Honors/Biology Lab - Cell Respiration
This investigation uses a device called a respirometer to measure the rate of
oxygen consumption (cellular respiration) in germinating pea seeds.
Background
The overall process of cellular respiration breaks down glucose (a simple sugar),
using the energy from broken bonds to turn ADP into ATP. The chemical
changes are:
You can measure respiration based n the amount of oxygen it uses, the CO2 it
produces, the H2O it produces, even the small amount of heat it produces. We’re
going to use the change of oxygen into CO2.
Respirometers
To do this, we put
our subjects into
respirometers:
closed bottles with
some air (which
contains oxygen)
and a substance
which removes CO2
as fast as it’s
produced.
Thus, if O2 is
converted into CO2,
the overall volume
of gas in the bottle
will get smaller. In
order to see this
change, we keep
the respirometer
under water – as
the amount of gas
gets smaller, water
will move into the
measuring tube.
Assembling the Respirometers
You will use three respirometers in this lab. One respirometer will contain
sprouted seeds, one will contain seeds that haven’t sprouted plus some glass or
plastic beads, and a third will contain only beads.
The purpose of the beads is to ensure that each respirometer has the same
amount of test material in it.
Answer: If we think that only growing seeds will show respiration, why do we also
test dormant seeds and glass beads?
-
-
Label 3 respirometer bottles with your name or initials, and numbers 1, 2,
3
In the bottom of each respirometer, put a little KOH. (You may get this as
a solid, or as a liquid that you dip a piece of cotton ball into). DON’T
TOUCH KOH. IF YOU GET IT ON YOUR SKIN, IMMEDIATELYWASH
FOR SEVERAL MINUTES.
Then add a bit more cotton. This keeps the KOH from touching your test
materials
Add as many sprouted seeds as you can fit into R1, counting them. Leave
enough room to push the stopper firmly in.
Add the same number of unsprouted seeds to R2, then beads to fill to the
same level as R1. Fill R2 with beads.
Add a respirometer top (stopper with measuring tube) to each bottle,
pushing in firmly. Smear some petroleum jelly around the outside of the
stopper where it joins the glass. (Think – why do we do this?)
Lay the respirometers down in a water bath. Some water will enter the tip of
the pipet, but this should stop fairly quickly. If it does not stop, check the
respirometer for leaks. If a respirometer floats, put a weight on the bottle to
hold it down. Make sure you can read the markings on the tube.
Record the water level in each pipet onto the data table at the beginning and
then every 5 minutes.
DATA
Record where on the tube the water line is for each respirometer
Time
0
R1
R2
R3
5 min
10 min
15 min
20 min
Make a graph of this data with a different-colored line for each sample
Full Lab Writeup
For this lab, you must write a full lab report in the standard Island School format,
WITH THE FOLLOWING EXCEPTIONS/ALLOWANCES:
- you don’t have to use any equations
- your hypothesis is that the respirometer with the germinating seeds will have
water moving up the tube throughout the experiment, as the seeds use oxygen,
and the other 2 will not.
- you may use the first few paragraphs of this handout as your Introduction.
You do have to
-
-
describe the method in your own words,
list the materials used,
include a drawing of the respirometers in use,
present your data and graph,
analyze your data (tell me what they show or mean),
describe anything about the experiment that may have made your results
less precise or reliable than would be ideal [you may not say “human
error” or “we did it wrong” – this is way too vague], and
give a brief conclusion for the whole experiment.
You may want to think about what would happen if you compared sets of
respirometers at different temperatures, or used a similar setup to compare
oxygen use in animals as opposed to plants.