Carnivorous plants actually get their energy
from photosynthesis, just like other plants do.
As you probably know, in photosynthesis plants use
light energy to make sugar from carbon dioxide and
water. Oxygen is a waste product. Plants make
other molecules from the sugar, like starch for
energy storage, or cellulose for structure.
They use the insects for nutrients like
nitrogen and phosphorus. These atoms are the
building blocks for proteins and other molecules.
The plants break down the insects using enzymes,
acids, and even little bacterial helpers. This is
how we break down our food in our digestive
systems. Then they absorb the broken-down
molecules of their prey.
Carnivorous plants grow in places where there
aren’t many nutrients in the soil. Bacteria in
soil usually help break down dead plants and
animals into molecules that other plants can use
as fertilizer. In sandy places there isn’t much
“dead stuff” in the soil. Venus fly traps do well
in sandy soil. I live in Wisconsin where we have
bogs that are very acidic. Bacteria don’t grow
well in acidic water, so when plants die, they
don’t break down quickly. Pitcher plants and sun
dews grow in the bogs.
Why don’t other plants evolve into carnivores?
Well, it costs the plants a lot of energy to make
traps, enzymes, and acids. If there are enough
nutrients in the soil, the plant is better off
investing energy in reproduction and other
If you were a carnivorous plant, how would you
lure insects into your traps?
If questions like this interest you, you may
want to study plant ecology.
Thanks for asking,
This is a great question! Most plants get their
energy through photosynthesis meaning they just
need the gasses in the air, water from the soil,
and some sunlight, so why do Venus Flytraps eat
insects? Well, it turns out that Venus Flytraps
actually get a good deal of energy in the same way
that other plants do, through photosynthesis. As
you likely know, during photosynthesis, plants use
the energy in the sun to drive a reaction that
converts carbon dioxide and water into sugar and
oxygen. The sugar produced is then converted to
energy which the plants use to live, grow, and
reproduce. But in addition to sugar, plants also
need amino acids (protein), vitamins, and other
cellular components to survive.
So where do these things come from? Well plants
get most of their protein (amino acids) from
nitrogen and sulfur in the soil. Phosphorous in
the soil is also used by plants as a source of
energy. Plants take up magnesium too as it helps
their enzymes function. Does your mom every tell
you to drink your milk so you get some calcium?
Well, plants need calcium too which they also pull
from the earth where they live. Finally, potassium
is a key vitamin needed by plants as it helps
regulate water movement in and out of the plant.
Most plants can extract these things from the soil
where they live, but Venus Flytraps are not always
Venus Flytraps come from bogs and marshes where
the soil is very acidic and minerals and other
nutrients are scarce. The vast majority of plants
could never survive in an environment like this
because they would not get all the vitamins and
nutrients and energy sources they need from the
soil to grow. But Venus Flytraps evolved.
Specifically, the Venus Flytrap evolved to
thrive in exactly these low nutrient environments
by finding other ways to get the nutrients it
needs. And that´s where the insects come in.
Insects provide a great source of nutrients like
nitrogen and phosphorous and carbohydrates that
are missing from the soil in the typical Venus
Once an insect lands on a Venus Flytrap, the
trap constricts tightly around the insect and the
plant begins to secrete digestive juices, much
like the ones in your stomach. These digestive
juices dissolve the soft, inner part of the insect
but leave the tough, outer part intact. At the end
of the digestive process, which takes between five
to twelve days, the trap reabsorbs the digestive
fluid it let out and then it reopens, ready to
catch another insect. The leftover, hard, outer
shell from the now digested insect is blown away
in the wind or washed away by the rain.
They don't. Venus fly traps and pitcher plants
are green, photosynthetic plants that get their
energy from the sun like almost all other plants.
What they need from animals is nitrogen and
phosphorous, two elements that most plants get out
of the soil, but carnivorous plants live in such
poor soils that these elements are not available.
For this reason, they digest animals using enzymes
the same way carnivorous animals digest other
animals, but for these plants, the main purpose in
doing so is to get these necessary elements,
rather than energy itself.
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