What are the chemical elements that form most of living biological matter?

What are the chemical elements that form most of living biological matter? 
The chemical elements that form most of the molecules of living beings are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). Life on Earth can be understood as a form of existence of matter. All the living matter, i.e. living organisms, is composed of the same particles (atoms, ions, molecules) as the non-living organisms and chemical laws and laws of physics apply to both of them.

There is a close connection between living and non-living nature, however, they differ in chemical composition, structure, complexity, and organization. While the chemical composition of the non-living nature is varied, the existence of living organisms is based on the presence of a few chemical elements, especially carbon, oxygen, nitrogen, and hydrogen.

All the chemical compounds in living organisms are composed of chemical elements. These days almost 120 chemical elements are known. Out of this number 92 elements are naturally present in nature (the rest were made in laboratories). Out of the 92 elements, only 30 elements create the living matter and they are called biogenic elements. There are 92 elements in the Earth´s crust. Oxygen and silicon represent the highest percentage - 75% of all elements. Both these elements of the Earth´s crust, as well as the other elements, are bonded especially in minerals (e.g. oxides, silicates) and rocks. The remaining 90 elements represent about 25 % of all elements.

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In all living systems, we can always find 4 basic elements: carbon, oxygen, nitrogen, and hydrogen. Carbon is the basic building unit contained in living matter. The percentage of carbon in the mass of living matter is 19.4 %. Oxygen and hydrogen are present in almost all organic compounds which create living organisms. The percentage of oxygen in the mass of living systems is 62.8 %, and the percentage of hydrogen is 9.3 %. The source of hydrogen for organisms is water, and the source of oxygen is water and the atmosphere. Nitrogen is bonded mainly in amino acids, proteins, and nucleic acids. Its percentage is 5.1 %.

All elements contained in living matter are called biogenic elements. They are present in compounds, in the form of ions, and in some special cases they are unbound (e.g. oxygen). According to their representation in organisms, the biogenic elements are divided into 3 groups: macrobiogenic, microbiogenic, and trace elements. Trace and microbiogenic elements are sometimes also called oligogenic elements.

Macrobiogenic elements – C, O, H, N, S, P, Na, K, Ca, Mg, Cl, Fe.  Four of these elements – O, C, H, and N – represent up to 95 % of living matter. The rest of the elements mentioned above represent up to 4.9 %. Macrobiogenic elements have a building function.

Carbon is the basis for all living matter. The typical feature of carbon atoms is the ability to bond to each other or to atoms of other elements. That is why there are many organic compounds of carbon. Carbon is also present in carbon dioxide and carbonates.

Oxygen and hydrogen in organisms are present both in the form of organic and inorganic compounds and they are a part of the basic micromolecule – water. Oxygen is produced by autotroph organisms (especially plants and cyanobacteria) during the process of photosynthesis.

Nitrogen is a component of proteins and nucleic acids. It is also a part of nitrates and ammonium carbonate, which are necessary for the mineral nutrition of plants and also the synthesis of plant proteins. What are the chemical elements that form most of living biological matter?

Questions on Chemical compositions of living organisms

1) Which two chemical elements are the most frequent in the Earth’s crust and what is their form? 
Look at the properties of Oxygen and Silicon - the two most abundant elements in the Earth's crust - by clicking on their symbols on the Periodic Table.

2) What are biogenic elements, and how do we divide them?
Biogenic elements are chemical elements that take part in the biological processes of live organisms. The most important of them are chemical elements that makeup 97.5% of the mass of the organism. These are organogenic elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur).

3) Name 4 basic macroelements. Why are they important? What is their content (percentage) in living organisms?

4) Name the microbiogenic elements and give examples of their importance.

5) What is the function which is common for trace elements and what is their content in living organisms?

6) Explain the term biomolecule. Which element forms biomolecules?

7) What is the average content of water in organisms and what is its function? 

8) Give 3 examples of non-dissociated salts which are present in the human body. Give examples of tissues, where the salts are present.

9) Name the basic groups of biopolymers and name the building units they consist of.

10) Give the average percentage of proteins, saccharides, lipids, and nucleic acids in living organisms. 

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