Cells and Energy
Cellular Respiration
Chapter 2 Lesson 4 Part 1

Cells and Energy
• How does a cell obtain energy?
• How do some cells make food molecules?

Cells and Energy
Cellular Respiration

Cellular Respiration is a series of chemical reactions that convert the energy in food molecules into a usable form of energy called ATP the breaking down of an energy source by cells to obtain usable energy

Sugar (glucose) is the most common energy source in cellular respiration.
(some can use fats, oils, proteins, etc.)

Cellular respiration requires many enzymes.
Enzymes are catalysts
(substances which help to change other substances without being permanently changed themselves).

2 types of cellular respiration

 aerobic – requiring oxygen anaerobic – not requiring oxygen
(some bacteria and fungi)
Most cells carry on aerobic respiration.

Aerobic Cellular Respiration
First few steps for breaking down glucose takes place in the cytoplasm and it is called glycolysis.
Most takes place in the mitochondrion (called reactions in the mitochondria).

Cellular Respiration
Essentially cellular respiration takes place in three parts:
1. Glycolysis
2. Krebs Cycle (or The Citric Acid
Cycle)
3. Electron Transport

Glycolysis the first step in cellular respiration, is a process by which glucose is broken down into smaller molecules.
It occurs in the cytoplasm.
Glycolysis literally means "splitting sugars."

Cellular Respiration
Glycolysis produces some
ATP molecules and uses energy from other ATP molecules.

Aerobic Cellular Respiration
• The second step of cellular respiration requires oxygen and occurs in the mitochondria of eukaryotic cells.
• The smaller molecules made from glucose during glycolysis are broken down.
• Large amounts of ATP—usable energy— are produced. Cells use ATP to power all cellular processes.

Reactions in the Mitochondria

Aerobic Cellular Respiration glucose + oxygen ---> ATP
+ carbon dioxide + water

Anaerobic Cellular Respiration
Some cells exist in environments that do not have oxygen available.
Many bacteria in the lower layers of swamps, lakes, or the ocean do not have oxygen.
Other cells which operate best with a supply of oxygen can occasionally operate without oxygen.

Types of anaerobic cellular respiration
(usually named by the products that are produced from the glucose)


Alcoholic fermentation
Lactic acid fermentation

Fermentation
 Fermentation is a reaction that eukaryotic and prokaryotic cells use to obtain energy from food when oxygen levels are low.
 Fermentation occurs in a cell’s cytoplasm, not in mitochondria.

Alcoholic fermentation anaerobic cellular respiration that produces alcohol and carbon dioxide from glucose example: yeast in bread dough

Lactic acid fermentation a type of anaerobic cellular respiration that produces lactic acid from glucose examples: yogurt, cottage cheese,buttermilk,sauerkraut, human muscle cells

Fermentation