Stimuli

?
  • Created by: Hindleyc
  • Created on: 26-01-19 19:48
how do organisms increase there change of survival?
By responding to changes in their environment
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In flowering plants what move from growing regions to other tissues
Specific growth factors
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What do they do here
Regulate growth in response to directional stimuli
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What do plants lack?
A nervous system
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However what are they able to do
Respond to changes in their external and internal environments
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How?
Use chemicals
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What is the effect of light on plants
Stems grow towards light (+vely phototropic because light is needed for photosynthesis)
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What is the effect of gravity
Plants need tp be firmly anchored in the soil
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What are roots sensitive to?
Gravity and grow in the direction of its pull ie they are +vely gravitropic
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What do almost all plant roots grow towards
Water (+vely hydrotropic in order to absorb it for use in photosynthesis and other metabolic processes as well as for support
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What do plants respond to external stimuli by
Means of plant hormones (plant growth factors)
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What do plant growth factors do?
Exert their influence by affecting growth
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Where are they made
By cells located throughout the plant rather than a particular organ
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What can some plant growth factors do?
Affect the tissues that release them unlike animal hormones
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Eg of a growth factor
IAA causing cells to elongate
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Response of a young shoot towards light steps
1- Cells in the tip of the shoot produce IAA which is then transported down the shoot via diffusion 2. IAA initially transported to all sides as it begins to move down the shoot
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3.
Light causes movement of IAA from the light side as it begins to move down the shoot 4,Greater conc of IAA build up on the shaded side of the shoot rather than the light side
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5.
As IAA casues elongation of cells and there is a greater conc of IAA on the shaded side of the shoot the cells on this elongate more 6. shaded side of the shoot bend towards the light
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What are roots
+vely geotropic while stem -vely geotrophic
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What does IAA have a different effect on
Root cells than stem cells
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How
As cells germinate IAA accumulates on bottom and moves in direction of gravity
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Then in the stem?
Cells elongate upward
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Roots?
Diff effect on root- inhibits cell elongation process - shorter so grows down and inhibits growth
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If thicker cuticle
Lower uptake as larger diff pathway
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What are taxes and kinesis
How organisms inc chance of survival by responding tp changes in their environment
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What are they
Responses that can maintain a mobile organism in a favourable environment
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Whats a Taxis
Simple response whose direction is determined by the direction of the stimulus
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What happens as a result
A motile organism (or separate motile part of it) responds (+ve taxis) or away from the stimulus (-ve taxis)
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Whats kinesis
Form of response in which an organism doesn't move towards or away from the stimulus
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What happens instead
The more unpleasant the stimulus the more rapidly it moves and the more rapidly it changes direction (eg woodlice slow down and turn less in the dark)
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What does this action have the effect of?
Keeping organism in an area it finds favourable and making it move away from areas it finds uncomfortable
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If woodlice in dry area?
Move more rapidly and change direction more often thus inc their chance of moving into a different area
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What if new area moist
Slow down and change direction less often
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What is the CNS
Brain and spinal cord
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Sensitivity
Ability to respond to a stimulus
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Stimulus
Change inside or outside an organism that brings about a response in an organism
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Effector
Usually muscle or gland that brings about a response
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Receptor
Structure that detects a stimulus and initiates a nerve impulse
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Peripheral nervous system
Neves made up of neurones that carry info to and from the CNS
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What are there between receptor and effector
Many nerve cells (neurones) that vary in their size and shape but have many basic features in common
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3 types of neurones
Sensory- Nerve cell the carries impulses from a receptor to CNS. Motor- Nerve cell that carries impulses from CNS to an effector . Interneurone- Nerve cell that lies entirely within the CNS
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Card 2

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In flowering plants what move from growing regions to other tissues

Back

Specific growth factors

Card 3

Front

What do they do here

Back

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Card 4

Front

What do plants lack?

Back

Preview of the front of card 4

Card 5

Front

However what are they able to do

Back

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