Cell: Structural Unit of Life

let's by looking at a cup and onion first we peel off a thin piece of the onion and put it on a glass slide a drop of water keeps the onion from drying out a cover glass keeps it flat then we place the slide on the stage of the microscope and we lower the lens carefully looking through the eyepiece we adjust the microscope and focus it we see that the piece of great many little sections close together these are living cells each one about a hundredth of an inch long thousands of them make up the onion plant the cells we are looking at are pale but we can see the structure of the cells more clearly by staining them with a Dy such iodine solution when a drop of iodine is put on the slide it seeps into the onion cells and colors them now we can see the parts of each cell distinctly each cell is a separate little structure the pointer shows us the cell wall scientist have discovered that almost every plant cell has a cell wall and a nucleus the cells we've been looking at appear flat because we are seeing only one side a diagram will help us see a cell as it really is every cell has thickness here is the cell wall inside it is the nucleus the small white drops are called vacuoles most of the material inside the cell wall is protoplasm let's look at the protoplasm in the cells of this common water plant the microscope shows us that protoplasm is alive see how it moves continually streaming about within the cell wall protoplasm is the life substance of plants and of animals scattered throughout the protoplasm of this Leaf are many tiny green particles these green particles are important to all of us for in them is made the food of the plants and plants in turn are the food of animals and of man some of the food produced by the cells is used to make more protoplasm and thus produce growth some of the food is stored as starch applying a dark stain to the stored starch helps us to see it better in the cells and so some plant cells manufacture food but are all the cells in a single plant alike are the cells of the leaves the same as those of the stem or of the roots let's look at the cells in this Snapdragon Leaf within a single leaf we find three kinds of cells different in shape and different in function the outer cells protect the leaf the cells just below these are the chief food makers notice that they have the most green matter the Loosely packed cells below allow circulation of air and water in the stem of the same plants as in the leaf certain cells have certain functions for example these cells are lined up end to end and may carry liquids through the stem in these cells food may be stored and this layer of cells forms a protective covering on the out of the stem now if we take the root of the same plant and make a cross-section of it we see cells that are different from the cells of the leaf and of the stem we can see too that all root cells are not alike the pointer shows us those that carry water through the root up to the stem and so we see that a plant is made up of different kinds of cells although these cells may be different in shape and different in function they are all made up of protoplasm animal cells also consist of protoplasm this tiny animal called aneba has but a single cell we can study it as an example of an animal cell the amoeba has a nucleus it has living streaming protoplasm unlike most plant cells it has no stiff cell wall it can move slowly from place to place whereas green plant cells can produce their own food an amoeba must find its food here an amoeba is approaching a tiny bit of plant the protoplasm slowly closes around the food and takes it into the cell this amoeba has captured a tiny animal for food as the amoeba takes in food it grows in other words growth is the making of more protoplasm when an amoeba grows to a certain size it may divide as this one is beginning to do here we actually see a large amoeba dividing it is surrounded by other tiny animals that live in the water with it the two halves of the amiba move apart and finally separate now there are two cells Each of which can grow and divide again in any plant or animal the cells change food into new protoplasm the cells reproduce their own kind the cells are basis of life and growth just as we saw different kinds of plant cells we can find different kinds of animal cells the skin of a frog for instance is made up of these cells which contain color or pigment the muscle of a frog is made up of long thin cells closely resembling these are the muscle cells of a water bug cells which do similar work are often similar in structure these cells are from a cricket by their structure we can guess that they too are muscle cells most of us have heard about blood cells these blood cells of the Frog are very different from the long muscle cells we saw but frog blood cells look somewhat like human blood cells at this very moment blood cells like these are streaming through our bodies the human body like any living thing is made up of millions of cells of different kinds now what are some of the things we've learned about cells a cell is not flat it has thickness in most cells there is a nucleus and a cell wall all living cells are made of protoplasm the protoplasm must be supplied with food in green plants food is made within the cell in animals such as the amoeba food is taken into the cell with sufficient food cells grow full grown cells are continually de all cells are not alike the cells within a single plant may be of different kinds just as the cells of a single animal may be of different kinds but we have know about cells