Unit 6 - Response to Stimuli Flashcards
Stimulus
A detectable change in the internal or external change in the environment of an organism
Receptor
Detects the stimulus
Coordinator
Coordinates a suitable response to a stimulus
Effector
- Produces a response to a stimulus
- Response carried out by an organ, tissue or cell
Response
Action produced by the effector
Why is responding to stimuli important?
Increases chance of survival by:
- Moving towards beneficial resources
- Evading predators
Taxes
- A response to a stimuli in which the direction of movement is determined by the direction of the stimuli
- Directional
Positive Taxis
Movement towards a favourable stimulus
Negative Taxis
Movement away from an adverse stimulus
Phototaxis
Movement towards or away from a light stimulus
Chemotaxis
Movement towards or away from a certain concentration of a chemical
Kineses
-When an organism adjusts their movement speed and turning frequency based on the favourability of their environment
- Non-directional
How does favourability of conditions impact kineses?
- Increased turning in unfavourable conditions
- Accelerated movement in favourable conditions
Tropism
The growth of a part of an organism like a plant in response to a directional stimulus
Phototropism
Growth towards/away from light
Gravitropism (AKA Geotropism)
Growth towards or away from gravity
Hydrotropism
Growth towards or away from moisture/water
What tropisms do plant shoots display?
- Positive Phototropism and Negative Gravitropism
- Optimises light absorption for photosynthesis
What tropisms do plant roots display?
- Positive Gravitropism and Negative Phototropism
- Increases absorption of minerals and water in the soil
Why is Tropism important to Plants?
Increases chance of survival by:
- Optimising photosynthesis
- Anchoring the plant for support
- Efficient access to nutrients, minerals and water
Plant Growth Factors
chemicals that influence plant development mainly by regulating cell elongation and division
Difference between Plant Growth Factors and Animal Hormones
- PGFs act locally at the site where they are produced whereas animal hormones are usually secreted and travel in the bloodstream to act on an organ
- PGFs are produced in a variety of tissues throughout the plant whereas animal hormones are produced in specialised cells within glands
IAA
- Type of Auxin
- Stimulates/inhibits cell elongation
- Results in growth of roots and shoots
- Synthesised in growing tips (meristems) of shoots and roots (where mitosis occurs)
Control of Positive Phototropism in Shoots using IAA
- IAA is produced in cells in the tip of the plant shoot and transported down the shoot by diffusion
- Light stimulates IAA to move from the light side of the shoot to the shaded side
- IAA becomes concentrated on the shaded side
- IAA causes cell elongation of shoot cells so the shaded side grows longer
- The shoot tip bends towards the light
Control of Negative Phototropism/Positive Gravitropism in Shoots using IAA
- IAA is produced in cells in the tip of the plant shoot and transported along the root by diffusion
- Any available light stimulates IAA to move to the shaded side of the root
- Gravity also pulls IAA to the lower side of the root
IAA becomes concentrated on the shaded side - IAA inhibits cell elongation of root cells so the shaded side doesn’t grow
- The root bends away from any available light and downwards towards the pull of gravity
Acid Growth Hypothesis
- Auxin binds to the cell-surface membrane
- Hydrogen ions are actively transported from the cytoplasm into the cell wall
- The cell wall becomes more plastic
- Cells elongate and the plant grows
