Download Photosynthesis and Cellular Respiration

Photosynthesis
Energy Transformations – TWO
TYPES
ATP (Adenosine Triphosphate): is the
energy molecule used in all living things, so
supplies must be constantly replenished.
 Energy must be added to make ATP
 Phosphorylation is the addition of a
phosphate molecule to ATP
 ADP + P + energy --- ATP
 Dephosphorylation the removal of a
phosphate molecule from ATP gives off
energy and is called
 ATP --- ADP + P + energy
Electron Transport System (ETS)
 It is the means by which
energy production occurs
within cells.
 Consists of a series of
progressively stronger
electron acceptors.
 Each time an electron is
transported, energy is
either released or
absorbed.
 This is how most of the
ATP in plants and animals
is formed
Redox Reactions – Some simple
Chemistry…
 Oxidation – loss of
electrons, producing a
substance with a more
positive charge.
 Reduction – gain of
electrons, producing a
substance with a more
negative ( or less
positive) charge.
Photosynthesis
 Photosynthesis is the most important chemical
process on earth.
 Photosynthesis harnesses sunlight energy and
converts it into a form of energy (glucose and
starch) that is useable by all living organisms.
 The process also produces oxygen, which is
essential for higher life forms.
 CO2(g) + H2O(l) + light C6H12O6(s) + O2(g) + H2O(l)
Sunlight energy is converted into chemical potential energy (glucose)
Pigments responsible for
Photosynthesis
A pigment is a compound that absorbs certain wavelengths of visible light,
while reflecting others that give the pigment its specific color. Thus,
chlorophyll, does not absorb green.
Chlorophylls a and b and the carotenoids are photosynthetic pigments that
absorb light
 A chlorophyll solution will absorb red and blue
light while it transmits or reflects green light.
Therefore, the light that reaches your eyes is
green.
 The carotenoids absorb blue and green light, so
they are yellow, orange, and red in color.
 Each photosynthetic pigment absorbs light of
different colors. Having a variety of pigments
enables a plant to use a greater percentage of
the Sun’s light.
Site of Photosynthesis
Photosynthesis
occurs within the
chloroplasts of
plant cells, within
the thylakoid
membrane and
the stroma.
Stages of Photosynthesis
LIGHT REACTIONS– Thylakoid Membrane
STAGE ONE:
Solar energy is captured and
transferred to the electrons, and water is split.
 Photolysis – the splitting of water with light.
 2H2O(l) + light --- 4H+(aq) + 4 e- + O2(g)
Photosystems
 Within the chloroplasts, chlorophyll is
found in clusters within the thylakoid
membranes.
 These clusters are called
photosystems.
 When light hits the photosystem,
energy is absorbed and electrons
are promoted to an electron acceptor
at a higher energy level.
 As the electrons fall down the
electron transport chain, energy is
released and can be used to make
ATP.
STAGE TWO: Electron transfer and the
production of ATP.
 Light energy is captured by the pigments within
the photosystems and is used to form more
stable energy rich molecules, and to make ATP
from ATP and phosphate.
 This occurs by cyclic photophosphorylation
and chemiosmosis.
CHEMIOSMOSIS
 As H+ ions are pulled across the
thylakoid membrane by the ETC, an
concentration gradient of H+ ions is
created.
 H+ ions travel down the concentration
gradient, across the membrane, through
an ATP synthase complex.
 As they do this, ATP is produced.
DARK REACTIONS – Stroma
STAGE THREE:
Calvin Benson cycle and
carbon fixation.
 The Calvin Benson cycle uses ATP, high energy
electrons, NADPH and CO2 to produce glucose
in the stroma.
 Sunlight energy is not required.
 RuBP, a 5 carbon sugar acts as a CO2 acceptor
 The resulting 6 carbon sugar is split into two 3
carbon PGA molecules.
 Using H from NADPH, PGA is converted to PGAL
 PGAL can be used to produce glucose, starch,
sucrose, glycerol or cellulose.
 PGA can also be converted into amino acids or
fatty acids.
Calvin-Benson Cycle
The Calvin Benson cycle must turn THREE times to
produce each PGA molecule, and SIX times to
produce one glucose molecule.
The plant cell can manufacture all necessary organic
compounds from the products of photosynthesis.
6CO2(g) + 12H2O(l)  C6H12O6(s) + 6O2(g) + 6H2O(g)