Understand that chemical control in plants is brought about by plant growth substances such as auxins, cytokinins and gibberellins.

Know that auxin has several effects, including cell elongation, suppression of lateral buds (apical dominance) and promoting root growth.

Understand that plant growth substances often interact with each other as shown by the antagonistic actions of cytokinin and auxin on apical dominance.

Understand how phytochrome controls flowering and photomorphogenesis.