Respiration
Overview
Every second you are alive, the cells in your body are quietly taking glucose apart and using what is released to keep you going. Lift a bag, climb a stair, hold a thought: all of it is paid for by respiration. It is the one chemical process that never stops, in every living cell, in every organism, from the moment life begins.
In this lesson you will follow the energy from a glucose molecule to a contracting muscle. You will write the equation for aerobic respiration, work out what your body changes when you start to run, and see what happens when your muscles cannot get oxygen fast enough: the switch to anaerobic respiration, the lactic acid that builds up, and the oxygen debt you repay while you are bent over catching your breath. You will also plan and pick apart the required practical that puts all of it on a stopwatch.
Objectives
- Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.
- During aerobic respiration chemical reactions occur that use glucose (a sugar) and oxygen and transfer energy.
- Aerobic respiration is represented by the equation: glucose + oxygen → carbon dioxide + water
- Aerobic respiration takes place continuously in both plants and animals.
- Most of the reactions in aerobic respiration take place inside mitochondria.
- During exercise the human body needs to react to the increased demand for energy. A number of changes take place: the heart rate increases, increasing blood flow to the muscles; the rate and depth of breathing increases; glycogen stored in the muscles is converted back to glucose.
- These changes increase the supply of glucose and oxygen to, and increase the rate of removal of carbon dioxide from, the muscles.
- If insufficient oxygen is reaching the muscles, energy is transferred by anaerobic respiration. glucose → lactic acid C6H12O6 → 2C3H6O3
- Anaerobic respiration in muscles is the incomplete breakdown of glucose, which causes a build-up of lactic acid. An oxygen debt needs to be repaid to oxidise the lactic acid to carbon dioxide and water.
- As the breakdown of glucose is incomplete, much less energy is transferred in anaerobic respiration than during aerobic respiration.
- During long periods of vigorous activity muscles become fatigued and stop contracting efficiently. One cause of muscle fatigue is the build-up of lactic acid in the muscles. Blood flowing through the muscles eventually removes the lactic acid. Required practical: Investigate the effects of exercise on the human body.
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Respiration. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Where do most of the reactions of aerobic respiration take place? A. In the nucleus B. In the mitochondria C. In the chloroplasts D. In the cell wall Answer: B
- Which products are formed by anaerobic respiration in a human muscle cell? A. Carbon dioxide and water B. Ethanol and carbon dioxide C. Lactic acid only D. Lactic acid and oxygen Answer: C
- A student's pulse rate is 60 beats per minute at rest and 96 beats per minute immediately after exercise. What is the percentage increase in her pulse rate? A. 36% B. 60% C. 62.5% D. 160% Answer: B
- Which change does NOT happen in the human body during exercise? A. Heart rate increases B. Breathing becomes deeper C. Glycogen in the muscles is converted to glucose D. The concentration of oxygen in the air breathed in increases Answer: D
- Why does anaerobic respiration transfer less energy per glucose molecule than aerobic respiration? A. It happens outside the mitochondria B. Glucose is broken down incompletely C. It uses less glucose D. It produces carbon dioxide Answer: B
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Recommended Books
Further learning from open sources
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Textbook section
Metabolism without Oxygen
Discuss the fundamental difference between anaerobic cellular respiration and fermentation
"Biology: Metabolism without Oxygen" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/biology/pages/7-5-metabolism-without-oxygen. Access for free at https://openstax.org/books/biology/pages/1-introduction
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Textbook section
Glycolysis
Describe the overall result in terms of molecules produced in the breakdown of glucose by glycolysis
"Biology: Glycolysis" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/biology/pages/7-2-glycolysis. Access for free at https://openstax.org/books/biology/pages/1-introduction
Published by other organisations under open licences, credited as they ask. Links open their websites.
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