CHAPTER ONE THE CHEMICAL COMPONENTS OF THE CELL Biology Form Three Student Book
1. What is the percentage by mass of oxygen, carbon, hydrogen, nitrogen,
phosphorus and sulfur in the earth and in the human body? What do you
observe?
(MB
2. Which elements have a higher percentage in the nature and in the human
body? State some compounds that contain these elements in their struc-
ture.
3. Many chemical substances enter the structure of the of the cell. In your
opinion, what is the importance of these substances? Why have you select-
ed these substances?
4. There are other elements that exist in a fewer percentage, search these
elements and state the percentage abundance of each in the cells of living
organisms.

1. Almost 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium.
2. The four most abundant elements in the human body – hydrogen, oxygen, carbon and nitrogen – account for more than 99 per cent of the atoms inside you.

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