organisms response to internal and external stimuli

What are the two simple responses in organisms

• taxis

• Kinesis

What is a stimulus

A detectable changed in the environment detected by receptors

Why is it beneficial for receptors detecting change in stimulus effectively

So they have a greater chance of survival to pass on their alleles

What is taxis

Directional response in stimulus determined by direction of stimulus

What is the difference between between positive and negative taxis

• positive = towards stimulus

• Negative = away from stimulus

What is kinesis

Non directional response in stimulus

What two factors are affected in kinesis

The speed of movement and the frequency of turning determined by the intensity of stimulus

What happens in kinesis in less favourable conditions

• higher speed

• Fewer tuns

  • So can move away from the area

What happens in kinesis on border of unfavourable conditions and favourable

• lower speed

• More turns

  • More likely to stay in or return to area with favourable conditions

What is a tropism

Growth of a plant in response to a directional stimulus

What are the two examples of tropisms

• phototropism

• Gravitropism