Biology 12

3.1 Cellular Respiration

64 MHR • Unit 1 Metabolic Processes

You are running late for school. The bus stop is

five minutes’ walking distance away, and the bus

is due to arrive in only three minutes. Taking a

shortcut, you sprint the full distance, arriving just

as the bus comes to the stop. You board the bus

and collapse into a seat, breathing heavily. During

your sprint, molecules of glucose were broken

down in your cells. This process provided your

muscles with the energy they needed to carry you

to the bus. As you recall from Chapter 2, the

breakdown of glucose is an exothermic reaction

that releases energy. In this reaction, hydrogen

atoms and electrons are removed from glucose and

added to oxygen. Glucose is oxidized, and oxygen

is reduced. Energy from this reaction is used for

the production of ATP molecules, which are the

energy source for cells. Metabolic pathways that

contribute to the production of ATP molecules in

cells are collectively referred to as aerobic cellular

respiration. The term aerobicmeans that the

process requires oxygen. The overall equation of

aerobic cellular respiration is shown in Figure 3.1.

Figure 3.1Aerobic cellular respiration most often involves

the breakdown of glucose, coupled with the manufacture

of ATP.

When a molecule of glucose undergoes aerobic

cellular respiration, 36 molecules of ATP are

produced. Glucose is an energy-rich molecule. The

breakdown of glucose results in the formation of

low-energy molecules and energy. ATP synthesis

requires energy; it involves a series of endothermic

reactions. The exothermic breakdown of glucose

is coupled (linked) to the endothermic reactions

involved in the synthesis of ATP. This coupling

of reactions results in about 40 percent of the

chemical energy in the glucose molecule being

energy

water

+++

carbon

dioxide

glucose oxygen

ADP + ATP

C 6 H 12 O 6 6O 2 6CO 2 6H 2 O

Pi

transformed into energy in ATP molecules. The rest

of the energy is waste thermal energy.

Releasing energy from a stable molecule, such as

glucose, within the cell requires controlled oxidation.

Controlled oxidation is made possible by a series of

reactions involving various enzymes and metabolic

pathways, as well as coupled reactions. In this way,

each reaction releases only a small portion of

energy, while other reactions conserve this energy

in molecules of ATP.

Figure 3.2All organisms, including these E. colibacteria,

manufacture ATP to fuel cellular functions.

Stages of Aerobic

Cellular Respiration

The process of aerobic cellular repiration can be

divided into four distinct stages. These stages are

summarized in Figure 3.3. Refer to the figure as you

read the following overview. Section 3.1 describes

glycolysis in detail. Section 3.2 examines the three

remaining steps in aerobic cellular respiration.

Overview of Cellular Respiration

The first step in this process is a chain of reactions

called glycolysis. “Glycolysis” means breaking

sugar. This process is anaerobic(without oxygen)

and occurs in the cytosol of cells, outside the

organelles. The process of glycolysis produces

EXPECTATIONS

Identify and describe the four stages of aerobic cellular respiration.

Outline the key steps of glycolysis.

Identify the products of glycolysis.