Rate of respiration practical (16)

Question 1

What could the changing variables be?

Answer 1

Temperature or mass of organism

Question 2

Control variables:

Answer 2

-Number, age and species of organisms
-Time, recordings of position of fluid taken every 1 minute
-Amount of soda lime
-Temperature could be kept same with water bath
-Mass, with weight boat or weighting scale

Question 3

Devise the method for maggots:

Answer 3

1)Place number of maggots of same mass into the tube
2)Use CO2 absorber, e.g. soda lime or sodium hydroxide, limewater too
3)Mark starting position of coloured liquid with marker
4)Close connection to syringe and atmosphere, start the stopwatch
5)Measure distance moved by coloured liquid every minute for 5 minutes
6)At the end of 5 minutes open the connection so maggots can get oxygen from outside
7)Control tube containing glass or plastic beads of same mass can be used, they don’t respire so if there’s no movement for coloured liquid it means it’s due to no oxygen uptake

Question 4

Devise method for germinating seeds:

Answer 4

1)Test to see if seeds can germinate a day or two before experiment, spread them in wet paper towel
2)Moisten cotton wool and place it on top of limewater (CO2 absorber)
3)Place number of seeds with same mass on top of moist cotton
4)Close the tube and start stopwatch
5)Take readings of distance travelled by coloured liquid every minute
6)After 15 minutes open connections so seeds can get oxygen from outside air
7)Can use same control tube that was done for maggot experiment

Question 5

How to measure change in volume of oxygen?

Answer 5

Multiply the cross sectional area of capillary tube by the distance travelled by coloured liquid