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Energy in a Cell
Cells need energy to do a variety of work:Making new molecules.Building membranes and organelles.
Moving molecules in and out of the cell.
Movement.
Food is broken down to a form the cell can use.
Extra energy is stored in an ATP molecule, a nucleotide.
ATP – adenosine triphosphate is a molecule made up of an adenine, ribose, and 3 phosphate groups.
Adenine
Ribose
Energy is stored in the bond between the second and third phosphate group.
When the bond is broken, energy is released and ADP is formed.
Adenine
Ribose
• Within a cell, formation of ATP from ADP and phosphate occurs over and over, storing energy each time.
• As the cell uses energy, ATP breaks down repeatedly to release energy and form ADP and phosphate.
Cells make energy in two ways:Photosynthesis – takes place in the chloroplasts.
Respiration – takes place in the mitochondria.
Autotrophs make their own food by trapping light energy and converting it to chemical energy (carbohydrates).
Using light from the sun, plants combine water and carbon dioxide to make sugar . General Equation:
6CO2 + 6H2O + energy C6H12O6 + 6O2
Reactants Products
2 ReactionsLight ReactionsCalvin Cycle
Light Reactions – Light energy is converted to chemical energy to split hydrogen from water.Takes place in the grana of the chloroplasts (the coin-like stacks of sacs).
Byproducts are oxygen, NADPH, and ATP.
Calvin Cycle – ATP and NADPH from the light reactions are used along with CO2 to form a simple sugar (glucose).Takes place in the stroma of the chloroplasts (the liquid filling).
Byproducts are C6H12O6 (glucose), ADP, and NADP+ (which return to the light reactions).
Sunlight
NADP+
ADP NADPH
CO2
H2O
O2
CHLOROPLAST
ATP
Some autotrophs can convert inorganic substances to energy.
Most are adapted to live in conditions where there is no oxygen.Marshes.Lake sediments.Digestive tracts of mammals.Deep in the ocean.
The process of breaking down food molecules to release energy.
Occurs in the mitochondria. Two types:
Aerobic – requires oxygen.Anaerobic – requires an absence of oxygen.
Two types of anaerobic respiration:Fermentation – occurs when
bacteria break down plants (vegetables and fruit) and release alcohol or vinegar.
Lactic Acid Fermentation – occurs in muscles – a buildup of lactic acid causes soreness.
StepsGlycolysisKrebs Cycle (or Citric Acid Cycle)
Electron Transport Chain
Glycolysis – glucose is split to form pyruvate.Takes place in the cytoplasm of the cell.
ATP is a byproduct.
Krebs Cycle – pyruvate is used to build citric acid (a carbon compound), which is broken down to release ATP.Takes place in the cristae (the
folded membrane in the mitochondrion).
CO2 is released, and NADH carries hydrogen ions to the electron transport chain.
Electron Transport Chain – hydrogen ions are stripped of their energy, and large amounts of ATP are formed.Takes place in the inner
membrane of the mitochondrion.The used ions are combined with
oxygen to form H2O.
MITOCHONDRION
CO2
H2O
O2 ATP
NADH
HeatElectron
TransportSystem
ATP
NAD+
Pyruvate
GlucoseATP
Sunlight
Photo-System
I
Photo-system
II
NADP+
ADPNADPHATP
CalvinCO2
H2O
O2
ATP
ATP
NAD+ NADH
ElectronTransportSystem
Cycle
Krebs
Heat
CHLOROPLAST MITOCHONDRIONATP
Glycolysis
Glucose Pyruvate
Cycle
Sunlight
Photo-System
I
Photo-system
II
NADP+
ADPNADPHATP
CycleCalvin CO2
H2O
O2
ATP
ATP
NAD+ NADH
ElectronTransportSystem
Cycle
Krebs
Heat
CHLOROPLAST MITOCHONDRION
Glucose
ATP
Pyruvate
Glycolysis
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