CPAC 09- Factors affecting the rate of aerobic respiration

Question 1

Describe how a respirometer works

Answer 1

• it is a chamber connected to a capillary tube with a drop of dye
• as the organism in the chamber respires + uses oxygen, the pressure decreases and the liquid moves in the capillary

Question 2

What is the control for this practical?

Answer 2

-replacing the organism with an inert object of the same mass e.g. glass beads

Question 3

How do you find the volume of oxygen consumed using a respirometer?

Answer 3

-place a fixed mass of soda lime in the respirometer with the organism
-measure distance coloured liquid moved and use the formula:
volume=distance x pi x r2 (r squared)

Question 4

How is the rate of respiration calculated?

Answer 4

volume of oxygen used/time/mass

units: mm3min-1g-1

Question 5

State the hazard and safety precaution involved in the practical

Answer 5

• soda lime is corrosive
• wear eye protection
• use gloves and transfer with a spatula
• do not inhale any dust
• wash hands after handling organisms

Question 6

State the control variables for this practical

Answer 6

• temperature
• mass of organism
• time
• age or stage of development of organisms
• mass of soda lime
• apparatus must be airtight and replace air after each setup