Photosynthesis
and
Chemosynthesis
Energy in a cell
 Cells need energy to:
 Grow
 Reproduce
 Live
 Energy for these reactions can be stored
in glucose
 To use energy, though, it needs to be in
molecules called ATP
ATP –
Adenosine
Triphosphate
 Energy – carrier molecule
 3 phosphate groups
 Energy is released when 3rd phosphate
group is cut off
 ATP  ADP + P + Energy
 Released energy is used to power cell
activity
Energy from the
Sun
 Some organisms gain energy
from consuming other
organisms – called heterotrophs
 Other organisms can make their own food
– called autotrophs
 Plants, algae, and some bacteria capture
about 1% of the sun’s energy
 convert it to chemical energy through the
process of photosynthesis
Photosynthesis
Equation
LIGHT
 6CO2 + 6H2O
Occurs in the
chloroplast of plant cells
C6H12O6 + 6O2
Chloroplast Structure
•Little “coin-like” structures
called Thylakoids
•Membrane surrounding
thylakoids contains
chlorophyll
•Stacks of Thylakoids
called Grana
•Space surrounding Grana
is called the Stroma
Photosynthesis Video
Stages of Photosynthesis
1. Light
Reactions
2. Light-Independent
Reactions (Calvin Cycle)
Stages of Photosynthesis
1. The Light Reactions
 Light energy is absorbed and converted
to chemical energy in the bonds of ATP.
1. Light strikes electrons in the chlorophyll
2. Energy from excited electrons used to make
ATP molecules
3. Energy now available to do work.
Light Reactions…
 Water is split into hydrogen ions, oxygen,
and electrons
 Electrons replace those lost by the
chlorophyll molecule
 Oxygen is given off as waste
 Hydrogen ions are used to create NADPH
(another energy carrier molecule) for use in
later steps of photosynthesis
Calvin Cycle
Light – Independent reactions
 The ‘synthesis’ part of
photosynthesis
 Takes place in the stroma
of the chloroplast
 Uses ATP and NADPH from
light reactions
 Enzymes combine CO2 with
hydrogen (from NADPH) and
energy from ATP
Light
Energy
ROY G. BIV
 Light energy has different wavelengths – we
see them as different colors
 Pigment – a protein that absorbs light
 Chlorophyll – a pigment in the chloroplast
 Absorbs red and blue light
 Reflects green and yellow light – we see that reflected light.
 Carotenoids – pigments that make plants yellow and
red in the fall
Chemosynthesis
 Similar to
Photosynthesis – but no
light!
 Inorganic compounds
are used for energy to
make sugars
 Ex: bacteria can do this
in the hydrothermal
vents at the bottom of
the ocean
Chemosynthesis Video