Cell Respiration

Jennifer NaplesDI Biology

Why Do We Need Food?

• How do you feel when you are hungry?• Stomach growls• Tired• Weak• Dizzy• Why do you feel that way?• Take 2 minutes to write down why your body

acts the way it does when you are hungry?

Why Do We Need Food?

• Why do we need food?• Food provides our bodies with the chemical

building blocks that we need to grow and reproduce.

• Food is a source of raw materials from which our bodies make new molecules

• Food is a source of energy

Chemical Energy and Food

• How much energy is in food?• A lot!• One gram of sugar (glucose)when burned

releases 3811 calories of heat energy• A calorie is the amount of energy needed to

raise the temperature of 1 gram of water 1 degree celcius

• The calorie(capital “C”) that is used on food labels is a kilocalorie or 1,000 calories

The Process of Cell Respiration

• Cell respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.

• The equation cell respiration is:• 602+C6H12O6 6CO2+6H2O+Energy• oxygen+glucose carbon dioxide+water+energy

The Process of Cell Respiration

• Cell respiration requires oxygen and glucose• Cell respiration releases carbon dioxide, water

and energy• There are three stages of cell respiration:• Glycolysis• Krebs Cycle• Electron Transport Chain

Glycolysis

• The first stage of cell respiration • One molecule of glucose is broken in half• Produces 2 molecules of pyruvic acid• Occurs in the cytoplasm of a cell• Requires 2 molecules of ATP to start• Makes 2 molecules of ATP

No Oxygen?

• If there is no oxygen present glycolysis is followed by a pathway called fermentation

• Fermentation releases energy from food molecules by producing ATP in the absence of oxygen

• Fermentation is anaerobic – it requires NO oxygen

Two Types of Fermentation

• There are two types of fermentation• Alcoholic Fermentation and Lactic Acid

Fermentation• Alcoholic Fermentation produces carbon

dioxide and alcohol• Causes dough to rise• Gives of bubbles of carbon dioxide that form

the air spaces that you see in bread.

Lactic Acid Fermentation

• Lactic acid fermentation produces lactic acid • Produced in your muscles during rapid exercise

when the body can not supply enough oxygen to the tissues

• Without oxygen your body is not able to produce all of the ATP required.

• When you do vigorous exercise your body quickly begins to produce ATP through Lactic Acid Fermentation.

Check for Understanding

• What is Cell Respiration?• What are the products of glycolysis?• What are the two main types of fermentation?• What is a calorie? A Calorie?

The Krebs Cycle

• The second stage of cell respiration in the presence of oxygen

• Pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions

• Also called the citric acid cycle because citric acid is one of the compounds formed during this cycle

The Krebs Cycle

• The Krebs cycle occurs in the Mitochondrion• The Krebs Cycle produces high energy

electrons that are used in the next cycle of cell respiration to create large amounts of ATP

• The Krebs Cycle produces ATP

Electron Transport Chain

• High energy electrons that are produced in the Krebs Cycle are passed on to Electron Transport Chain.

• Converts ADP into ATP

ATP Totals

• Glycolysis produces 2 ATP molecules per glucose

• The Krebs Cycle produces 1 molecule of ATP• The Electron Transport Chain produces 33

molecules of ATP• Cellular Respiration produces 36 molecules of

ATP and uses only 2 to get started

Short VS. Long Term Energy

• Quick energy like that used for a sprint is usually obtained through lactic acid fermentation

• About a 50 meter mark ATP store are used up• Lactic acid build up is a by product of fermentation• The only way to get rid of the build up is through a

chemical pathway that requires oxygen• That is why we breathe heavily after exercise

Short VS. Long Term Energy

• What happens when you are exercising for a long period of time?

• Cell respiration is the only way to generate a continuing supply of ATP.

• Cell respiration releases energy more slowly that fermentation• Energy is stores in muscle tissue and other tissues in the

body(glycogen) which last for 15-20 minutes• After that your body begins to break down other stored

molecules including fats for energy• That is why aerobic forms of exercise are beneficial for weight

control