PHOTOSYNTHESIS
&
CELLULAR RESPIRATION
Photosynthesis for Beginners
• THE LIGHT REACTION
(light dependent because it can only occur in the light)
– Plants take in water through the roots and carbon
dioxide through the stomata underneath the leaves.
These travel to the stacks of thylakoids inside the
chloroplast where chlorophyll molecules are found
– Sunlight provides energy to split the water
molecules into hydrogen ions and oxygen
molecules
– The oxygen molecules are then released through
the stomata
– Hydrogen ions are picked up by carrier molecules
called NADP to make a molecule of NADPH+
Photosynthesis for Beginners
– The energy of the sun in also used to excite the
electrons of the chlorophyll molecule, boosting them
to higher energy levels. When the electrons fall
back to their original lower levels, the energy
released as they fall back is used to attach a
phosphate molecule to adenosine diphosphate to
make adenosine triphosphate (ADP ATP)
– NADPH+ and ADP diffuse out of the thylakoid to the
surrounding region called “Stroma”
Photosynthesis for Beginners
• THE DARK REACTION
(light independent reaction because it can occur with OR
without light)
– Carbon dioxide that is taken into the stroma through
the stomata will be split by enzymes into carbon
and oxygen molecules. Excess oxygen atoms are
released through the stomata
– NADPH+ drops off the hydrogen atoms and
enzymes chemically bond one carbon, two
hydrogens and one oxygen atom. This process
occurs six times to create a molecule of glucose:
C6H12O6
Photosynthesis for Beginners
• THE BALANCED CHEMICAL EQUATION
FOR PHOTOSYNTHESIS IS:
6CO2 + 6H2O  C6H12O6 + 6O2
(using light, in plants with chlorophyll)
Cellular Respiration for Beginners
• GLYCOLYSIS
(occurs in the cytoplasm)
– Glucose molecules diffuse through the plasma
membrane into the cytoplasm
– Enzymes use two ATP molecules to split glucose
into two smaller molecules with three carbons, six
hydrogens, and three oxygens.
– Additional enzymes convert these molecules into
pyruvic acid. Four ATPs are produced (Energy in
the bonds is released when atoms are separated).
– If sufficient oxygen is present in the cell, pyruvic
acid will diffuse into the mitochondrion and continue
aerobic respiration (aerobic means with oxygen)
Cellular Respiration for Beginners
– If oxygen is not present in sufficient quantities, the
pyruvic acid remains in the cytoplasm and begins
anaerobic respiration. (anaerobic means without
oxygen)
• In animal cells, pyruvic acid is broken down by enzymes into
lactic acid, releasing two ATP molecules. This process is called
lactic acid fermentation. Lactic acid builds up creating “oxygen
debt” and leaving muscles sore. Taking in O2 breaks down
lactic acid.
• In yeast cells, pyruvic acid is broken down by enzymes into
alcohol, releasing two ATP molecules. This process is called
alcohol fermentation. Alcohol builds up until it becomes toxic
and kills the yeast.
Cellular Respiration for Beginners
• KREBS CYCLE
and
ELECTRON TRANSPORT CHAIN
(Aerobic Respiration)
– Pyruvic acid diffuses into the mitochondrion and is broken
down by enzymes.
– Electrons from these atoms are shuttled through membranes
inside the mitochondrion building up a supply of H+ ions. As
H+ ions are passed through the membranes, the energy
released is used to attach phosphates to adenosine
diphosphate to make 36 molecules of adenosine
triphosphate (ATP) for each original molecule of glucose)
– Oxygen is chemically bonded to the hydrogen ions to make
water which is then released as waste during exhaling
• THE BALANCED CHEMICAL EQUATION
FOR CELLULAR RESPIRATION IS:
C6H12O6 + 6O2  6CO2 + 6H2O + ENERGY
36ATP
glucose  pyruvic acid
2 ATP
2 ATP
32 ATP