seCTion

4.4 Overview of Cellular Respiration

Teacher Notes and Answers

SeCtion 4Instant Replay

1.Itmeansthatitneedsoxygentohappen. 2.6CO2moleculesand6H2Omoleculesshouldbe

circled.

Vocabulary Check

1.aerobicandanaerobic 2.glycolysis 3.Krebscycle 4.cellularrespiration

The Big Picture

5.mitochondria 6.reactants:C6H12O6and6O2,products:6CO2and

6H2O 7.theelectrontransportchain

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seCTion

4.4

CellularrespirationmakesATPbybreakingdownsugars.

You probably know that you need to breathe oxygen to survive. But how does your body use that oxygen? That oxygen helps your body to release chemical energy that is stored in sugars and other carbon-based molecules. The energy is released to produce ATP. This process of using oxygen to produce ATP by breaking down carbon-based mol-ecules is called cellular respiration. Cellular respiration makes most of the ATP that a cell needs. Cellular respiration is an aerobic process. Aerobic (air-OH-bihk) means that it needs oxygen to happen.

Cellular respiration takes place in mitochondria. These organelles are sometimes called the cell’s “powerhouses” because this is where most of the cell’s ATP is made. Mitochondria do not make ATP directly from food. ATP is made through many chemical reactions.

Before cellular respiration can happen, food has to be broken down into smaller molecules. Food gets broken down into smaller mol-ecules like glucose. Then, glucose gets broken down. Remember that glucose is a six-carbon sugar. Glycolysis (gly-KAHL-uh-sihs) breaks glucose into two molecules that each have three carbons.

Glycolysis is an anaerobic process. Anaerobic means that it does not need oxygen to happen. Glycolysis happens in the cell’s cytoplasm. The three-carbon molecules from glycolysis then enter the mitochondria. The products of glycolysis—the three-carbon molecules—enter the mitochondria and are used in cellular respiration.

Why is cellular respiration called an aerobic process?

Glycolysis breaks glucose into 2 three-carbon molecules.

C C C C C C C C C

C C C

2 ADP 2 ATP

glucose 2 three-carbon molecules

Overview of Cellular RespirationKEyConCEPT The overall process of cellular respiration converts sugar into ATP using oxygen.

Mitochondria (middle) are found in both animal (top) and plant (bottom) cells. They make ATP through cellular respiration.

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Cellularrespirationislikeamirrorimageofphotosynthesis.

A mirror image is like an opposite—the same thing, but in reverse. Cellular respiration and photosynthesis are not really opposites, but it can be helpful to think about them in that way. Photo-synthesis makes sugars and cellular respiration breaks down sugars. The chemical equations of the two processes are basically opposites.

The structures of mitochondria and chloro-plasts are very similar. Remember that part of photosynthesis happens inside the stroma— the fluid in the chloroplast—and part of photosyn-thesis happens inside the membrane of the thyla-koid. Similarly, part of cellular respiration happens in the fluid inside the mitochondria, called the matrix. The other part of cellular respiration happens in the inner membrane of the mitochondria.

After glycolysis, the three-carbon molecules enter the mitochondria and begin the process of cellular respiration. There are two main parts of cellular respiration:

stage 1: krebs cycle The molecules from glycolysis enter a series of reactions called the Krebs cycle. The Krebs cycle produces a small amount of ATP and other molecules that carry energy to the next part of cellular respiration. It also makes carbon dioxide as a waste product.

stage 2: electron Transport Energy is moved through a chain of pro-teins and a large number of ATP molecules are made. Oxygen enters the process here. The oxygen is used to make water molecules, which are waste products.

CoMPARinGPRoCEssEs

photosynthesis

Cellular respiration

The products of photosynthesis—sugars and o2—are the reactants in cellular respiration.

light energy

ATP, heat

energy

light energy

ATP, heat

energy

reaCTanTsproDUCTs

Sugars (C6H12o6)

o2

Co2

H2o

reaCTanTs proDUCTs

Co2

H2o

Sugars (C6H12o6)

o2

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oVERViEwofCELLuLARREsPiRATion

6H2o6o2

1

2

3

4

sTAGE2:ElectronTransport

sTAGE1:KrebsCycle

Three-carbon molecules from glycolysis enter cellular respiration in mitochondria.

energy-carrying molecules from glycolysis and the Krebs cycle enter Stage 2 of cellular respiration.

ATP molecules are produced. Heat and water are released as waste products.

ATP

ATP

6Co2

mitochondrion

energy

ANDAND

AND

energy-carrying molecules transfer energy to Stage 2.

matrix (area enclosed by inner membrane)

inner membrane

Up to 38 ATP molecules are made from the breakdown of one glucose molecule. The equation for cellular respiration is shown below. You can see that there are many arrows between the reactants—C6H12O6 and 6O2—and the products—6CO2 and 6H2O. These arrows are there to tell you that there are many steps in the process. For example, the equation for cellular respiration includes glycolysis. Many enzymes also play important roles in the production of ATP.

C6h12o6 1 6o2 6Co2 1 6h2oa sugar oxygen carbon dioxide water

energy from glycolysis

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Follow the steps of cellular respiration shown on in the figure on the previous page.

Circle the products of cellular respiration in the figure on the previous page.

cellular respiration anaerobic

aerobic Krebs cycle

glycolysis

1. Which two terms are opposites?

2. Which term is a process that must happen in the cell’s cytoplasm before cellular respiration?

3. Which term is a process that happens within the mitochondria as part of cellular respiration?

4. Which term is the name for this chemical equation:

5. In which organelle does cellular respiration take place?

6. What are the products and the reactants for cellular respiration?

7. Where is most of the ATP made during cellular respiration?

4.4 VocabularyCheck

Go back and highlight each sentence that has a vocabulary word in bold.

Mark It Up

C6h12o6 1 6o2 6Co2 1 6h2oa sugar oxygen carbon dioxide water

4.4 TheBigPicture

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