Living cells need energy to function and during exercise they need much
more energy.
Examples of the body's energy requirements include muscle
contraction, protein synthesis and control of the body temp in mammals.
Plants respire as well. They need energy for making new substances,
growth and transport of materials.
Aerobic respiration
The circulatory system carries oxygen and
glucose to all the body's cells so that energy
can be released through aerobic respiration.
Aerobic respiration takes place inside the
cells. The oxygen and glucose molecules
react and the glucose molecules are broken
down to release energy. It involves a
combination of chemical reactions.
Glucose + oxygen -> carbon dioxide +
water (energy released)
Energy from respiration is locked up in a
molecule called ATP. ATP is called upon when
the cell requires energy to be released.
Measuring
energy
release
The sum of the chemical reactions in the body is called the metabolic
rate. It is useful for scientists to be able to measure this rate in
experiments so that they can investigate factors that might affect it.
Since aerobic respiration requires oxygen, a good measure is how
quickly an organism, tissue or cell can take up oxygen; this is called
the oxygen consumption rate.
Carbon dioxide output can also be used as a measure of metabolic
rate. This will be an estimate because living tissue often uses both
aerobic and anaerobic respiration depending on circumstances.
Due to the fact that respiration is a series of enzyme-controlled
reactions, the rate will be influenced by temperature and pH.
Respiratory
Quotient
The Respiratory quotient
measures the ratio
between the oxygen that
an organism takes in and
the carbon dioxide that it
gives out.
To determine which type of substrate
molecule is being respired in an organism,
a respiratory quotient can be calculated
RQ - Carbon dioxide produced /
Oxygen used.
The respiration of
carbohydrate results in an
RQ of 1.0. The respiration of
fat gives an RQ of 0.7. The
respiration of protein gives
an RQ of 0.8.
Effect of
Exercise
When a person exercises, their breathing and pulse rate increase to deliver
oxygen and glucose to the cells in their muscles more quickly.
This increase helps to remove carbon dioxide produced during respiration more quickly.
To investigate how heart rate responds to exercise, measure your resting heart rate immediately after exercise.
Then measure it every minute until it returns to normal - the time taken to do this is called your recovery rate.
Anaerobic
respiration
Anaerobic respiration takes place in the absence of oxygen. It quickly releases a small amount of energy per
gram of glucose through the incomplete breakdown of glucose.
Glucose -> Lactic acid
(Small quantity of
energy released)
Anaerobic respiration occurs when the muscles are working so hard that the lungs and circulatory system
cannot deliver enough oxygen to break down all the available glucose through aerobic respiration.
At this point, anaerobic respiration starts to take place in addition to aerobic respiration.
The lactic acid produced during respiration is relatively toxic to the cells and can
cause pain (cramp) and a sensation of fatigue in the muscles.
Because anaerobic respiration involves the incomplete breakdown of glucose,
much less energy (20th) is released than in aerobic respiration
It can produce energy much faster over a short period of time, until fatigue sets in. This makes anaerobic
respiration a real necessity in events that require a short, intense burst of energy.
Recovering
after Anaerobic
respiration
The heart rate stays high - pumping blood through the muscles to remove
the lactic acid and transport it to the liver to be broken down.
Deep breathing continues - ensuring enough oxygen is taken in to
oxidise the lactic acid (producing carbon dioxide and water)
In effect, the body is taking in the oxygen that was not available
for aerobic respiration during exertion. Oxygen debt.