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INTRODUCTION

Although life at the macro level is diverse, the chemistry making up that life is remarkably similar. All living things are made up of basic building blocks called elements. An element is a substance that cannot be broken down into simpler substances using chemical means. Carbon, oxygen, hydrogen, nitrogen, sulfur, calcium, sodium and iron are examples of elements you will come across in Life Sciences.

Each element is distinguished by the composition of its atom. An atom is the basic unit of matter. Molecules are formed when one or more atoms are covalently bonded together. The atoms of a molecule can be identical, such as O₂ or H₂ or differ such as H₂O. A compound is formed when atoms of different elements join together. Because all compounds contain more than one atom, all compounds are molecules. However, not all molecules are compounds.

Compounds are divided into organic and inorganic compounds.  Organic compounds always contain carbon, but not all compounds that contain carbon are organic. A general rule of thumb is that organic compounds contain carbon, with at least one of these carbons bonded to hydrogen atoms.

 Carbon dioxide is therefore an inorganic compound even though it contains carbon.

The major organic compounds found in living organisms include: carbohydrates, fats, proteins and nucleic acids.

Inorganic compounds 

1. The role of water in the maintenance of life 
2. As shown in the table above, up to 65% of our bodies are made up of water. Water is an inorganic compound made up of two hydrogen atoms and one oxygen atom. Its molecular formula is H₂ Water plays an important role in the maintenance of biological systems.
3. Temperature regulation: in humans, the sweat glands produce sweat which cools the body as it evaporates from the body surface in a process called perspiration. In a similar way, plants are cooled by the loss of water vapour from their leaves, in a process called transpiration.
4. Form and support: water is an important constituent of the body and plays an important role in providing form and support in animals and plants. Animals, such as worms and jellyfish, use water in special chambers in their body to give their bodies support. This use of water pressure to provide body form, and enable movement is called a hydrostatic skeleton . Plants grow upright and keep their shape due to the pressure of water (turgor pressure) inside the cells.
5. Transport medium: water transports substances around the body. For example, water is the main constituent of blood and enables blood cells, hormones and dissolved gases, electrolytes and nutrients to be transported around the body.
6. Lubricating agent: water is the main constituent of saliva which helps chewing and swallowing and also allows food to pass easily along the alimentary canal. Water is also the main constituent of tears which help keep the eyes lubricated.
7. Solvent for biological chemicals: the liquid in which substances dissolve is called a solvent. Water is known as the universal solvent as more substances dissolve in water than in any other liquid.
8. Medium in which chemical reactions occur: all chemical reactions in living organisms take place in water.
9. Reactant: water takes place in several classes of chemical reactions. During hydrolysis reactions, water is added to the reaction to break down large molecules into smaller molecules. Water can also be split into hydrogen and oxygen atoms to provide energy for complex chemical reactions such as photosynthesis.

Minerals 

Dietary minerals are the chemical elements that living organisms require to maintain health. In humans, essential minerals include calcium, phosphorous, potassium, sulfur, sodium, chlorine and magnesium.

Macro-elements (macro-nutrients) are nutrients that are required in large quantities by living organisms (e.g carbon, hydrogen, oxygen, nitrogen, potassium, sodium, calcium, chloride, magnesium, phosphorus and sulfur).

Micro-elements (micro-nutrients) are nutrients that are required in very small quantities for development and growth and include iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc and molybdenum.

Nutrients required for human health

The tabble below summarises some important minerals required for proper functioning of the human body. Proper nutrition involves a diet in which the daily requirements of the listed mineral nutrients are met.

Minerals required by humans.

Nutrients required for plant growth

The previous section examined the key nutrients important for animal growth. In Table 1.4 we will now look at the key nutrients required for plant growth.

 Chlorosis is the yellowing of the leaves due to low production or loss of chlorophyl

Nutrients required for plant growth.