LABADOR, WENYL B.
BS-CRIMINOLOGY
SUNLIGHT
All living things use a process called respiration to get energy to stay alive. Cellular
respiration in plants is the process used by plants to convert nutrients obtained from
soil into energy which fuels the plants’ cellular activities.
On the other hand, photosynthesis is the process where light energy is converted
into chemical energy stored in glucose that can later be used in respiration. on the
green parts of the plant that contain chlorophyll.
During respiration, plants consume nutrients to keep plant cells alive while during
photosynthesis, plants create their own food.
Respiration:
oxygen + glucose -> carbon dioxide + water + heat energy
Photosynthesis:
carbon dioxide + water+ light energy -> oxygen + glucose
Depending on the amount of sunlight, plants can give out or take in oxygen and
carbon dioxide as follows.
Dark – Only respiration takes place. Oxygen is consumed while carbon dioxide is
released.
Dim sunlight – Photosynthesis rate equals respiration rate. A plant consumes all
the oxygen photosynthesis generates. It also uses all the carbon dioxide respiration
creates. As a result, no gas exchange takes place with the environment.
Bright sunlight – Photosynthesis uses carbon dioxide and makes oxygen faster
than respiration produces carbon dioxide and consumes oxygen. Extra oxygen is
released into the atmosphere.
During daytime, photosynthesis produces oxygen and glucose faster than
respiration consumes it. Photosynthesis also uses carbon dioxide faster than
respiration produces it. Oxygen surplus is released into the air and unused glucose
stored in the plant for later use.
This is why plants are so important to human and other animals’ survival. Without
photosynthesis, we wouldn’t have oxygen or food to stay alive.
NIGHT TIME
Photosynthesis and cell respiration are two separate biochemical processes that
function in different ways.
Photosynthesis can occur during the night, but requires light for the process to begin.
The light independent portion of the cycle is called the dark reaction/ Calvin cycle and is
a continuation of photosynthesis from light dependent stages. The dark reaction is not a
separate cycle, but a continuation of photosynthesis and is independent of the presence
of light.
Cell respiration occurs continually during the plant life cycle because it produces the
energy necessary for the plant to maintain itself through grow and development. If the
plant didn’t have this energy available, it would die.
1. Carbon fixation. A \text {CO}_2CO2 molecule combines with a five-carbon acceptor
molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound
that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-
PGA). This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase,
or rubisco.
Simplified diagram (showing carbon atoms but not full molecular structures) illustrating
the reaction catalyzed by rubisco. Rubisco attaches a carbon dioxide molecule to an
RuBP molecule, and the six-carbon intermediate thus produced breaks down into two 3-
phosphoglycerate (3-PGA) molecule
Diagram showing the molecular structures of RuBP and carbon dioxide, the unstable
six-carbon intermediate formed when they combine, and the two 3-PGA molecules
produced by the intermediate's breakdown.
2. Reduction. In the second stage, ATP and NADPH are used to convert the 3-PGA
molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P).
This stage gets its name because NADPH donates electrons to, or reduces, a three-
carbon intermediate to make G3P.
[Details of this step]
Simplified diagram of the reduction stage of the Calvin cycle, showing carbon atoms but
not full molecular structures. A molecule of 3-PGA first receives a second phosphate
group from ATP (generating ADP). Then, the doubly phosphorylated molecule receives
electrons from NADPH and is reduced to form glyceraldehyde-3-phosphate. This
reaction generates NADP+ and also releases an inorganic phosphate.
Reactions of the reduction stage of the Calvin cycle, showing the molecular structures of
the molecules involved.
3. Regeneration. Some G3P molecules go to make glucose, while others must be
recycled to regenerate the RuBP acceptor. Regeneration requires ATP and involves a
complex network of reactions, which my college bio professor liked to call the
"carbohydrate scramble." ^11
In order for one G3P to exit the cycle (and go towards glucose synthesis), three \text
{CO}_2CO2 molecules must enter the cycle, providing three new atoms of fixed carbon.
When three \text {CO}_2CO2 molecules enter the cycle, six G3P molecules are made.
One exits the cycle and is used to make glucose, while the other five must be recycled
to regenerate three molecules of the RuBP acceptor.
