Aerobic respiration
Explain aerobic respiration as the process by which organisms release energy from glucose using oxygen, producing carbon dioxide and water; write and interpret the word equation: glucose + oxygen → carbon dioxide + water
What a learner can do afterwards
- Writes and explains the word equation for aerobic respiration
- Explains that aerobic respiration in human muscle cells starts in the cytoplasm and continues mainly in mitochondria
- Links aerobic respiration to why breathing rate and heart rate increase during exercise
- Explains that respiration is not the same as breathing
1 · Read
You have followed air into the alveoli. Breathing moves air in and out of the lungs, and gas exchange transfers oxygen into blood and carbon dioxide out. Aerobic respiration is a series of chemical reactions in cells. It uses oxygen to release energy from glucose. Air movement and chemical reactions are different processes.
The word equation is glucose + oxygen → carbon dioxide + water. Glucose and oxygen are reactants: cells use them. Carbon dioxide and water are products: the reactions make them. The arrow means 'react to form'. Energy is released, but energy is not a substance, so we describe its release beside this word equation.
In human muscle cells, aerobic respiration starts in the cytoplasm. Most of its stages take place in mitochondria, small structures inside the cell. Muscle cells contain many mitochondria because they need energy for movement. Lung cells also respire to meet their own energy needs.
During PE, Priya's muscles need more energy. Faster aerobic respiration uses oxygen and glucose more quickly and produces more carbon dioxide. Her heart beats faster to move blood to working muscles. Blood delivers oxygen and glucose and carries carbon dioxide away. Faster breathing brings fresh air into the lungs and removes carbon dioxide. Muscle cells release energy through their own chemical reactions.
Here are made-up breathing rates for one pupil: 14 breaths per minute at rest and 30 after PE. To find the increase, read both bar values and subtract the resting rate from the rate after PE: 30 - 14 = 16. The increase is 16 breaths per minute. These numbers show a rate change, not how much energy the cells release.
Example breathing rates in breaths per minute.
Aerobic respiration uses glucose and oxygen and makes carbon dioxide and water, releasing energy. In human cells it starts in the cytoplasm and continues mainly in mitochondria.
Lesson, questions and flashcards written for this dataset.
Four readings and four flashcards written for this dataset. Supplied Khan Academy and OpenStax records were consulted for scientific background; their passages are not reproduced.
More to read
Check each side of the equation
Suppose someone writes oxygen after the arrow in an equation for aerobic respiration. You can check the mistake by asking whether cells use oxygen or make it in this process.
Cells use oxygen, so it belongs with glucose before the arrow. Carbon dioxide and water are made, so they belong after it:
glucose + oxygen → carbon dioxide + water
The names before the arrow are the reactants. The names after it are the products. The plus signs join substance names, and the arrow means 'react to form'.
The reactions release energy. That does not make energy another substance in the list. You can describe the energy release beside the equation.
Respiration inside a muscle cell
Oxygen arriving at a muscle has not yet done its job in aerobic respiration. It must reach the muscle cells and take part in their chemical reactions.
These reactions happen in stages. In a human muscle cell, the first stage starts in the cytoplasm. Most stages take place in mitochondria. Saying 'mainly in mitochondria' leaves room for the starting stage elsewhere in the cell.
Muscle cells need energy for movement and contain many mitochondria. The mitochondria are structures inside the cells, not separate organs that send energy around the body.
Lung cells carry out respiration too. Their need for energy is separate from the lungs' work of moving air and exchanging gases.
Carbon dioxide makes the return journey
A working muscle uses glucose and oxygen in aerobic respiration. The reactions release energy and produce carbon dioxide and water.
Follow the carbon dioxide. It leaves the muscle cells and enters nearby blood. Circulating blood carries it to the lungs. There it moves into the air in the alveoli, and breathing out carries it away.
Oxygen travels toward the muscles, while carbon dioxide travels back toward the lungs. These journeys connect reactions inside cells with gas exchange at the alveoli.
During exercise, faster blood flow helps deliver oxygen and glucose and carry carbon dioxide away. Faster breathing brings fresh air into the lungs and removes carbon dioxide. Neither process replaces respiration inside the muscle cells.
Reading a change in breathing rate
A breathing rate tells you how many breaths someone takes in one minute. It is different from the total number of breaths over a whole PE lesson.
Imagine a record showing 16 breaths per minute before activity and 32 afterwards. Subtract the earlier rate from the later rate: 32 - 16 = 16. The increase is 16 breaths per minute.
Keep the units with the result. An increase of 16 breaths per minute does not mean the pupil took only 16 breaths during the activity.
The record shows a change in breathing. The respiration lesson explains why exercise can raise the body's need for oxygen. The breathing rates alone do not measure how much energy the muscle cells release.
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