Optics fun

While getting a lesson together about evolution and natural selection, using eye evolution as an example, I ran across a nice pin-hole imaging 'home science tool' idea from this site:

http://www.hometrainingtools.com/pinhole-camera-science-project/a/1322/

Could be nice to try out! Let me know if you do!!


 * esp for students who missed class 2feb12, we saw most of the Utah 'learngenetics' site's slideshow about eye evolution at the end of our class time! Check it out!

Here is the main info from the 'key take home point' handout about the lesson!

Natural selection: eye evolution example

a) general points about optics:


 * Visible light is a part of the electromagnetic spectrum, which has both particle and wave properties.


 * Light travels in a straight line, thus images formed on retinal surfaces are upside down (pin-hole camera effect).


 * Integration by the brain turns the image right side up. You really mainly 'see' with your brain. The eye is the sensory organ.   (We didn't talk about contralateral processing, but left and right sides of images also get put together in interesting ways by the brain - a topic for another year perhaps...)


 * Cones and rods, retinal photoreceptor cells, express pigment proteins (opsins) that transduce the light signal down the optic nerve to the brain. Such opsins include the red and green (long and medium wavelength) proteins, expressed in cones and encoded by a cluster of genes on the X chromosome. This gene cluster is the basis for the sex-linked recessive 'colorblind' phenotype, as discussed.

b) particular items of note:

1)   Eye evolution is an ancient process, starting from the simplest clusters of light detecting cells and going on via cup, pin-hole, simple chambers and lens systems to the 'camera' -like lens and iris systems of human and octopus eyes.

2)   Big lenses can gather more light to excite retinal photoreceptor cells, while clusters of photoreceptor cells containing wavelength specific pigments allow perception of a wide range of the wavelengths (for some organisms, not just in the visible spectrum).

3)   The human 'blind spot' was not really necessary, but more like an evolutionary glitch of development. The strikingly similar octopus eye, due to convergent evolution, not shared ancestry, but with photoreceptor cells turned the other way around, lacks a blind spot because of the orientation of the nerve cells and fibers in the retina.

4)   However the cells become arranged, depending on the phylogeny of the organism, they somehow are able to make the most of their situation, for apparently consistent visual function. For instance, the blind spot is rarely if ever noticed by most people. Another example, the network of blood vessels in between the incoming light stimulus and the photoreceptor cells, is usually never visualized. The 'pinhole' experiment performed in class 'tricks' the retina into allowing us to actually see these fine capillary networks (with a gap or small region with no vessels in the area where rods and cones are most concentrated, the fovea). About 7 of 10 students were able to visualize their retinal capillaries and foveal gap in class.

Note: Further details about this amazing pinhole based experiment can be found at this link:

http://ezinearticles.com/?Biology-Experiments-for-Teachers---Human-Senses:-Retinal-Capillaries&id=388699