by Jason Amores Sumpter
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photo reception is the detection of light, and this is carried out by many different organisms from us. Humans with are very complex eyes to nematodes, you know, little round worms in the soil that have photo receptors that can detect the presence or absence of light. Now we're going to take a look at some more sophisticated systems that carry out photo reception. Namely, we're gonna look at eyes now. Insects and arthropods in general have an interesting I called the compound I This is an I composed of many little repeating units called a materia. And hopefully you can see here all thes little repeating units all over the I. I mean, I can't even begin to dot com all those air all, oh, material which are basically structures that contain clusters of photoreceptors. Here we have what you could think of as like a cross section of the compound I So if we cut a slice into our compound, I This stuff at the top represents the surface of the eye and these air all those subsurface structures and each one of these is an O materia. And if we go over here, you can see a zoomed in version of the O materia and it's going to contain a cluster of photo receptors. And that is how these eyes were going to detect light. Now, this simple I, which is just a single lens, I is what we have and this is going to operate similar to a camera with its single lens. Now, the human eye can Onley perceive light in what's called the visible spectrum, which is just a small portion of the electromagnetic Uh uh the spectrum of electromagnetic radiation, which you can see down here. In fact, this visible light is not even close to proportional with, uh, in this chart, the visible light is just a teeny little sliver on this huge range of different types of electromagnetic radiation. Now, looking at the I, the white of the eye is known as the school era, and this is basically a protective structure, and it's gonna be composed of in part collagen and elastic fibers to give it a tough, resilient structure that can, you know, take a little squishing in motion. Now the cornea is basically the fluid filled, transparent cover over the iris and the pupil. It's kind of hard to see in a head on image. But here you can see it as this area in here, above the lens right here. Now, the iris is the colored area around the pupil, the pupil being this dark center of the eye. The iris is this region that I'm just kind of scratching. And around here, that is our iris and the irises, not just there to make our eyes look pretty and give him some color. It's actually there to control pupil diameter and lens shape, which is going to be very important for focusing lights so that we can perceive a clear image. I mean, look at me. Clearly my eyes air. Incapable of that is I wear corrective lenses. I actually need a little assistance because my eyes can't quite focus the light properly. Now the pupil is that black hole, as I said, and it's going to be the thing that allows the light to pass through the lens. So if you look over here, this structure is our lens. And this opening here, that eyes on top of it, that is our pupil. It appears black because light is getting sucked in there and black is, of course, what we see when there is an absence of light. Now the lens is going to actually change its, uh shape in order to focus light from the cornea. However, the cornea itself has some strong refractive capabilities. We'll get into that in just a little bit and essentially, ah, light is going to move through the cornea through the lens and then get focused onto the retina, which is the back of the eye that contains photo receptors. Let me jump out of the way here. So this area at the back of the eye is the retina and light is going thio, enter cornea, get refracted through the lens and project some image onto the retina paying. That is where our photo receptors are, and they will take it from there. So with that, let's flip the page and actually see how those photo receptors work