organisms respond to changes in their internal and external environments Flashcards
1
Q
what is a stimulus?
A
detectable change in the environment
2
Q
what is a stimulus detected by?
A
receptor
3
Q
what is a tropism?
A
when plants respond via growth to stimuli, they can be positive or negative
4
Q
what are tropisms controlled by?
A
indoleacetic acid (IAA), a type of auxin that controls cell elongation
5
Q
IAA causes cell elongation in…
A
shoots
6
Q
IAA inhibits cell elongation in…
A
roots
7
Q
positive phototropism in shoots
A
- shoot tip cells produce IAA
- this causes cell elongation
- IAA diffuses to cells on shaded sides
- resulting in a high conc. in shaded side
- causing shaded to elongate and bend towards light
8
Q
negative phototropism in roots
A
- high conc. of IAA inhibits cell elongation
- causes root cells to elongate more on lighter side
- root bends away from the light
9
Q
negative gravitropism in shoots
A
- IAA will diffuse from upper side to lower side of shoot
- causes cell elongate and plant grows upwards
10
Q
positive gravitropism in roots
A
- IAA moves to lower side of roots
- upper side elongates
- root bends down so anchor plant in
11
Q
taxis
A
movement of an organisms body towards favourable stimuli or away from unfavourable stimuli (directional response to external stimuli)
12
Q
kinesis
A
organism changes the speed of movement and the rate it changes the direction (non-directional response)
13
Q
why do many organisms respond to temperature and humidity via kinesis rather than taxis?
A
often no clear gradient from one extreme to another
14
Q
simple reflex arc
A
- receptor detects stimulus
- sensory neuron
- relay neuron in CNS
- motor neuron
- response by effect
15
Q
advantages of simple reflex arc
A
- rapid response to potentially dangerous stimuli
- instinctive
16
Q
what are pacinian corpuscles?
A
pressure receptors located deep in skin, mainly in fingers and feet
17
Q
structure of pacinian corpuscle
A
- single nerve fibre surrounded by layers of connective tissue which are separated by a viscous gel contained by a capsule
- stretch-mediated Na+ channels on plasma membrane
- capillary runs along base layer of tissue
18
Q
what stimulus does a pacinian corpuscle respond to and how?
A
- pressure deforms membrane, causing stretch-mediated Na+ ion channels to open due to widening of sodium channels
- if influx of Na+ ions raises membrane to threshold potential, a generator potential is produced
- action potential moves along sensory neuron
19
Q
two types of photoreceptor in retina
A
rods and cones
20
Q
where are rods located?
A
evenly distrubted around periphery of retina and not in the fovea
21
Q
where are cones located?
A
central fovea
22
Q
rod cells
A
- cannot distinguish different wavelengths of light so process images in black and white
- can detect light of very low intensities
- linked by spatial summation
- low visual acuity
- conatin only one pigment, rhodopsin
23
Q
how is a generator potential created in a rod cell?
A
- rhodopsin is broken down by light energy
- there is enough low-intensity light to cause this
- enough pigment has to be broken down for the threshold to be met in the bipolar cell
- this threshold can be reached because so many rod cells are connected to a single bipolar cell
24
Q
how does retinal convergence impact rod cells?
A
retinal convergence means that the brain cannot distinguish between separate sources of light (low visual acuity)
25
cone cells
- three types of cone cell that contain different iodopsin pigment which all absorb different wavelengths of light
- can only detect high intensity light
- no spatial summation
- high visual acuity
26
why can we not see colour in the dark?
only one cone cells connects to a bipolar cell so cones so there is no spatial summation and cones can only respond to high light intensity
27
why are cones located in the fovea?
the fovea receives the highest intensity of light
28
myogenic definition
cardiac muscle is myogenic beacause it contracts within the muscle itself rather than by nervous stimulation
29
what are the two nodes involved in heart contraction?
