Cellular Respiration - HOCO Biology



Cellular Respiration

The Chemical Breakdown of Glucose

Energy & Food

Most foods contain usable energy stored in organic compounds such as proteins, carbohydrates and fats.

After we eat, cells break down the complex organic compounds in our food into simpler molecules. 

Some of the energy that is released during the breakdown is used to make ATP.

From food to energy

Autotrophs produce glucose during the photosynthesis.

For cells to obtain energy from the glucose, it must be broken down.

The process that releases energy by breaking down food molecules in the presence of oxygen is called cellular respiration.

Cellular Respiration

BOTH plants & animals breakdown glucose for energy.

Cellular respiration releases energy for cells to use

Instead of making glucose, it is broken down!

How does cellular respiration work?

6O2 + C6H12O6 ( 6CO2 + 6H2O + 36 ATP

WITH OXYGEN PRESENT, glucose is broken down and energy is released. This is called AEROBIC RESPIRATION.

Three main steps of aerobic cellular respiration

1. Glycolysis

2. Kreb’s Cycle

3. Electron Transport Chain

1. Glycolysis

Glycolysis is the breakdown of one molecule of glucose into two molecules of pyruvic acid.

1glucose ( 2 pyruvic acid (AKA pyruvate)

Glycolysis does not need any oxygen

At the end of glycolysis:

2 ATP

2 NADPH

2. The Krebs cycle

At the end of glycolysis, about 90 percent of the energy in glucose is still unused.

The Krebs cycle is a series of reactions that converts pyruvic acid into CO2

Each turn of the Krebs cycle creates:

3 CO2 4 NADH

1 ATP 1 FADH

3. The Electron Transport Chain

Electron carriers drop off their electrons at the ETC.

2 NADH from glycolysis

4 NADH from Kreb’s Cycle

1 FADH2 from Kreb’s Cycle

The ETC passes the electrons along a series of proteins until they reach an oxygen molecule at the end of the chain.

* Oxygen and Hydrogen combine to produce H20

The energy in the electrons is used to convert ADP into ATP.

When all is said and done, the cell will have…

• 34 molecules of ATP from the Krebs Cycle and the electron transport chain.

• 2 molecules of ATP from glycolysis.

This gives a total of 36 ATP molecules for each glucose molecule.

Where does cellular respiration take place in our cells? mitochondria

**An analogy can be drawn between the process of cellular respiration in our cells and a car. The mitochondria are the engines of our cells where sugar is burned for fuel and the exhaust is CO2 and H2O. Note that in a car that burned fuel perfectly, the only exhaust should theoretically be CO2 and H2O also.

Cellular Respiration Song:

•

What if Oxygen is NOT PRESENT?

If oxygen isn’t present, then cells will do anaerobic cellular respiration.

This process will convert the pyruvic acids into something else to be used.

2 steps in anaerobic cellular respiration:

1. Glycolysis

2. Fermentation (this is different in animals and plants)

1. Glycolysis:

1 glucose molecule is converted into 2 pyruvic acid molecules.

2. Fermentation:

-Because oxygen is not present, the pyruvic acid molecules will go through a chemical reaction to convert pyruvic acid into either alcohol (plants) or lactic acid (animals).

-These molecules can convert back to pyruvic acid when enough oxygen is available and then go through aerobic respiration.

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