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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
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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