1. Growth in plants
Topic 9.3

2. U: Undifferentiated cells in the meristems of plants allow indeterminate growth
Most plants have indeterminate growth = cells divide indefinitely (most animals have determinate growth)
Most plant cells are totipotent = ability of a single cell to divide and produce all of the differentiated cells in an organism (only an animal zygote/early embryo is totipotent)
Meristem = undifferentiated cells that are dividing (where plant growth takes place)
Primary meristems =
Root apical meristem = tip of root where growth occurs
Shoot apical meristem = tip of stem where growth occurs
Secondary meristems =
Lateral meristem = cause stem to grow laterally (in diameter); in dicots

3. U: Mitosis & cell division in the shoot apex provide cells needed for extension of stem & development of leaves

5. U: Plants hormones control growth in shoot apex
Hormone = chemical message produced & released in one part of organism to have an effect in another part
Auxins = plant growth hormones
IAA = indole-3-acetic acid (type of auxin)
Promotes elongation of cells in stems
Made in shoot apical meristem & transported down stem to stimulate growth
High concentrations can inhibit growth

6. Axillary buds = side stem
Apical dominance = axillary buds closer to shoot tip inhibited by auxin
Can be disrupted by pruning shoot tip
Cytokinins = hormones produced in root; promote axillary bud growth
Gibberellins = hormones that contribute to stem growth

7. If you want bushier, thicker plants, cut them back!

8. auxins vs cytokinins

9. U: Plants respond to environment by tropisms
Plant hormones control growth rate and direction of growth
Direction influenced by light & gravity
Stems grow towards brightest light
In absence of light, plants grow up
Tropism = directional growth in response to external stimuli (light & gravity)
Phototropism = growth towards light
Gravitropism = growth in response to gravity

10. U: Auxin influences cell growth rates by changing the pattern of gene expression
1st stage in phototropism = light absorption by photoreceptors called phototropin (blue-light receptors)
Phototropins bind to receptors, which control transcription of genes that code for PIN3 proteins that transport auxin from cell to cell

11. U: Auxin efflux pumps can set up concentration gradients of auxin in plant tissue
Auxin is transported to shady side of stem
Cells on shady side elongate, curving stem towards light
Leaves attached to stem will receive more light and photosynthesize faster
Auxin transported to bottom of cells
Auxin inhibits root cell elongation
Top cells elongate faster than bottom cells, causing root to bend downward