6.1- Stimuli Flashcards
(16 cards)
What is a tropism?
A growth movement in response to a stimulus
What is IAA?
IAA is Indoleacetic acid.
It is a growth factor (like a plant hormone). It is a type of auxin
Where is IAA produced? How does it move through the plant?
It is produced in the tips of roots and shoots
It moves by diffusion
What effect does IAA have on root cells?
It inhibits cell growth and elongation
What effect does IAA have on shoot cells?
It stimulates cell growth and elongation
Gravity roots
Gravity IAA moves downwards – towards gravity • Roots grow towards gravity
• because the cells in the upper surface of the root will grow and elongate more whereas the cells in the lower surface will be inhibited Positive gravitropism
Water roots
IAA moves towards moisture • Roots grow towards moisture
• because the cells in contact with the drier conditions will grow and elongate more whereas the cells in the side of the root exposed to moisture will be inhibited Positive hydrotropism
Light roots
IAA moves away from light • roots grow away from light
• because the cells nearer the light will grow and elongate more than the cells nearer the dark. The cells nearer the dark will be inhibited Negative phototropism
Gravity shoots
IAA moves towards gravity • shoots grow away from gravity
• because the lower side has more IAA so the cells there grow and elongate more, whereas the cells in the upper side of the shoot have less IAA so do not grow and elongate as much Negative gravitropism
Light shoots
IAA moves away from light • shoots grow towards light
• because the shaded side has more IAA so the cells there grow and elongate more Positive phototropism
What is a taxis?
A directional response to a stimulus
How would an animal which uses taxis respond to an unfavourable stimulus?
It would move directly away from the stimulus (probably in a straight line)
How would an animal which uses taxis respond to a favourable stimulus?
It would move directly towards the stimulus (probably in a straight line)
What is a kinesis
A non directional response to a stimulus
How would an animal which uses kinesis respond to experiencing an unfavourable stimulus?
It would have a lower rate of turning but a higher rate of movement
This would help it to get out of that area and move to different conditions
How would an animal which uses kinesis respond to experiencing a favourable stimulus?
It would have a higher rate of turning and a lower rate of movement
This would help the animal to stay in the same area
