Transcript Photosynthesis - Salisbury Composite High School

Photosynthesis
Energy Transformations
ATP
 is the energy molecule used in all living
things, so supplies must be constantly
replenished.
 energy must be added to make ATP, thus ATP
formation is an endergonic reaction.
 ADP + P + energy --- ATP
 the addition of a phosphate molecule to ATP is
called phosphorylation
 ATP --- ADP + P + energy
 the removal of a phosphate molecule from
ATP gives off energy and is called
dephosphorylation
Electron Transport System (ETS)
 is the means by which energy production
occurs within cells. It is 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
 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)
Site of Photosynthesis
Photosynthesis
occurs within the
chloroplasts of
plant cells, within
the thylakoid
membrane and
the stroma.
Chloroplasts - contain the photosensitive
pigment
chlorophyll, which reflects green light.
Caroteniods – other accessory pigments that
absorb blue and violet light, but reflect yellow.
Stroma – interior space of the Chloroplast, The
dark reaction occurs here.
Thylakoid disk – photosynthetic membrane,
where the light reactionoccurs.
Grana – stacks of thylakoid disks.
Lamellae – unstacked thylakiods between
grana.
Stages of Photosynthesis
Light Reactions – Thylakoid Membrane
Stage 1: 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)
 http://www.stolaf.edu/people/giannini/flashanima
t/metabolism/photosynthesis.swf
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.
NetLearning - Examples – Flash
Photosynthetic Electron Transport and ATP Synthesis
Stage 2: 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.
 http://student.ccbcmd.edu/~gkaiser/biotutorials/p
hotosyn/hpumpp.html
 Animation of Chemiosmosis Proton Pumping
Dark Reactions – Stroma
Stage 3: 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 3 times to produce
each PGA molecule, and 6 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)
Calvin cycle
Photosynthesis Animated…
 Photosynthesis
 photosynthesis dark phase