3.6.1.1 - Survival and response Flashcards
What is a stimulus?
A stimulus is a detectable change in the internal or external environment of an organism that leads to a response in the organism
Why is it important organisms can respond to stimuli?
Can increase their chances of survival by responding to changes in their environment
How is a response coordinated from a stimulus (nervous system)?
> stimulus
receptor
coordinator
effector
response
Give two examples of when an organism would need to respond to a stimulus to increase chance of survival…
- Detect and move away from harmful stimuli
>eg: predators, extreme temperatures - Detect and move towards a source of food
What is taxis?
= a simple response whose direction is determined by the direction of the stimulus
How are taxes classified by direction of the taxis?
- Positive taxes
= movement towards stimulus - Negative taxes
= movement away from stimulus
How are taxes classified by nature of the taxis
- Phototaxis
> stimulus = light - Chemotaxis
> stimulus = chemical
> direction corresponding to increasing/decreasing concentration of a chemical
How might positive phototaxis increase survival?
- increase survival of photosynthetic organisms that require light to manufacture food
How might negative phototaxis increase survival?
- increase survival of earthworms by taking them into the soil where they can better conserve water, avoid predators and find food.
What is Kinesis?
= Simple response in which the organisms changes the speed at which it moves and the rate at which is changes direction.
What does increasing rate of turning do in kinesis?
- increases its chances of returning to a favourable environment after crossing dividing line to unfavourable environment.
Why might an organisms rate of turning decrease in kinesis?
- if it has moved a considerable distance into unfavourable environment, it allows it to move in long straight lines before it turns sharply - bringing organism into a new region with favourable conditions
Explain how woodlice use kinesis…
- woodlice lose water from their bodies in dry conditions
- when they move from a damp area into a dry one, they move more rapidly and change direction more often
- increases its chance of returning to damp area
- when they are in a damp area, they slow down and change direction less often
- more likely to stay damp area
- if they remain in a dry area, move rapidly in straight lines
- increases chances of moving into new damp area
> prevents them drying out
increases chance of survival
What is a tropism?
= the directional growth of part of a plant in response to a directional stimulus
What do plants respond to?
- light
> phototrophic - light needed for photosynthesis - gravity
> gravitropic - need to be firmly anchored in soil - water
> hydrotrophic - needed for photosynthesis + other metabolic processes
What is IAA (indoleactic acid)
- a plant growth factor
- belongs to group of substances called auxins
- controls cell elongation in plants
Where is IAA produced?
- in tips of shoots and roots of plants
How are plant growth factors different to hormones?
- affect tissues that release them rather than acting on distant target organs
What do plant responses to external stimuli involve?
- plant growth factors
> exert influence by affecting growth of plant
What impact does IAA have on shoots?
- IAA stimulates cell elongation in shoots
What impact does IAA have on roots?
- IAA inhibits cell elongation in roots
Describe which phototropism occurs in shoots and roots of flowering plants…
- shoots grow towards light = positive phototropism
- roots grow away from light = negative phototropism
Describe the process in which shoots of flowering plants respond to light…
1) cells in tip of shoot produce IAA, which diffuses down the shoot
2) IAA is initially transported evenly throughout all regions as it begins to move down the shoot
3) light causes the movement of IAA from the light side to the shaded side of the shoots
4) greater concentration of IAA builds up on shaded side of shoot
5) IAA causes cell elongation of shoot’s cells, so cells on shaded side elongate more.
6) Shaded side of shoot elongate faster than light side, causing the shoot tip to bend towards light.
> positive phototropism
describe the process in which roots of flowering plants respond to light?
1) cells in tips of roots produce IAA which initially diffuses evenly down the root
2) light causes IAA to move from light side to shaded side of root
3) greater concentration of IAA builds up on shaded side of root
5) IAA inhibits cell elongation of root’s cells, so cells on light side elongate more.
6) cell elongation on light side is greater causing the root tip to bend away from light.
> negative phototropism
