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Reading Passage
Inside the thylakoids is where the first stage of photosynthesis occurs.
This is called light-dependent reactions. The light-dependent reactions
require light and water. It is from this part of photosynthesis that oxygen
is produced. The light-dependent reactions occur using what's called
an electron transport chain. When the light shines on the leaf, electrons
inside the chlorophyll are moved to an excited state. This energy is used
to produce ATP (chemical energy) and NADPH (electron carrier), which
will travel to the stroma for the Calvin cycle. It is important to note that
while ATP and NADPH are products of the light-dependent reaction,
they are not represented in the photosynthesis formula because they are
immediately used in the second stage of photosynthesis.
The second stage of photosynthesis is called light-independent
reactions or Calvin cycle. This process requires carbon dioxide and
takes place in the fluid inside the chloroplast, called the stroma. The
Calvin cycle is able to transform carbon dioxide into glucose through
a series of complicated chemical reactions using the ATP and NADPH
that was produced in the light-dependent reactions. During this
process, ATP is converted to ADP and NADPH is converted to NADP+.
The ADP and NADP+ travel back to the thylakoid to be reused in the
light-dependent reactions. Finally, after the glucose is produced, it is
used as an energy source (for cellular respiration) or stored for later use.
Photosynthesis is not only important for the survival of plants but
also for the survival of humans and animals. Plants produce the oxygen
needed for humans and animals to breathe. The glucose produced is
often consumed by animals and humans and used as energy to fuel
their bodies. Life as we know it depends on this very important process.
Without photosynthesis we would cease to exist!
Here is the chemical equation for photosynthesis:
Sunlight
6CO
2
+ 6H
2
O ➔ C
6
H
12
O
6
+ 6O
2
Activity #2
