What is an eye?
A: Eyes are organs of the visual system.
Complex eyes can distinguish what?
A: Shapes and colors.
The visual fields of many organisms, especially
predators, involve large areas of binocular vision to do what?
A: To improve depth perception.
In other organisms, eyes are located to maximize what?
A: The field of view, such as in rabbits and horses, which have monocular
vision.
The first proto eyes evolved among
animals how long
ago?
A: 600 million years ago.
In most vertebrates and some mollusks, the eye works by
allowing light to enter and project onto a what?
A: A light-sensitive layer of cells at the end of the eye, known as the
retina.
The cone cells (for color) and the rod cells (for
low-light contrasts) in the retina detect and convert light into what?
A: Into neural signals for vision.
The visual signals are then transmitted to the
brain
via what?
A: The optic nerve.
Such eyes are typically roughly spherical, filled with
what?
A: A transparent gel-like substance called the vitreous humor, with a
focusing lens and often an iris.
What does the relaxing or tightening of the muscles
around the iris do?
A: It changes the size of the pupil, thereby regulating the amount of light
that enters the eye.
The eyes of most cephalopods, fish, amphibians, and
snakes have fixed what?
A: Lens shapes, and focusing vision is achieved by telescoping the
lens—similar to how a camera focuses.
Compound eyes are found among what?
A: Arthropods.
Compound eyes are composed of what?
A: Many simple facets.
Each sensor has its own lens and what?
A: Photosensitive cell(s).
Some eyes have up to how many such sensors?
A: 28,000.
Compound eyes are very sensitive to what?
A: Motion.
Some arthropods, including many Strepsiptera, have
compound eyes of only a few facets, each with what?
A: A retina capable of creating an image, creating vision.
With each eye viewing a different thing, a fused image
from all the eyes is produced in the brain, providing very different what?
A: High-resolution images.
Mantis shrimp has been reported to have the world's
most complex what?
A: Color vision system.
Trilobites, which are now extinct, had unique what?
A: Compound eyes.
What did they use to form the lenses of their eyes?
A: Clear calcite crystals.
In this, they differ from most other arthropods, which
have what?
A: Soft eyes.
In contrast to compound eyes, simple eyes are those
that have what?
A: A single lens.
Jumping spiders have a large pair of simple eyes with a
narrow field of view, supported by an array of other, smaller eyes for what?
A: Peripheral vision.
Some insect larvae, like caterpillars, have a different
type of simple eye (stemmata) which usually provides only a what?
A: A rough image.
In organisms dwelling near deep-sea vents, compound
eyes have been secondarily simplified and adapted to see what?
A: The infra-red light produced by the hot vents—in this way the bearers can
avoid being boiled alive.
