Chapter 3: Section 3 Energy for Life

Trapping and Using Energy Where does energy for life come from? The food we eat All of the activities of an organism involve chemical reactions. The total of all chemical reactions in an organism is called metabolism

Trapping and Using Energy The chemical reactions of metabolism need enzymes. Enzymes cause a change, but the enzyme is not changed and can be used again.

Trapping and Using Energy Without the right enzyme, a chemical reaction in a cell cannot take place Each chemical reaction in a cell requires a specific enzyme

Photosynthesis All living thing are divided into two groups – producers and consumers – based on how they obtain their food. Organisms that make their own food are called producers Organisms that cannot make their own food are called consumers

Photosynthesis Plants and many other kinds of producers can convert light energy into another kind of energy called chemical energy. This process is called photosynthesis. During photosynthesis, producers use light energy to make sugars, which can be used as food.

Producing Carbohydrates Carbohydrates are organic molecules that supply energy for cell processes. Producers that use photosynthesis are usually green because they contain a green pigment called chlorophyll. Chlorophyll and other pigments are used in photosynthesis to capture light energy, these pigments are found in chloroplasts.

Producing Carbohydrates The captured light energy powers chemical reactions that produce sugar and oxygen from the raw materials, carbon dioxide and water. Some of the captured light energy is stored in the chemical bonds that hold the sugar molecules together.

Storing Carbohydrates Plants make more sugar during photosynthesis than they need for survival. Excess sugar is changed and stored as starches or used to make other carbohydrates. Plants use carbohydrates as food for growth, maintenance, and reproduction.

Storing Carbohydrates Consumers take in food by eating producers or other consumers. No matter what you eat, photosynthesis was involved directly or indirectly in its production

Respiration To get energy, cells break down food. Some of the energy from the food is used when you move and some of it becomes thermal energy (heat energy). Most cells also need oxygen to break down food.

Respiration During cellular respiration, chemical reactions occur that break down food molecules into simpler substances and release their stored energy.

Using Respiration to Break Down Carbohydrates The food molecules most easily broken down by the cells are carbohydrates. The carbohydrates are broken down into glucose molecules. As glucose molecules are broken down, energy is released.

Using Respiration to Break Down Carbohydrates The breakdown of energy occurs in the mitochondria of the cells of plants, animals, fungi, and many others. This process uses oxygen , releases much more energy, produces carbon dioxide, and water as waste.

Fermentation When cells do not have enough oxygen for respiration, they use a process called fermentation. Fermentation releases some of the energy stored in glucose molecules

Fermentation Some microscopic organisms, such as bacteria, carry out fermentation and make lactic acid. Some of these organisms are used to produce yogurt and some cheeses.

Related Processes Some producers use photosynthesis to make food. All living things use respiration or fermentation to release energy stored in food.

Related Processes Photosynthesis and respiration are almost opposite of each other. Photosynthesis produces sugars and oxygen, respiration uses these products. Respiration produces carbon dioxide and water, photosynthesis uses these products.

Related Processes

Question 1 The total of all chemical reactions is __________. A. Respiration B. Metabolism C. Photosynthesis D. Enzyme

Question 2 Organisms that make their own food are consumers. A. True B. False

Question 3 In what organelle does photosynthesis take place? A. Chloroplast B. Mitochondria C. Nucleus D. Vacuole

Question 4 Food molecules most easily broken down by cells are _____________. A. Proteins B. Lipids C. Fats D. Carbohydrates

Question 5 Fermentation releases some of the energy stored in protein molecules. A. True B. False

Question 6 __________ produces sugars and oxygen, and ___________ uses these products. A. Respiration, photosynthesis B. Fermentation, respiration C. Photosynthesis, respiration D. Photosynthesis, fermentation