SAN (sinoatrial node) and AVN (atrioventricular node)
30
where is the SAN located?
wall of the right atrium (also known as the pacemaker)
31
where is the AVN located?
between the border of the right and left ventricle within the two atria
32
where is the bundle of His located?
the septum
33
where are the Purkyne fibres loacted?
walls of the ventricles
34
how are heartbeats coordinated and initiated?
- SAN releases a wave of depolarisation across the atria, causing it to contract
- AVN releases wave of depolarisation
- non-conductive layer between the atria and ventricle prevent the wave travellings to ventricles
- the budle of His conduct and pass the wave of depolarisation down the septum and the Purkyne fibres in the walls of the ventricles
- apex and then walls of ventricles contract
- delay of AVN WOD means atria can pump all blood into ventricles
- cells repolarise and the cardiac muscles relax
35
what area of the brain controls heart rate?
medulla oblongata, via the ANS
36
what does the heart rate change in response to?
blood pressure and pH
37
what receptors decect pH change?
chemoreceptors
38
where are the chemoreceptors located?
carotid artery and aorta
39
what receptors detect blood pressure change?
baroreceptors
40
where are the baroreceptors located?
carotid artery
41
how does the body produce an increase in HR?
stimulus: low pH/low pressure
receptor: chemo/baroreceptor
coordinator: more action potentials to medulla oblongata
effector: SAN via sympathetic nervous system increases frequency of AP
42
how does the body produce a decrease in HR?
stimulus: high pH/high pressure
receptor: chemo/baroreceptor
coordinator: more action potentials to medulla oblongata
effector: SAN via parasympathetic nervous system increases frequency of AP
43
describe the general structure of a motor neuron
- cell body that contains organelles and RER
- dendrons that branch into dendrites which carry AP to cell body
- axon that is a long unbranched fibre that carries AP down neuron
- nodes of ranvier that are gaps in myelin which allow for saltatory conduction
- myelin sheath is a lipid which does not allow charged ions to pass through
44
what is resting potential?
the difference between electrical charge inside and outside of the neuron when there is no AP
45
what is the value for resting potential?
-70mV
46
how is resting potential established?
- higher concentration of potassium ions inside
and higher concentration of sodium ions outside
- membrane contains many Na-K pumps
- actively transports 3Na+ out and 2K+ in
- membrane is more permeable to K+
- creates electrochemical gradient
47
what is an action potential?
when the neurone's voltage increases beyond a set point beyond the resting potential, creating an electrical impulse
48
what is the value for an action potential?
+40mV
49
what is the threshold value?
-55mV
50
how is an action potential generated?
- stimulus provides energy to cause voltage-gated sodium channels to open
- causes Na+ to diffuse into axon whilst K+ diffuses out
- this increases voltage
- voltage above -55mV exceeds threshold, providing more energy, so more channels open
- this is depolarisation
- peaks at 40mV
- sodium channels close and voltage-gated potassium channels open
- decreases voltage as K+ diffuses out (repolarisation)
- hyperpolarisation occurs when voltage is less than resting
51
all or nothing principle
if depolarisation does not exceed threshold, then an action potential is not produced (nothing). all stimuli that does trigger depolarisation will peak at 40mV (all).
52
why is the all or nothing principle important?
makes sure than animals only respond to large enough stimuli to prevent sensory overload
53
refractory period
no action potential can be generated because sodium channels are recovering and cannot be opened (hyperpolarisation)
54
why is the refractory period important?
- ensures discrete impulses are produced
- ensures action potentials travel in one direction
- limits frequency of action potentials
55
what factors affect the speed of an action potential?
- myelination and saltatory conduction
- axon diameter
- temperature
56
why does myelination and saltatory conduction affect the speed of an action potential?
- gaps between myelin called NOR
- action potential jumps from node to node (saltatory conduction)
- myelin provides electrical insulation
- in non-myelinated axons, AP occurs along whole length
57
why does axon diameter affect the speed of an action potential?
the wider the diameter, the faster the speed of conduction because there is less leakage of ions and less resistance to the flow of ions
58
why does temperature affect the speed of an action potential?
the higher the temperature, the faster the speed of conduction because the ions diffuse faster and the enzymes involved in respiration work faster (ATP)
59
what is a synapse and what is its function?
synapses are gaps between the end of the axon and the dendrite of another neuron. this is where the AP is transmiited as a neurotransmitter.
