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 + P i  ATP Bond of the 3 rd phosphate group is tenuous  easily broken Renewable Unlimited supply of energy in the presence of P i

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 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

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

2H 2 O  4H + + 4e- + O 2 (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 CO 2 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 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O Opposite of photosynthesis

Types of respiration Aerobic  uses O 2 Anaerobic  no O 2 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 respiration  oxygen 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 PhotosynthesisCellular Respiration Food is producedFood is broken down Energy from the sun is stored in glucose Energy of glucose is released CO 2 taken in, O 2 given off O 2 taken in, CO 2 given off Occurs only with chlorophyll Occurs in all living cells