Biogenic elements and their importance in living organisms
Elements that enter a living organism and are needed for life are called biogenic elements. The Earth’s crust consists mostly of O, Si, Al, Fe, Ca, Na, K and Mg, yet carbon forms the basis of life. By mass the human body is about 65 % oxygen, 18 % carbon, 10 % hydrogen, 3 % nitrogen, plus calcium and phosphorus; these are the macrobiogenic elements. Elements present in very small amounts (below 0.01 %) but still essential are microbiogenic elements, or trace elements: Fe, Zn, Cu, Mn, Co, Mo, I, F and others. Iron in the blood’s haemoglobin carries oxygen, and its lack causes anaemia; iodine is part of thyroid hormones, and its lack causes goitre; fluorine is needed for tooth enamel and strong bone; about 99 % of the body’s calcium is in bones and teeth; cobalt is part of vitamin B₁₂. In plants a lack of iron turns leaves yellow, a lack of zinc makes leaves small, and boron, copper and molybdenum affect the yield. Trace elements are useful only in the right amount, an excess is poisonous; a balanced diet supplies them. Vitamin and mineral supplements should be taken only on a doctor’s advice.
“Chemistry of my body”: draw a body outline and write the macro- and trace elements on it with their function (bone — Ca, P; blood — Fe; thyroid — I; teeth — F, Ca). From the list write 3 deficiency diseases and foods that prevent them (milk, fish, meat, iodized salt). Nothing is swallowed or tasted.