5.5.1: Plant responses to the environment Flashcards
What are the specific responses to the threat of herbivores that plants show? (chemical defenses)
Tannins
Alkaloids
Pheromones
What is the role of tannins?
- Toxic to microorganisms and larger herbivores
- In leaves, they are found in the upper epidermis and make the leaf taste bad.
- In roots, they prevent infiltration by pathogenic microorganisms.
What are alkaloids derived from and what is their role?
- Derived from amino acids.
- Feeding deterrent to animals as they taste bitter.
Where are alkaloids located?
In growing tips and flowers, and peripheral cell layers of stems and roots.
What are pheromones?
-Chemicals which are released by one individual and which can affect the behaviour or physiology of another.
What are tropisms?
Directional Shoot responses of plants.
What do tropisms include?
- Phototropism
- Geotropism
- Chemotropism
- Thigmotropism
Describe phototropism.
- Shoots grow towards light (+vely phototrophic)
- Enables them to photosynthesise.
Describe geotropism.
- Roots grow towards the pull of gravity.
- Anchors them to the soil.
- Helps them to take up water which is needed for 1.support (to keep cells turgid)
2. Raw material for photosynthesis
3. To help cool the plant. - Also minerals e.g. nitrates, needed for amino acid synthesis.
Describe chemotropism.
-On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.
Describe thigmotropism
Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support.
What is a positive tropic response?
-If a plant responds towards a stimulus
What is a negative tropic response?
-If a plant responds away from a stimulus
What is a non-directional response to external stimuli called?
-Nastic responses
What is an example of thigmonasty?
-The sensitive plant, Mimosa pudica, responds to touch with a sudden folding of the leaves.