Respiration

Question 1

Where does glycolysis take place in respiration

Answer 1

Cytoplasm

Question 2

Where does link reaction take place in respiration

Answer 2

Mitochondrial matrix

Question 3

Where does krebs cycle take place in respiration

Answer 3

Mitochondrial matrix

Question 4

Where does oxidative phosphorylation take place in respiration

Answer 4

Inner mitochondrial membrane

Question 5

Where does NAD regeneration take place in respiration

Answer 5

Cytoplasm

Question 6

Glycolysis

Answer 6

Glucose phosphorylated to glucose phosphate

Using inorganic phosphates from 2 ATP

Hydrolysed to 2 triose phosphate

Oxidised to 2 pyruvate

Question 7

What are the products of glycolysis

Answer 7

2 NADH

4 ATP produced - net gain of 2

Question 8

What happens after glycolysis if respiration is anaerobic

Answer 8

Pyruvate converted to lactate or ethanol

Oxidising NADH - NAD regenerated

So glycolysis can continue which needs NAD allowing continues production of ATP

Question 9

Why does anaerobic respiration produces less ATP per molecule of glucose

Answer 9

Only glycolysis involved which produces little ATP

No oxidative phosphorylation which forms majority of ATP

Question 10

What happens after glycolysis in aerobic respiration

Answer 10

Pyruvate is actively transported into mitochondrial matrix

Question 11

Link reaction

Answer 11

Pyruvate oxidised and decarboxylated to actetate

Acetate combines with coenzyme A forming acetyl coenzyme A

Question 12

Products of link reaction per glucose molecule

Answer 12

2 Acetyl Coenzyme A

2 CO2

2 NADH

Question 13

Krebs cycle

Answer 13

Acetyl coenzyme A reacts with a 4C molecule

Releasing coenzyme A

Producing a 6C molecule

In a series of redox reactions 4C molecule is regenerated

2CO2 lost

NAD and FAD reduced

Substrate level phosphorylation occurs producing ATP

Question 14

Products of krebs cycle per glucose molecule

Answer 14

6 NADH

2 FADH

2 ATP

4 CO2

Question 15

Oxidative phosphorylation

Answer 15

NADH/FADH oxidised to release H atoms

Split into protons and electrons

Electrons transferred down electron transfer chain by redox reactions

Energy released by electrons used by electron carriers to actively pump protons from matrix into inter-membrane space

Protons diffuse into matrix down an electrochemical gradient via ATP synthase

Releasing energy used to synthesis ATP from ADP + Pi

In matrix at end of ETC oxygen is final electron acceptor

Protons electrons and oxygen combine to form water

Question 16

Examples of other respiratory substrates

Answer 16

Fatty acids from hydrolysis of lipids → converted to Acetyl Coenzyme A

Amino acids from hydrolysis of proteins → converted to intermediates in Krebs cycle

Question 17

Describe how a respirometer can be used to measure the rate of aerobic respiration

Answer 17

Add a set mass of single-celled organism (eg. yeast) to a set volume/concentration of substrate (eg. glucose)

Add a buffer to keep pH constant

Add a chemical that absorbs CO2 (eg. sodium hydroxide)

Place in water bath at a set temperature and allow to equilibrate

Measure distance moved by coloured liquid in a set time

Question 18

Explain why the liquid moves in a respirometer in aerobic respiration

Answer 18

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

Question 19

Explain why the respirometer apparatus is left open for 10 minutes

Answer 19

Allow apparatus to equilibrate

Allow for overall pressure expansion/change throughout

Allow respiration rate of organisms to stabilise

Question 20

Explain why the respirometer must be airtight

Answer 20

Prevent air entering or leaving

Would change volume and pressure, affecting movement of liquid

Question 21

Describe a more accurate way to measure volume of gas

Answer 21

Use gas syringe

Question 22

Describe how the rate of respiration can be calculated

Answer 22

Calculate volume of O2/CO2 consumed/released

(calculate area of a cylinder)

Calculate cross-sectional area of capillary tube using π r²

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. cm3 min-1 g-1

Question 23

Describe how a respirometer can be used to measure the rate of anaerobic respiration

Answer 23

Repeat aerobic experiment 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

Question 24

Explain why the liquid moves in a respirometer in anaerobic respiration

Answer 24

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

Question 25

Explain why the apparatus is left for an hour after the culture has reached a constant temperature

Answer 25

Allow time for oxygen to be used or respired

Question 26

Describe how redox indicator dyes such as Methylene blue can be used to measure rate of respiration (info)

Answer 26

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

Question 27

Describe how redox indicator dyes such as Methylene blue can be used to measure rate of respiration (steps)

Answer 27

Add a set volume of organism eg. yeast and a set volume of respiratory substrate (eg. glucose to tubes) Add a buffer to keep pH constant Place in water bath at a set temperature and allow to equilibrate for 5 mins Add a set volume of methylene blue, shake for a set time (do not shake again) Record time taken for colour to disappear in tube

Question 28

Examples of variables to be controlled in redox indicator reaction

Answer 28

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)

Question 29

Why leave tubes in the water bath for 5 minutes

Answer 29

Allow for solutions to equilibrate and reach the same temperature as the water bath

Question 30

Describe a control experiment in redox indicator reaction and why it would be done

Answer 30

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

Question 31

Suggest and explain why you must not shake tubes containing methylene blue.

Answer 31

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

Question 32

Suggest one source of error in using methylene blue. Explain how this can be reduced

Answer 32

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