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Living things, like all matter in the universe, are made up of very small particles called atoms. These particles are so small you would not be able to see them, even if you used a microscope.
Atoms are the first structural level of matter and they organise themselves into molecules.
We know 117 different types of atom. Each of them constitutes a chemical element. A chemical element is a form of matter composed of atoms of the same type.
The atoms that make up all living things mostly consist of six different chemical elements: carbon (C), oxygen (O) hydrogen (H), nitrogen (N), phosphorus (P) and sulphur (S). These elements constitute more than 99% of the matter found in living things. They are called primary bioelements.
Carbon atoms have the ability to link to other atoms. This allows life to take place and is why carbon is the most important bioelement.
Other chemical elements are found in living things; however, they appear in smaller quantities. We refer to them as secondary bioelements. They are: calcium (Ca), sodium (Na), magnesium (Mg) and potassium (K).
Lastly, trace elements are elements which are found in living things, but only in small amounts (0.1%). Although trace elements are not common, they are also important for certain functions. Examples of these are: iron (Fe) and iodine (I).
Some biomolecules are exclusive to living things. They are known as organic biomolecules. These are: carbohydrates, lipids, proteins and nucleic acids.
Inorganic biomolecules (water or mineral salts) are also found in both living things and non-living things.
Water is essential for the existence of life and is the most common biomolecule. Between 50% and 95% of the weight of any living thing is water.
| Organism | Water (%) |
| adult | 63 |
| crab | 77 |
| snail | 80 |
| jellyfish | 95 |
| algae | 98 |
| fungus | 91 |
| lichen | 55 |
Percentage of water content of some living things
| Characteristics | Biomolecules | Functions | Examples | |
| Organic | They are unique to living things. Its main element is carbon (C). |
Carbohydrates | They provide instant energy for organisms. | Glucose, lactose, sucrose. |
| Lipids | They store energy for future needs. | Fats, waxes, cholesterol. | ||
| Proteins | They form structures such as hair, skin and muscles. | Haemoglobin, collagen, keratin. | ||
| Nucleic acids | They contain an individual's genetic information. This information is responsible for the functioning of every cell. | DNA, RNA | ||
| Inorganic | Also found in non-living things. Its main element is not carbon (C). |
Water | It is involved in many different functions such as thermal regulation and the transport of substances. | |
| Mineral salts | They participate in the formation of the rigid structures (bones) which organisms have, and in important cellular processes. | Calcium carbonate, calcium phosphate. |
Activity 6
What is the most common chemical element found in matter?
Activity 7
7. Listen and identify the biomolecules, then match them to their definitions.
Activity 8
Classify the following elements depending on whether they are primary bioelements, secondary bioelements, trace elements, organic biomolecules or inorganic biomolecules:
Activity 9
Do some research and find out why iron is so important for human beings.
