3.6 organisms respond to changes in their internal and external environments

Question 1

why do organisms respond toc changes in their environment

Answer 1

to increase their chance of survival

Question 2

what can affect the cell elongation in the roots and shoots of flowering plants

Answer 2

different concentrations of indoleacetic acid- IAA

Question 3

explanation of gravitropism and phototropism in flowering plants

Answer 3

due to the effect of different concentrations of IAA on cell elongation in the roots and shoots of flowering plants

Question 4

simple responses

Answer 4

• simple responses keep mobile organisms in a favourable environment
• present in simple mobile organisms e.g woodlice
• their responses can either be tactic or kinetic

Question 5

tactic response verb

Answer 5

taxis

Question 6

tactic response

Answer 6

• directional movement in response to a stimulus; direction of stimulus affects response
• positive taxis = towards light

Question 7

kinetic response verb

Answer 7

kinesis

Question 8

kinetic response

Answer 8

• ## non directional movement in response to a stimulus; intensity of stimulus affects response

Question 9

simple reflex

Answer 9

• rapid and involuntary response
• communication goes through spinal cord and not through concious part of brain
• simple reflexes are protective; they help organisms avoid damage

Question 10

role of simple reflexes

Answer 10

• help organism avoid damage

Question 11

role of receptors

Answer 11

• they’re specific cells that detect a particular stimulus

Question 12

variation in types of receptors + examples

Answer 12

• some receptors are cells
• e.g photoreceptors = receptors that connect to nervous system
• some receptors are proteins on the cell surface membranes e.g glucose receptors = proteins found in cell membranes of pancreatic cells

Question 13

what do receptors in the NS convert energy of stimulus into

Answer 13

electrical energy which is used by neurones

Question 14

what is resting potential

Answer 14

potential difference when a cell is resting

Question 15

difference in charge when a receptor is in resting state

Answer 15

• inside is negatively charged, relative to its outside
• means that there is a voltage or potential difference across the membrane

Question 16

how is the resting potential generated

Answer 16

• by ion pumps and ion channels

Question 17

what is generator potential

Answer 17

change in potential difference due to a stimulus

Question 18

how is a generator potential generated

Answer 18

• when a stimulus is detected, the cell membrane is excited and becomes permeable
• this allows more ions to move in and out of the cell; altering the potential difference
• bigger stimulus excites membrane more, causing a bigger movement of ions and therefore a greater change in potential difference; hence a bigger generator potential

Question 19

what is an action potential

Answer 19

• an electrical impulse along a neurone
• it is only triggered if the generator potential reaches the threshold level

Question 20

how is an action potential triggered

Answer 20

• if the generator potential is big enough, it will trigger an action potential

Question 21

how are action potentials measured

Answer 21

• they are all one size, so the strength of the stimulus is measured by the FREQUENCY of action potential (number of action potentials at a time)
• if stimulus is too weak, the generator potential won’t reach the threshold, so there is no action potential

Question 22

what do mechanoreceptors detect

Answer 22

changes in pressure

Question 23

example of a specific mechanoreceptor

Answer 23

pacinian corpuscle

Question 24

structure of pacinian corpuscle

Answer 24

• receptors that occur deeply in skin
• its a sensory neurone surrounded by layers of connective tissue separated by viscous gel

Question 25

how is a generator potential established in the pacinian corpuscle

Question 26

what does the pacinian corpuscle act as and why

Answer 26

• acts as a transducer
• converts mechanical energy (pressure) into energy of a nervous impulse