photosynthesis ch. 7
DESCRIPTION
Photosynthetic Organisms Photosynthesis coverts solar energy into the chemical energy of a carbohydrate. Photosynthetic organisms are called autotrophs because they produce their own food. With a few exceptions, it is possible to trace any food chain back to plants and algae.TRANSCRIPT
Photosynthesis Ch. 7 Photosynthetic Organisms
Photosynthesis coverts solar energy into thechemical energy of a
carbohydrate. Photosynthetic organisms are called autotrophsbecause
they produce their own food. With a few exceptions, it is possible
to trace anyfood chain back to plants and algae. Photosynthesis
takes place in the green portionsof plants.
The raw materials for photosynthesis are waterand carbon
dioxide.The roots absorb water,while carbon dioxide enters a leaf
throughstromata. Then CO2 and H2O diffuse into chloroplasts,
whichcarries out photosynthesis. Carbon Dioxide and Water then
diffuse into chloroplasts,which are the organelles that carry out
photosynthesis. A double membrane surrounds a chloroplast, and
itssemifluid interior called the stroma. A different membrane
system within the stroma formsflattened sacs called thylakoids. The
thylakoid membrane contains chlorophyll and otherpigments capable
of absorbing solar energy. The Photosynthesis process
The overall process of photosynthesis can berepresented by the
following equation: In the reaction, CH2O represents
carbohydrates.
Photosynthesis is a redox reaction Lose of electrons is oxidation
and gain of electrons isreduction. It takes a lot of energy to
reduce CO2.Solarenergy is not used directly to provide the
energy,but instead is used to generate the ATP needed. Solar Energy
Chemical Energy (ATP, NADPH)
Two Sets of Reactions Light Reactions These reaction only occur
when solar energy is present. The solar energy energizes electrons
to move down theelectron transport chain. As the electrons move,
energy is released and capturedto produce ATP molecules. Solar
Energy Chemical Energy (ATP, NADPH) Chemical Energy (ATP, NADPH)
Chemical Energy (carbohydrate)
Two Sets of Reactions Calvin Cycle Reactions Named after Melvin
Calvin. He discovered the enzymatic reactions that reducecarbon
dioxide to a carbohydrate in the stroma ofchloroplasts. These
reactions can occur during both day and night. During the Calvin
Cycle, CO2 is taken up and thenreduced to a carbohydrate that can
later be convertedto glucose. Chemical Energy (ATP, NADPH) Chemical
Energy(carbohydrate) Pigments and Photosystems
Pigment molecules absorb wavelengths of light.Most pigmentsabsorb
only some wavelengths and reflect or transmit theothers. The
pigments in chloroplasts are capable of absorbing portionsof
visible light called their absorption spectrum. Pigments and
Photosystems
Photosynthetic organisms differ in the type of chlorophyll
theycontain. Chlorophyll a and chlorophyll bplay a prominent role
inphotosynthesis. Chlorophyll a and b absorb violet, blue, and red
light better than others. Green light is reflected by chlorophyll
giving plants their green color. Carotenoids play an accessory
role. Carotenoids, which are shades of yellow and orange, absorb
the violet- blue-green range.These pigments become noticeable in
fall whenchlorophyll breaks down. A photosystem consists of a
pigment complex and electron acceptormolecules within the thylakoid
membrane.Its the antenna forgathering solar energy. Electron Flow
in Light Reactions
The light reactions utilize 2 photosystems, calledphotosystem I (PS
I) and photosystem II (PSII). During light reactions, electrons
usually follow anoncyclic pathway that begins with PS II. Electron
Flow in Light Reactions
PS II, which consists of pigment complexes and electron- acceptor
molecules, receives electrons from water aswater splits, releasing
oxygen. The electron transport chain (ETC), consisting
ofplastoquione and cytochrome complexes, carries electronsfrom PS
II to PS I via redox reactions. PS I, which also consists of a
pigment complex andelectron acceptor molecules, is adjacent to
NADPreductase. The ATP synthase complex which has a channel and
aprotruding ATP synthase, is an enzyme that joins ADP + P. Plants
are Carbon Dioxide Fixers
Step 1: Fixation of Carbon Dioxide Carbon dioxide fixation is the
first step in the calvincycle.During this step, CO2 is attached to
RuBP(ribulose-1,5-bisphosphate) to form a 6 carbonmolecule.The
resulting 6 carbon molecule is then splitinto two 3 carbon
molecules. RuBP carboxylase is the enzyme that speeds thisreaction
and makes up 20-50% of the protein content inchloroplasts. Plants
as Carbon Dioxide Fixers
Step 2: Reduction of Carbon Dioxide 3PG (3-phosphoglycerate is
reduced to G3P (glyceraldehyde-3- phosphate) in 2 steps: Plants of
Carbon Dioxide Fixers
Step 3: Regeneration of RuBP For every 3 turns of the Calvin cycle,
5 molecules of G3P are usedto reform 3 molecules of RuBP.