Simple Responses Flashcards
What are the advantages of organisms being able to respond to a stimuli?
In increases the chance of survival for an organism- escaping from a predator, moving away from extreme heat, moving towards a food source, moving towards a light source.
What is the definition of taxis?
A directional response to a stimuli
What is positive phototaxis and why is it important?
Organisms move towards light, which increases the chance of survival as they gain more light for photosynthesis.
What is negative phototaxis and why is it important?
Organisms move away from light into the soil. This allows them to avoid losing too much water, allows them to find food and avoid predators.
What is movement towards or away from chemicals?
chemotaxis
What is the definition of kinesis?
A kinesis is a non-directional response to a stimulus
What stimulates kinesis?
An organism finding itself in an unfavourable condition.
Why are insects prone to rapid water loss?
large SA:vol ratio
Name 2 adaptations found in insects to limit water loss?
1) They have a waterproof covering as their body surface is made of chitin.
2) They have spiracles closed by valves.
What is a tropism?
A growth of a movement of part of a plant in response to a directional stimulus.
Explain positive phototropism
Shoots grow towards light. This is a survival response because leaves absorb maximum light for faster rate of photosynthesis.
Explain negative phototropism
Roots grow away from light. This is a survival response because roots grow into soil where they can absorb ions and water.
Explain positive gravitropism
Roots grow directly downwards towards gravity. This is a survival response because roots grow into soil where they can absorb ions and water.
Explain negative gravitropism
Shoots grow upwards away from gravity. This is a survival response because shoots grow up out of the dark soil into the light.
What is IAA?
the growth factor involved in the phototropism and gravitropism responses.
What is IAA made and released by?
apical meristem cells in the shoots and roots cells
How does IAA affect cells close by?
1) Causes cell elongation
2) Increases the stretchiness of the cell wall
3) When water enters by osmosis, the cell can lengthen
How does IAA cause the phototropism response in shoot tips?
1) Cells in the shoot tip
