In a very old tree, you may be certain that the sapwood is on the outside, while the heartwood is in the middle.

Fertilizers are chemicals added to plants to help them grow. Important elements in fertilizers include nitrogen, phosphorus and potassium. Manure (animal waste) is also used as a fertilizer.

Plant matter found at the bottom of areas with water such as swamps can eventually turn into coal due to a process called metamorphosis (changing form).

In the agricultural industry, to ensure crops of food grow well water is often added to soil in the form of irrigation.