60
outline the process of synaptic transmission
- depolarisation of synaptic knob membrane
- voltage gated calcium ion channels open and calcium ions diffuse into synaptic knob
- synaptic vesicles fuse with with presynaptic membrane and release a neurotransmitter
- neurotransmitter diffuses down neuron across synaptic cleft
- binds to complementary receptors on postsynaptic membrane
- sodium ions diffuse in by sodium ion channels leading to depolarisation
- neurotransmitter is degraded and released from receptor and resting potential is established
61
why is synaptic transmission unidirectional?
vesicles are only found in presynaptic membrane and receptors are only on postsynaptic membrane
62
what is the neurotransmitter in a cholinergic synapse?
acetylcholine
63
what enzyme breaks down acetylcholine?
acetylcholinesterase
64
what does acetylcholinesterase break acetylcholine into?
acetate and choline
65
what is summation?
the rapid build up of neurotransmitters in the synapse to help generate an action potential
66
what are the two types of summation?
spatial and temporal
67
spatial summation
many different presynaptic neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed threshold
68
temporal summation
one neurone releases neurotransmitter repeatedly over a short period of time to add up enough to exceed threshold
69
inhibitory synapses
cause chloride ions to move into postsynaptic neurone and potassium ions to move out, hyperpolarising the membrane to make an AP unlikely
70
what is a neuromuscular junction?
synapse between a motor neurone and a muscle
71
similarities between neuromuscular junction and cholinergic synapse
- both unidirectional
- acetylcholine is the neurotransmitter
72
differences between neuromuscular junction and cholinergic synapse
- NJ is only excitatory, CS is excitatory or inhibitory
- NJ connects a motor neurone to a muscle, CS connects two neurones
- NJ is the end point of an action potential, CS is where a new action potential is generated in the next neurone
- NJ acetylcholine binds to receptors on muscle fibre membranes, CS acetylcholine binds to receptors in postsynaptic membrane
73
how might drugs increase synaptic transmission?
- inhibit acetylcholinesterase
- mimic shape of neurotransmitter
74
how might drugs decrease synaptic transmission?
- inhibit release of neurotransmitter
- decrease permeability of ions in postsynaptic membrane
- hyperpolarise postsynaptic membrane
75
what are the three types of muscle in the body and where are they located?
cardiac: heart
smooth: walls of blood vessels and intenstines
skeletal: attached to incompressible by tendons
76
what does antagonistic muscle pair mean?
as one muscle contracts, the other relaxes
77
what is a myofibril?
fused cells that share nuclei and sarcoplasm that have a high number of mitochondria, they are the site of contraction
78
what is the sarcomere?
small units of a myofibril
79
what proteins make up myofibril?
actin and myosin
80
what is the thick protein in the sarcomere?
myosin
81
what is the thin protein in the sarcomere?
actin
82
process of sliding filament theory
- depolarisation of muscle causes calcium ions from sarcoplasmic reticulum to diffuse into myofibrils
- calcium ions causes the protein tropomyosin to move and uncover the binding sites on actin
- myosin heads attach to binding site on actin to form a cross bridge (creating tension)
- hydrolysis of ATP (ADP) causes actin to bend
- attachment of new ATP to myosin head causes it change shape slightly and detaches from actin
- ATPase from sarcoplasm hydrolyses ATP on myosin head to return to ADP and myosin can return to its orginial position
83
evidence for sliding filament theory
H-zone narrows
I-band narrows
Z-line gets closer
A-band remains same
84
what is the role of phosophocreatine in muscle relaxation?
phosphorylates ADP into ATP when oxygen for aerobic respiration is limited (anaerobic)
85
what are the 5 sarcomere bands?
