Unit 6: organisms respond to changes in their internal and external environments

Question 1

stimulus

Answer 1

a change in the internal or external environment

Question 2

receptor

Answer 2

detects a stimulus
-specific to one type of stimulus

Question 3

coordinator

Answer 3

formulates a suitable response to a stimulus

Question 4

effector

Answer 4

produces a response towards the stimulus

Question 5

taxis

Answer 5

a simple directional response determined by the direction of the stimulus

Question 6

positive taxis

Answer 6

motile organism moves towards the favorable stimulus

Question 7

negative taxis

Answer 7

motile organism moves away from the unfavorable stimulus

Question 8

positive phototaxis

Answer 8

organism moving towards light
e.g. single celled algae

Question 9

kinesis

Answer 9

form of response in which the organism does not move towards or away from the stimulus. instead it changes at the speed it moves and the rate at which it changes direction

Question 10

kinesis in favourable conditions

Answer 10

movement will be slower and direct, so the organism spends longer here

Question 11

kinesis in unfavourable conditions

Answer 11

movement is faster and involve more turns, to find the favourable condition

Question 12

tropism

Answer 12

the growth of a plant in response to a directional stimulus

Question 13

positive phototropism and negative gravitropism

Answer 13

plant shoots grow towards light and away from gravity

Question 14

negative phototropism and positive gravitropism

Answer 14

plant shoots grow away from light and towards gravity

Question 15

what do plants respond do

Answer 15

-light, shoots grow towards light because it is needed for photosynthesis
-gravity, plants need to be firmly anchored into the soil. roots are sensitive to gravity and grow in the direction of its pull
-water, almost all plants grow towards water (e.g. positively hydroptropic) in order to absorb it for use in photosynthesis and other metabolic processes

Question 16

what is plant growth controlled by

Answer 16

indoleacetic acid (IAA) which is an important auxin produced in the tips and shoots of flowering plants. the distribution of IAA around the plant controls tropisms.

Question 17

IAA on the effect of phototropism

Answer 17

when the shoot is illuminated from all side, the auxins are evenly distributed and move down the shoot tip thus causing elongation of cells across the cells of elongation.
whereas, if the shoot is only illuminated from one side, the auxins move towards the shaded part of the shoot thus causing elongation of the shaded side only which results in the bending of the shoot towards the light

Question 18

IAA on the effect of gravitropism

Answer 18

gravitropism in the roots is the opposite. IAA will build up on the lower side of the root. In roots IAA inhibits growth, therefore causing the cells on the upper side to grow faster, causing the root to bend downwards

Question 19

explain how the movement of IAA in shoots helps plants to survive

Answer 19

more IAA moves towards the shaded side of shoots than the light side when light is unidirectional. in repose to this uneven distraction of IAA, the cells on the long acted side elongate faster than those on the light side and the shoot bends towards the light
-this ensures that the shoot and the leaves attached to it have a greater chance of being illuminated
-as light is essential for photosynthesis, the process by which organic material for respiration is manufactured, the plant has a greater chance of survival

Question 20

what are the nervous systems two major division

Answer 20

central nervous system- made up of brain and spinal cord
peripheral nervous system- made up of pairs of nerves that originate from either the brain or the spinal cord

Question 21

what is the peripheral nervous system divided into

Answer 21

sensory nervous system- carry nerve impulses from the receptors the cns
motor nervous system- carry nerve impulses from the cns to the effectors

Question 22

what is the motor nervous system divided into

Answer 22

voluntary nervous system- which carries nerve impulses to body muscles and is under voluntary control
autnomic nervous system- carries nerve impulses to glands, smooth muscle and cardiac muscle. under involuntary control

Question 23

what is a reflex

Answer 23

type of involuntary response to a sensory stimulus

Question 24

what is a reflex arc

Answer 24

the pathway of neurons involved in a reflex

Question 25

order of the reflex arc

Answer 25

stimulus, receptor, sensory neuron, coordinator, motor neuron, effector, response

Question 26

importance of reflex arcs

Answer 26

-they are involuntary and therefore do not require the decision making powers of the brain. allows the brain to be free to carry out more complex responses
-they protect the body from harm, present from birth and do not have to be learnt
-they are fast, because the neuron pathway is short with very few synapses where neurons communicate with each other

Question 27

features of a Pacinian corpuscle

Answer 27

-is specific to a single type of stimulus, it only responds to mechanical pressure
-produces a generator potential by acting as a transducer. Pacinian corpuscle transduces the mechanical energy of the stimulus into a generator potential

Question 28

basic structure of a Pacinian corpuscle

Answer 28

-single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
-stretch mediated sodium channels on plasma membrane
-capillary runs along base layer of tissue

Question 29

what stimulus does a Pacinian corpuscle respond to and how

Answer 29

-pressure deforms membrane, causing stretch mediated sodium ion channels to open
-if influx of sodium raises membrane to threshold potential (and the membrane becomes depolarised), a generator potential is produced
-action potential moves along the sensory neuron

Question 30

2 types of photoreceptor cells located in the retina

Answer 30

-cone cells
-rod cells

Question 31

location of rod cells

Answer 31

distribution more at the periphery of the retina
-rod cells are in abundance because light intensity is lowest

Question 32

explain the low intensity response of rod cells

Answer 32

rhodopsin can break down the pigment in rod cells to create a generator potential. there is enough energy from low intensity light to cause this breakdown.
-the stimulation of multiple rod cells can be combined to exceed the threshold value and therefore create a generator potential

Question 33

explain the visual acuity of rod cells

Answer 33

in perception, the brain cannot distinguish between the separate sources of light due to multiple rod cells only linking to one bipolar cell therefore it is only able to send a single nerve impulse

Question 34

location of cone cells

Answer 34

concentrated at the fovea as this is what receives the highest intensity of light

Question 35

explain the high intensity response of cone cells

Answer 35

each cone cell has their own sperate bipolar cell, so the stimulation of multiple cone cells cannot be combined to exceed the threshold value which produces a generator potential.
-iodopsin requires a higher intensity for its breakdown and creation of a generator potential

Question 36

explain the visual acuity of cone cells

Answer 36

high visual acuity because each cone cell is connected to its own bipolar cell, which means that if two adjacent cone cells are stimulated, the brain receives two separate impulses. the brain cannot distinguish between the two separate sources of light that stimulated the cone cells

Question 37

what is visual acuity

Answer 37

the clarity of vision, determined by the individuals ability to recognise small details with precision

Question 38

what are the colours seen by rod + cone cells

Answer 38

rod- cannot distinguish different wavelengths of light so black and white only
cone- each cone cell is sensitive to a specific range of wavelengths so can see in full colour (three types of cone cells)

Question 39

define myogenic

Answer 39

the hearts ability to initiate its own contraction

Question 40

pacemaker of the heart

Answer 40

sinoatrial node located in the wall of the right atrium
-this initiates a wave of electrical stimulation which causes the atria to contract roughly at the same time