces less ATP per molecule of
glucose than aerobic respiration
● Only glycolysis involved which produces little ATP (2 molecules)
● No oxidative phosphorylation which forms majority of ATP (around 34 molecules)
What happens after glycolysis if respiration is aerobic?
Pyruvate is actively transported into the mitochondrial matrix.
Describe the link reaction
- Pyruvate oxidised (and decarboxylated) to acetate
○ CO2 produced
○ Reduced NAD produced (picks up H) - Acetate combines with coenzyme A, forming Acetyl
Coenzyme A
products of link reaction per glucose mol
2 x Acetyl Coenzyme A,
2 X CO2 and 2 X reduced NAD
Describe the Krebs cycle
- Acetyl coenzyme A (2C) reacts with a
4C molecule
○ Releasing coenzyme A
○ Producing a 6C molecule that
enters the Krebs cycle - In a series of oxidation-reduction
reactions, the 4C molecule is
regenerated and:
○ 2 x CO2
lost
○ Coenzymes NAD & FAD reduced
○ Substrate level phosphorylation
(direct transfer of Pi from
intermediate compound to ADP)
→ ATP produced
products per glucose mol in the krebs cycle
6 x reduced NAD,
2 x reduced FAD, 2 x ATP and 4 x CO2
Give examples of other respiratory substrates
Breakdown products of lipids and amino acids, which enter the Krebs cycle. For example:
● Fatty acids from hydrolysis of lipids → converted to Acetyl Coenzyme A
● Amino acids from hydrolysis of proteins → converted to intermediates in Krebs cycle
Describe the process of oxidative phosphorylation
- Reduced NAD/FAD oxidised to release H atoms → split into protons (H
+
) and electrons (e
-
) - Electrons transferred down electron transfer chain (chain of carriers at decreasing energy levels)
○ By redox reactions - Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory):
○ Energy used by electron carriers to actively pump protons from matrix → intermembrane space
○ Protons diffuse into matrix down an electrochemical gradient, via ATP synthase (embedded)
○ Releasing energy to synthesise ATP from ADP + Pi - In matrix at end of ETC, oxygen is final electron acceptor (electrons can’t pass along otherwise)
○ So protons, electrons and oxygen combine to form water
Describe how a respirometer can be used to measure the rate of aerobic
respiration
Measures O2 uptake:
1. Add a set mass of single-celled organism
eg. yeast to a set volume / concentration
of substrate eg. glucose
2. Add a buffer to keep pH constant
3. Add a chemical that absorbs CO2 eg.
sodium hydroxide
4. Place in water bath at a set temperature
and allow to equilibrate
5. Measure distance moved by coloured
liquid in a set time
Explain why the liquid moves.
● Organisms aerobically respire → take in O2
● CO2 given out but absorbed by sodium hydroxide solution
● So volume of gas and pressure in container decrease
● So fluid in capillary tube moves down a pressure gradient towards
organism
Explain why the respirometer
apparatus is left open for 10
minutes.
● Allow apparatus to equilibrate
● Allow for overall pressure expansion/change throughout
● Allow respiration rate of organisms to stabilise
Explain why the apparatus
must be airtight.
● Prevent air entering or leaving
● Would change volume and pressure, affecting movement of liquid
Describe a more accurate way
to measure volume of gas.
Use a gas syringe
Describe how the rate of respiration can be calculated
- Calculate volume of O2 / CO2 consumed / released (calculate area of a cylinder)
a. Calculate cross-sectional area of capillary tube using π r2
b. Multiply by distance liquid has moved - Divide by mass of organism and time taken
- Units - unit for volume per unit time per unit mass eg. cm3min
-1g
Describe how a respirometer can be used to measure the rate of anaerobic
respiration
Measures CO2 release:
● Repeat experiment as above but remove chemical that absorbs CO2
● Make conditions anaerobic, for example:
○ Layer of oil / liquid paraffin above yeast → stop O2 diffusing in
○ Add a chemical that absorbs O2
○ Leave for an hour to allow O2 to be respired and used up
Explain why the liquid moves.
● Yeast anaerobically respire → release CO2
● So volume of gas and pressure in container increase
● So fluid in capillary tube moves down a pressure gradient away
from organism
Explain why the apparatus is left for
an hour after the culture has
reached a constant temperature.
● Allow time for oxygen to be used / respired
Describe how redox indicator dyes such as Methylene blue can be used to
measure rate of respiration
● Redox indicators (eg. methylene blue)
change colour when they accept electrons
becoming reduced
● Redox indicators take up hydrogens and
get reduced instead of NAD / FAD →
modelling their reactions
1. Add a set volume of organism eg. yeast
and a set volume of respiratory substrate
eg. glucose to tubes
2. Add a buffer to keep pH constant
3. Place in water bath at a set temperature
and allow to equilibrate for 5 mins
4. Add a set volume of methylene blue,
shake for a set time (do not shake again)
5. Record time taken for colour to disappear
in tube
Give examples of variables that
could be controlled.
● Volume of single-celled organism
● Volume / conc. / type of respiratory substrate
● Temperature (with a water bath)
● pH (with a buffer)
● Volume of redox indicator (only control)
Why leave tubes in the water
bath for 5 minutes?
Allow for solutions to equilibrate and reach the same temperature
as the water bath
Describe a control experiment
and why it would be done.
● Add methylene blue to boiled / inactive / dead yeast (boiling
denatures enzymes)
● All other conditions the same
● To show change is due to respiration in organisms
Suggest and explain why you
must not shake tubes
containing methylene blue.
● Shaking would mix solution with oxygen
● Which would oxidise methylene blue / cause it to lose its electrons
● So methylene blue would turn back to its original blue colour
Suggest one source of error in
using methylene blue. Explain
how this can be reduced.
● Subjective as to determination of colour change / end point
● Compare results to a colour standard (one that has already
changed)
● Or use a colorimeter for quantitative results
