Ever wondered why we can't see small things?

Why we don’t see bacterias every day? We know microorganisms are everywhere, its in the air we breathe and the water we drink. Its in-front of our eyes. Then why can’t we see them? Why can't we see small things? To understand that, first we have to know how we SEE things.

Everyone knows, we see things when light from an object falls on our eyes. But how that image reach us? Does light carry information of that image? Yes, in the sense, each photon in the light ray have a different wavelength that matches the colour of the object where it is emitted or reflected. Each photon acts like a pixel of an image. When this light ray reaches our eyes, the signals are detected by the cones and rods in the retina.

Cones detect the colour and the rods detect the brightness. The brain will then formulate the image using this information. Now lets see, what’s the problem while viewing smaller objects. 

The photons that can be detected by our eyes has a limit. A typical human eye is capable of detecting the visible light with wavelength ranging, 390nm to 700nm. We are not adapted to see infrared, ultraviolet, radio waves etc. 

The reason we cannot see too smaller objects is that the wavelength of visible light is much bigger than the size of that object. The photons of visible range (390nm to 700nm) when reflected from smaller objects, like an atom, is too weak. Since an atom is very small compared to the wavelength of visible light, the wave equation requires that the light bounce off with a very broad spread of directions, not at all like reflection from a surface. Thus it makes hard to detect an atom.

Even using a conventional microscope, its hard to see objects below the length of the minimum wavelength of visible light, because a conventional microscope uses visible light to detect objects. It simply magnifies the things it detects.

So what should we do to see an atom? We makes use of an Electron microscope. In an electron microscope, the light source is replaced by a beam of fast moving electrons. As the electron's size is too small, it can successfully create image of smaller objects.

There are several types of electron microscopes for various uses. You can find the details and differences from here : http://www.explainthatstuff.com/electronmicroscopes.html

If you are wondering, the tiniest objects we can see is about 0.1mm, it is the size of a hair, lice etc.

What is Evolution?

Stated Clearly

Transcript

What is Evolution?

In Biology, the theory of Evolution doesn’t tell us exactly how life began on earth, but it helps us understand how life, once it came into existence, diversified into the many incredible forms we see now and in the fossil record. It also helps us make sense of the way in which modern creatures continue to adapt and change today. In biology, evolution can be defined as any change in the heritable traits (those are physical traits like fur color in mice, spots on the wings of butterflies, or instinctive traits like the way in which dogs greet their friends with a sniff) within a population, across generations . This definition can be a bit confusing so let’s see how it works.

All healthy living things, from single celled amoebas, to flowers, to dolphins: are capable of reproduction. We have children, we make copies of ourselves. We do this by duplicating our DNA and passing that DNA on to future generations. DNA is a chain like chemical stored inside each one of your cells, which tells them how to grow and function. Your DNA contains coded information on how to build you. The information in your DNA is different than that of, say, a daffodil’s DNA which is why you look and function differently than a daffodil. The information in your DNA is slightly different than that of Elvis Presley, which is one of many reasons you don’t look or act quite like he did.

Single celled amoebas (and other simple creatures) reproduce by copying their DNA inside their guts, moving both copies to either side of their body, splitting in two right down the middle, and then growing back to full size. If all goes well, the two new amoebas will be exact copies of each other, but in nature, things aren’t always perfect. When DNA is being copied, errors can occur which modify the DNA code. This is what we call a DNA mutation. These mutations (which happen completely on accident and randomly to any part of a DNA strand) can produce variation in the body shape and function of the creature who inherits the modified DNA.

In this case, our new little friend has an arm that stretches extra long. If he survives to grow and reproduce, that extra stretchy arm (which is now coded for in his DNA) will be passed on to his children. Evolution, any change in the heritable traits within a population, across generations, has officially occurred. As you know, reproduction for Dolphins and badgers and people, is a little more complicated. We have to find ourselves a partner. When two badgers get together and... ya know, fall in love, a sperm cell from the father (which contains a copy of half of his DNA - ONLY half), combines with the egg cell of the Mother (which contains half a copy of her DNA). The result is a new cell with a complete set of DNA instructions, all the information needed to divide and grow up into a brand new badger.

The new child matures to be similar to her parents but also unique because she developed some traits from her mother’s DNA and some from her father. Her new combination of traits can be passed to her children and again, evolution, any change in the heritable traits, within a population, across generations, has officially occurred.

Besides the unique recombination of her parents traits, she might also have developed some completely new traits due to DNA mutations. Maybe extra hairy ears for example. If she survives long enough to have kids of her own, her DNA will combine with the DNA of her partner, and she’ll pass on those extra hairy ears to at least some of her children. This of course, is also evolution. So there you have it, evolution is really pretty simple. Scientists and normal folks everywhere, witness evolution happening all around them  

Small changes like the ones we’ve seen here can add up over multiple generations to create dramatic changes.

If you were to go back in time just a few thousand years, you’d find that all dogs for example, originally evolved from an ancestral group of gray wolves. The evolution of those wolves, from generation to generation, was guided by humans. People were selecting wolves with traits they liked, letting them breed, and then only keeping the puppies with the most desirable traits. As time went on, different breeders preferred dogs with different features, some selected for large size, some for small size, some for brains, others for braun. Today, wolves have branched out into hundreds of dog breeds, very few of which look and behave much like their ancestors.

A massive amount of observable evidence from many of different fields such as Genetics, Chemistry, Paleontology and Mathematics, overwhelmingly suggest that just like all dogs share a common ancestor, all living things; me; you; puffer fish; banana trees; if you go back far enough, also share a common ancestor. We are literally related.

We don’t know what the first life form was or exactly how it came to be, but the simple process of reproduction with variation over billions of years looks to be responsible for all the diversity in of life we see today. Now you might be saying: “Wait a minute! Hold on here. Isn’t evolution random? To do something functional like turn a wolf into an adorable mini poodle, random evolution had to be guided by a dog breeder. Researchers say all mammals evolved from an ancient shrew like creature but the difference between a shrew and an elephant is far greater than that of a wolf and a poodle. Who guided that process? Who was the breeder?”

In the mid 1800s two men, Charles Darwin and Alfred Russel Wallace independently discovered, that a breeder is not necessarily needed. There is another force capable of guiding random evolution to produce order and complex function. They called it Natural Selection which happens to be the entire topic of our next video, but before you move on let’s recap what we have learned so far.

Biological evolution is any change in the heritable traits within a population across generations. All healthy living things can make copies of themselves, but they do so imperfectly. Small variations can add up over time to create dramatic differences in body form and function. Evidence overwhelmingly suggests that all living things are related.

So remember, next time you invite family and friends over for a holiday feast, you’re actually just inviting family. That includes the turkey and the pumpkin in the pumpkin pie.