Response To Stimuli Flashcards
Define stimulus
A detectable change in the internal/external environment of an organism that leads to a response
Describe plant phototropism
- plant growth in response to a directional stimulus
- (phototropism) shoots grow towards unilateral light so leaves receive more light for photosynthesis
Describe the features of IAA (5)
- produced by actively dividing cells in the plant tip
- diffuses down the shoot
- effects cell elongation —>
- concentrates on the ‘shaded side’ of the plant
- promoting cell elongation causing the shoot to bend towards the light
Detail plant gravitropism in relation to IAA
- growing root tips produce IAA, it diffuses downwards
- IAA accumulates on the lower side of the root
- inhibits cell elongation
- above cells elongate faster and root bends downwards in the direction of gravity
Define Taxis
- direction response to a stimulus (positive- towards, negative- away)
Define kinesis
The non-directional speed of movement and frequency of turning
Describe kinesis in favourable conditions
Organism will move slowly and turn frequently (to stay in favourable area)
Describe kinesis in unfavourable conditions
Organism will move rapidly and turn less frequently
What is the reflect arc
The pathway of neurones involved in a reflex
What is a reflex
Involuntary rapid response to a sensory stimulus
- brain not involved
Describe the reflex arc
- stimulus (light, heat, etc..)
- receptor (in hands etc..) converts stimulus into nerve Impulses
- sensory neurone
- relay neurone
- motor neurone
- effector (muscle activated)
- response
Importance of the reflex arc (3)
-automatic and rapid
- avoids damages do body tissues (e.g. burning)
- involved in maintaining balance (controlling neck, trunk + limbs)
