Cell Energetics  Honors Photosynthesis and Cellular Respiration (Chapters 8 & 9)

Cell energy Necessary for life  must be able to produce, store, and use energy ATP  chemical energy

ATP  adenosine triphosphate ADP + P i  ATP Bond of 3 rd phosphate is tenuous Renewable Unlimited supply of energy in presence of P i

When bond breaks, energy is released

Cells use energy to: Obtain and transform nutrients Transport materials Eliminate wastes Maintenance of homeostasis

Photosynthesis Process by which light energy is converted into chemical energy

Factors involved in photosynthesis Light  energy form consisting of a combination of different wavelengths ROYGBIV  visible (white) light

Factors cont. Water  provides H + and O 2 (by- product) Atmospheric O 2 comes from here CO 2  amount directly affects the rate of photosynthesis

Factors cont. Chlorophyll  pigments that absorb certain wavelengths of light A and b  absorb blue-violet and red light Green is never absorbed  reflected back

Light dependent reactions  daytime only Also called photolysis Provides energy to run the next set of reactions

H 2 O is split into H and O 2H 2 O  4H + + 4e- + O 2 (released as a gas) H + transferred to hydrogen carriers 2NADP + + 2H +  2NADPH (energy storage) 4e- used to make ATP

Light-independent reactions  day and night Also called the Calvin Cycle or the carbon fixation cycle CO 2 is split C is added to RuBP (5-C sugar) to form two 3-C molecules CO 2 + RuBP  2PGA

Light-independent cont. ATP and NADPH convert PGA to another 3-C molecule PGA + ATP + NADPH  PGAL ADP and NADP + return to light dep. Reactions 2 molecules of PGAL are used to make glucose

Light-independent cont. Some PGAL molecules and ATP reform RuBP  back to beginning Any excess glucose is stored as starch

Calvin Cycle

Photosynthesis Overview

Chemical equation for photosynthesis 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

Stomates allow for gas exchange

Cellular respiration Process by which cells release energy (mitochondria)

Chemical equation 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O Opposite of photosynthesis

2 types of respiration Aerobic  uses O 2 Anaerobic  no O 2 Both start with the same reaction  glycolysis

Glycolysis  Step 1 Glucose is split

Involves oxidation-reduction reactions (redox) Oxidation  e- are lost (or H atoms) Reduction  e- are gained (or H atoms) O 2 is the final e- acceptor  H 2 O Energy is released during each transfer

First part: C 6 H 12 O 6 + 2ATP  2PGAL + 2ADP + P i Energy is added to break C-H bonds

Second part: 2PGAL  2 pyruvic acid + 4ATP 2NADH and 2H + are also formed Pyruvic acid moves into mitochondrion

Net energy gain 4ATP  end product - 2ATP  put into reaction 2ATP  net gain Not very efficient

Aerobic respiration

Step 2  intermediate reaction Pyruvic acid is oxidized Pyruvic acid + coenzyme A  acetyl- CoA CO 2 is released, NADH and H + are formed

Step 3  the citric acid cycle (the Krebs cycle) Each molecule of acetyl-CoA takes a turn 1 acetyl-CoA = 1 ATP produced 1 glucose = 2 acetyl-CoA 2 ATP are released and various energy carriers

Krebs Cycle

Step 4  the electron transport chain Energy carriers move down the chain  releases energy gradually (32 ATP)

Net energy yield 2ATP  glycolysis + 2ATP  Krebs cycle +32ATP  e- transport chain 36ATP  grand total

Cell Respiration Overview

Anaerobic respiration Fermentation

Pyruvic acid is converted to: Lactic acid  human muscle cells Ethanol (ethyl alcohol)  yeast Both produces still contain most of the chemical energy of glucose Release of 4 ATP

Anaerobic overview

Net energy yield 2ATP  glycolysis + 0ATP  anaerobic reactions 2ATP  grand total Much less efficient than aerobic

Comparing photosynthesis to respiration PhotosynthesisCellular Respiration Food is producedFood is broken down Energy from the sun is stored in glucose Energy of glucose is released as ATP 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