1. Communication Topic 2: The Electromagnetic Spectrum
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis

2. DOT Point(s)
identify the limited range of wavelengths of the electromagnetic spectrum detected by humans and compare this range with those of other vertebrates and invertebrates
use available evidence to suggest reasons for the differences in range of electromagnetic radiation detected by humans and other animals (this is on the handout you’ll get for homework)

3. Introduction
The Electromagnetic spectrum is a major stimulus that impacts on our senses. It is a range of energy forms that all travel at the speed of light ( m/s) but have different wavelengths and frequencies. These energy forms are disturbances of electrical and magnetic fields rather than disturbances of a material medium such as water. This is why they are called electromagnetic radiation.

4. The Electromagnetic Spectrum
Electromagnetic radiation travels in waves.
The distance between successive crests of a wave is called a wavelength (λ). The symbol for the speed of light is (c). This comes from the Latin word ‘celeritas’ meaning swiftness. The frequency (f) is the number of waves that pass a point in a second and is measured in hertz (Hz). 1 Hz is one wave (or wavelength) passing a point each second.

5. The Electromagnetic Spectrum
The mathematical equation that connects these three quantities is: c = λf

6. The Electromagnetic Spectrum
Electromagnetic waves all travel at the speed of light but differ in their wavelengths. So they range from very short gamma rays and X-rays with wavelengths of 0.001μm or less to very long radio waves with wavelengths of 1 or more meters.
timitzers.deviantart.com

7. The Electromagnetic Spectrum
Since all electromagnetic radiation travels at the speed of light, the longer wavelengths have shorter frequencies and the shorter wavelengths have higher frequencies. A spectrum is a range of wavelengths hence the term electromagnetic spectrum.
imagine.gsfc.nasa.gov

8. The Electromagnetic Spectrum
Visible light is somewhere in the middle of the electromagnetic spectrum with wavelengths of nm.
All other forms of electromagnetic radiation will pass us by undetected. The only range of wavelengths the human eye can detect are those of visible light.
9-4fordham.wikispaces.com

9. Visible Light
Newton ( ) discovered that if a beam of visible light is passed through a prism, it can be broken up into the seven colours of the spectrum. This splitting of white light is known as dispersion. These are the colours of the rainbow with which we are all familiar: Red, Orange, Yellow, Green, Blue, Indego, Violet

10. Visible Light
Most humans are able to see all of the wavelengths (colours).
Studies have shown that the greatest sensitivity to light in humans is in the green range of the spectrum.
lisathatcher.wordpress.com

11. Visible Light
Objects tend to absorb some wavelengths of light and reflect others. Objects appear coloured because of the light that they reflect. White light is a mixture of all the colours of the spectrum so when white light falls on an object like a green leaf, green light is reflected off the object into our eyes and this is the colour we see. The other wavelengths are absorbed and not detected by our eyes.

12. Visible Light
When an object appears black, it is absorbing all of the light that falls on it. A white object reflects all of the wavelengths of light that reach it. The human eye has evolved to see colours in bright daylight.

13. Visible Light
We have receptors that are sensitive to light mainly in three regions of the spectrum: red, green and blue wavelengths.
This is termed trichromatic vision.

14. Invertebrates and Other Vertebrates
Most living organisms have a visual range close to that of humans, however some are very different.
Many insects, including honeybees, are able to detect wavelengths in the ultraviolet range of the spectrum.
Their light sensitive cells can detect the shorter wavelengths present in the electromagnetic spectrum.
commons.wikimedia.org

15. Invertebrates and Other Vertebrates
UV patterns on flowers that attract bees may have a ‘bullseye’ pattern, directing bees to the pollen and nectar in the centre of the flower.

16. Invertebrates and Other Vertebrates
Honeybees are unable to detect some of the longer wavelengths in the red part of the spectrum. It is thought that they see red objects as black of the absence of colour. Therefore honeybees do not see a wider range of colours than humans, but rather a different range (from Ultraviolet through the blue and green range but not red).
photographyoftheinvisibleworld.blogspot.com

17. Invertebrates and Other Vertebrates
Most studies of colour vision in insects use honeybees as a model animal, but recent research involving the use of butterflies indicates that they may have even more visual pigments and receptor sites than honeybees. This suggests that some butterflies may be able to detect a greater range of colours than honeybees or humans.

18. Invertebrates and Other Vertebrates
Many bird species are able to detect light well into the ultraviolet range of the spectrum.
In addition to this birds tend to be able to detect light most efficiently in the red (longer wavelength) and green ranges of the spectrum.
outandaboutincooloola.blogspot.com

19. Invertebrates and Other Vertebrates
They are also able to detect light in the blue range, suggesting tetrachromatic vision. Some studies on pigeons have even led to suggestions of pentachromatic vision in birds.

20. Invertebrates and Other Vertebrates
Sensitivity to light in the near UV range, previously thought to occur only in insects and birds, has been found to be present in some reptiles like geckos and rodents such as mice. The blue cone receptor in mice are actually UV sensitive.
physicsworld.com

21. Invertebrates and Other Vertebrates
Many animals that are able to fly are also able to detect polarised light which humans cannot. Polarisation of light is through to be used by these animals for navigation during flight.
photographylife.com

22. Homework
-Students to complete DOT Point 2.4 Range of electromagnetic radiation detected by humans and other animals