B5 - Responses to External Stimuli
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1
Define stimulus
Detectable change in internal/external environment of an organism that leads to a response
2
What are 3 examples of innate behaviour?
Reflexes
Taxes + kineses
Instincts
Taxes + kineses
Instincts
3
Define taxis
Simple directional response
Direction of movement determined by direction of stimulus
Direction of movement determined by direction of stimulus
4
2 types of taxis
+ive taxis
-ive taxis
-ive taxis
5
Define +ive taxis
Motile organisms move body towards stimulus
6
Define -ive taxis
Motile organisms move body away from stimulus
7
Define and describe kinesis
Non-directional response
Non-favourable: rapid movement and direction changes
Favourable: slows down and turns more often
Non-favourable: rapid movement and direction changes
Favourable: slows down and turns more often
8
Define tropism
Growth of part of plant in response to a directional stimulus
9
Difference between shoot and root tropisms
Shoots:
+ive phototropism
Roots:
-ive phototropism
+ive gravitropism
+ive phototropism
Roots:
-ive phototropism
+ive gravitropism
10
What do plant growth factors do?
Control cell elongation
11
Image occlusion: name the hidden labels
12
Describe meristem
Tips of shoots / roots
Where mitosis occurs
Where mitosis occurs
13
Describe normal movement of IAA
Made in tips shoots / roots
Diffuses down shoot / root
Diffuses down shoot / root
14
Describe what happens to shoot in sunlight
IAA stimulates cell elongation
Goes to dark side
Shoot bends towards light
Goes to dark side
Shoot bends towards light
15
Describe what happens to roots
IAA inhibits cell elongation
Root grows away from light
IAA goes down (towards gravity)
Amyloplasts (starch grains) in root tip fall to bottom
IAA move to where amyloplasts are
Root grows away from light
IAA goes down (towards gravity)
Amyloplasts (starch grains) in root tip fall to bottom
IAA move to where amyloplasts are