• “The growth and development of a plant are influenced by genetic factors, external environmental factors, and chemical hormones inside the plant. Plants respond to many environmental factors such as light, gravity, water, inorganic nutrients, and temperature.” ~Biology Online ~ Growth and Plant Hormones.
How does a seed ‘know’ when to germinate? How does a tree ‘know’ when to start changing leaf colour and drop it’s leaves for winter? How does a plant ‘know’ which direction to grow leaves and roots and where the light is? How does a plant ‘know’ when to produce flowers and what colour they should be? Instead of having a brain, central nervous system and endocrine system that co-ordinate communication, every plant cell can produce hormones (growth substances) that are transported throughout the plant via diffusion from cell to cell and through the xylem and phloem. (How mobile are plant hormones?).
Botanists recognize five major groups of hormones:
  • auxins
  • gibberellins
  • ethylene
  • cytokinins
  • abscisic acids
Although plants usually appear not to move, time-lapse photography shows that plants do, in fact, move and sometimes quite quickly. There are different types of movement, tropisms and nastic movements:
  • phototropism
  • thigmotropism
  • geotropism (or gravitropism)
  • chemotropism
  • thigmonastic movements
  • seasonal responses
  • photoperiodism
Draw up a table with three columns, with each of the key concepts above in the first column, a definition in the second column and an example in the third column. You can get your information from these resources:
Use digital tools to create a labelled image showing the different plant hormones, where they act (leaves, stems, roots, fruits, flowers etc) and what they do.