Stimuli and response

Question 1

what is a stimulus?

Answer 1

a detectable change in the internal or external environment of an organism that produces a response in the organism

Question 2

how do organisms increase their survival chances?

Answer 2

by responding to stimuli via different response mechanisms

Question 3

what sequence is involved in any animal survival strategy?

Answer 3

detection
processing
response system

Question 4

what are taxes and kinesis?

Answer 4

simple responses to keep organisms within their favourable conditions

Question 5

define taxes

Answer 5

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

Question 6

4 different taxes

Answer 6

positive taxis
negative taxis
phototaxis
chemotaxis

Question 7

what is a positive taxes?

Answer 7

favourable stimulus that an organism moves towards

Question 8

what is a negative taxes?

Answer 8

unfavourable stimulus that organisms move away from

Question 9

what is a phototaxis?

Answer 9

light stimulus

Question 10

what is a chemotaxis?

Answer 10

chemical stimulus

Question 11

example of a positive phototaxis and how it is a survival advantage

Answer 11

e.g. single celled algae move towards light
increases survival because they are photosynthetic
more light, higher rate of photosynthesis, more carbs for respiration

Question 12

example of negative phototaxis and how it was a survival advantage

Answer 12

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

Question 13

example of a positive chemotaxis and how it is a survival advantage

Answer 13

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

Question 14

define Kineses

Answer 14

an organism that moves randomly until it reaches a more favourable environment
movement depends on the intensity not direction of stimulus

Question 15

what happens if an organism changes its speed of movement and rate it changes direction?

Answer 15

it will increase the likelihood of returning to favourable conditions

Question 16

what would an organism do in areas of unfavourable conditions?

Answer 16

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

Question 17

what happens if an organism is surrounded by negative stimuli?

Answer 17

the rate of turning will decrease
so it moves in a straight line
increases the chances of finding a new location with favourable conditions

Question 18

what will an organism do in favourable conditions?

Answer 18

slow down and turn less to stay in favourable conditions

Question 19

Gove an example of an organism that shows kinesis

Answer 19

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

Question 20

how is the behaviour of small invertebrates investigated?

Answer 20

choice chambers and mazes

Question 21

when is kinesis especially important?

Answer 21

when the stimulus is less directional and shows a less clear gradient
e.g. temperature and humidity

Question 22

what are plant growth factors?

Answer 22

specific growth factors in flowering plants move from growing regions to other tissues where they regulate growth in response to directional stimuli

Question 23

why are plant growth factors used?

Answer 23

plants have no nervous system so they have to respond to changes in environment using plant growth factors in order to survive

Question 24

3 features of plant growth factors

Answer 24

1. exert influence by affecting growth
2. made by cells located throughout the plants
   3.may affect tissues near to those releasing them

Question 25

IAA

Answer 25

Indoleacetic acid

Question 26

what is IAA

Answer 26

a type of auxin
first chemical identified to be involved in the growth response

Question 27

what is the main effect of IAA

Answer 27

on the elongation region, the growth of a root or shoot has cell division taking place

Question 28

where is IAA synthesised?

Answer 28

in the tip of the root or shoot and diffuses into the elongating region where it attaches to receptors on the cell membrane

Question 29

role of IAA

Answer 29

It controls cell elongation in shoots
it inhibits growth of cells in roots
can also diffuse to other cells

Question 30

explain the acid growth hypothesis

Answer 30

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

Question 31

define phototropism

Answer 31

the name given to tropisms where the plant is responding to ligh

Question 32

define gravitropism

Answer 32

term given for responses to gravity

Question 33

what is the growth response of a young shoot to a positive phototropism?

Answer 33

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

Question 34

why is it important that plants respond to a positive phototropism

Answer 34

improves their chances of survival because light is needed for the light dependent reaction in photosynthesis

Question 35

plant response to a negative phototropism

Answer 35

1. 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

Question 36

plant response to a positive gravitropism

Answer 36

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

Question 37

how does the plant response to a positive gravitropism increase survival?

Answer 37

because it helps to anchor the plant

Question 38

plant response to a negative gravitropism

Answer 38

• 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