A-band
H-zone
I-band
M-line
Z-line
86
A-band
overlap of actin and myosin (total width of the myosin)
87
H-zone
myosin only (no overlap with actin)
88
I-band
actin only (no overlap with myosin)
89
M-line
middle point of myosin
90
Z-line
boundary between sarcomeres (end points)
91
where are slow-twitch muscle fibres found?
sites of sustained contraction (e.g calf muscle)
92
where are fast-twitch muscle fibres found?
sites of rapid contraction (e.g biceps)
93
structure of STF
- large store of myoglobin (stores lots of oxygen)
- rich blood supply
- many mitochondria
94
structure of FTF
- thicker and more myosin filamements
- large store of glycogen
- phosphocreatine and enzymes for anaerobic respiration
95
properties of STF
- contract slower
- can respire aerobically for longer periods of time due to rich blood supply and myoglobin
- adapted for endurance
96
properties of FTF
- contract faster
- short bursts of powerful contraction
- adapted for intense exercise
97
what is homeostasis?
when the internal bodily environment is maintained set limits around an optimum by physiological control systems
98
why is it important core temperature remains stable?
stable- maintain rate of enzyme controlled reactions and prevent membrane damage
low- insufficient kinetic energy
high- denaturing
99
dangers of too acidic pH
H+ ions interact with hydrogen and ionic bonds in tertiary structure of enzymes= no E-S complexes formed
100
why is it important blood glucose concentration remains stable?
- maintains constant water potential
- constant concentration of respiratory substrate
101
what is negative feedback?
self-regulatory mechanisms return internal environment to optimum when there is deviation
102
what is positive feedback?
a fluctuation triggers changes that result in an even greater deviation from the normal level
103
factors that affect blood glucose concentration
- carbohydrate digestion
- glycogenolysis
- gluconeogenesis
104
what is glycogenesis?
process of excess glucose being converted to glycogen when blood glucose levels are higher than normal
105
what is glycogenolysis?
hydrolysis of glycogen back into glucose when blood glucose levels are too low
106
what is gluconeogenesis?
process of creating glucose from non-carbohydrate stores (amino acids and glycerol)
107
what happens when blood glucose concentration increases?
- blood glucose increases
- detected by beta cells in islets of Langerhans in pancreas
- beta cells release insulin
- liver becomes more permeable to glucose and enzymes are activated to convert glucose to glycogen
- glucose is removed from the blood and stored as glycogen
108
what happens when blood glucose concentration decreases?
- blood glucose decreases
- detected by alpha cells in the islets of Langerhans
- alpha cells release glucagon and adrenal glands release adrenaline
- second messenger model occurs to activate enzymes to hydrolyse glycogen
- glycogen is hydrolysed bacl to glucose and more glucose is released back into blood
109
how does insulin decrease blood glucose?
- beta cells
- attaches to receptors on the surface of liver cells, changing the tertiary structure of channel proteins so more glucose is absorbed
- more protein carriers are incorporated into cell membranes so more glucose is abosrbed from the blood into cells
- actiavtes enzymes involved in glycogenesis
110
how does glucagon increase blood glucose?
- alpha cells
- attaches to receptors in the surface of target cells
- when glucagon binds adenlylate cyclase is activated and this converts ATP into cyclic AMP which activates protein kinase why hydrolyses glycocen into glucose
- actiavtes enzymes involved in gluconeogenesis
111
role of adrenaline when blood glucose concentration decreases
- adrenal glands produce adrenaline which binds to receptors on liver cells and activates enzymes for glycogenolysis
- glucose diffuses into blood stream
112
glucagon second messenger model
- glucagon binds to glucagon receptors
- this causes a change in the tertiary structure of adenylate cyclase, activating it
- this converts ATP into cyclic AMP (cAMP)
- cAMP activates protein kinase
- protein kinase catalyses the hydrolysis of glycogen to glucose (glycogenolysis)
113
secondary messenger model (with adrenaline)
- adrenaline binds to receptor on target cell
- protein G is actiavte
- adenylate cyclase converts ATP into cAMP
- cAMP actiavtes protein kinase
- glycogenolysis
114
insulin in type I diabetes
body is unable to produce insulin
115
insulin in type II diabetes
body stops responding to insulin
116
causes of type I diabetes
autoimmune disease where beta cells are attacked
117
causes of type II diabetes
obesity and poor diet
118
treatment of type I diabetes
insulin injections
119
treatment of type II diabetes
regulating carb intake, increase exercise and injections (extreme cases)
120
what is osmoregulation?
