Survival & Response Flashcards
What is a stimulus?
a detectable change in the internal or external environment of an organism that produces a response in the organism
What is an effector?
Responds to stimulation by nerve cells
effector could be:
A muscle
A gland
An organ
A cell
Simple reaction pathway
Stimulus:
Increase in blood glucose concentration
Receptor:
Detected by beta cells in the pancreas
Coordinator:
The same beta cells now secrete insulin into the blood plasma
Effector:
Tertiary proteins act as receptors in cell membranes for insulin (complementary shapes) = binding then increases number of glucose carrier proteins in cell membranes
Response:
Decrease in blood glucose conc. as glucose goes into cells by FD
Why do organisms need to respond to changes in their environment?
Increase survival and reproduction by:
* Avoiding harmful environments, competition and predators
* Keep in a favourable environment (correct temperature/humidity) – Mobile organisms
* Grow towards/away from stimuli (flowering plants)
* Dispersing to find new mates
Simple responses to stimuli: Behaviour patterns
Instinctive behaviour is an innate response to stimuli
Innate behaviour is genetically determined, it is not learned
Members of a species which inherit alleles for a particular behaviour will produce the same response to a particular stimulus
Types of simple responses to stimuli
Kinesis (RANDOM)
Taxes (DIRECTIONAL)
A simple reflex action
Kinesis
Kinesis (RANDOM)
This is a behaviour pattern where an animal responds to a change in stimulus by increasing or decreasing activity.
It is a change in rate of movement.
Example
-Response of woodlice to change in humidity
-Woodlice move around more (increase speed and rate of turning) when the humidity is low (dry)
-The rate of movement is related to the intensity of the stimulus
-The movement is random it is not directional
Taxes
directional movement towards or away from a stimulus (not random)
POSITIVE TAXIS – towards the stimulus
NEGATIVE TAXIS – away from the stimulus
Explain the advantages of simple reflex arcs
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control;
example of the simple reflex.
Tropisms in plants
A growth movement of part of a plant in response to a DIRECTIONAL STIMULUS.
The direction of growth can be towards or away from the stimulus
POSITIVE tropism – growth towards stimulus
NEGATIVE tropism- growth away from stimulus
Tropism name examples
Halo = salt
Geo = gravity
Photo = light
Hydro = water
e.g. positive phototropism
Plant growth factors
synthesised in cells located throughout the plant, they then diffuse through the tissue in response to stimulus.
So growth factors affect the tissues that release them, not distant target organs
e.g gibrellins, auxins, IAA
indole-acetic acid (IAA)
- IAA is produced in tips of roots and shoots
- diffuses to growing region
- Causes cell elongation in the shoots
- Inhibits cell elongation in the roots
- IAA is transported to more shaded parts of the roots and shoots (phototropism)
- IAA moves to underside of roots and shoots (geotropism)
IAA In Shoots (promotes cell elongation)
- IAA synthesised in shoots tips.
- IAA is diffuses into growing (elongating) region.
- Light causes movement of IAA from light side to shaded side.
- Higher concentration of IAA on shaded side.
- Causes directional growth as there is greater cell elongation on shaded side.
- Shaded side grows faster and causes shoot to bend towards the light.
IAA promotes growth of shoots on the dark side of the shoot
