Internal + External Stimuli Detected & Lead to Response

Question 1

stimuli

Answer 1

a detectable change in the internal/external environment

Question 2

receptor

Answer 2

a cell or organ that detects change in internal/external environment

Question 3

coordinator

Answer 3

connects information between receptor and the appropriate effector

Question 4

effector

Answer 4

a cell, tissue or organ that carries out a response
muscles and glands

Question 5

response

Answer 5

a change brought due to a stimulus

Question 6

plant growth factors and where are they produced

Answer 6

chemicals that regulate plant growth response to directional stimuli
produced in plant growing regions
diffuse from cell to cell/ phloem mass transport

Question 7

positive phototropism in shoots

Answer 7

-cells in tip of shoot produce IAA, transported down the shoot
-light causes IAA to diffuse to shaded side of shoot tip
-greater concentration of IAA on shaded side
-as IAA causes elongation and greater concentration on shaded side, cells on this side elongate more.
-shaded side elongates faster than light side, causes shoot tip to bend towards light.

Question 8

gravitropism in roots

Answer 8

-gravity causes IAA to accumulate in lower side of root
-IAA inhibits elongation in root cells
-cells on upper side of root grow faster relative to lower side causing root to bend downwards towards gravity

Question 9

define taxis and kinesis and state their advantage

Answer 9

taxis-directional movement in response to external stimuli
kinesis-non-directional response to presence and intensity of external stimulus

-maintain mobile organism in optimum environment e.g. to prevent desiccation.

Question 10

tropism

Answer 10

growth of part of a plant in response to directional stimulus

Question 11

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

Answer 11

less directional stimuli; often no clear gradient from one extreme to another.

Question 12

stages of reflex arc

Answer 12

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

Question 13

importance of reflex arc

Answer 13

-involuntary: doesn’t require a decision, frees brain from executing more complex decision
-protection: protects from potentially dangerous stimuli
-rapid response: neuron pathway short, very few synapses

Question 14

autonomic nervous system

Answer 14

system that controls all involuntary activities of internal muscles and glands.
has 2 subdivisions: parasympathetic & sympathetic

Question 15

difference between parasympathetic and sympathetic

Answer 15

parasympathetic: inhibits effectors so slows down activity, controls activity in normal resting conditions.
-concerned with conserving energy & replenishing body’s reserve
sympathetic: stimulates effectors so speeds up activity, involved in ‘fight or flight’ response.
-heightens awareness, helps cope in stressful conditions.

Question 16

medulla oblongata and its function

Answer 16

located in brainstem and controls involuntary functions
function is transmitting signals between spinal cord and higher parts of brain-controls autonomic activities.

Question 17

events that control basic heart rate

Answer 17

-SAN initiates wave of electrical energy- spreads across both atria, causes the atria to contract= atrial systole
-wave of excitation enters AVN-between atria
-AVN, after a short delay, conveys wave of electrical excitation between the ventricles along Purkyne tissue (bundle of His)
-Bundle of His conducts wave through atrioventricular septum to base of the ventricles, where bundle branches into smaller Purkyne fibres
-wave of excitation released quickly from Purkyne fibres, contracts quickly from apex upwards.

Question 18

centres in medulla oblongata to mediate heart rate

Answer 18

-1 centre causes sympathetic nerve to release neurotransmitter noradrenaline-connects to SAN, increases heart rate
-2nd centre causes parasympathetic (vagus) nerve to release neurotransmitter acetylcholine, connects to SAN-decreases heart rate.

Question 19

receptors involved in changing heart rate and their location

Answer 19

chemoreceptors: sensitive to changes in pH of the blood as a result of CO2 concentration
-found in wall of carotid artery and aortic body
baroreceptors: detects changes in blood pressure
-carotid body

Question 20

how does body respond to increase in CO2 concentration

Answer 20

-higher CO2 concentration=production of carbonic acid-lowers pH of blood
-chemoreceptors detect & increase frequency of impulses to centre of medulla oblongata that increases heart rate + respiration rate
-centre increases impulses to SAN via sympathetic nervous system
-heart rate increases-rate of blood flow increases-rate of gas exchange increase so more CO2 removed
-pH of blood rises to normal , chemoreceptors reduce frequency, medulla oblongata reduces impulses to SAN=reduction in heart rate