Response To Stimuli

Question 1

Stimulus

Answer 1

Detectable change in the internal and external environment of an organism that leads to a response in the organism

Question 2

Ability to respond is necessary because

Answer 2

It increases chances of survival for organism - detect and move away from harmful stimuli or move towards a source (food)

Question 3

Stimuli are detected by

Answer 3

Receptors

Question 4

Receptors are

Answer 4

Specific to one type of stimulus

Question 5

A coordinator

Answer 5

Formulates suitable response to a stimulus may be at a molecular level or involve a large organ like the brain

Question 6

Response is produced by an

Answer 6

Effector

Question 7

Hormones as a means of communication

Answer 7

Slow process via chemicals(hormones ), in large mulitcullular organisms, plants and animals

Question 8

Animals have a more rapid means of communication

Answer 8

Nervous system

Question 9

Central coordinator

Answer 9

Each receptor and effector is linked to one. It connects information from each receptor with the appropriate effector

Question 10

Sequence of events

Answer 10

Stimulus - receptor - coordinator - effector- response

Question 11

Taxis

Answer 11

Simple response whose direction is determined by the direction of the stimulus - an organisms moves whole body towards a favourable stimulus or away from unfavourable one

Question 12

Towards stimulus

Answer 12

Positive taxis

Question 13

Eg towards the light is

Answer 13

Positive phototaxis

Question 14

Algae moving towards light advantage

Answer 14

Increases chances of survival as being photosynthetic they require light to manufacture there food

Question 15

Earthworms moving away from the light is

Answer 15

Negative phototaxis

Question 16

Earthworms moving away from light increases survival rate because

Answer 16

Takes them into the soil where they are better able to conserve water , find food and avoid some predators

Question 17

Bacteria move towards region where glucose is more highly concentrated as it’s a source of food which is ?

Answer 17

Positive chemotaxis

Question 18

Kinesis

Answer 18

Organism doesn’t move towards or away from stimulus instead it changes the speed at which it moves and the rate at which it changes direction

Question 19

If an organism(kinesis)crosses a sharp dividing line between favourable and unfav environment what happens

Answer 19

It’s rate of turning increases raising its chances of a quick return to a fav environment

Question 20

(Kinisis) if moves a considerable amount into unfav environment what happens to rate of turning

Answer 20

Decreases so that it moves in long straight lines before it turns sharply . This tends to bring the organism to a region favourable

Question 21

When a stimulus is less directional (kinesis)

Answer 21

Humidity and temperature eg don’t always produce a clear gradient from one extreme to another

Question 22

Example of kinesis - spend more time in damp than less fav dry preventing then drying out increase survival

Answer 22

Woodlice- lose water in dry conditions so when move from damp to dry move more rapidly to increase chance of getting back to damp. Once in damp they slow and don’t change direction as much so more likely to stay in damp. But if been in dry for a while and been changing direction they move rapidly in straight lines instead to increase chance of getting into damp quicker

Question 23

Tropism

Answer 23

Growth of part of a plant in response to a directional stimulus (grows towards or away from stimulus- stimulus names the type of response )

Question 24

Plant shoots response so that leaves are in most favourable position to capture light for photosynthesis

Answer 24

Shoots grow - towards light (positive phototropism) and away from gravity ( negative gravitropism)

Question 25

Roots response to increase probability they’ll grow in soil and why need to

Answer 25

Grow away from light ( negative phototropism) and towards gravity(pos gravitropism) so there better able to absorb water and min ions

Question 26

Example of a plant growth factor

Answer 26

Indoleacetic acid (IAA)

Question 27

IAA

Answer 27

Controls plant cell elongation. Belongs to group called auxins

Question 28

Unilateral light

Answer 28

Light directed at a shoot from one side

Question 29

Phototropism in flowering plants process

Answer 29

Cells in the tip of the shoot produce IAA which is then transported down the shoot
Initially it’s transported evenly but then the light causes the movement of it from the light side to the shaded side of the shoot.
Greater conc builds up on shaded side and as they cause cell elongation the cells on shaded side elongate faster than the light side , causing the shoot to bend towards the light

Question 30

Phototropism. High concentration of IAA in roots affect ?

Answer 30

Inhibits cell elongation so in roots the cell elongation is greater on the light side than the shaded so roots bend away from the light(neg)

Question 31

Protein pigment in rod cells

Answer 31

Rhodopsin

Question 32

Receptor

Answer 32

, detect stimulus if big enough create generator potential or action potential

Question 33

Rod cells

Answer 33

Absorb light intensity and the protein pigment inside rhodopsin (if a big enough light intensity is absorbed) it will break down pigment and this triggers an action potential

Question 34

How does an action potential occur in rod cells

Answer 34

If enough pigment has been broken down for threshold to be met in bipolar cell an action potential can occur

Question 35

2 reasons we can see in dark

Answer 35

Not a lot of energy needed to break down rhodopsin and the Threshold can be reached in low light as there’s multiple rod cells connecting to 1bipolar cell (retinal convergence ) creates spatial summation

Question 36

Spatial summation

Answer 36

Collectively all broken down pigment results in big enough stimulus to trigger action potential-rod cells

Question 37

Rod cells accuracy of vision

Answer 37

Low visual acuity - can’t distinguish between separate light sources

Question 38

Cone cells colour pigment

Answer 38

Iodopsin (3 types red green and blue )all absorb diff wavelengths of light

Question 39

How do we perceive range of colours

Answer 39

Depending on proportion of each cone cell stimulated

Question 40

No retinal convergence or special summation

Answer 40

Cone cells so can’t see colour in dark

Question 41

Going towards Spinal cord

Answer 41

Afferent

Question 42

Going away from spinal cord

Answer 42

Efferent

Question 43

Macula

Answer 43

High density of rods and cones