Bioenergetics

Organisms must be able to transform energy from one form to another.◦ Autotrophs —can transform energy from

sunlight into chemical energy (can make food). Then use the food energy for life processes.

◦ Heterotrophs —obtain energy for life processes by eating food.

Obtaining Energy

Photosynthesis is the process that converts light energy into chemical energy.

Uses a biochemical pathway. Overall reaction is:

Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

The Stages of Photosynthesis There are two stages to

the process◦ Light Reactions —light

energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH

◦ Dark Reactions (Calvin Cycle)—organic compounds are formed using CO2 and the chemical energy stored in ATP and NADPH

http://bioweb.uwlax.edu/bio203/s2009/schroeer_paul/images/484px-Simple_photosynthesis_overview_svg.png

Require light and chlorophyll. Take place in thylakoid membranes of the

chloroplast. Products of the light reactions are NADPH and

ATP. These are sent to the Calvin Cycle (dark

reactions) The oxygen released by photosynthesis comes

from the splitting of water. A hydrogen ion gradient through ATP

synthase drives the synthesis of ATP. The electron transport chain drives the

synthesis of NADPH.

Light Reactions

Does not require light. Happens in the stroma of the chloroplasts

and requires CO2. Uses the energy stored in the ATP and

NADPH from the light reactions to produce organic compounds in the form of sugars.

Most common pathway for carbon fixation (changing CO2 into carbohydrates)

The Calvin Cycle

Plants that use photosynthesis to fix carbon are called C3 plants.

Alternate pathways include C4 plants and CAM plants.◦ C4 plants: corn, sugar cane and crab grass.

This pathway uses an enzyme to fix CO2 into a four carbon sugar and conserves water.

◦ CAM plants: cactuses, pineapples, and jade plants Open stomata at night and close during day to

prevent water loss.

Alternate Pathways

Cellular Respiration

Cellular Respiration —the process by which cells get energy from carbohydrates; oxygen combines with glucose to form water and carbon dioxide

C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)

Aerobic Respiration —oxygen is present: most efficient

Anaerobic Respiration —no oxygen is present: less efficient.

Both types start with glycolysis.

Aerobic and Anaerobic Respiration

Glycolysis One glucose (6C) is broken into two

molecules of pyruvic acid (3C). Occurs in cytosol. No oxygen is needed. 2% efficient.◦ If oxygen is available, the pyruvic acid will move into

the mitochondria and aerobic respiration will begin.◦ 4 ATP molecules are produced. Two are used to

break apart the next glucose molecule and keep glycolysis going.

◦ This leaves a net yield of 2 ATP molecules for use by the cell.

◦ Two NAD+ are converted into 2 NADH and 2H+. These go to Electron Transport.

Aerobic Respiration In most cells, the pyruvic acid produced in

glycolysis enters the pathway of aerobic respiration.

More efficient than glycolysis. Oxygen is required. There are two major stages: The Krebs

Cycle and the Electron Transport Chain

The Krebs Cycle

The Krebs Cycle --occurs in the mitochondrial matrix. Two turns of the Krebs Cycle produce:◦ 2 ATP molecules◦ 4 CO2 molecules◦ 6 NADH molecule◦ 2 FADH2 molecules

http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

Electron Transport Chain The Electron Transport Chain, linked with

chemiosmosis makes up the second stage of aerobic respiration.◦ Electrons are transferred from one molecule to

another by several electron carrying molecules located in the membrane of the mitochondria.

◦ All steps occur in the cristae (inner membrane)◦ This step generates the most amount of ATP: 32-

34 molecules.

Efficiency of Cellular Respiration

Through Aerobic Cellular Respiration, a maximum of 38 ATP molecules can be produced from one glucose molecule.◦ 2 from Glycolysis◦ 2 from Krebs cycle◦ 32-34 from the Electron Transport Chain

Anaerobic Respiration If no oxygen is present, the Krebs Cycle

and Electron Transport Chain are not utilized.

Fermentation is used instead.

Fermentation Fermentation is the chemical pathway

that recycles NAD+ in the absence of oxygen. It keeps glycolysis going. No additional ATP is made. Therefore, you still have the 2% efficiency rate for energy release.

Two types of fermentation:◦ Lactic Acid Fermentation◦ Alcoholic Fermentation

  PHOTOSYNTHESIS RESPIRATION

FUNCTION   Production of Glucose   Oxidation of Glucose

LOCATION   chloroplasts   mitochondria

REACTANTS   6CO2 + 6H2O   C6H12O6 + 6O2

PRODUCTS   C6H12O6 + 6O2   6CO2 + 6H2O

EQUATION   light 6CO2 + 6H2O C6H12O6 + 6O2

 C6H12O6 +6O2 6CO2 + 6H2O +ATP

COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION

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