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ULTRAVIOLET

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Test for color blindness

We don’t all see things the same,
As shown by a dotty picture game.
People who see no dog (one in ten)
Are color-blind, mostly boys and men.

You can use this  part of the book to…

  • talk about different colors in the spectrum
  • explain that there is stuff out there that we cannot see
  • check for some types of color blindness
Ultraviolet

UV affects life in other ways;
The scorpion’s outer glaze,
And of related organisms too,
Reflects some UV as blue.

The fluorescence of the (Mozambique thick tailed) scorpion (Parabuthus mossambicensis)  tells us that there is something going on with colors that we do not normally see.  Check out what this scorpion normally looks like.  Perhaps try to list the differences.  Whenever a scorpion is exposed to ultraviolet light, its skeleton produces a blue color. Normally, we would not see it, but when the animal is in the dark, the blue is much more obvious.

How.  Fluorescence is not uncommon.  Some chemicals absorb radiation that has more energy (the shorter wavelengths of light – towards the blue end of the spectrum), the chemical becomes more energized and releases that extra energy as radiation, but with less energy than the initial radiation.  Scorpions, like most arthropods (such as crabs, spiders, insects), have an external skeleton. It contains several chemicals that are fluorescent. If you really want to know, they are β-carbolin,  7-hydroxy-4-methylcoumarin, and  a phthalate ester.

Why?  No good reasons as to why scorpions fluoresce have been given. Indeed, the ‘Why question’ is probably a bad question.  We talk more about this in the Consider section below. 

Swift river cruiser dragonfly feeding
Swift river cruiser dragonfly feeding

Ultraviolet radiation (UV)
Is outside the spectrum we see.
But, the big green eyes
Of cruiser dragonflies
Use thousands of little tubes
To tell its brain what it views.
Theirs and other insects’ sight
Detects ultraviolet light.

Here we introduce eyes that are not like our own.  This can be used to develop an awareness that not all organisms will see the world as we do. 

We started with an example of  how we do not see Ultraviolet light, but we do see the fluorescent results of it.  Eyes do not all have the same plan. Some organisms do not have round eyes with a single pupil. The dragonfly sees with hundreds of little telescopes that wrap around its head, pointing out in almost all directions.  What do they see?  Is it the same world that we see, or is it a mosaic pattern?  Whose view of the world is right? The answer to the last question is ‘None of the above’.  There is are very many kinds of radiation out there, different organisms perceive some but not all, and do so in different ways. Our way is simply one of many. 

Influencing the design of flowers
To attract more insect visitors.
To the left below is human sight
UV reflection to the right
Many insects see a combination
More contrasty with UV radiation.

Here are two views of a common yellow flower, the cinquefoil (Potentilla).   To the left, a pattern of colors that are visible to us.  To the right is a similar flower, but it looks different.  This is because the flower has been illuminated with Ultraviolet light, and has been photographed in a way that the reflected light can be seen as colored.  Do not think too much about the color – it is artificial. What is important is that much of the petals reflect radiation very well and have a bright appearance. But, the more central regions of the petals absorb the radiation and they look very dark.  

Our eyes only see what is on the left, but an insect will see a combination of what is on the left and what is on the right. Insects see a flower with much more contrast than we do.  If contrast in the flower is something that attracts insects, then this feature is likely to attract more pollinators to the flower. 

Consider ….

  • The answer to the “Why?’ question in biology is usually ‘It just is!’  BUT, you can improve understanding by asking for a list of the benefits (or disadvantages) of any features.  What are the benefits or disadvantages of having eight legs, or a stingy thing at the end of the tail?  A question that is more likely to lead to engagement is to ask what are the benefits and disadvantages of having a skeleton on the outside, or having it – like we do – inside the body. Have fun with that one.
  • The lack of certainty can be frustrating.

Can you see all colors?  Remember that some children, especially boys, will be color blind.  Use this opportunity to check if they can see the colors the same way as you do. Perhaps when you ask ‘What color is that beak?’ they use an unexpected word. The spotty diagram shows a dog using orangey/yellow dots.  People who are red-green color blind will not be able to work out what is in the picture.  There are many different kinds of color blindness, although red/green is the most common in boys. There are plenty on-line sites, such as here, where you can try different tests.

If you have more ideas, please let us know below.

Nature Reader colors web Ultraviolet

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