Paper 5

Question 1

What is a respirometer used for

Answer 1

We read the manometer scale to measure rate of oxygen uptake during respiration of small terrestrial invertebrates/germinating seeds

Question 2

Describe how a respirometer is formed

Answer 2

1) Pressure and temperature must be kept constant while reading is taken
→Use thermostatic water bath
2) Use control tube with equal volume of inert material (e.g. glass beads)
→Compensate for changes in atmospheric pressure
3) Soda lime/KOH/NaOH
→Absorb carbon dioxide produced
4) Volume of air in test tube with organisms decrease=oxygen consumption
→Level of manometer fluid nearer to experimental tube increases

Question 3

How do we use the respirometer to measure RQ:

Answer 3

• Use same apparatus twice
  1) Find volume of oxygen (x cm3 min-1) consumed at a fixed temperature with soda lime
  2) Repeat by setting up with the same organism at the same fixed temperature but remove chemical that absorbs carbon dioxide
  →Manometer fluid is now affected by both oxygen consumption and carbon dioxide release
  → check changes to manometer scale fluid

Question 4

What is the RQ value if manometer fluid (nearer to experimental tube) level does not change:

Answer 4

If manometer fluid 9nearer to the xtperimemtal tube0 level does not change:

→Oxygen absorbed=carbon dioxide produced
RQ=1

Question 5

What is the RQ value if the manometer lowers by y cm:

Answer 5

→Carbon dioxide produced>oxygen absorbed

→Volume of air in respirometer increase
RQ=(x+y)/x

Where x is the initial increase in manometer fluid

Question 6

What happens to the RQ value if manometer fluid increases by z cm:

Answer 6

→Oxygen absorbed>carbon dioxide produced

→Volume of air in respirometer decrease

RQ=(x-z)/x

Where x is the initial increase in manometer fluid increases

Question 7

How can we use the respirometer to measure the effect of temperature on oxygen consumption

Answer 7

Take measurements at various temperatures
Plot graph of oxygen consumption against temperature

Expetted result;
Higher temperature. Higher rate of respiration
Therefore faster absorption of oxygen

Question 8

How can we investigate the rate of respiration of yeast

Answer 8

A redox indicator for example DCPIP, methylene blue can be used to investigate the rate of respiration of yeast.

Redox indicator/ dye dries not damage cells
So can add dye to suspension of yeast cells
When reduced, the blue dye becomes colourless

Measure time taken for dye to change from blue to colourless =rate of respiration of yeast

Can measure time taken at diff temp, with diff (s) or diff substrates
To measure effect on rate of respiration