Laboratory 5: Cell Respiration YOU MUST KNOW
• The equation for cellular respiration.
• Howa respirometer works.
• The relationship between movement of water in a respirometer and cellu­
lar respiration.
• The effect of temperature and increased metabolic activity on respiration .
• How to calculate the rate of respiration.
Overview of the Lab
In this experiment respirometers are used to measure the rate of cellular respi­
ration in pea seeds. You investigate the rate of respiratio n in both germinating
and nongerminating peas at two different temperatures.
Hints and Review
I The equation for cellular respiration is
C6 H 1206
+ 602 --7 6 H 20 + 6 CO 2 + ATP
I How can the rate of cellular respiration be measured? When you study the
equation for cellular respiration, you will see that there are at least three ways:
1. Measure the amount of glucose consumed.
2. Measure the amount of oxygen consumed.
3. Measure the amount of carbon dioxide produced.
In this experiment, a respirometer is used to measure the amount of oxygen
consumed.
I A respirometer is an air-tight chamber except for one opening for gases to enter
or leave. Potassium hydroxide (KOH) soaks a cotton ball and will combine with
the CO 2 produced by the organism (peas in our AP Lab). A solid precipitate
forms. Since CO 2 and 02 are produced and consumed in equal amounts, any
changes in the sealed container (assuming temperature and pressure remain
constant) will be caused by a change in gas volume due to cellular respiration.
With the CO 2 being removed as a solid precipitate, then it is 0 2 that is con­
sumed, lowering pressure within the respirometer, and allowing water to enter
the pipette. Study Figure 5.1 to see the components of a respirometer.
I A seed contains an embryo plant and a food supply surrounded by a seed coat.
I The germinating (sprouting) seeds will show a higher rate of respiration than
the nongerminating seeds. However, be sure that you know these dry, nonger­
minating seeds are not dead, but dormant. They can be stored for years and,
when soaked in water, will germinate.
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PART III : THE LABORATORY
Pipette: Fresh air
The ai r in the vial
is a mix ture of
gases, including 02
0 2 equilibrates 'Ni th the air
in the vial via th is tube .
Cotton protects
the organism
from caustic KOH.
Stopper
Thi s preve nts gases
and ,vater from leaking
into the resp irometer.
Living organi sm: .- _ _ _ _ _--=--.;:::­
Most organisms require 02' KOH comb ines with CU' o----------...:::......~~
to form a solid precipitate.
Figure 5.1
I There
are actually two variables in this experiment. Besides germination versus
nongermination, the second variable is the effect of temperature on metabolic
rate. You run the two experiments simultaneously, with vials exposed to room
temperature water (25°C), and vials that are exposed to cooler temperatures
(1 DOC) by adding ice to the surrounding water.
I Notice that each experimental setup includes a vial of germinating peas; a vial
of dry, nongerminating peas; and a vial of glass beads alone to act as a control
for this experiment. The control will compensate for any change in pressure or
temperature.
I Students are often confused by the difference between a control (the glass beads
in this experiment) and factors that are held constant. In this experiment, you
hold constant the volumes within the containers, the number of peas, and the
temperature of the water for each set of three vials .
• Figure 5.1 shows a graph of typical results from this experiment.
I Be able to calculate the rate for each condition. Go back to Lab 2 on Enzymes to
review this lesson.
Questions
1. \"lhat is the rate of oxygen consumption in germinating corn at 12°C as shown
in the graph below?
2.0
(A) 0.08 mllmin
1. 8
Germinating corn
(B) 0.04 mllmin
'r at 22°C
1.6
u
(C) 0.8 mllmin
,
~ 1A
(D) 0.6 mllmin
"
~ 1.2
c
,,
(E) 1.00 mllmin
8 1.0
,
'l'" Germ inating corn
0' 0.8
at 12°C
,"
~
~E 06
.
,,
,~
OA
0.2
, , .../'
~
00 5
---
../'
--10
Nongerminating corn
at 22°C
-.~~.
Nongerminating corn
20 at 12°C
15 Time (minutes) Figure 5.2
LABORATORY 5 CELL RESPIRATION
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