6.1 Detection and Response Flashcards
What is a stimulus?
A change in the environment
What is a receptor?
A cell or group of cells that detects the stimulus
What is an effector?
The structure that brings about the response to the stimulus change
What are the prefixes indicating the stimulus changes?
Photo - light Hydro - water Geo - gravity Thermo - heat Hygro - humidity Rheo - water currents Chemo - chemical Anemo - air current Baro - pressure
What is the stimulus response process?
Stimulus Receptor Coordinator Effector Response
What are the three types of response?
Taxes
Kineses
Tropisms
If a questions says what type of behaviour is shown - what do you put?
Either taxis, kinesis or tropism
Nothing else
What is taxes?
Movement in a specific direction that are directed by a stimulus such as light or food
Examples of taxes?
Euglena - shows positive phototaxes useful in photosynthesis
Earth worm - responds to water, gravity, light
Some bacteria - move to regions of high glucose concentration = positive chemotaxis
What is kineses? Example?
More random movements that are not directed by a stimulus
Eg Woodlice (prone to desiccation) - move randomly to find dark when in the light
What is tropisms? Example?
A growth movement of part of a plant in response to a directional stimulus
Roots - positive hydrotropism
Shoots - initially negative phototropism (as no light in soil)
When should a response be deemed positive or negative?
Taxes and tropisms are positive and negative
Whereas kineses can’t be positive or negative as it is random
In kineses when does an organism move more frantically?
The more unfavourable the stimulus the more rapidly the organism moves and the more frequently it changes direction
What are auxins?
Plant growth factors
NOT hormones
What is the most common auxin?
IAA
Indole-3-acetic acid
What is significant about the different parts of a plant?
They have different optimum auxin concentrations
What do the concentrations of auxins lead to in the stems and roots?
A high concentration of IAA in the stem stimulates growth (the cells don’t replicate but elongate the ones already there)
A high concentration of IAA in the roots inhibits growth
Why can growth be inhibited by too high a concentration of IAA?
As IAA is an acid it can denature the enzymes
Describe phototropism in flowering plants?
When reacting to sunlight
Cells in the tip of the shoot produce IAA
IAA is distributed evenly down the stem
The light causes the IAA to move to the ‘shaded’ side
A greater concentration of IAA causes cell elongation on the ‘dark’ side
The shades side grows faster so the shoot grows towards the light
How does elongation take place?
It activates a protein pump which lowers the pH
This activates an enzyme to break bonds in the cell wall - loosening the cell wall
So the shoot bends to the light
Describe geotropism in flowering plants?
When reacting to gravity
Cells in the tip of the root produce IAA
This settles at the bottom, no matter the branch
The greater concentration of IAA at the bottom causes cell elongation on the other side and bends down as a result (as high IAA in roots inhibits growth)
What happens if a tip of the shoot is covered or has been cut off?
It will grow normally with no directional response i.e straight up