Chapter 5

1. Chapter 5 Section II: The Cell and Energy

2. Introduction • Believe it or not, the energy comes from the sun. • Sun is the primary source of energy.

3. What is photosynthesis? • Plants and some other organisms are autotrophs that use the sun’s energy to make their own food. • The process by which a cell of an autotroph captures the energy in sunlight and uses it to make food is called photosynthesis (foh toh sin thuh sis). • Chlorophyll and other light-absorbing chemicals capture light energy and use it to power photosynthesis. • In plants, it occurs in their cells’ chloroplasts. (See Notes on Parts of a cell Chapter 4 section III)

4. Chloroplasts • Chloroplasts Photosynthesis occurs inside chloroplasts in the cells of plants and some other organisms.

5. The Events of Photosynthesis • Photosynthesis is a complex process that results in chemical change. • During photosynthesis, cells capture energy from sunlight and use it to change carbon dioxide gas and water into oxygen and sugars, such as glucose.

6. Left side: 6 molecules of carbon dioxide 6 molecules of water Right Side: 1 molecule of glucose 6 molecules of oxygen yields Understanding the Equation An arrow, which is read as “yields,” connects the raw materials to the products. Light energy, which is necessary for the chemical reaction to occur, appears above the arrow.

7. Storing and Releasing Energy In Food • Plant cells use some of the glucose for food. • cells break down the glucose molecules to release the chemical energy the molecules contain • Other glucose molecules are converted to cellulose • a chemical that plays an important role in the structure of the cell walls of plants

8. Storing and Releasing Energy In Food • When heterotrophs eat food from plants or animals that have eaten plants, they take in the plant’s stored food. • Remember:Bird eats caterpillar, which eats the leaf, that produced its energy through the process of photosynthesis – that uses the energy from the sun.

9. Storing and Releasing Energy In Food • The other product of photosynthesis is oxygen • oxygen passes out of the plant and into the atmosphere. • Autotrophs have produced about 21 percent oxygen in the Earth’s atmosphere. • Most living things use oxygen in the cells of their bodies to release the energy in food.

10. Storing and Releasing Energy In Food • Cells store and use energy • during photosynthesis, plants capture energy from sunlight and “save” it in the form of substances such as sugars (glucose). • When their cells need energy, they break down the sugars and releasing energy.

11. What is Respiration? • The process in which cells obtain energy that they need from glucose. • During respiration, cells break down simple food molecules such as glucose and release the energy they contain. • Cellular respiration occurs in the mitochondria of an organism’s cells.

12. The Respiration Equation • The raw materials for cellular respiration are glucose and oxygen. • Plants and other organisms that undergo photosynthesis make their own glucose. • The glucose in animals and other organisms comes from the food they eat. • The oxygen comes from the air or water surrounding the organism.

13. Comparing Photosynthesis and Respiration • Photosynthesis and respiration can be thought of as opposite processes.

14. Comparing Photosynthesis and Respiration • During photosynthesis, carbon dioxide and water are used to produce sugars and oxygen. • During respiration, sugars and oxygen are used to produce carbon dioxide and water. • Together, they form a cycle that keeps the levels of oxygen and carbon dioxide fairly constant in Earth’s atmosphere.

15. Fermentation • Fermentation = an energy-releasing process that does not require oxygen. • There are two types of fermentation: • Alcoholic Fermentation • Lactic Acid Fermentation

16. Alcoholic Fermentation • Occurs in yeast and some other single-celled organisms. • Called alcoholic fermentation because alcohol is one of the products made when these organisms break down sugars. • The carbon dioxide produced by yeast causes dough to rise, and it creates the air pockets you see in bread.

17. Lactic Acid Fermentation • Takes place at times in your body. • Your muscle cells used up the oxygen faster than it could be replaced. • Because your cells lacked oxygen, they used the process of fermentation to produce energy. • One by-product of this type of fermentation is a substance known as lactic acid. • When lactic acid builds up, your muscles feel weak, tired, and sore.