13.10 Survival and Response Flashcards
Stimulus
Detectable change in the environment
Can either be external (light intensity, temp, pressure)
or internal (pH change, glucose conc, blood water potential)
Simple reaction pathway
Stimulus–>Receptor–>Coordinator–>Effector–>Response
Why do organisms need to respond to changes in their environment?
Increased survival and reproduction by:
- Avoiding harmful environments, competition and predators
- Keep in a favourable environment
- Grow towards/away from stimuli
- Dispersing to find new mates
Describe innate behaviour
- Instinctive behaviour is an innate response to stimuli
- Innate behaviour is genetically determined, it is not learned
- Members of species which inherit alleles for a particular behaviour will produce the same response to a particular stimulus
Types of simple responses to stimuli
Kinesis
Taxes
Reflex action
Kinesis- response to stimuli
- Random
- Behaviour pattern where an animal responds to a change in simulus by increasing or decreasing activity
- It is change in rate of movements
Taxes- response to stimuli
- Directional
- Organism moves either towards or away from a stimulus
- The directional of the response is related to the direction of the stimulus
Two types of taxes
Positive taxes
Negative taxes
Example of negative taxes
Earthworms move away from light
Negative phototaxes
More chance of survival as move into soil
More likely to find food
More likely to avoid predators
Less likely to dehydrate
Reflex action- response to stimuli
Where a certain stimulus produces a specific short-lived response
How would you describe a reflex action?
Rapid
Unlearnt
Automatic
How do reflex actions help organisms?
- Protect against damage to the body tissues
- Help escape from predators
- Enable homeostatic control
- Finding food, mates or suitable environmental conditions
What is included in reflex arc?
Receptor
Sensory neurone
Relay neurone
Motor neurone
Effector
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 response
OR - Insect is not moving towards a particular 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;
Tropism
Direction of growth can be towards and away from stimulus
Types of tropism
Positive
Negative
Example of positive tropism
Plant shoots grow TOWARDS light
Example of negative tropism
Plant roots grow AWAY from light
Halo
Salt
Geo
Gravity
Photo
Light
Hydro
Water
What are specific growth factors?
- Synthesised in cells located throughout the plant
- Then diffuse from growing regions to other tissues, regulating growth in response to directional stimulus
e.g. auxins, IAA
IAA process in the shoots
PROMOTES CELL ELONGATION
1. IAA synthesised in shoot tips
2. IAA diffuses into growing region
3. Light causes movement of IAA from light side to shaded side
4. Higher conc. IAA on shaded side
5. Causes directional growth as there is greater cell elongation on shaded side
6. Shaded side grows faster and causes shoot to bend towards the light
Where is IAA produced?
In tips of roots and shoots
What does IAA do in shoots?
Causes cell elongation in shoots
What does IAA do in roots?
Inhibits cell elongation in roots
IAA process in the roots
INHIBITS CELL ELONGATION
- IAA synthesised in root tips
- IAA diffuses into growing region
- Light causes movement of IAA from light side to shaded side towards gravity
- Higher conc. IAA on shaded side
- Cell elongation inhibited on shaded side
- Results in directional growth away from light and towards gravity
Compare & Contrast taxis and tropism
- Both are directional responses to stimuli
- Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism
Describe the effect of IAA on root and shoot growth.
- IAA synthesised in shoots tips.
- IAA diffuses into growing (cell elongating) region.
- Light causes movement of IAA from light side to shaded side.
- Proportionally more 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 synthesised in root tips.
- IAA diffuses into growing (cell elongating) region.
- IAA moves towards underside/shaded side.
- Inhibits cell elongation.
- Uneven growth (more elongation on side with less IAA).
- Causes directional growth away from light and downwards towards gravity.
