PLANT RESPONSES TO ENVIRONMENT- Responding To Stimuli Flashcards
PLANTS are more likely to survive if they respond to herbivory so…
They employ chemical defences
Tannins
Toxic to micro organisms and herbivores. Found in upper epidermis and make the leaf taste bad.
They bind to salivary proteins and digestive enzymes that deactivate them. This prevents the insect from growing and die. Prevent infiltration by pathogenic organisms.
Alkaloids
Derived from amino acids. Nitrogen containing compound which are bitter to taste.
Act as a deterrent to animals.
Pheromones
Chemicals released by one individual which can affect the behaviour or physiology of another.
Could act as alarm- pheromone. Alarm nearby plants.
Responses can be either:
Directional or non directional
Tropism: directional growth response
Positive tropism: growth towards the stimulus
Negative tropism: growth away from stimulus
Phototropism: the growth of a plant in response to light
Shoots are positively phototrophic: grow towards the light to photosynthesise.
Roots are negatively phototrophic: grow away from the light.
Geotropism: directional growth of plant in response to gravity.
Shoots are negatively geotropic and grow upwards.
Roots are positively geotropic and grow downwards.
This anchors them in the soil and helps them to take up water: needed for support (turgid), photosynthesise and gain nitrates in the soil- synthesise of amino acids.
Chemotropism:
In flowers, pollen tubes grow downwards, attracted by chemicals- towards the ovary where fertilisation takes place.
.
Thigmotropism :
Plant growth in response to contact with object. E.g climbing plant. Wind around plants or structures to gain support.
Non directional: grow neither towards or away from stimulus.
Nastic response:
Specific nastic response is a thigmonasty response: responding to touch with a sudden folding of the leaves. Helps knock of any small insects feeding. Scare off animals.
