Respiration practical

Question 1

Method 1

Answer 1

Add set mass of single called organism to a set volume/concentration of substrate e.g. glucose

Add buffer to keep ph constant

Add chemical that absorbs co2 e.g. NaOH

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

Measure distance moved by coloured liquid in set time

Question 2

Why does the liquid move (o2)

Answer 2

Yeast aerobically respires > take in O2

CO2 given out but absorbed by NaOH solution

So volume of gas and pressure in container decreases

So fluid in capillary tube moves down a pressure gradient towards organism

Question 3

Measuring rate of anaerobic respiration by measuring co2 release

Answer 3

Repeat experiment 1 but

Remove chemical that absorbs co2

Make conditions anaerobic by
- layer of oil > stop o2 from diffusing in
- add a chemical that absorbs o2
- leave for an hour to allow o2 to be respired and used up

Question 4

Why does the liquid move (co2)

Answer 4

Yeast anaerobically respires > releases co2

So volume of gas and pressure in container increases

So fluid in capillary tube moves down a pressure gradient away from the yeast

Question 5

Calculate rate of respiration (oxygen consumption)

Answer 5

Calculate volume of o2/co2 consumed/released (area of a cylinder)

Calculate cross-sectional area of capillary tube using pi r^2

Multiply by distance liquid has moved

Divide by mass of organism and time taken

Question 6

Redox indications

Answer 6

Change colour when they accept electrons, becoming reduced

Redox indicators take up hydrogens and get reduced instead of NAD/FAD > modelling their reactions

Question 7

Redox method

Answer 7

Add a set volume of organism e.g. yeast and a set volume of respiratory substrate e.g. glucose to tubes

Add a buffer to keep ph constant

Place in water bath at a set temperature and allow to equilibrate for 5 minutes

Add a set volume of methylene blue, shake for a set time

Record time taken for colour to disappear in tube

Question 8

Rate of respiration equation (s-1)

Answer 8

1/ time (sec)

Question 9

Redox variables

Answer 9

Volume of single celled organism

Volume/conc/type of respiratory substrate

Temperature

Ph

Question 10

Redox explanation

Answer 10

Investigating temp/ph - results expected as enzyme controlled reaction

Faster change of colour indicates faster respiration
- hydrogen is removed faster