A chemical change is the conversion of a substance into a completely different substance, as for example when propane burns in oxygen and these two substances are converted into carbon dioxide and water. All life processes, including the growth of a plant from seed, involve numerous chemical changes.
Metabolism is a complicated network of chemical changes that all living plants and animals effect in their individual cells. For example, respiration (the conversion of carbohydrates into carbon dioxide and water accompanied by the release of free energy) is a metabolic process.
A seed contains a tiny little plant called an embryo. This embryo is engaged in the chemical changes of metabolism, but at a very slow rate.
Hormones called "gibberellins" are important in germination. They cause the embryo to speed up its metabolic activities, especially the process of respiration.
Another chemical change effected by the growing embryo is a production of enzymes and other proteins.
These enzymes produce further chemical changes. Some enzymes digest the starches stored in the seed.
Continued Chemical Changes
As a plant grows and flowers it continues to produce such chemical changes as protein and DNA synthesis, respiration, photosynthesis, and digestion.