9.3: Growth in plants
Annuals die every year.
Life span limited to one
year e.g. corn, wheat,
lettuce, rice
Biennials take two
years to complete life
cycle e.g. Parsley, wild
carrots
Perennials live longer
than two years, death
usually due to
environmental factors or
disease e.g. daisies
Plants show indeterminate growth – they grow throughout their lives.
Humans display determinate growth, we stop growing at a certain
point.
Dicotyledonous plants have two types of meristematic tissue (growing
part of the plant):
Apical – tip of roots/stems. Called primary growth
Lateral – growth in the thickness of the plant. Secondary growth.
Again there are two types of lateral meristems:
- Vascular cambium – between xylem & phloem in vascular
bundles, inside the bundle secondary xylem are produced. Outside
the bundle secondary phloem are produced.
- Cork cambium – cork cells produced on the outer bark
Apical Meristem
Lateral Meristem
Tropism
What do plants respond to?
Light, chemicals, gravity, water, touch
Plants demonstrate positive phototropism
What are the advantages of this behaviour?
What causes this behaviour?
Auxins!
Auxins are found in:
1. seed embryos
2. Meristems of apical buds
3. Young leaves
The hormone can only work if the
plant cells contain an auxin
receptor.
Auxin increases a plants flexibility, allowing
it to move towards the stimulus.
Auxin is redistributed in the plant, not
produced. The redistribution of auxin to
cells on the dark side cause those cells to
elongate – result – shoot moves towards
the light.
What’s the proof?
What experiments could be conducted?