|If plants absorb sunlight and we eat plants or
other organisms who eat plants, does that mean we
have a fraction of the energy of the sun in our
|Question Date: 2014-09-11|
ALL of the energy in our bodies started off as
sunlight! Plants use energy from the sun to take
the elements in water and carbon dioxide and put
them together as sugar. Oxygen is left over.
When we eat plants, or things that ate plants, we
are harvesting energy in our food that started off
We don’t get all the energy that the plant got,
even if we eat the entire plant, from the top of
the plant to the bottom of its roots. Every time
energy changes form, some is lost as heat that
drifts away. Also, the plant has already used
some of the sun energy for its own needs. When an
animal eats a plant, it only gets about 10% of the
energy that the plant took in as light. When an
animal eats another animal, it gets a maximum of
about 10% of the energy that its prey ate.
Why do you think that there are so few
carnivores (meat eaters) compared to herbivores
(plant eaters)? In other words, why are you a lot
more likely to see a deer than a mountain lion?
If these questions interest you, check out a
career in ecology.
Thanks for asking,
Since humans eat organisms that directly or
indirectly get their energy from the sun, yes
we do have a fraction of the energy of the sun.
The energy of the sun is sent to the Earth
through “thermal radiation.” When this radiation
hits certain molecules, they start vibrating or
move faster which increases their energy. In the
case of plants, they use this energy from the sun
to turn carbon dioxide and water into sugar. When
we eat the sugar in the plants, we are indirectly
absorbing some of the energy the sun gave to make
the sugar in the first place.
Interestingly though, not every organism on the
planet gets its energy from the sun. The
organisms that live around deep sea vents rely
solely on the chemicals dissolved in the vents,
which does not come from the sun. These ecosystems
deep under the ocean are considered to be
independent of solar energy, so if you ate one of
those organisms, you wouldn’t get any energy from
the sun. Of course, nobody would ever eat a deep
sea vent critter.
We sure do! Plants are only able to harvest a
small fraction of the light energy and turn it
into chemical energy. When we consume plants that
transfer of energy is an even smaller proportion.
This is called the 2nd Law of
Thermodynamics: With each transfer of energy,
heat is lost.
Thus we have to eat a lot of plants to fulfill
our energy needs.
We have a fraction of the *power* of the sun in
our solar system. Power is energy expended over
time. The sun continually emits more energy, thus
having a certain level of power. The power
reaching the Earth is a fraction of that, the
power taken up by plants is less still, and the
power that we take from plants is even less still,
but yes, it is a fraction of the sun's power.
Yes, definitely. Almost all living things on
earth are fueled by the sun either directly or
indirectly. (The exception is organisms that live
near volcanic vents deep in the ocean.) Energy
from the sun is taken in by plants and eaten by
animals. Without the sun, that foundation level of
energy would be gone, and no large life on earth
would exist. So yes, we definitely do have
fractions of the sun's energy in our system. Even
cooler, the universe many billion years ago was
almost entirely hydrogen. It took a whole
generation of stars to take the hydrogen and turn
it into heavier elements like carbon and oxygen
and iron. What this means is that our bodies are
literally made of matter from dead stars.
We have definitely used the suns energy, but
the sun's energy has been converted into a form
that we can use in our bodies. The plants
transform the sunlight into energy that they use
to grow things like leaves and fruits. In the
same way, when we eat those leaves and fruits, we
transform the plant's energy into bones, muscles,
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