survival and response

Question 1

how do organisms increase their chance of survival

Answer 1

by responding to changes in their environment

Question 2

what do flowering plants do

Answer 2

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

Question 3

taxis

Answer 3

directional movement response towards or away from a stimulus

(generally used when talking about simple behaviour of small invertebrates)

Question 4

kinesis

Answer 4

non-directional movement response involving a change in movement rate or rate of turning

Question 5

what are plant growth factors and where are they produced

Answer 5

chemicals that regulate plant growth response to directional stimuli

produced in plant growing regions (meristems)

diffuse (migrate) from cell to cell / phloem mass transport

Question 6

explain why shoots show positive phototropism

Answer 6

IAA diffuses to shaded side of shoot tip

as IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall

disruption to H-bonds between cellulose molecules and actions of expansins make cell more permeable to water

cells on shaded side elongate faster due to higher turgor pressure

shoot bends towards light

Question 7

explain why roots show positive gravitropism

Answer 7

gravity causes IAA to accumulate on lower side of the root

IAA inhibits elongation of root cells

cells on the upper side of the root elongate faster, so the root tip bends downwards

Question 8

mammalian hormones vs plant growth factors

Answer 8

CASTS

concentration
action
synthesis
transport
speed

mammalian
C - response not always dependent on concentration
A - bind to complementary proteins in/ on target cells
S - specialised glands
T - circulatory system
S - faster-acting (homeostasis)

plant
C - response proportional to concentration
A - can affect all cells
S - various tissues in growing regions
T - diffusion or phloem translocation
S - slower-acting (plant growth)

Question 9

define taxis and kinesis - state their advantage

Answer 9

taxis - directional movement in response to external stimulus

kinesis - non-directional response to presence and intensity of external stimulus

maintain mobile organism in optimum environment

Question 10

many organisms respond to temperature and humidity via kinesis rather than taxis

Answer 10

less directional stimuli; often no clear gradient from one extreme to the other

Question 11

how could a student recognise kinesis

Answer 11

• organism crosses sharp division between favourable and unfavourable - turning increases
• organisms moves considerable distances into unfavourable environment - turning slowly decreases - begins to move in long, straight lines, sharper turns

Question 12

outline what happens in a simple reflex arc

Answer 12

receptor detects stimulus -> sensory neuron -> relay neuron in CNS coordinates response -> motor neuron response by effector

Question 13

give the advantage of a simple reflex

Answer 13

• rapid response to potentially dangerous stimuli since only 3 neurons involved
• instinctive - innate

Question 14

suggest a suitable statistical test - whether a factor has a significant effect on the movement of an animal in a choice chamber

Answer 14

chi squared

Question 15

what features are common to all sensory receptors

Answer 15

act as energy transducers which establish a generator potential

respond to specific stimuli

Question 16

what is a tropism

Answer 16

slower growth responses

phototropism - shoots - maximise photosynthetic surface area - more glucose, more growth, outcompete other plants

geotropism - roots - grow down to locate water and mineral ions - helps to anchor plant