12.
Respiration
Cell respiration is the controlled release of energy from organic compounds
to produce energy (ATP)
• Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically)
• It takes place in all living cells, usually in the mitochondria
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What’s the energy used for?
Active transport
Muscle contraction
Growth
Cell division
The passage of nerve
impulses
Protein synthesis
Maintaining constant body
temperature
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Aerobic respiration: Chemical reactions in cells that use
oxygen to break down nutrient molecules to release energy
Glucose + Oxygen Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 6CO2 + 6H20
• This is an efficient process. Enough energy is made to supply the whole body.
• Our bodies perform aerobic respiration for much of the day. In fact, as long as the
supply of oxygen remains high enough, we will continue to perform aerobic
respiration.
• Of course, the amount of energy we produce will drop if the level of oxygen drops.
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But, what happens when you are running a race? Or climbing a really high mountain?
Are they performing aerobic respiration?
• Sometimes, during strenuous exercise, the breathing rate and blood flow
are not able to deliver enough oxygen to the body’s cells.
• How does this affect the release of energy?
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Anaerobic respiration: Chemical reactions in cells that break
down nutrient molecules to release energy without using
oxygen
• In humans anaerobic respiration involves breaking down glucose into a
substance called lactic acid and some energy is released.
lactic
glucose acid energy
anaerobic = ‘without oxygen’
• Anaerobic respiration involves the incomplete breakdown of glucose and so
releases less energy than aerobic respiration.
• Our bodies can only release energy @TracyPower
without oxygen for a short period of time.
There are two problems with anaerobic respiration:
1. Anaerobic respiration releases much less energy from glucose compared to
aerobic respiration.
2. In humans, lactic acid is a poisonous waste product. It builds up in muscles and
causes cramps. It lowers the pH level of the blood which could denature enzymes
• Oxygen must be absorbed to break it down. The oxygen need is called the
oxygen debt
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• Anaerobic respiration can also happen in microorganisms, such as yeast
glucose alcohol Carbon dioxide
• We take advantage of the products of the products of anaerobic respiration
in yeast to make bread and to brew alcohol
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Comparison of aerobic and anaerobic respiration
Aerobic Anaerobic
Oxygen Needed Not needed
Glucose breakdown Complete Incomplete
Products Carbon dioxide and water Animal cells: Lactic acid
Yeast: Carbon dioxide and
ethanol
Energy released A lot A little
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Investigating Uptake of Oxygen by Respiring Organisms
•We can investigate aerobic respiration in living
organisms by measuring the amount of oxygen that
they take from the air using a device called a
respirometer
•This is done by measuring the change in volume in an
enclosed tube containing the organisms
•However, as they respire the organisms release carbon
dioxide, which increases the gas volume
•The carbon dioxide must therefore be removed from
the tube using a chemical like soda lime or sodium
hydroxide, otherwise it will make the experiment results
inaccurate
•Any small organisms can be used in the apparatus,
including seeds or arthropods
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