Photosynthesis In Detail
Phosynthesis is a
complex process that transforms light energy into starch. For
photosynthesis to occur in a plant, Carbon Dioxide and water
along with light energy must be present, so the formula for
photosynthesis is 6CO2 + 12H2O + Light == C6H12O6 +
6H2O + 6O2. After the reaction occurs, the plant releases oxygen
and water, and it stores the glucose to use as energy on a cloudy
day. Photosynthesis can be broken down further into two sections:
Light-dependent and Light-independent. The light-dependent
reactions, also known as photochemical reactions, is a fast
process where the pigments in chlorophyll a and b absorb light
energy. The chlorophyll is located on the thylakoids inside the
chloroplast. The thylakoids are held in place by lamellae, and
form columns called grana that look like stacked poker chips.
There are two main systems that absorb the light energy:
Photosystem 1 and Photosystem 2. Photosystem 2 absorbs the light
energy which excites the electron on the photosystem2 which sends
it to a higher energy level. At the same time, photosystem 2 is
breaking down H2O into 1/2(O2) and 2H+. This produces a
concentration gradient of hydrogen cations in the thylakoid
space, and the electrons released from hydrogen when H2O is
broken down is used to fill the excited electron that was
released in photosystem2. The excited electron goes through an
electron transport chain located on the thylakoid membrane where
it is energy is slowly decreasing. The electron attracts hydrogen
cations as it travels down the membrane due to it?s charge. The
protons enter the thylakoid space through proteins on the
thylakoid membrane. Meanwhile, photosystem1 is absorbing light
energy and it?s electron is getting excited and going to higher
energy levels. The electron that just went through the electron
transport chain from photosytem2 is used to replace the electron
from Photosystem1. The electron from photosystem2 undergoes the
electron transport chain where it is absorbed by NADP+ to form
NADPH which will be used in the Calvin Cycle. The protons that
have built up in the thylakoid membrane want to diffuse across
the thylakoid membrane due to its higher concentration gradient
inside the thylakoid than on the outside. The protons diffuse
through a protein that performs ATP synthase. The energy is used
to convert ADP into ATP, and the light reactions have finished
their process. The ATP and NADPH that was created by the light
reactions is then sent to the Calvin Cycle where it will be used
to create glucose. The Calvin Cycle, known as the dark reactions,
uses the ATP and NADPH in a series of three cycles to create
gliceraldehyde 3-phospate (G3P). The ATP is transformed back into
ADP and NADPH into NADP+ where they will both be sent back into
the light reactions where they will be reused.
Paper chromatography is used to separate compounds, such as:
chlorophyll, carotene, and xanthophyll. The pigments are absorbed
onto the paper. If the tip of the strip is then placed in a
solvent, the solvent slowly moves up the paper. As the solvent
moves up the paper, the pigments dissolve in the solvent. The
pigment moves up the paper as the solvent does, but the pigment
mostly moves at a slower rate than the solvent. As a result, four
color bands will appear--a yellow band of carotenes, a
yellow-orange band of xanthophylls, a blue-green band of
chlorophyll a, and a yellow-green band of chlorophyll b.
(Vodopich 122). A relationship exists between the distance moved
by the pigment and the distance moved pigment origin to the
solvent front, so the formula Rf=(Distance moved by
pigment)/(Distance from pigment origin to solvent front) has been
created to determine the pigment.
Flourescence occurs when chlorophyll is extracted from plants and
brought into a room. The pigment system is disrupted and the
excited electron quickly returns to it?s
beginning position, and it emits a photon with a
longer-wavelength of light.
Another phenomenon that was introduced early this century is that
isolated chloroplasts can transfer electrons in the absence of
carbon dioxiode, but a artificial electron-acceptor must be
present. DCPIP is a dye that changes colors, blue to a colorless
state, that can be used to record the rate of some reactions in
photosynthesis.
The rate of photosynthesis is determined by what wavelengths of
light are present. The light-dependent reactions absorb the color
blue and red, and reflect the color green.
According to Mr. Barnhart, a biology teacher at SMSU, if aliens
put a green filter over the Earth, plants rate of photosynthesis
would slow down and all the plants would die. Humans and other
animals eat plants or eat animals that eat plants to get energy
(sugar),
so without the survival of plants life is doomed. We use the
sugar produced by
photosynthesis as a fuel for cellular respiration. My hypothesis
is that when a spec20, a machine that measures the amount of
light that is transmitted or absorbed through a given substance,
is used to measure transmittance of certain light colors through
a chlorophyll extract that red and blue will have the lowest
transmittance while green will have the highest
transmittance.
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