How Does a Cactus Survive?
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Adaptations. We put on coats in wintertime because it's cold outside. That's an adaptation. Some of us put
on glasses so that we can see to read. That's an adaptation. Some of us use a stepladder to reach something
on a high shelf. That's an adaptation. People use adaptations for all sorts of things. Anything that helps us get
along better in our environment is an adaptation.
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Animals and plants use adaptations, too. Without them, it would be impossible to survive in harsh
environments such as the desert. One plant with some amazing adaptations is the cactus.
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In fact, a cactus is a marvel of adaptation. It thrives in the hottest, driest climates where few other plants
can survive. From a tiny barrel cactus in a flowerpot to a monster saguaro cactus in the Sonoran Desert, these
plants have many specialized survival features.
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The sections of a saguaro cactus are called stems. The leaf-shaped sections that make up a prickly pear
cactus are called pads. All of these parts that make up a cactus are designed especially for life in the desert.
Cactus parts are basically reservoirs waiting to be filled with water. When it finally does rain in the desert, cacti
collect and store an amazing amount of water. A large saguaro can take in three thousand liters of water in just
ten days - enough to keep it alive for months.
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The shape of a cactus helps it to store water and also to survive in the blazing sun. Many cacti, such as the
barrel cactus, have accordion-shaped folds called ribs. When it rains, the ribs open to allow the cactus to hold
even more water. The ribs also create patches of shade.
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Like other plants, cacti have stomata, or small openings that collect carbon dioxide, but here, too, they
have special adaptations. The stomata on a cactus stay tightly closed during the heat of the day. This prevents
moisture loss. At night when it is cooler, they open to do their work of collecting carbon dioxide.
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But plants need sunlight in order to use their carbon dioxide to make plant sugars for energy. This is
photosynthesis, and all plants need to do it to live. Since cacti can't do their photosynthesis at night when they
collect the carbon dioxide, they store the carbon dioxide and then go to work making plant sugars during the
day when the sun is shining.
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Another special adaptation that cacti have is their spines. Spines protect cacti from being eaten. Some
spines are hard and as sharp as a bayonet. Others are tiny and barbed like a fishhook. In addition to protecting
cacti from herbivores, spines create more shade on the cactus plants. Some spines also help to channel
rainwater down the sides of the plants to their roots.
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Cacti have specially adapted roots, too. The roots of many cacti spread out just below the surface of the
soil. Whenever it rains, the main roots shoot out additional little roots to take in as much water as possible. In
dry periods, these small roots die off so that they will not use unnecessary energy.
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Some cacti change their stored water into a thick, gluey substance. This gluey substance doesn't
evaporate as quickly as plain water. It also helps to protect the cacti from freezing when the temperatures drop.
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By using all of their adaptations, cacti thrive in the desert. In fact, some cacti live for a hundred years or
more. Like all plants, cacti are a valuable part of our world. People use them for food and even to build living
fences. Cacti produce a wide variety of beautiful flowers. None of this would be possible without the cactus'
many adaptations to life in the desert.
How Does a Venus Flytrap Trap Flies?
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Plants get their nutrients from the soil. They get energy from the sun, and photosynthesis takes care of
their food needs. But some unlucky little plants live where the soil just isn't nutritious enough. What do they do?
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One of those plants is the Venus flytrap, and when it needs more nutrients, it just traps itself some meat
and has a hearty meal like all of us carnivores in the animal world do. Most plants can't do that, but a few really
can. Venus flytraps are one of the plants capable of moving to trap food. Sundews and waterwheel plants also
have this unusual ability. It is an adaptation to the environments in which they live. Their environments have
soil that is unusually low in nutrients, and so the plants supplement their diet by trapping insects.
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Venus flytraps have built-in traps. They have two-sectioned leaves that are hinged in the middle so that
they can snap shut. On each of the two lobes, there are tiny hairs called cilia that bend when an insect lands
there. This movement allows the Venus flytrap to sense when an insect lands on it. Around the edges of each
lobe there are stiff spikes that mesh together to hold the insects in whenever the trap snaps shut.
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The trap will only spring shut after a moving insect has touched the cilia twice. This prevents the flytrap
from wasting its energy on non-food items, such as raindrops, that may land there. When they do snap shut,
the movement is very fast, as fast as one-tenth of a second, so that the insect does not have time to escape.
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The spikes around the edges of the lobes prevent large insects from escaping. Tiny insects, the ones too
small to bother with, can climb back out between the spikes.
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What happens next after the trap closes depends on what is inside. If it is a tiny insect that escapes
through the spikes, the trap will reopen within about twelve hours ready to try again. If there is no movementfor example, if the trap accidentally catches a stone instead of an insect- the trap will reopen, spit the stone
out, and be ready to try again.
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But if a good meal is inside the trap, digestion begins. The trap gets tighter and tighter until it is airtight.
Then it produces digestive juices, like the juices in our stomachs. The digestive juices break down the insect
into nutrition for the plant. Digestion takes about ten days. After it is completed, there is nothing left of the
insect but its hard exoskeleton. The trap opens and spits out the exoskeleton, and it is ready to trap another
unsuspecting insect.
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Sundews have this same unusual ability, but they operate a little differently from Venus flytraps. Sundew
leaves trap insects with a sticky substance. Then they slowly roll up their edges and trap their prey inside.
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Waterwheel plants use a method similar to the flytraps, but they operate underwater to catch tiny aquatic
creatures.
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Venus flytraps, sundews, and waterwheels are all carnivorous plants. Carnivorous seems like a strange
word to describe a plant. Usually, we talk about carnivores as a group of animals. But nature seems to have an
endless variety of surprises, and plants that can snap shut on their unsuspecting prey are just one of them.