Plant nutrients are necessary for plant growth. Carbon and oxygen are absorbed by the leaf from the air, while other nutrients are absorbed by the roots. If essential elements needed by the plants are not enough to sustain its growth cycle, signs of nutrient deficiency can be observed through the leaves. See below infographic on the signs of nutrient deficiency:

My Infographic

Two types of plant nutrients are the macro-nutrients and the micro-nutrients. The macro-nutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.2% to 4.0% on a dry matter weight basis. Micro-nutrients are present in plant tissue in quantities measured in parts per million, ranging from 5 to 200 ppm, or less than 0.02% dry weight.

Macro-nutrients derived from air and water:
1. Carbon
2. Hydrogen
3. Oxygen

Primary Macro-nutrients:
1. Phosphorus
2. Potassium
3. Nitrogen

Secondary and Tertiary Macro-nutrients:
1. Sulphur
2. Calcium
3. Magnesium
4. Silicon

Micro-nutrients or trace minerals:
1. Iron
2. Molybdenum
3. Boron
4. Copper
5. Manganese
6. Sodium
7. Zinc
8. Nickel
9. Chlorine
10. Cobalt
11. Aluminium

Source: Wikipedia