Written for this site from the class slides. The chapter is on pages 405–411 of the course textbook. Image credits are on slide 15.
ATP (adenosine triphosphate) is a nucleotide. It is soluble, so it moves easily around a cell. It cannot pass through membranes, so it stays where it is needed. It also releases a useful quantity of energy, enough for many tasks.
Hydrolysis of ATP to ADP and phosphate releases energy. Energy from respiration is required to make ATP from ADP and phosphate.
Respiration uses the energy that carbon compounds release to produce ATP. Glucose and fatty acids are the main substrates, but many others can be used.
Watch out: respiration is a set of reactions in cells. Gas exchange is the movement of oxygen and carbon dioxide across a surface.
| Anaerobic | Aerobic | |
|---|---|---|
| Word equation | glucose → lactate | glucose + oxygen → carbon dioxide + water |
| Substrates | Glucose only | Glucose, fatty acids and others |
| Yield of ATP | Small, but fast | Large |
| Waste products | Lactate | Carbon dioxide and water |
| Where | Cytoplasm | Cytoplasm and mitochondria |
Temperature, substrate and oxygen supply all affect the rate. A respirometer measures oxygen uptake: a CO2 absorber removes carbon dioxide, so a drop of liquid moves as oxygen is used. If a drop moves 45 mm in 15 minutes in a tube of 1 mm², the rate is 3 mm³ per minute.
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A printable worksheet covering all six statements, from quick recall to a data question and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
Questions built on realistic experimental data, in the style of Paper 1B and Paper 2. Work them on paper and show your working. 23 marks in total. Your teacher has the mark scheme.
The respiratory quotient (RQ) is the volume of carbon dioxide produced divided by the volume of oxygen used. Zebra finches were fasted overnight, then fed either seeds (mostly carbohydrate) or insect larvae (mostly lipid and protein). Their RQ was measured for six hours. Typical RQ values: carbohydrate 1.0, protein 0.8, lipid 0.7.
Oxygen consumption of house mice was measured at different air temperatures. Mice were tested alone, or in groups of four that could huddle together.
Mitochondrial myopathy is a group of disorders in which the electron transport chain does not work properly. Thirty patients and thirty healthy people (controls) cycled to exhaustion. Oxygen delivery to the muscles (from blood flow) and oxygen use by the muscle cells were measured at peak exercise. Error bars show ± 1 SD.
You will need: Dried yeast, sugar solution, flasks or bottles, balloons, water baths, string and ruler
Safety: Keep water baths below 45 C. Vent flasks at the end and wash hands.
Carry this out with your teacher's supervision and follow your school's lab rules.
In the 1780s Lavoisier and Laplace compared the heat from a guinea pig with burning charcoal, linking respiration to combustion.
The experiment treated life as chemistry. Consider what a comparison can show, and where it can mislead.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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