1. Nitrogen, phosphorus, potassium and magnesium are four macro-elements needed by plants for healthy growth.
2. A plant grown in a water culture experiment lacking one essential macro-element displays certain deficiency symptoms.
3. Lead inhibits the action of certain enzymes. It is poisonous to humans and may have a detrimental effect on the intelligence of children.
4. Iron is essential to humans for the formation of haemoglobin.
5. Calcium is essential to humans for the formation of healthy bones and teeth.
6. Vitamin D is needed by humans to promote the uptake of calcium ions…