core prac 16

Question 1

What are the control variables for the respiration rate prac?

Answer 1

• number of organisms (e.g. weight/mass)
• temperature (as temp can affect gas volumes and resp rate)
• time (every minute for 5 minutes recordings will be taken)

Question 2

What is a possible negative control test for the respiration prac?

Answer 2

Plastic beads can be placed in the tube as they shouldn’t respire

Question 3

Method for respiration prac…

Answer 3

1. Place 5g of organism into tube and replace bung.
2. Add a drop of dye into the glass tube.
3. open the connection (3-way tap) to the syringe and move the fluid to a convenient place on the pipette (point on scale furthest away from test tube)
4. mark starting position of fluid on pipette tube with marker
5. isolate respirometer by closing connection to syringe and atmosphere then start stop watch.
6. mark position of fluid on pipette at 1min intervals for 5mins
7. after 5mins open connection to outside air, measure distance travelled by liquid during each minute.
8. If tube doesn’t have volumes marked onto it you’ll need to convert distance moved into volume of oxygen used.
9. record results in a table.

Question 4

ADV/DIS of using a simple respirometer

Answer 4

ADV - very simple to set up, minimal number of connections making a good seal easier to obtain.
DIS - cannot be reset, needs a control tube used alongside it, no scale so measurements are less accurate.

Question 5

ADV/DIS of U-tube respirometer

Answer 5

ADV - doesn’t need an additional control, syringe allows dye in apparatus to rest.
DIS - more expensive and connections in old models tend to leak.