Respiration
Plants
Oxygen diffuses into the leaf via stomata. It enters the air spaces in the leaf and then
dissolves in the moisture covering the cell surfaces and then passes through the membrane
into the cell in solution.
Respiration
This is the oxidation of food to produce energy.
Oxygen
+
Glucose
6O2
+
C6H12O6
Carbon dioxide
6CO2
+
water
+
energy
+
6H2O
+
38 ATP
Not all the energy is released at once. Some is stored as A.T.P.
This reaction occurs in the mitochondria of cells – without this, the cell would die as it
would have no source of energy.
Do not confuse respiration with breathing.
Experiment to demonstrate respiration in living organisms
suction:
- speeds the end
result
- draws air
through the
system
sodium hydroxide
- to absorb all of
the CO2
limewater:
to check that all
the CO2 is
absorbed
living organism
limewater:
to indicate CO2
and therefore,
respiration
Explanation
Air is drawn through the system.
It is first taken through the sodium hydroxide, which absorbs the CO2 from it.
The next beaker contains limewater, which would turn cloudy if CO2 is present.
The air is then passed through a beaker with the living organism in it.
The air from this is then taken to the next beaker containing limewater.
If CO2 is present, it would turn cloudy and therefore respiration has taken place.
There are two forms of respiration:
(a)
(b)
aerobic
anaerobic
(a)
Aerobic:
(with oxygen (O2))
(without oxygen)
Oxygen
+
Glucose
O2
+
C6H12O6
Carbon dioxide
CO2
+
water
+
energy
+
H2 O
+
38 ATP
The oxygen comes from the air, which is breathed in. In the case of fish, the oxygen is
dissolved in the water.
(b)
Anaerobic:
1.
Animals
Glucose
Lactic acid
+
energy (only 2 A.T.P.)
This occurs in muscle cells which are actively working and which have a shortage of
oxygen. It also occurs in some bacteria (e.g. the making of yogurt).
When glucose is broken down without oxygen, lactic acid is produced in the process
shown above: anaerobic respiration. Although the energy, which is released, is
little, the energy released is rapid. The lactic acid, which is produced, is toxic and so
anaerobic respiration cannot be used for a long period of time. As the lactic acid
levels increase, a person would feel exhausted. The person would then need to rest to
repay the oxygen debt. The lactic acid is oxidised and is no longer harmful.
100 metre sprint
A well trained athlete does not breathe during the race – only before and after the
race. This is because the race is sufficiently short – all the energy can be gained by
the anaerobic process. The reason for this is:
it is a rapid release
energy is not wasted in the movement of the rib cage and diaphragm
At the end of the race, the person would pant so that they can take in oxygen to
oxidise the lactic acid and repay the oxygen debt.
However, the anaerobic process is inefficient:
-
only 2 A.T.P. is produced in comparison to 38 A.T.P. in aerobic respiration.
the lactic acid is toxic and causes fatigue, cramps and stitches.
Experiment to demonstrate the build up of lactic acid
1.
2.
3.
(a)
(b)
(c)
(d)
(e)
2.
Raise one hand above the head and let one hand hang down your side
Clench and unclench both fists continuously
Proceed for as long as possible and then let both arms rest on the table
Which arm tires first?
The arm above the head
Describe the feeling in that arm.
Pain!
Describe the feeling in the other arm
Pain is not as bad
Describe what happens at rest.
The pain stops / fades away
Explain
The blood flown to the arm held up above the head slower and so less oxygen
reaches it. Therefore, anaerobic respiration must occur for muscle contraction to
take place. Therefore, there is a build up of lactic acid. This is then oxidised when the
arm is placed to rest on the table.
Plants
Glucose
Alcohol
Example of alcohol produced:
Example of CO2 produced:
+
Carbon dioxide
+
energy
brewing
bakery
Yeast can respire both aerobically and anaerobically. This can be proved by an experiment,
where yeast is placed in an excess amount of glucose (so that this is not the limiting factor)
and then sealed so that no oxygen can get in. A tube letting gas out would later (when the O2
is no longer there) go into limewater to test for carbon dioxide. An indicator shows whether
there is any O2 present.
At the start of the experiment, there is O2 present, but then the indicator colour changes as
the O2 is used in aerobic respiration. When the tube is put into the limewater, the limewater
turns cloudy – CO2 is produced in the anaerobic respiration.
Summary
Anerobic respiration
without oxygen
intermediate – lactic acid – not completely
broken down
less energy produced – only 2 A.T.P. per
molecule of glucose
fast reaction
limited – alcohol and lactic acid are toxic
less efficient
Aerobic respiration
with oxygen
complete breakdown of glucose
more energy released – 38 A.T.P. per
molecule of glucose
slow reaction
no limit as long as oxygen is present
more efficient