5.1.5 Plant hormones Flashcards
In plants, hormones are transported by:
- Active transport
- Diffusion
- Mass flow (in phloem or xylem)
Hormones affect processes of:
- Cell division
- Cell elongation
- Cell differentiation
Effect of auxins
- Control cell elongation
- Prevent abscission
- Maintains apical dominance
- Involved in tropisms
- Stimulates release of ethene
- Involved in fruit ripening
Effect of gibberellin
- Causes stem elongation
- Trigger mobilisation of food stores in seed at germination
- Stimulation of pollen tube growth in fertilisation
Effect of ethene
- Causes fruit ripening
* Promotes abscission in deciduous trees
Effect of ABA (abscisic acid)
- Maintains dormancy of seeds and buds
- Stimulates cold protective responses (e.g. antifreeze production)
- Stimulates stomatal closing
Synergism
substances working together –> greater response than when hormones work alone
Antagonism
substances have opposite effects; the balance between them determine the response
Steps in seed germination
1) Seed absorbs water ⟶ embryo is activated and begins to produce gibberellins
2) Gibberellins stimulate production of enzymes to break down food stores in seed
Monocots (seeds)
• Have only 1 seed leaf inside the seed coat
often because endosperm to feed new plant is not inside seed leaf
Dicots (seeds)
• Have 2 seed leaves inside the seed coat
usually rounded and fat because they contain endosperm to feed embryo plant
Role of gibberellins in seed germination
• Cause synthesis of amylase in seed
⟶ Amylase breaks down starch into glucose for respiration
⟶ Respiration provides energy for growth
⟶ Enabling seed germination
Food store in dicot seeds?
Cotyledons
Food store in monocot seeds?
Endosperm
Endosperm:
the food store into monocot seeds.
Cotyledon:
the food store in dicot seeds.
What are food stores in seeds used for?
• To produce ATP for building materials
⟶ Allows growth and breaking out of seed
Testa
Seed coat
Seed coat
Testa
Where does growth occur in plants?
Meristems ONLY
Away from meristems, how can a plant become bigger?
The cell can elongate (not divide)
Apical meristems are where?
at tips of roots and shoots
Lateral bud meristems are where?
in buds, can give rise to side shoots
