Chapter 3 Cellular Energy • MHR 736.In test tube 3, add a piece of beef heart, 8 drops of
methylene blue, and sufficient distilled water to
equal the volume of the mixture in test tube 1.
7.Gently swirl the contents of each test tube. Then,
quickly but carefully, use a medicine dropper to add
about a 2 cm layer of mineral oil to each test tube.
To do this, tip the test tube slightly to one side and
allow the mineral oil to flow down the inside of the
test tube.8.Place the test tubes in the water bath. Record the
initial colour of the mixture in each test tube. Use a
colour chart or make a series of categories, such as
dark blue, medium blue, light blue, colourless. You
can also make a series of sketches using coloured
pencils. If possible, take a series of photographs of
the samples to augment your written observations.
9.Observe the colour of the mixture in each test tube
every 5 min. for about 30 min. Use a data chart to
record your observations.Post-lab Questions
1.Which sample(s) showed the most pronounced
change in colour? Why?2.Methylene blue is a dye (indicator) that changes
from blue to colourless when it is reduced by other
substances in a chemical reaction. Describe the
chemical reaction that was responsible for changing
the colour of the methylene blue in the test samples.
3.What other controls could be incorporated into this
procedure?
4.Why was it necessary to add a layer of oil to the
surface of each mixture?Conclude and Apply
5.What cell structures (organelles) contain succinic
dehydrogenase? Why would you expect to find high
concentrations of these cell organelles in
mammalian heart tissue?
6.Would this procedure work with other types of
animal tissue? Explain briefly.
7.How could you modify this procedure to obtain
more accurate evidence of succinic dehydrogenase
activity?Exploring Further
8.Repeat the investigation using the additional
controls you outlined in answer to question 3.
How would these controls help you to interpret
the results?
9.Does plant tissue produce similar succinic
dehydrogenase activity? Repeat the procedure
using germinating white beans in place of beef heart
tissue. What other plant parts might be suitable for
this investigation? Explain briefly.two carbon dioxide molecules and one ATP molecule
(produced by substrate-level phosphorylation).
During the cycle, energetic electrons reduce NAD+
and FAD, which combine with H+ions to form
NADH and FADH 2. Remember that an additional
NADH was produced in the transition reaction.
As you learned in Chapter 2, FAD is a coenzyme
involved in redox reactions. Figure 3.9 shows the
various reactions involved in the Krebs cycle.
Four NADH molecules and one FADH 2 molecule
are produced for each molecule of pyruvate that
enters the mitochondrion for aerobic respiration.
Because two molecules of pyruvate enter the
matrix for each molecule of glucose oxidized,
eight NADH and two FADH 2 are produced for each
molecule of glucose. Of these, six NADH and two
FADH 2 , along with two ATP molecules, result
from the reactions of the Krebs cycle. At this
point, oxygen has not been used in the reactions
described. Oxygen plays a crucial role in the
electron transport chain, during oxidative
phosphorylation. NADH and FADH 2 molecules that
have been formed by redox reactions in the Krebs
cycle will donate electrons to the electron transport
chain. Energy from these electrons fuels ATP
synthesis by aerobic respiration.
At the end of the cycle, the glucose molecule
that entered glycolysis has been completely