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  3. Why roses are red and violets are blue? Did you ever wonder why you see the colors you do or if other animals see the same co

Why roses are red and violets are blue? Did you ever wonder why you see the colors you do or if other animals see the same co

admin2011-01-02  27
问题                      Why roses are red and violets are blue?
   Did you ever wonder why you see the colors you do or if other animals see the same colors that you see? We see light that bounces off of things around us. When the light enters our eyes, special cells tell our brains about the light. These cells are called photoreceptors. Light is made of little bits called photons. When the sun shines, trillions and trillions of these little bits of light fall on the earth. The photons bounce off of almost everything and some of them enter our eyes. Those bits that enter our eyes allow us to sec. So, where does the color come from?
   Starting in the 1600s with Sir Isaac Newton, scientists have believed that there are different kinds of photons. Different types give rise to our sense of colors. The different photons are said to have different wavelengths. Sunlight contains all the different wavelengths of photons. The visible wavelength colors can be seen when you look at a rainbow. Raindrops acting as natural prisms produce the colors.
                           How do our photoreceptors work?
   We have two main types of photoreceptors called rods and cones. They are called rods and cones because of their shapes. These cells are located in a layer at the back of the eye called the retina. Rods are used to see in very dim light and only show the world to us in black and white. This is why you see only black and white when you are outside in the evening or in a dimly lit room. The other type of photoreceptors, the cones, allow us to see colors. They arc not as sensitive as the rods so they only work in bright light. There are three types of cones, one for each of the three main colors we see, red, green and blue.
   Some people have a genetic defect that makes one or more of the cones fail. This condition is known as color deficiency. You may have heard it called color blindness. Color blindness is fairly common, affecting about nine percent of all humans. It is much more common in men than in women. To test for color blindness a special picture called an Ishihara test is used.
   What about other animals? What kind of colors do they see? Most animals see fewer colors than we do, but some see more! We know this by looking at how many kinds of cone photoreceptors they have. Another good indication of what an animal can see is by looking at their own colors. The colors of their prey are also an indication of an animals ability to see color.
In what part of the eye are the rods and cones located?
选项 A、Cornea.
B、Lens.
C、Retina.
D、Optic nerve.
答案C
解析
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