most living organisms, such as bacteria, plants or animals, consist of single cell or many cells.

virus show characteristic of life because it entered the cell and performed with the help of cellular operating mechanism.

let's see the cell and virus size:

一 elements

    what is element?

          element is a substance that can't be broken down into simpler chemical substance.

          organisms are composed of 30 elements and accout for about 25% of elements on     Earth. these elements distribute at the above and middle parts of the periodic table.

from this figure, we find that oxygen, carbon, hydrogen and nitrogen account for 65%, 18%, 10% and 3% of the mass of our human body. totally, these four elements account for 96% of the mass of our human body. therefore, these four elements are very important for us!

question: We can’t live without oxygen, but if the earth’s atmosphere is pure oxygen….

                 please write whatever you think.

  there are 7 elements account for nearly 4% of the mass of our human body. they are Ca, P, K, S, Na, Cl and Mg.

  

二  trace element

      there are some elements account for lower than 1%. they are lower in human body, but they play a key role in our life. for example, Fe is the essencial component of oxyphorase(血红蛋白). so they are essential for us to keep healthy.

(note:trace element means that percentages of some elements are smaller than 1%. this is not a teconology that can trace some dieases in human body. that is isotope, for example, check HP)