Biology aqa unit 9.1

key terms and points to remember

  • Created by: lauren
  • Created on: 27-02-13 13:53
what is a stimulus
a stimulus is a detecable change in the internal or external evironment of an organism that produces a response
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what are stimuli detected by
cells or organs known as receptors
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what does a receptor do
transform energy of a stimulus to a form of energy that can be processed by the organism leading to a response
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effectors are...
a range of diferent cells, tissues, organs or systems that carry out a response
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what is needed between receptors and effectors and why?
a form of comunication, because they are usually some distance apart
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two methods of communication between receptors and effectors...
1) hormones (slow animals and plants) 2) the nervous system (rapid animals)
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what is each receptor linked to within the nervous system
a central coordinator
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events from stimulus response is summarised as
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what is a taxis
a simple response whose direction is detirmined by direction of stimulus
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how does a motile organism ( or motile part of it) respond as a result of a taxes
by moving either towards or away from the stimulus depending on conditions
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how are taxes classified
Positive taxis ( moving towards the stimulus) negative taxis ( moving away from stimulus) and by the ature of the stimulus
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if a single celled algae move towards light it is a
positive phototaxis
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earthworms move away from light
negative phototaxis
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bacteria moving towards a higher concentration of glucose
positive chemotaxis
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what is a kinesis
a form of response whereby the more unpleasent the stimulus the more rapid the organism moves and changes direction
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a kinesis results n an increase
in random movements
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what is a kinesis response designed to do
bring the organism back into favourable conditions
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when are kinesises important
when a stimulus is less directional
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two example of stimuluses to a kinesis response
temperature and humidity
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what is a tropism
a growth movement of part of a plant in response to a directional stimulus.
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example of tropism
plant shoots grow towards light (positive phototropism) plant roots grow away from light ( negative phototropism) plant roots grow towards water ( positive hydrotropism)
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some species of bacteria move away from the waste products they produce ... this is known as
negative chemotaxis
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the sperm cells of a moss plant are attracted towards a chemical produced by the female reproductive organ on another moss plant
positive chemotaxis
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the young stems of seedlings grow away from gravity
negative geotropism
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Card 2


what are stimuli detected by


cells or organs known as receptors

Card 3


what does a receptor do


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Card 4


effectors are...


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Card 5


what is needed between receptors and effectors and why?


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