5.5.1 Plant Responses Flashcards
How do plants respond to their enviornments?
Plants can respond to their environment in various ways
The environmental stimuli to which plants respond can be abiotic or biotic
Examples of plant responses include:
responses to abiotic stress
responses to herbivory, e.g.
chemical defences
response to touch
tropisms
What are responses to abiotic stress?
Abiotic stress for plants can include:
freezing
drought
increased soil water salinity
presence of heavy metals, e.g. lead, copper, zinc, mercury
Plants can respond to drought in ways that reduce water loss by transpiration, e.g.:
shutting stomata
dropping leaves
Some plants can respond to freezing temperatures by producing an antifreeze chemical in their cells that decreases the formation of ice crystals
Ice crystals can destroy plant cells if allowed to form within them
What are chemic responses to herbivory?
Many plants have adaptations that help them to avoid being eaten by herbivores
Herbivory is a biotic stress factor
Some plants produce chemicals that provide a defence against herbivory, e.g.
alkaloids
pheromones
Alkaloids, e.g. caffeine, nicotine:
- Bitter-tasting or toxic, either deterring or killing herbivores
Pheromones:
- A signal to nearby plants of the same species that they are under attack from herbivores, triggering other defences
A signal to attract a herbivorous insect’s natural predators
What are the responses to touch?
Some plants are sensitive to touch, e.g. Mimosa pudica
In Mimosa the leaflets of the 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 (the leaflets also fold in at night and reopen at dawn)
The response occurs very rapidly and is most likely caused by local bioelectrical signals
What are tropisms?
A tropism is a growth response of a part of a plant in response to a directional stimulus
Tropisms can be towards a stimulus (positive tropisms) or away from a stimulus (negative tropisms)
Plant responses include a variety of tropisms, including:
Phototropism- In response to light. Is abiotic and Ensures plant gets access to as much light as possible, maximising photosynthesis
Geotropism- In response to gravity. Is abiotic and Shoots show negative geotropism (i.e. grow away from the pull of gravity) and roots show positive geotropism (i.e. grow towards the pull of gravity). Ensures shoots/roots from germinating seeds grow in the right directions, regardless of the orientation of the seed
Hydrotropism- In response to moisture. Is abiotic and Root tips normally grow towards damper areas of soil, increasing their access to water
Thigmotropism- In response to touch. Can be Abiotic or biotic and is Important in climbing plants (which are adapted to climb as it provides them with certain advantages e.g. greater access to light in dense rainforests). Allows these plants to detect a living or non-living support and curl around it
Chemotropism- In response to chemicals. Can be Abiotic or biotic and same plants show a tropic response to certain chemicals (eg. pollen tubes grow down the flower’s stigma towards the ovules due to chemo tropism)
