Stimuli
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What is a stimulus?
Change in an organisms internal or external environment to which they respond
What are receptors?
Detect changes in environment
What are effectors?
Innitiate response
Why must organisms respond to stimuli?
To increase their chance of survival and pass on alleles to the next generation
What is tropism?
Growth of a plant in response to a directional stimulus
What is positive and negative tropism?
Positive tropism - towards a stimulus Negative tropism - away from a stimulus
What are specific growth factors in plants?
hormone-like growth substances (e.g auxins like IAA) which move via phloem or diffusion from growing regions like shoots/root tips where they are produced to other tissues where they regulate growth in response to directional stimuli
What is taxes?
Directional response determined by direction of stimulus Movement towards or away from a directional stimulus
What is Kinesis?
Non-directional response Speed of movement or rate of direction change/turning changes in response to a non-directional stimulus
What does high concentrations of IAA do to shoots?
Stimulates cell elongation
What does high concentrations of IAA do to roots?
Inhibits cell elongation
Give a similarity between a taxis and tropism
Both are directional responses to stimuli
Give a difference between a taxis and tropism
Taxis occurs in animals Tropism occurs in plants Taxis organism move Tropism is a growth response
What are the types of tropism?
Phototropism - response to light Gravitropism - response to gravity Hydrotropism - response to water
Explain gravitropism in roots
Cells in root produce IAA IAA diffuses down root IAA moves to lower side of root (concentration increases) In roots, this inhibits cell elongation Roots bend towards gravity
Explain gravitropism in shoots
Cells in tip of shoot produce IAA IAA diffuse down shoot IAA moves to lower side of shoot (concentration increases) In shoots, this stimulates cell elongation Shoots bend away from gravity
Explain phototropism in roots
Cells in root produce IAA IAA diffuses down root IAA moves to shaded side of root (concentration increases) In roots, this inhibits cell elongation Roots bend away from light
Explain phototropism in shoots
Cells in top of shoot produce IAA IAA diffuses down shoot IAA moves to shaded side of shoot (concentration increases) In shoots, this stimulates cell elongation Shoots bend towards light
Give examples of taxis
Woodlice moving away from light (to avoid predators) Algae moving towards light (to photosynthesise for survival) Earthworm moving away from light (takes them to soil to conserve water, find food and avoid predators)
Give an example of kinesis
Woodlice moving faster in drier environments (to increase their chance of moving to an area with higher humidity to prevent drying out)
Give a summary of tropism, taxes and kinesis
Tropism is a directional growth response in plants Taxes is a directional movement response in mobile organisms Kinesis is a non-directional movement response where mobile organisms change speed/turning rate
What is the difference between where IAA moves to in gravitropism vs phototropism
Gravitropism - IAA moves to lower side of shoots/roots Phototropism - IAA moves to shaded side of shoots/roots