Plants need many other elements for proper growth in addition to carbon, hydrogen and oxygen. Some elements are needed in large quantities while others are needed in very small quantities. Elements needed in large quantities are called macronutrients and are nine in number. They include nitrogen, sulphur, phosphorus, carbon, hydrogen, oxygen, calcium, potassium and magnesium. Absence of any of these essential elements will result in unhealthy plants with poor yields.
Various individual elements play different specific roles in plant growth and reproduction. Nitrogen is a major component of proteins which form the building blocks of cells and enzymes while phosphorous is important in nucleic acids and ATP. Potassium is important in osmosis and transpiration while magnesium is a basic component of chlorophyll, the pigment involved in photosynthesis. Calcium is needed for the formation of cell walls.
Elements that are needed in very small amounts are called micronutrients. These include iron, chlorine, copper, magnesium and zinc. These elements play minor but equally vital roles in enzyme reactions as cofactors.
It is possible to identify the effect of a missing element in the soil on plant growth by carrying out a hydroponics experiment.
Identification of Essential Elements
This entails carrying out a hydroponics or a water culture experiment. Transfer two seedlings grown in a pot with their roots intact to two flasks A and B. as shown in the diagram. In A introduce a solution containing all the essential elements.
In B introduce the same amount of mineral solution but omit one element. The solvent in both flasks should be triple distilled or de ionised water. Keep air blowing through the apparatus to ensure that the roots are oxygenated. Leave the set-up exposed to sunlight for at least two weeks or more. Repeat the experiment with other elements. Then note the sizes of the two seedlings and the colour of the leaves in each case.
Hydroponic culture:
Insert diagram
A hydroponics experiment involves growing plants in two flasks, in which one flask has all the essential elements, while the other flask has one element less.
Deficiency in any of the nutrients can result in poor plant growth or failure to carry out an essential function. For example, a magnesium deficiency causes the yellowing of leaves, which reduces photosynthesis. Lack of calcium, caused retardation in plants. This is because the plant meristematic cells lack cell walls necessary to complete cell elongation.
An essential element must fulfil two criteria:
1. Be needed for normal growth and reproduction in several plants.
2. It should not be replaceable by other elements.
Table? Showing essential elements and the role of each one it.
| Element | Its characteristics and function | Effect due to deficiency |
| Nitrogen (N) | Component of proteins, amino acids, Enzymes, Hormones and nucleic acids | Loss of colour and stunted growth. |
| Phosphorous (P) | Component of nucleic acids, Phospholipids, ATP, and several coenzymes | Stunted growth and mottled leaves |
| Potassium (K) | Present in guard cells of stomata in leaves, Necessary in osmosis, Transpiration and protein synthesis. | Weak stems and roots, yellowing of leaves and mottled appearance of leaves |
| Magnesium(Mg) | Component of chlorophyll, cofactor for Enzymes | Yellowing of leaves |
| Calcium(Ca) | Necessary for cell wall formation, Permeability of membranes | Death of plant shoots and roots especially of young plants |
| | Component of amino acids | Leaves become pale green with dark spots |
| Boron(B) | Sugar transportation by phloem vessels | Death of stem, root and apical meristem |
| Manganese(Mn) | Formation of amino acids, activates Enzymes involved in cellular respiration, needed in photosynthesis | Yellowing of leaves and some signs of necrosis |
| Iron(Fe) | Compound of cytochrome in respiration, needed for chlorophyll | Leaves become yellow and the short and slender |
| Molybdenum (Mn) | Needed in nitrogen fixation | Yellowing of leaves, death of young leaves |
| Zinc(Zn) | Synthesis of chlorophyll | Stunted growth |
Study Questions
1.Name the elements that make up most of a plant body.
2.Briefly describe one method used to determine the effect of an essential nutrient on a growing plant.
3.How are mineral elements categorised and why are they categorised in this manner?
4.Discuss a plant’s need for nitrogen, phosphorus and manganese.
5.Expound on the characteristics of an essential element in plants
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