Cells

Essential Understandings about Cells:

• All living organisms are composed of one or more cells. A cell is the basic structural & functional unit of all living organisms.  All cells come from other cells. All humans start as one cell, that cell was made by their parents. The average human adult is made up of about 30 trillion cells.

• Cells are very small. You need a microscope to see cells. Cells are smaller than 1 millimeter. Biologists divide 1 millimeter into 1000 parts, and one of those parts is called a micron or micrometer. The abbreviation for a micron is µm. There are 1000 microns in 1 millimeter. A human hair can be anywhere within the range of 50 to 120 microns. Some life forms are made of just one cell, these are called unicellular organisms, like an amoeba.

• Cells come in an amazing variety of shapes. Blood cells are round, muscles cells are long and thin. The shape of the cell helps the cell do its job. Cells have smaller parts inside them, called organelles. Two examples of organelles include mitochondria which supply power to cells that contain a nuclues, and chloroplasts which are organelles that allow plants to capture & use light.

• Cells that do not have a nucleus are very small & are called prokaryotic. Bacteria are prokaryotic cells & are usually between 1 and 10 microns. Cells that do contain a nucleus are called eukaryotic. Most plant & animal cells are eukaryotic and range from 10 to 100 microns. On this  Learning Page, we feature the CELL SIZE AND SCALE Interactive from Learn.Genetics, a fantastic site from the University of Utah. This will help you learn about the size of cells. The green organelles in the picture above are chloroplasts (3-4 µm ) and they are inside a plant cell.

• Cells are constantly dividing to form new cells. When regular body cells divide it is called mitosis. When sex cells (egg & sperm) divide it is called meiosis.

• The best way to see living cells is with a light microscope. A typical light microscope with magnify your vision by 40 times (40X) and by 100 times (100X) and by 400 times (40X).  Collecting a small amount of pond water and using 100X's magnification will allow you to see many living cells.

Learn.Genetics has produced this elegant and effective way for you to get a sense of the scale of cells, molecules, and viruses.