Yes, photosynthesis does require water.
The reason is a bit complicated, but the bottom
line is that hydrogens and electrons from water
are needed in the process that turns light energy
into chemical energy. The oxygen from the
H2O is a waste product.
All cells need energy to do work. We
take chemical energy in food and turn it into
chemical energy in molecules like ATP and NADH.
Plants do that too, but they can also take the
energy in light and use it to make ATP and
NADPH. They can “spend” the energy in these
molecules to make sugar and do other work. You
can think of these energy-carrying molecules like
batteries. The low-energy forms are ADP and NADP+.
The charged-up forms are ATP and NADPH.
When a pigment like chlorophyll absorbs light,
it uses that energy to boost the energy of
electrons. If the electrons just fall back to
their lower-energy state, all that energy would
turn into heat. Instead, the system in a
chloroplast (an organelle inside a leaf cell) uses
the energy to power up the ADP to ATP and the
NADP+ to NADPH. Electrons from the water replace
the ones in the pigments that got an energy boost.
The “boosted” electron and the hydrogen from water
will end up as part of the high energy NADPH.
This may all be pretty confusing, but there are
a few key ideas to take away from it. One is the
idea that things can’t appear from nothing or
disappear into nothing. If H shows up in one
place, it must have come from another place.
Energy can’t be created or destroyed either.
It can be transformed from one type to
another, though. These ideas are the first
law of thermodynamics. The second law of
thermodynamics tells us that every time energy
is converted from one form to another, some is
given off as heat. Some of the energy in light
goes to charge up the ADP into ATP and NADP+ to
NADPH, but some is also “wasted” as heat.
Plants aren’t the only organisms that do
photosynthesis. What else does it? How do you
know that plants can also break down sugar to
release energy? Here are a couple
ofclues: maple syrup & trees without leaves
You may be interested in studying plant
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