Transcript 6 CO 2 + 6 H 2 O and light energy makes sugars (CH 2 O) + O 2

Photosynthesis
• Takes place only in autotrophs
(make their own food)
• (e.g. plants, Archaea, also some
Protists and Bacteria)
• Basically, light energy is used to
make CO2 and H2O into sugars
(chemical energy). O2 and H2O
are waste products.
• Happens in the chloroplast of the
plant cell
Others…
• Chemosynthesis…getting energy
from chemicals
• Bacteria by hydrothermal vents at
bottom of ocean take chemicals
out of water, break them down
and get energy from them.
• Some called heterotrophs have to
eat other things for food.
• (e.g. animals, fungi, also some
Protists and Bacteria)
Chemosynthesis
2 steps
• Light Dependent Reactions
– Also just called Light Reactions
– Must have light to take place
• Light Independent Reactions
– Also called Dark Reactions or Calvin
Cycle
– Can happen in light or dark
Light Dependent Reactions
• Happens in the thylakoid (inside
membranes) of the chloroplast
• Chlorophyll (green chemical) traps
sunlight
• Energy is used to split water into
O2 (waste product) and H2
• Energy from H2 is stored as ATP
and NADPH
ATP & NADPH
• ATP is the molecule all cells use as
energy
• It has an amino acid (adenine) a sugar
(ribose) and 3 phosphates.
• Energy stored in the phosphates’
bonds
• Break bond…use energy…become
ADP + P
• ADP + P + energy = ATP
• NADP+ carries 2 electrons and a
hydrogen atom
ATP and NADPH
• The energy from light is passed
from protein to protein in the
thylakoid membrane as part of
an electron transport chain.
• As H+ ions and electrons are
moved into/out of the thylakoid
membrane, energy is stored in
ATP and NADPH used in the
light independent reactions.
Electron Transport Chain
Summary of
Photosynthesis
Light Independent Reactions
• CO2 is made into 3-carbon sugars
in a process called carbon fixation
• Uses the ATP and NADPH from the
light reactions
• Water is a waste product, but is
reused by the cell and not given off
• These sugars are the end product of
photosynthesis. They are used by
the plant as energy and stored for
later use.
• Happens in the stroma (open areas) of
the chloroplast
Summary of
Photosynthesis
Summary of
Photosynthesis
• In the chloroplast…
• 6 CO2 + 6 H2O and light energy
makes sugars (CH2O) + O2 (waste)
• (Actually it takes 12 H2O, but there’re
6 H2O left over, so they cancel out)
• CH2O is a generic formula for a
carbohydrate (sugars). You could
also write C6H12O6
• ATP and NADPH are energy carriers
from light dependent reactions to
light independent reactions
Technically…
• Photosynthesis does not make
glucose (C6H12O6)
• It makes a 3-carbon sugar called
G3P which is used to make
other organic compounds, like
cellulose (many sugars linked
together) used in the cell wall.
• The sugars can be used for energy by
the plant (in the mitochondria) or
to build structures
So why…
• Have you been taught that the
end product is glucose?
• Scientists (and teachers) often say
that it makes glucose, because
it is one of the things
photosynthesis can make, and
it helps show the relationship
between photosynthesis and
cell respiration (next unit).
Factors Affecting Photosynthesis
• Temperature:
– between 0oC and 35oC
is best.
• Light:
– “perfect” amount
– More is good, up to a certain point
• Water
– “perfect amount”
– More is good up to a certain point