chapter 14 - responses to stimuli Flashcards
What is a stimulus
A stimulus is a detectable change in the internal or external environment of an organism that leads to a response in the organism.
Describe the overall method when a change(stimulus) is detected
Stimulus
Receptor
Coordinator [central nervous system]
Effector
Response
What is a taxes
A taxes is a simple response who’s direction is determined by the direction of the stimulus. It is a directional response
Give an example of a taxes response
For example when earth worms move away from sunlight [negative phototaxis] this increases the chance of survival because it takes them into the soil where they are better able to conserve water, find food and avoid predators.
What is kinesis
It is a response in which the organism does not move towards or away from a stimulus instead it changes the speed at which it moves and changes the rate at which it changes direction.
Give an example of a kinesis response
For example wouldlice lose water from their bodies and dry conditions, when they move from a damp area to a dry area they move more rapidly and change direction more often this increases the chance of moving into a favorable condition [damp areas].
Tell me about the hormonal system
Main communication is by chemical is called hormones
Transmission is by the blood system and is usually relatively slow
Hormones travel to all parts of the body but only target cells respond
The responses often long-lasting and the effects could be permanent and irreversible.
Tell me about the nervous system
Main communication is by nerve impulses
Transmission is by neurons and is usually very fast
Nerve impulses only travel to specific parts of the body that for the response is localized
The response is short-lived and the effect is usually temporary and reversible
What is a tropism
A tropism is the growth of part of a plant in response to a directional stimulus.
Give an example of a tropism
For example plant shoots great towards light [positive phototropism] and away from gravity [negative gravitropism]
Plant roots grow away from the light [negative phototropism and they grow towards gravity [positive gravitropism]
Plants have no nervous system but they respond to changes in their internal and external environment. Give three examples of things plants respond to
Light - plant shoots grow towards light because light as needed for photosynthesis
Gravity - plants need to be firmly anchored into the soil.
Water - plant roots grow towards water [positively Hydrotropic] in order to absorb it for the use of photosynthesis and all the metabolic processes as well as for support.
What do plants use to respond to external stimuli
Plant growth factors
What are plant growth factors made from and why are they made
They are made by the cells located throughout the plant rather than in a specific organ.
However on like animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distinct target Oregon.
What is IAA
IAA is indoleacetic acid
It belongs to auction switch control cell elongation
Describe phototropism and flowering plants
Cells in the tip of the shoot produce IAA which is then transported down the shoot
IAA is initially transported evenly throughout all regions as it begins to move down the shoot
Light causes the movement of IAA to the shaded side of the shoot
A high concentration of IAA builds up on the shaded side
IAA causes elongation oh shoot cells, the shaded side elongates more
The shaded side of the shoot elongates faster than the light side causing the shoot to bend towards light.
What does IAA do in roots
IAA inhibits cell elongation in the roots. Therefore elongation is greater on the light side than the shaded side causing the roots to bend away from light that for the roots are negatively phototropic.
Describe gravitropism in flowering plants
Cells in the tip of the root produce IAA. IAA is initially transported to all sides of the shoot.
Cravity influences the movement of the hormone from the upper side to the lower side of the root
A greater concentration of the hormone builds up on the lower side
Therefore the upper side will elongate faster than the lower side causing roots to bend down towards the force of gravity.
What is the acid growth hypothesis
IAA increases plasticity to the cell walls. However the response only occurs on young cell walls. As cells mature they developed greater rigidity therefore parts of the shoot/roots will not be able to respond.
The active transport of hydrogen ions from the cytoplasm to the cell wall causes the cell wall to become more plastic allowing the cell to elongate by expansion.
What is the central nervous system and what is it made up of
It is made up of the brain and the spinal cord
What is the peripheral nervous system [PNS]
Is made up of pairs of nerves that come from either the brain or spinal cord