1. The Working Cell: Energy from Food
Chapter 7
Sections 1-4

2. Sunlight Powers Life

3. Food Stores Chemical Energy
Energy is the ability to do work (or applying a force across a distance)
Two Basic Types of Energy:
Kinetic Energy - the energy of motion
Potential Energy - stored energy due to position or arrangement

4. Energy Transfers
When you slide down a slide into a swimming pool, you convert potential energy into kinetic energy.
As your body collides with air and water molecules, you transfer energy to the molecules in random directions. That random molecular motion is thermal energy or HEAT.

5. The Energy to Move Again
The thermal energy created CANNOT be retrieved and put back to work inside the body.
So to move again, you must use a fresh supply of energy.
That energy is the chemical energy stored in FOOD (organic molecules).

6. Making Chemical Energy Available for Work
Cells break complex organic molecules into smaller molecules with less chemical energy
This process is called cellular respiration
Glucose + Oxygen → Carbon Dioxide + Water + Energy
60%
Thermal
40%
Chemical

7. 1000 calories = 1 kcal or Calorie (a nutritional calorie)
Measuring Energy
Energy is measured in units called calories
A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1◦C
1000 calories = 1 kcal or Calorie (a nutritional calorie)
However, food is not used directly by cells to do work, it must be converted into another usable form called ATP.

8. What is ATP? ATP is called the "currency" of the cell
ATP is a small packet of Energy that can be used a little at a time, like coins
ATP is constantly reused and recycled
You can’t buy things without $$, cells can’t Work without Energy from ATP

9. Copyright Pearson Prentice Hall
ATP Structure
ATP consists of:
adenine
ribose (a 5-carbon sugar)
3 phosphate groups (TP = tri phosphate)
Adenine
Ribose
3 Phosphate groups
ATP
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10. Adenosine Triphosphate (ATP) Adenosine Diphosphate (ADP) + Phosphate
Chemical Energy and ATP
Storing Energy
ADP has two phosphate groups instead of three.
A cell can store small amounts of energy by adding a phosphate group to ADP.
ATP
ADP
Energy +
Energy
Adenosine Triphosphate (ATP)
Adenosine Diphosphate (ADP) + Phosphate
Partially charged battery
Fully charged battery
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11. Chemical Energy and ATP
Releasing Energy
Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates.
2 Phosphate groups P
ADP
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12. The ATP Cycle ATP → ADP + phosphate + energy for Work
ADP + Energy (from food) + phosphate → ATP

13. Why does the process of cellular respiration release energy?
In an atom the positive nucleus attracts negative electrons
When electron “fall” towards the nucleus, potential energy is released
OXYGEN attracts electrons very strongly compared to carbon and hydrogen
During respiration, the carbon-hydrogen bonds in sugar are rearranged to bond with oxygen instead (CO2 + H2O)

14. Electron Transport Chains
Instead of releasing all the energy stored in food at once (like burning), cellular respiration releases the energy in controlled “steps”
Glucose gets broken down in several steps, transferring electrons to molecules called electron carriers
The electron carriers accept high-energy electrons from glucose and pass them along a chain of electron carriers (ETC) releasing ATP
Oxygen comes in at the end to accept 2 low energy electrons, bond with hydrogen, and form water

15. ETC Animation