Biology Study Guide

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9.1 Cellular Respiration: An Overview

Lesson Objectives
Explain where organisms get the energy they need for life processes. Define cellular respiration.
Compare photosynthesis and cellular respiration.
Lesson Summary
Chemical Energy and Food Chemical energy is stored in food molecules. Energy is released when chemical bonds in food molecules are broken. Energy is measured in a unit called a calorie, the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. Fats store more energy per gram than do carbohydrates and proteins.

Overview of Cellular Respiration Cellular respiration is the process that releases energy from food in the presence of oxygen. Cellular respiration captures the energy from food in three main stages: • glycolysis

• the Krebs cycle
• the electron transport chain
Glycolysis does not require oxygen. The Krebs cycle and electron transport chain both require oxygen. • Aerobic pathways are processes that require oxygen.
• Anaerobic pathways are processes that occur without oxygen.

Comparing Photosynthesis and Cellular Respiration The energy in photosynthesis and cellular respiration flows in opposite directions. Their equations are the reverse of each other. Photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses oxygen to release energy from food.

Chemical Energy and Food
For Questions 1–4, complete each statement by writing the correct word or words. 1. A calorie is a unit of energy.
2. The Calorie used on food labels is equal to 1000calories. 3. A Calorie is also referred to as a kilocalorie.
4. Cells use the energy stored in chemical bonds of foods to produce compounds that directly power the cell’s activities, such as ATP.

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Overview of Cellular Respiration
For Questions 5–10,...
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