mineral salt

In nutrition, simple inorganic chemicals that are required, as nutrients, by living organisms. Plants usually obtain their mineral salts from the soil, while animals get theirs from their food. Important mineral salts include iron salts (needed by both plants and animals), magnesium salts (needed mainly by plants, to make chlorophyll), and calcium salts (needed by animals to make bone or shell). A trace element is required only in tiny amounts.

Mineral salts are taken up in soluble form. When mineral salts dissolve in water they separate into particles called ions. Mineral salts do not usually contain the element carbon and are therefore inorganic (organic compounds always contain carbon).

Plant roots absorb individual mineral ions from soil water. Some of the ions travel by diffusion into the root; others are absorbed by active transport. The minerals required in the greatest amounts are those containing the element nitrogen, for example nitrate ions (or ‘nitrates’), which are a key component of inorganic fertilizer. A plant uses nitrates in the production of proteins such as enzymes, so they are important for plant growth. They are often in short supply in the soil, which is why inorganic fertilizers are required. Plants also require magnesium in order to make chlorophyll, the green chemical that absorbs the energy of sunlight for photosynthesis.

Mammals absorb the mineral salts they need from their food. Important mineral salts include iron salts (needed for haemoglobin) and calcium salts (needed by animals to make bone). Both plants and animals need a range of other minerals in tiny amounts (trace elements).

Eutrophication Farmers add fertilizers to soil to replace the nutrients that crops remove. Excess fertilizers may be washed into lakes and rivers. Pollution of water by fertilizers may cause an effect called eutrophication. The stages in this process are: the rapid growth of water plants; the death of some of these plants due to competition, for example for light; an increase in the number of micro-organisms that feed on dead organisms; the increased use of oxygen from the water by these micro-organisms for respiration; and the resultant death due to oxygen shortage of fish and other aquatic animals.

Untreated sewage provides food for micro-organisms. It is especially rich in the mineral ion phosphate. Sewage has even more effect in water (eutrophication) than dead vegetation.

Pollution from fertilizers In pollution from fertilizers and sewage, the mineral that causes the most lasting problem is phosphate. It can remain in soil and mud and cause problems for hundreds of years.