Chapter 3.6 Response To Change In Conditions Flashcards
Why do plants need to respond to the environment?
- prevent water loss
- reproduce
- increase chance of survival
- maximise photosynthesis
-reduce damage
Types of stimuli that a plant can respond to
Plants respond to; light, gravity and water to avoid abiotic stress
Also respond to predication by producing chemical toxins
How do plants respond to change in stimulus?
Plants change orientation of roots/leaves/stems to favourable conditions
By producing growth factors called tropism from growing regions to other tissues, where they regulate growth in response to stimuli
How do plants respond to light
+ what is it called
Stems respond to light by moving towards it = positive phototropism
Roots respond to light by moving away from= negative phototropism
How do plants respond to gravity
+what is it called
Stems respond by moving upwards = negative geotropism
Roots respond by moving downwards = positive geotropism
What is the growth factor produced by plant in response
Auxin (IAA) is the plant hormone which acts as growth factor
Describe the process of IAA synthesis and movement into shoot in plant response
1) IAA is synthesised in cells in shot tip (as stimuli detected by specific receptor proteins)
2) IAA diffuses down shoot equally on all sides
Describe the effect of different concentrations of IAA on cells in plants in response to light stimuli
3) light on 1 side causes IAA to be transported to shaded side
4) concentration of IAA increases on shaded side causing elongation of cells
5) IAA activates proteins in plasma membrane H+ ion breaks H bond between cellulose microfibrils = easier for cell wall to expand. Elastin enzymes in cell wall break bonds between cellulose microfibrils allowing cell walls to stretch
6) on shaded side, there is greater elongation of cells, causing the shoot to bend towards light
What type of response are taxes and kineses?
Simple innate responses that can maintain a Mobile organism in a favourable environment
Def of taxis response
Movement of whole organism in response to direction of a stimulus
E.g
Some move directly towards (positive taxis) or away (negative taxis) to stimulus
Def of kinesis response
Non-directional response in which rate of movement is related to the intensity of stimulus, not directional
What are the 2 types of kinesis response
Orthokinesis - change in rate of movement
Klinokinesis - change in the rate of turning
Outline the reflex arc
Stimuli, sensory receptor, sensory neurone, relay neurone, motor neurone, effector, response
Why are reflexes important
1- involuntary as do not require decision making (adv of simple organisms)
2- brain is not overloaded with situations in which response is always the same
3- some responses are still sent to brain and can be over ridden if needed
They protect body from handful stimuli ^survival
They are effective from birth so don’t have to be learned
They are fast, because the neurone pathway is short with very few synapses
2 parts of the nervous system
The central nervous system (CNS) and Peripheral nervous system (PMS)
(Brain and spinal cord). (All other peripheral nerves originating from brain and spinal cord)
