The Process of
Photosynthesis
Plant Biology 1030
Megan Anderson
11/2/2011
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The Process of Photosynthesis
What is Photosynthesis? It’s the process of converting light energy to chemical energy
and storing it in the bonds of sugar. This process occurs in plants and some algae (Kingdom
Protista). Plants need only light energy, CO2, and H2O to make sugar. The process of
photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment
involved in photosynthesis. In this paper I will be talking about the process of Photosynthesis
and what photosynthesis does good or bad for plants and why do plants need photosynthesis.
Photosynthesis occurs to furnish life, directly or indirectly, with chemical energy in
organisms. Plants use photosynthesis as a means of obtaining energy from sunlight. Plants do
not use light energy directly but rather they convert and store it as chemical energy- packets
called ATP and NADPH. These energy packets are, in turn, used with carbon dioxide to build a
variety of chemicals in the plant, including carbohydrates, fats and proteins - the common
compounds we call food. When we eat plants as food, we break down, or metabolize, food
compounds to small molecules. Some of these molecules are used to build more complex
structures, such as bones and muscles in every part of our bodies. Other metabolites are used to
produce the energy packets, such as ATP, needed to put together those complex structures.
The creation of ATP in animals requires oxygen and produces carbon dioxide, just the opposite
of photosynthesis, which uses carbon dioxide and produces oxygen. This molecular recycling of
gases makes animals and plants dependent on each other. So photosynthesis provides food for
most forms of life on Earth, including you.
Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems,
etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the
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vascular bundle(s) (veins), and the stomates. The upper and lower epidermal cells do not have
chloroplasts, thus photosynthesis does not occur there. They serve primarily as protection for
the rest of the leaf. The stomates are holes which occur primarily in the lower epidermis and are
for air exchange: they let CO2 in and O2 out. The vascular bundles or veins in a leaf are part of
the plant's transportation system, moving water and nutrients around the plant as needed. The
mesophyll cells have chloroplasts and this is where photosynthesis occurs.
Chlorophyll looks green because it absorbs red and blue light, making these colors
unavailable to be seen by our eyes. It is the green light which is NOT absorbed that finally
reaches our eyes, making chlorophyll appear green. However, it is the energy from the red and
blue light that are absorbed that is, thereby, able to be used to do photosynthesis. The green
light we can see is not/cannot be absorbed by the plant, and thus cannot be used to do
photosynthesis.
The overall chemical reaction involved in photosynthesis is: 6CO2 + 6H2O (+ light
energy)
C6H12O6 + 6O2. This is the source of the O2 we breathe, and thus, a significant factor
in the concerns about deforestation.
Photosynthesis is a two stage process. The first process is the Light Dependent Process
(Light Reactions), requires the direct energy of light to make energy carrier molecules that are
used in the second process. The Light Independent Process (or Dark Reactions) occurs when the
products of the Light Reaction are used to form C-C covalent bonds of carbohydrates. The Dark
Reactions can usually occur in the dark, if the energy carriers from the light process are present.
Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by
light, thus the term Dark Reaction is somewhat of a misnomer. The Light Reactions occur in the
grana and the Dark Reactions take place in the stroma of the chloroplasts.
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The energy that drives photosynthesis originates in the center of the sun, where
mass is converted to heat by the fusion of hydrogen. Over time, the heat energy reaches the sun's
surface, where some of it is converted to light by black body radiation that reaches the earth. A
small fraction of the visible light incident on the earth is absorbed by plants. Through a series of
energy transducing reactions, photosynthetic organisms are able to transform light energy into
chemical free energy in a stable form that can last for hundreds of millions of years (e.g., fossil
fuels). A simplified scheme describing how energy is transformed in the photosynthetic process
is presented in this section. The focus is on the structural and functional features essential for the
energy transforming reactions. For clarity, mechanistic and structural details are omitted. A more
highly resolved description of oxygenic and anoxygenic photosynthesis is given in the remaining
sections.
The photosynthetic process in plants and algae occurs in small organelles known as chloroplasts
that are located inside cells. The more primitive photosynthetic organisms, for example oxygenic
cyanobacteria, prochlorophytes and anoxygenic photosynthetic bacteria, lack organelles. The
photosynthetic reactions are traditionally divided into two stages - the "light reactions," which
consist of electron and proton transfer reactions and the "dark reactions," which consist of the
biosynthesis of carbohydrates from CO2. The light reactions occur in a complex membrane
system (the photosynthetic membrane) that is made up of protein complexes, electron carriers,
and lipid molecules. The photosynthetic membrane is surrounded by water and can be thought of
as a two-dimensional surface that defines a closed space, with an inner and outer water phase. A
molecule or ion must pass through the photosynthetic membrane to go from the inner space to
the outer space. The protein complexes embedded in the photosynthetic membrane have a unique
orientation with respect to the inner and outer phase. The asymmetrical arrangement of the
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protein complexes allows some of the energy released during electron transport to create an
electrochemical gradient of protons across the photosynthetic membrane.
Plants need to photosynthesis because this is how they make their own food, as they cant
eat like we do. They use sunlight energy, water and carbon dioxide to make glucose, which is a
form of food. Plants that photosynthesis contain chloroplasts, which contain the chemical
chlorophyll. This traps the sunlight and is a fluid. The trapped energy is stored in the stroma. The
Hydrogens from the water, H20, is combined with CO2, in the Calvin cycle, and glucose
(sugar)is produced. The food is then used so that the plant can make energy so it can live and
respirate. Some plants do not photosunthesise. There are also carnivorous and parasitic plants.
In all my research I have found out that Photosynthesis is very important to plant life and
if they didn’t have it they would have a really hard time living, and I have also found out that
there is two different stages of Photosynthesis and they are both just as important as the other. I
have also had a lot of fun looking up this topic because I thought I knew about it and how it
worked but in the research I found that there is a lot more to it than what I thought.
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Work Cite
http://biology.clc.uc.edu/Courses/Bio104/photosyn.htm
http://wiki.answers.com/Q/Why_do_plants_need_photosynthesis
http://www.pa.msu.edu/sciencet/ask_st/091593.html
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BiobookPS.html
http://www.life.illinois.edu/govindjee/paper/gov.html