Close your eyes and picture a brick wall. What is the wall's basic building block? It is a single brick. Like a brick wall, cells are the building blocks that make up your body.
Your body has many kinds of cells, each specialized for a specific purpose. Just as we use a variety of materials to build a home, the human body is constructed from many cell types. For example, epithelial cells protect the body's surface and cover the organs and body cavities within. Bone cells help to support and protect the body. Immune system cells fight invading bacteria. Additionally, blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role during the body's growth, development, and day-to-day maintenance. In spite of their enormous variety, however, cells from all organisms—even ones as diverse as bacteria, onion, and human—share certain fundamental characteristics.
Funga macho yako na ufikirie ukuta wa matofali. Ni nini kiini cha msingi cha ukuta huo? Ni matofali moja tu. Kama vile ukuta wa matofali, chembe ni vipande vya ujenzi vinavyofanyiza mwili wako. Mwili wako una aina nyingi za chembe, kila moja ikiwa na kusudi hususa. Kama vile tunavyotumia vifaa mbalimbali kujenga nyumba, mwili wa mwanadamu umefanyizwa kwa aina nyingi za chembe. Kwa mfano, chembe za epithelial hulinda uso wa mwili na kufunika viungo na mashimo ya ndani ya mwili. Chembe za mifupa husaidia kutegemeza na kulinda mwili. Chembe za mfumo wa kinga hupigana na bakteria zinazoingilia. Kwa kuongezea, damu na chembe za damu hubeba virutubisho na oksijeni kotekote mwilini huku zikiondoa kaboni dioksidi. Kila moja ya aina hizo za chembe hutimiza fungu muhimu katika ukuzi, ukuzi, na utunzaji wa kila siku wa mwili. Hata hivyo, licha ya utofauti wao mkubwa, chembe za viumbe wote - hata zile tofauti-tofauti kama bakteria, vitunguu, na wanadamu - zina sifa fulani za msingi.