Survival And Response Flashcards
What is a stimulus
A detectable change in the environment which can either be external (such as temperature, light intensity) or internal such as pH, glucose concentration.
Define effector
Responds to stimulation by the nerve cells, an effector could be a muscle, gland or organs cell
What is the simple reaction pathway
Stimulus - receptor - coordinator - effector - response
Why do organisms need to respond to changes in the environment
To increase survival and reproduction by
- avoiding harmful environments, competitions and predators
-keep in favourable environments
- grow towards/away from stimuli
- dispersing to find new mates
What are the types of responses to stimuli
Kinesis (random)
Taxes (directional)
Reflex action
Kinesis
- this is a behaviour pattern where an animal responds to a change in stimulus by increasing or decreasing activity.
- It is the change in rate of movement.
Example: - woodlice spend more time in humid areas as there’s less dehydration. Therefore when exposed to low humidity they move around more. The moment is random and non directional and they increase their rate of movement by chance that they will be more likely top reach and area of high humidity.
Taxes
- this is the directional movement of an organism either towards or away from a stimulus
- direction of the response is related to the direction of the stimulus
Positive taxis - towards the stimulus
Negative taxis - away from the stimulus
Example:
Earthworms move away from light - negative phototaxis
More chance of survival as move into soil
More likely to find food
More likely to avoid predators
Less likely to dehydrate
Describe what is meant by the term taxis
Moves towards or away from directional stimulus
Describe what is meant by the term Kinesis
Movement is random/ non directional
Animal does not move towards a particular stimulus
Explain the advantages of a simple reflex arcs
- rapid
- protect against damage to body tissue
- does not have to be learnt
- help escape from the predators
- enable homeostatic control
- finding food, mates or suitable environmental conditions
Tropisms in plants
This is where only PART of an organism responds to a stimulus
Direction can be towards or away from stimulus (similar to taxis)
Positive tropism - growth towards a stimulus
Negative tropism - growth away from stimulus
Example:
Plant shoots grow towards light - positive phototropism
Plant roots grown away from light - negative phototropism
What are plant growth factors
Specific growth factors are synthesised in cells coated throughout the plant and diffuse to growing regions to other tissues where they regulate growth in response to directional stimulus
Examples include auxins and IAA
What is IAA
- A growth factor
- produced in roots and shoots
- diffuses to growing region
- causes cell elongation in the shoots
- inhibits cell elongation in roots
- transported to shaded parts of roots and shoots
- moves to underside of roots and shoots
What does IAA do in the shoots
- Promotes cell elongation
- light causes movement of IAA from light side to shaded side
- higher conc of IAA on shaded side
- causes directional growth
- shaded side grows faster and causes shoot to bend towards the light
What does IAA do in the roots
- inhibits cell elongation
- light causes movement of IAA from light side to shaded side and towards gravity
- higher conc of IAA on shaded side
- cell elongation inhibited on shaded side
- results in directional growth from light towards gravity
