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Cell Energy
Chapter 3
 Cells need energy in order to work properly
 Plant cells get energy through
photosynthesis, which happens in the
chloroplast
 Animal cells get energy through cellular
respiration, which happens in the
mitochondria.
How are photosynthesis and cellular
respiration opposite or
complementary processes?
 This means that one cannot happen
without the other. The products of
photosynthesis are the reactants of
respiration and the products of respiration
are the reactants of photosynthesis.
PHOTOSYNTHESIS
Photosynthesis is the transformation of light
energy from the sun into the chemical energy of
glucose.
Reactants
Products
6 CO2 + 6 H2O + light  C6H12O6 + 6 O2
carbon dioxide + water + light energy  glucose + oxygen
CELLULAR RESPIRATION
Cellular respiration is the process of breaking
down food (such as carbohydrates and other
molecules) in order to release energy present in
food.
The energy molecule released in cellular
respiration is ATP (adenosine triphosphate)
Reactants
Products
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
Glucose + oxygen  carbon dioxide + water + ATP
Types of cellular respiration
1. Aerobic Respiration
2. Anaerobic Respiration.
Aerobic respiration
 Requires oxygen
 Glucose is completely broken down into CO2 and
H2O in the presence of O2 to release energy from
food
 It allows for the maximum amount of energy to
be released from the glucose
 It occurs in the cytoplasm and the mitochondria
of the cell in both plants and animals
Anaerobic respiration
 Does NOT require oxygen
 Glucose is broken down without oxygen to
release energy
 It generates little energy for the cell.
 It occurs in smaller organisms and in larger
organisms when oxygen is not present.
 It occurs in the cytoplasm of both plants and
animals.
Lactic Acid Fermentation
 When lactic acid builds up in muscles and a
person feels a stitch. This happens when
glucose is broken down and makes lactic acid,
instead of energy, because there is not enough
oxygen available. Lactic acid builds up in
muscles causing a burning/painful sensation.
The muscle will return to normal after rest.
C6H12O6
2 CH3CHOHCOOH