Biología General - Raven: Excelente Libro para aprender y Enseñar
Archivo: PDF | Tamaño: 54 MB | Idioma: English | Categoría: Capacitación Docente - Biología
Science is most fun when it tickles your imagination. This is
particularly true when you see something your common
sense tells you just can’t be true. Imagine, for example, you
are lying on a bed in a tropical hotel room. A little lizard, a
blue gecko about the size of a toothbrush, walks up the wall
beside you and upside down across the ceiling, stopping for
a few moments over your head to look down at you, and
then trots over to the far wall and down.
There is nothing at all unusual in what you have just
imagined. Geckos are famous for strolling up walls in this
fashion. How do geckos perform this gripping feat? Investi-
gators have puzzled over the adhesive properties of geckos
for decades. What force prevents gravity from dropping the
gecko on your nose?
The most reasonable hypothesis seemed suction—
salamanders’ feet form suction cups that let them climb
walls, so maybe geckos’ do too. The way to test this is to see
if the feet adhere in a vacuum, with no air to create suction.
Salamander feet don’t, but gecko feet do. It’s not suction.
How about friction? Cockroaches climb using tiny hooks
that grapple onto irregularities in the surface, much as rock-
climbers use crampons. Geckos, however, happily run up
walls of smooth polished glass that no cockroach can climb.
It’s not friction.
Electrostatic attraction? Clothes in a dryer stick together
because of electrical charges created by their rubbing to-
gether. You can stop this by adding a “static remover” like a
Cling-free sheet that is heavily ionized. But a gecko’s feet
still adhere in ionized air. It’s not electrostatic attraction.
Could it be glue? Many insects use adhesive secretions
from glands in their feet to aid climbing. But there are no
glands cells in the feet of a gecko, no secreted chemicals, no
footprints left behind. It’s not glue.
particularly true when you see something your common
sense tells you just can’t be true. Imagine, for example, you
are lying on a bed in a tropical hotel room. A little lizard, a
blue gecko about the size of a toothbrush, walks up the wall
beside you and upside down across the ceiling, stopping for
a few moments over your head to look down at you, and
then trots over to the far wall and down.
There is nothing at all unusual in what you have just
imagined. Geckos are famous for strolling up walls in this
fashion. How do geckos perform this gripping feat? Investi-
gators have puzzled over the adhesive properties of geckos
for decades. What force prevents gravity from dropping the
gecko on your nose?
The most reasonable hypothesis seemed suction—
salamanders’ feet form suction cups that let them climb
walls, so maybe geckos’ do too. The way to test this is to see
if the feet adhere in a vacuum, with no air to create suction.
Salamander feet don’t, but gecko feet do. It’s not suction.
How about friction? Cockroaches climb using tiny hooks
that grapple onto irregularities in the surface, much as rock-
climbers use crampons. Geckos, however, happily run up
walls of smooth polished glass that no cockroach can climb.
It’s not friction.
Electrostatic attraction? Clothes in a dryer stick together
because of electrical charges created by their rubbing to-
gether. You can stop this by adding a “static remover” like a
Cling-free sheet that is heavily ionized. But a gecko’s feet
still adhere in ionized air. It’s not electrostatic attraction.
Could it be glue? Many insects use adhesive secretions
from glands in their feet to aid climbing. But there are no
glands cells in the feet of a gecko, no secreted chemicals, no
footprints left behind. It’s not glue.
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