Organisms can be classified by how they get their energy and carbon. Autotrophs ( "selffeeders") use energy and carbon from inorgaric sources to create biological bonds through the process of primary production. Heterotrophs ("other-feeders') consume other organisms to get energy and the nutrition they need to survive. Ultimately, all heterotrophs rely on the primary production of autotrophs. Photo-autotrophs are autotrophs that use light as an energy source for primary production through the process of photosynthesis. Photosynthesis requires carbon dioxide, water, and light energy to produce the simple sugar glucose, oxygen, and water. Light travels from the sun in waves as photons. The distance a photon travels during one complete wave is its wavelength. Energy values associated Figare 7-1. Fhotosynthesis cunverts light energy, with photons increase as wavelengths decrease. Sunlight contains a wide range of wavelengths. Photosynthesis is driven by a range of wavelengths that occur in the spectrum of visible light; primarily within the range of red and blue. Energy from light is absorbed by pigments inside cells. Chlorophyll a is the most common photosynthetic pigment although others do occur. Red, orange, violet, and blue wavelengths ane absorbed by chlorophyll and green is reflected, thereby causing the green appearance of plants. Solar energy is absorbed by pigments and is used to excite electrons away from their atomic nucleus. Remember from lab 2 that electrons further from the nucleus of an atom have more energy associated with them than those close to the nucleus. This increase in electron energy can be harvested by the cell and used to form biologic bonds during photosynthesis. In plants, chlorophyll a is stored in chloroplasts. Chloroplasts are double membrane-bound organelles that contain several flattened membranous sacs called thylakoid membranes that enclose the thylakoid space. The space between the thylakoid membranes and the outer chloroplast membranes is called the stroma. Hundreds of chlorophyll molecules are embedded in the thylakoid membranes, Chlorophyll, proteins, and various pigments in an "antenna complex" absorb light energy and pass it to chlorophyll molecules and proteins that make up the "reaction center." One of two chlorophyll molecules located in the reaction center gives up an electron that is excited by the solar energy and the electron is passed to the first protein in one of many electron transport chains in the thylakoid membranes, Reaction center chlorophyll receives a replacement electron when additional light energy splits water molecules, releasing oxygen gas and hydrogen ions. As the excited electron is passed along adjacent molecules of the electron transport chain the energy of the electron is used to pump hydrogen ions from the stroma into the thylakoid space. Because hydrogen ions are protons, which are positively charged, an electrochemical gradient is established across the thylakoid membranes w.

1. Organisms can be classified by how they get their energy and carbon. Autotrophs ( "selffeeders")
use energy and carbon from inorgaric sources to create biological bonds through the process of
primary production. Heterotrophs ("other-feeders') consume other organisms to get energy and
the nutrition they need to survive. Ultimately, all heterotrophs rely on the primary production of
autotrophs. Photo-autotrophs are autotrophs that use light as an energy source for primary
production through the process of photosynthesis. Photosynthesis requires carbon dioxide, water,
and light energy to produce the simple sugar glucose, oxygen, and water. Light travels from the
sun in waves as photons. The distance a photon travels during one complete wave is its
wavelength. Energy values associated Figare 7-1. Fhotosynthesis cunverts light energy, with
photons increase as wavelengths decrease. Sunlight contains a wide range of wavelengths.
Photosynthesis is driven by a range of wavelengths that occur in the spectrum of visible light;
primarily within the range of red and blue. Energy from light is absorbed by pigments inside
cells. Chlorophyll a is the most common photosynthetic pigment although others do occur. Red,
orange, violet, and blue wavelengths ane absorbed by chlorophyll and green is reflected, thereby
causing the green appearance of plants. Solar energy is absorbed by pigments and is used to
excite electrons away from their atomic nucleus. Remember from lab 2 that electrons further
from the nucleus of an atom have more energy associated with them than those close to the
nucleus. This increase in electron energy can be harvested by the cell and used to form biologic
bonds during photosynthesis. In plants, chlorophyll a is stored in chloroplasts. Chloroplasts are
double membrane-bound organelles that contain several flattened membranous sacs called
thylakoid membranes that enclose the thylakoid space. The space between the thylakoid
membranes and the outer chloroplast membranes is called the stroma. Hundreds of chlorophyll
molecules are embedded in the thylakoid membranes, Chlorophyll, proteins, and various
pigments in an "antenna complex" absorb light energy and pass it to chlorophyll molecules and
proteins that make up the "reaction center." One of two chlorophyll molecules located in the
reaction center gives up an electron that is excited by the solar energy and the electron is passed
to the first protein in one of many electron transport chains in the thylakoid membranes, Reaction
center chlorophyll receives a replacement electron when additional light energy splits water
molecules, releasing oxygen gas and hydrogen ions. As the excited electron is passed along
adjacent molecules of the electron transport chain the energy of the electron is used to pump
hydrogen ions from the stroma into the thylakoid space. Because hydrogen ions are protons,
which are positively charged, an electrochemical gradient is established across the thylakoid
membranes with the stroma holding a negative charge relative to the thylakoid space: Proton
motive force is the potential energy stored in the electrochemical gradient across the thylakoid
membranes. ATP synthase is a protein complex that spans thylakoid membranes and can harvest
proton motive force and use it to attach an inorganic phosphate group to adenosine diphosphate
(ADP), thereby creating adenosine triphosphate (ATP). Other electron transport chains in the
thylakoid membranes use the electron energy to reduce NADP+ to NADPH. The remaining steps
of photosynthesis are referred to as the "carbon reactions," ATP and NADPH from the "light
reactions" are used as energy sources to drive the synthesis of glucose using carbon from carbon
dioxide in the steps of the Calvin cycle. An enzyme called rubisco uses ATP and NADPH to
catalyze a reaction that fixes carbon dioxide and ribulose bisphosphate (RuBP) into a six-carbon
molecule. The six-carbon molecule is unstable and is broken down by other enzymes into two
molecules of PGA. Later steps in the Calvin cycle convert some of the PGA into glucose and
some PGA is converted back into RuBP to perpetuate the cycle. ADP and NADP+ are recharged
to ATP and NADPH by later light reactions. The exercise this week will allow students to

2. measure photosynthetic rates of Elodea, a common. freshwater plant in various conditions.
Figure 7-2. The molecular activities associated with photosynthesis within a chloroplast of a
plant. 7. What is released as a byproduct of the light reactions? a. Oxygen b. Carbon dioxide c.
Water d. Glucose 8. The Calvin Cycle uses energy from the "light reactions" and carbon dioxide
to produce a. Pigments b. Proteins c. Lipids d. Glucose 9. Often students get confused because
there are different terms used to refer to the same process in photosynthesis. What is another
name for the "dark reactions"? a. Krebs cycle b. Photorespiration c. Calvin Cycle d.
Photosynthesis 10. True or False After the Calvin Cycle, NADP+ and ADP get recharged by the
light reactions.