Cell Energetics

Photosynthesis and Cellular Respiration (Chapter 9)

Cell energy

Necessary for life must be able to produce, store, and use energy

ATP adenosine triphosphate

ADP + Pi ATP Bond of the 3rd phosphate group is

tenuous easily broken Renewable Unlimited supply of energy in the

presence of Pi

When bond breaks, energy is released

Cells use energy to:

Obtain and transform nutrients Transport materials Eliminate wastes All this maintains homeostasis

Photosynthesis

Process by which light energy is converted into chemical energy

Chemical equation

6CO2 + 6H2O C6H12O6 + 6O2

Occurs in chloroplasts

Chlorophyll a and b absorb most wavelengths of light (ROYGBIV) All except green

Visible Light Spectrum

Light-dependent reactions daytime only Also called photolysis Provide energy for the next set of

reactions

2H2O 4H+ + 4e- + O2 (released as a gas)

ATP and other energy molecules are produced and move to the next reactions

Light-independent reactions both day and night Also called the Calvin Cycle Energy from the light reactions is used

to transform CO2 and other inorganic compounds into glucose

Glucose is an energy storage molecule Excess glucose gets stored as starch

Photosynthesis Overview

Cellular Respiration

Process by which cells release energy (usually in the

mitochondria)

Chemical equation

6O2 + C6H12O6 6CO2 + 6H2O Opposite of photosynthesis

Types of respiration

Aerobic uses O2

Anaerobic no O2

Both start the same glycolysis

Glycolysis step 1

Glucose is broken down split in half one 6-C molecule two 3-C molecules Requires the addition of 2 ATP to start Generates 4 ATP molecules

Aerobic respirationoxygen is present Step 2 products from glycolysis enter

the Krebs Cycle to generate 2 ATP Also called the citric acid cycle

Step 3 e- transport chain produces 32 ATP

Net yield 36 ATP

Anaerobic respiration no oxygen present Also called fermentation Products from glycolysis converted to

different molecules

Human muscle cells lactic acid Yeast cells ethanol Net yield 6 ATP Less efficient

Comparing photosynthesis and cellular respiration

Photosynthesis Cellular Respiration

Food is produced Food is broken down

Energy from the sun is stored in glucose

Energy of glucose is released

CO2 taken in, O2 given off

O2 taken in, CO2 given off

Occurs only with chlorophyll Occurs in all living cells