Ins and Outs of Photosynthesis
Photosynthesis, undergone by
plants, algae, and some bacteria, is a process that produces glucose, or sugar,
for the organisms to “eat”, or more aptly, to make energy or ATP. The organisms
that go through this process are known as producers because they produce their
food. And although many plants consider watering, planting, or putting it
outside is “feeding” it, in actuality, they use these things to make glucose.
To go through photosynthesis, they need oxygen, carbon dioxide, and water.
In simple terms, the roots of the
plants take in water. The leaves release oxygen while taking in carbon dioxide.
The chloroplasts in the plant take in sunlight and use its energy to make
glucose. However, the process is more complicated than that.
Photosynthesis is split into two
different categories: light-dependent reactions (light reactions) and
light-independent reactions (dark reactions). As the names suggests, light-
dependent reactions need light to occur while light-independent reactions don’t
need light to occur. This isn’t to say that plants can go without light for
long, however. Light reactions use the energy light gives it to make ATP and
NADPH. Then dark reactions use ATP and NADPH to produce glucose.
Light reactions occur in the Grana
of chloroplasts which are stacks of thylakoids. Energy is absorbed from sunlight
and is transferred to electrons (e-). High energy electrons leave the
chlorophyll and enter the electron transport chain. Water molecules split into
hydrogen ions (H+), oxygen, and electrons. The oxygen is given off as a waste product.
The electrons released from the water replace the one that left the chlorophyll.
Electrons move from protein to protein in the electron transport chain, their
energy used to pump H+ ions from outside to inside the thylakoid against the concentration
gradient. Light absorbing molecules absorb sunlight, and electrons are
energized and leave the molecules. Energized electrons are added to NADP+ to
form NADPH. Hydrogen ions flow through a protein channel in the thylakoid
membrane. The protein channel is part of an enzyme called ATP synthase. As ions
flow through the channel, ATP synthase makes ATP by adding phosphate groups to
ADP. The process of adding and removing phosphate groups is known as
phosphorylation. In the end, oxygen, ATP, and NADPH was produced. Oxygen was
given off as a waste product, and ATP and NADPH is transferred for use in the
The dark reactions, also called the
Calvin Cycle, occur in the stroma of chloroplasts. The stroma is the empty
space around the Grana. Carbon dioxide is taken in. The ATP and NADPH fuel this
reaction and carbon dioxide and the hydrogen atoms from before are used to make
glucose. CO2 (carbon dioxide) enters the Calvin Cycle and six-carbon molecules
are formed. Energy from the light reactions are used by enzymes to split the
six-carbon molecules into three-carbon molecules. Most of the three-carbon
molecules stay in the Calvin Cycle, but one high-energy three-carbon molecule leaves.
After two leave, they combine to form a six-carbon sugar molecule, i.e.
glucose. The three-carbon molecules left in the cycle are changed back to
five-carbon molecules using energy. They’ll stay in the cycle and be added to
new CO2 that enters the cycle. The end product of this process is glucose.
The chemical formula of this
process is: CO2+H2O+LightàC6H12O6+O2.
It takes carbon dioxide, water, and light (energy) to make glucose and
oxygen. And because it’s a cycle, it gets repeated constantly, over and over.
This process, a necessary one for all organisms, produces oxygen which other
organisms need for life. In return, we give out carbon dioxide for plants, and
the cycle repeats itself. In the end we coexist giving and receiving necessary
nutrients for life in a careful balance.
What is Photosynthesis, By Science and
Technology Concepts Middle School, (2017) https://ssec.si.edu/stemvisions-blog/what-photosynthesis
Introduction to Photosynthesis, by eSchooltoday,
Major Differences, by MCQ Biology,
Light and Dark Reactions in
Photosynthesis, by Kathie Z., (2005), https://www.wyzant.com/resources/lessons/science/biology/photosynthesis/light-dark-reactions
Photosynthesis Process Light and
Dark Reactions, Hamza Khan, (2017), https://www.slideshare.net/utmang/photosynthesis-process-light-and-dark-reactions
The Calvin Cycle, Khan Academy, (2015),