As above for animals.
glucose + oxygen ===> carbon dioxide
+ water + energy
C6H12O6(aq)
+ 6O2(g) ===> 6CO2(g) + 6H2O(l)
+ energy
In green plants, in
daylight, the rate of photosynthesis will exceed that of respiration, but at
night or very low light levels, the rate of respiration will exceed that of
photosynthesis which falls to virtually zero, otherwise the plant would die!
At dusk or dawn, in poor light,
the rates of photosynthesis and respiration are similar.
You
can use a plant example to show heat energy is released in
respiration (aerobic or anaerobic in living organisms).
(Diagram on right)
Such an experiment to show
germinating peas or beans (≡
germinating seeds) release energy using aerobic respiration
is illustrated (right diagram).
One lot of peas/beans is soaked
for at least 24 hours to get them germinating - look for little
shoots/sprouts. Another lot are boiled to kill the enzymes that
catalyse respiration - effectively killing the peas/beans. (the
'control' for a fair test).
Each lot is placed in a thermos
flask (vacuum flask) on top of some moist cotton wool - space ifs
left for an air supply to the peas/beans.
A thermometer is placed in each
flask and the neck sealed with a cotton wool plug - both flasks
should be kept under the same laboratory conditions of temperature
for a week..
Any heat released will produce a
temperature rise. If you record the temperature every day you should
find that the flask of germinating peas/beans will show an increase
in temperature - from heat energy release by respiration.
The control flask of boiled
peas/beans should not show a temperature rise.
You can do a similar experiment
with the boiled (dead) and unboiled (germinated by soaking for 24
hours) peas or beans to show the formation of carbon dioxide
(aerobic respiration) in respiring living organisms). - the
simple experiment is illustrated below using germinating peas or
beans and dead peas/beans.
The uptake of oxygen in respiration produces
carbon dioxide. (Diagram below)
Carbon dioxide is a slightly
acidic gas. If carbon dioxide dissolves in the red
hydrogencarbonate indicator solution, it turns it yellow. The
indicator solution contains a dissolved salt, sodium
hydrogencarbonate, and a coloured pH indicator that you see in your
chemistry lessons - the carbon dioxide lowers the pH of water.
The peas/beans are suspended on a
gauze or layer of cotton wool above some hydrogencarbonate indicator
solution in boiling tubes - the boiling tubes are sealed with bungs
to stop carbon dioxide from the air getting in
You leave the pair of boiling
tubes for an hour.
Left: The germinating peas/beans
are respiring and give off carbon dioxide turning the indicator
solution yellow.
Right: In the control boiling
tube, the dead peas/beans cannot respire (enzymes dead) and you see
no change in the indicator colour because no carbon dioxide was
formed.
You can do this experiment with
animals like woodlice or maggots, using glass beads in the control
tube - NOT dead animals and the living animals should not be kept
for too long to run out of oxygen and die - ethical points.
You can compare the rates of
respiration for different animals but its a pretty crude experiment
- I suppose you could weigh equal masses of the animal into the
boiling tubes.
