Plant responses 5.5.1 Flashcards
What is abiotic stimuli?
Concerned with the non living part of the environment
What is biotic stimuli?
Concerned with the living organisms in the environment
Give 4 examples of plant responses
- tropisms
- response to abiotic stress
- responses to herbivory e.g. chemical defences and response to touch
What are examples of abiotic stresses?
- Freezing
- Drought
- Increased soil water salinity
- Presence of heavy metals e.g. lead, copper, zinc
How do plants respond to drought?
In ways that reduce water loss by transpiration:
- shutting stomata
- dropping leaves
How can some plants respond to freezing temperatures?
By producing an antifreeze chemical in their cells that decreases the formation of ice crystals
What stress factor is herbivory?
Biotic
What are examples of chemicals that provide a defence against herbivory?
- alkaloids
- pheromones
What are alkaloids mode of action
Bitter teasing or toxic, either deterring or killing herbivores
What are pheromones mode of action
A signal to nearby plants of the same species that they are under attack from herbivores, triggering other defences
A single to attract a herbivorous insect’s natural predators
Give an example of a plant that is sensitive to touch
Mimosa pudica
What happens in Mimosa pudica (touch sensitive plant)
- Leaflets of touch-sensitive leaves fold rapidly when touched
- It is thought that this movement may be an adaptation to protect the leaflets from herbivorous insects, though it could also reduce transpiration when the leaves are no longer photosynthesising
- This response occurs very rapidly and is most likely caused by local bioelectrical signals
What is a tropism?
A growth response of a part of a plant in response to a directional stimulus
How can tropisms occur? (direction)
Towards a stimulus (positive tropisms) or away from a stimulus (negative tropisms)
Give 5 examples of tropisms
- Phototropism
- Geotropism
- Hydrotropism
- Thigmotropism
- Chemotropism
What is phototropism?
Response to light
What type of stimulus is light?
Abiotic
What is geotropism?
Response to gravity
What type of stimulus is gravity?
Abiotic
What is hydrotropism?
Response to moisture
What type of stimulus is moisture?
Abiotic
What is thigmotropism?
Response to touch
What type of stimulus is touch?
Abiotic or biotic
What is chemotropism?
Response to chemicals
What type of stimulus are chemicals?
Abiotic or biotic
Explain phototropism
Ensures plant gets access to as much light as possible, maximising photosynthesis
Explain geotropism
Shoots allow negative geotropism (i.e. grow away from the pull of gravity) and roots show positive geotropism (i.e. grow towards the pull of gravity).
This ensures that shoots/roots grow in the right directions
Explain hydrotropism
Root tips normally grow towards damper areas of soil, increasing their access to water
Explain thigmotropism
Important in climbing plants.
Allows these plants to detect a living or non-living support and curl round it
Explain chemotropism
Some plants show a tropic response to certain chemicals (i.e. pollen types grow down the flowers stigma towards the ovules due to chemotropism)
