Chapter 8 The Working Cell: Energy from Light. Ms. Levensailor Honors CS2. Brainstorm. With your shoulder partner: Brainstorm what you know about photosynthesis. Record this in your composition book. Intro to Photosynthesis.
Photosynthesisis the process by which plants (also some bacteria and protists) use the energy from sunlight to produce sugar
The conversion of unusable sunlight energy into usable chemical energy
6H2O + 6CO2 ---> C6H12O6+ 6O2
Electrons from water are boosted "uphill" by the energy from sunlight. The chloroplast uses these "excited" electrons, along with carbon dioxide and hydrogen ions, to produce sugar molecules.
A leaf may be viewed as a solar collector crammed full of photosynthetic cells
The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf, and the products of photosynthesis, sugar and oxygen, leave the leaf.
All green parts of a plant have chloroplasts.
-Leaves are the major site of photosynthesis.
Green color is due to the pigment, chlorophyll.
*Put these terms in order from largest to smallest: thylakoid, leaf, chloroplast, mesophyll.
6 CO2 12H2O
C6H12O6 6 H2O 6O2
Photosynthesis occurs in two main stages:
The light reactions (thylakoid)
The Calvin cycle (stroma)
The energy of light is inversely proportional to the wavelength: longer wavelengths have less energy than shorter ones.
The order of colors is determined by the wavelength of light.
Visible light is one small part of the electromagnetic spectrum.
Visible light consists of wavelengths from about 400 nanometers (nm), violet, to about 700 nm, red
Short wavelengths of gamma rays to the very long wavelengths of radio waves
A pigment is any substance that absorbs light.
Chlorophyll, the green pigment common to all photosynthetic cells, absorbs all wavelengths of visible light except green, which it reflects to be detected by our eyes.
Pigments have their own characteristic absorption spectra, the absorption pattern of a given pigment (you graphed this in the lab).
Various pigments in the thylakoids to absorb the maximum amount of light
Several modifications of chlorophyll occur among plants and other photosynthetic organisms.
All photosynthetic organisms (plants) havechlorophyll a.
Accessory pigments absorb energy that chlorophyll a does not absorb.
chlorophyll b(also c, d, and e in algae and protists)
carotenoids(such as beta-carotene)
When light shines on a material that contains pigments, three things can happen to the different wavelengths:
The pigments in the leaf's chloroplasts absorb blue-violet and red-orange light very well.
Chloroplast pigments do not absorb green light well. Most of the green light passes through the leaf (is transmitted) or bounces back (is reflected).
Leaves look green because the green light is not absorbed.
Rf = 5 cm / 10 cm = 0.5
0.5 : 1
Original Pigment Mark
I am the source!
Within the thylakoid membrane, chlorophyll and other molecules are arranged in clusters called photosystems
Energy "jumps" from molecule to molecule until it arrives at what is called the reaction center of the photosystem
Alternating from ground to excited state and back again
The reaction center consists of a chlorophyll a molecule located next to another molecule called a primary electron acceptor.
The primary electron acceptor is a molecule that traps the excited electron from the chlorophyll a molecule.
Other teams of molecules built into the thylakoid membrane can now use that trapped energy to make ATP and NADPH.
Two photosystems are involved in the light reaction:
Photosystem I is known as P700 (absorption peak at 700).
Photosystem II is known as P680 (absorption peak at 680).
Identical chlorophyll a molecules.
Associated with different proteins in the thylakoid membrane.
The electron transport chain connecting the two photosystems releases energy, which the chloroplast uses to make ATP.
An electron transport chain pumps hydrogen ions across a membrane (thylakoid membrane in photosynthesis).
Light-excited electrons from chlorophyll travel down the chain.
The second photosystem
This photosystem produces NADPH by transferring excited electrons and hydrogen ions to NADP+
NOTE: So far no sugar has been produced.
Job of the Calvin cycle, which uses the ATP and NADPH produced by the light reactions.