Stimuli and response Flashcards
what is a stimulus?
a detectable change in the internal or external environment of an organism that produces a response in the organism
how do organisms increase their survival chances?
by responding to stimuli via different response mechanisms
what sequence is involved in any animal survival strategy?
detection
processing
response system
what are taxes and kinesis?
simple responses to keep organisms within their favourable conditions
define taxes
a simple response of a cell, organism or part of an organism who’s direction is determined by the direction of the stimulus
it is direct response to the environment, an organism will move its entire body towards favourable conditions and way from unfavourable
4 different taxes
positive taxis
negative taxis
phototaxis
chemotaxis
what is a positive taxes?
favourable stimulus that an organism moves towards
what is a negative taxes?
unfavourable stimulus that organisms move away from
what is a phototaxis?
light stimulus
what is a chemotaxis?
chemical stimulus
example of a positive phototaxis and how it is a survival advantage
e.g. single celled algae move towards light
increases survival because they are photosynthetic
more light, higher rate of photosynthesis, more carbs for respiration
example of negative phototaxis and how it was a survival advantage
e.g. earthworms move away from light
worms move into the soil where they are more able to conserve water,avoid predators and reduce chances of dessicaiton
example of a positive chemotaxis and how it is a survival advantage
e.g. some bacteria move to a region where glucose is concentrated because it is a respiratory substance
more bacteria can replicate by binary fission
define Kineses
an organism that moves randomly until it reaches a more favourable environment
movement depends on the intensity not direction of stimulus
what happens if an organism changes its speed of movement and rate it changes direction?
it will increase the likelihood of returning to favourable conditions
what would an organism do in areas of unfavourable conditions?
if an organism crosses the dividing line between favourable and unfavourable conditions, the rate of turning will increase to increase Its chances of returning to a favourable environment
what happens if an organism is surrounded by negative stimuli?
the rate of turning will decrease
so it moves in a straight line
increases the chances of finding a new location with favourable conditions
what will an organism do in favourable conditions?
slow down and turn less to stay in favourable conditions
Gove an example of an organism that shows kinesis
woodlice
lose water from body in dry conditions
move more rapidly and change direction in dry conditions to increase chances of moving to a different areas
slow down in moist areas
how is the behaviour of small invertebrates investigated?
choice chambers and mazes
when is kinesis especially important?
when the stimulus is less directional and shows a less clear gradient
e.g. temperature and humidity
what are plant growth factors?
specific growth factors in flowering plants move from growing regions to other tissues where they regulate growth in response to directional stimuli
why are plant growth factors used?
plants have no nervous system so they have to respond to changes in environment using plant growth factors in order to survive
3 features of plant growth factors
- exert influence by affecting growth
- made by cells located throughout the plants
3.may affect tissues near to those releasing them
IAA
Indoleacetic acid
what is IAA
a type of auxin
first chemical identified to be involved in the growth response
what is the main effect of IAA
on the elongation region, the growth of a root or shoot has cell division taking place
where is IAA synthesised?
in the tip of the root or shoot and diffuses into the elongating region where it attaches to receptors on the cell membrane
role of IAA
It controls cell elongation in shoots
it inhibits growth of cells in roots
can also diffuse to other cells
explain the acid growth hypothesis
hydrogen ions are actively transported from the cytoplasm to spaces in the cell wall
lowers the PH which breaks the hydrogen bonds between microfibrils in the cellulose cell walls
makes the walls stretch more readily and become more plastic
define phototropism
the name given to tropisms where the plant is responding to ligh
define gravitropism
term given for responses to gravity
what is the growth response of a young shoot to a positive phototropism?
1.cells in the tip produce IAA, which is transported down the shoot
2.IAA is initially transported evenly through all regions as it begins to move down the shoot
3. unilateral light causes the movement of IAA from the light side to the shaded side of shoot
4.a greater conc. of IAA builds up on shaded side of shoot
5.greater conc. of IAA on shaded side so it elongates mmore
6. elongates faster so shoot is bent towards the light
why is it important that plants respond to a positive phototropism
improves their chances of survival because light is needed for the light dependent reaction in photosynthesis
plant response to a negative phototropism
- high conc of IAA inhibits cell elongation in roots
2.cell elongation is greater on light side of roots than shaded side
3.root bends away from light
helps their survival because it helps further anchor the plant in the ground and reach more water faster
plant response to a positive gravitropism
1.cells in the tip of the root produce IAA which is transported back along the root
2.IAA is initially transported evenly to all sides of the root
3.gravity influences movement of IAA from the uperside of root to lower side
4.greater conc. builds up on lower side of roots
5. greater conc. on lower side inhibits the elongation of root cells on lower side
6. greater elongation of cells on upper side-so root bends down towards force of gravity
how does the plant response to a positive gravitropism increase survival?
because it helps to anchor the plant
plant response to a negative gravitropism
- IAA diffuse from upper side to lower side of shoot-diffuses towards gravity
-if plant vertical, IAA will diffuse down so the lower plant cells elongate and plant grow upwards
-if a shoot is on its side,IAA will cause it to bend upwards against gravity because IAA diffuses down to cells on the lower side so they elongate and force shoot to point upwards
