6.1.1 survival and response Flashcards
What is a stimulus?
A detectable change in the internal and external environment of an organism that leads to a response in the organism.
How do organisms increase their chance of survival?
By responding to changes in their environment via different response mechanisms.
What detects stimuli?
Receptors (cells).
What is the structure of the response to survival?
Stimulus → Receptor → Coordinator → Effector → Response.
What is taxis?
A simple response in which an organism moves its entire body towards a favorable stimulus or away from an unfavorable stimulus.
What is the result of a taxis?
A motile organism responds directly to environmental changes by moving its whole body either towards a favorable stimulus or away from an unfavorable one.
What is positive taxis?
Moving towards a stimulus.
What is negative taxis?
Moving away from a stimulus.
What is negative phototaxis?
Moving away from light.
What is positive chemotaxis?
Moving towards certain chemicals to aid survival.
What is kinesis?
When an organism changes the speed of movement and the rate it changes direction.
What is the response of an organism moving from an area with beneficial stimuli to an area of harmful stimuli?
To increase the rate it changes direction to return to favorable conditions.
What happens if an organism is surrounded by negative stimuli?
The rate of turning decreases to keep it moving in a relatively straight line.
to increase the chance of finding new location with favourable conditions
What is the kinesis response of woodlice crossing from a damp to a dry area?
To turn rapidly to increase the probability that it will end up back in the damp area.
What happens if woodlice are in a fully dry area?
The turning rate would decrease so that it would move in a straight line to increase the chance of finding a new damp area.
What is tropism?
When a plant responds via growth to directional stimuli.
What is positive tropism?
Growing towards stimuli.
What is negative tropism?
Growing away from stimuli.
What do plants respond to?
Light, gravity, and water.
What controls tropisms?
Specific growth factors, e.g., indoleacetic acid (IAA).
What is IAA?
A type of auxin that controls cell elongation in shoots and inhibits growth of cells in roots.
Where is IAA made?
At the tip of roots and shoots, and it diffuses to other cells.
Why do shoots need light?
For light-dependent reactions (LDR) in photosynthesis; they bend towards light controlled by IAA.
What happens in positive phototropism in shoots?
IAA is produced in the shoot tip
IAA diffuses uniformly down the shoot
IAA builds up on the shady side if unilateral light
higher conc of IAA on shady side of shot
IAA stimulates shoot cell elongation the cell on the shady side elongate more
The shoot grows towards the light