Cells and What They Do

[Music] [Music] for [Music] do you think this is Alive looks like a pebble no I think it's a seed then is it alive what's one way to tell if it starts growing then I guess it's alive it takes a few days for a seed to sprout and start to grow but we're using a special camera that shows us several days in just a few seconds yeah it's a seed do all [Music] right a plant is made up of several parts and each part is alive to see the smallest living parts we can put a section of a leaf under a microscope in a piece of leaf just 1 in Long there are thousands of separate living Parts called cells this is how they look from the top and this is looking from the side you can see that the top layer of cells is different from the ones [Music] below are these the the cells in the stem right they're a lot different from the ones in the leaf because they have a different job to do and the cells and the roots are different from all the others because they have a different job to do so a plant has several kinds of living cells in various shapes and sizes how about animals let's look at some parts of a frog under the microscope cells from a frog's muscle a frog's nerve cell with a long fiber that carries signals to another nerve cell red blood cells moving through a blood [Music] vessel so an animal has several different kinds of living cells now in some ways every animal cell is alike every animal cell has a kind of control center called a nucleus and an outer covering called a membrane a plant cell also has a nucleus and a membrane but outside the membrane it has another covering called a cell wall and in every cell both plant and animal there are several smaller parts to see some of these smaller parts we'll put some cells from an onion under the microscope this is what goes on inside a living cell you can see that the cell contains many smaller parts and the small parts are moving around why do they do that we aren't really sure we just know that it happens inside every living [Music] cell we're not close enough to really see what the moving particles look like so we'll use some drawings to show just a couple of them the top half is cut away so you can see inside I suppose they're different because they have different jobs to do right some plant cells have another important kind of small particle here are cells from a leaf of a green plant the tiny green particles inside the cells are able to store up energy from the Sun the plant uses this energy to make its own food and of course a plant needs food in order to grow when a plant grows do the cells just get bigger and bigger well that's what happens at first but when a cell reaches a certain size something else begins to happen we'll speed up the action to show how it works the material in the cell begins to separate into two parts exactly alike this is the beginning of what we call cell division when it's finished the two parts of the cell will become two new [Music] cells watch again we'll see the first part of the process of cell division but not quite all of it [Music] the same thing happens with animal cells for a while the cells just grow larger and of course there's a lot of activity inside every living [Music] cell [Music] I think this one is starting to divide yeah there it goes the camera is speeding this up quite a bit all of the cells don't divide at the same time here it's just the one in the center of the screen that's [Music] dividing this kind of cell division produces new cells that are exactly like the old ones and this causes living things to grow larger but there's another kind of cell division one which makes it possible for living things to reproduce themselves a plant has certain special Parts where this kind of cell division take we've also moved in closer now there are thousands of cells some of them the ones with a darker color have begun to move they'll gather in certain places and begin to change into the specialized cells that form the various parts of the [Music] body is that part of the skeleton [Music] right we've already seen several kinds of cells different cells with different jobs to do cells that make make it possible for living things to reproduce themselves and cells that form the parts of plants and animals the story of every living thing begins with the story of the living [Music] cell