control of blood water potential via homeostatic mechanisms
121
structure of the nephron
-renal capsule which surrounds glomerulus
- proximal convoluted tubule (series of loops surrounded by capillaries, walls made of epithelial cells with microvilli)
- loop of Henle which extends from cortex into medulla
- distal convoluted tubule (similar to PCT but has fewer capillaries)
- collecting duct (DCT from several nephrons empty into collecting duct which leads to renal pelvis)
122
function of a nephron
filter blood to remove waste and selectively reabsorb useful substances back into the blood
123
blood vessels associated with a nephron
- wide afferent arteriole from renal artery which forms glomerulus
- narrow efferent arteriole which forms capllary network
124
process of filtering and reabsorptionin nephron
1. ultrafiltration
2. selective reabsorption
3 + 4. maintence of sodium ion gradient
5. water moving out of DCT
125
ultrafiltration in renal capsule
- blood enters through afferent arteriole which splits into capillaries making glomerulus
- this causes high hydrostatic pressure of blood
- this forces water and small molecules (glucose and mineral ions) out of gaps in capillary endothelium and basement membrane to form glomerulus filtrate
- large proteins and blood cells are too big to leave so remain in blood
- blood leaves via efferent arteriole
126
selective reabsorption in PCT
- concentration of Na+ ions in the PCT is decreased as they are actively transported out of the PCT cells into the blood in the capillaries
- Na+ diffuse down concentration gradient from the PCT lumen to the cells lining the PCT
- cotransport with glucose
- glucose can now diffuse from PCT epithelial cell into blood
- glucose has been reabsorbed
127
maintenence of sodium ion conecntration in LOH
- mitochondria in walls of cells provide energy to actively transport Na+ and Cl- ions out of the ascending limb
- accumluation of Na+ and Cl- ions outside of the nephron lowers the water potential
- water in the descending limb moves out by osmosis into the interstitial space and then the blood capillaries
- water is reabsorbed into the blood
- at the base of the ascending limb some Na+ ions are transported out by diffusion as the solution is very dilute
128
walls of the ascending limb
thick walls impermeable to water, where Na+ ions are actively transported out
129
walls of the descending limb
thin walls permeable to water so it can be moved out by osmosis
130
why is the loop of Henle longer in desert animals?
more sodium ions can be actively transported, making water potential very negative, so more water can move out by osmosis and be reabsorbed in blood
131
reabsorption of water in collecting duct
- filtrate reaches top of the PCT which is very dilute
- filtrate moves to DCT and collecting duct
- section of medulla surrounding these two parts are very concentrated
- so more water moves out of the DCT
- what remains is transported out and forms urine
132
how is the PCT adapted for selective reabsorption?
- microvilli for a larger SA for cotransporter proteins
- mitochondria for AT
133
what might cause blood water potential to change?
- sweating
- water intake
- ions in diet
134
what does hypotonic blood mean?
water potential is too high
135
what does hypertonic blood mean?
water potential is too low
136
what are changes in blood water potential detected by?
osmoreceptors
137
where are osmoreceptors located?
hypothalamus
138
what do osmoreceptors do when blood water potential is too low?
water leaves osmoreceptors by osmosis and they shrivel, which stimulates the hypothalamus to produce more ADH
139
what do osmoreceptors do when blood water potential is too high?
water enters osmoreceptors by osmosis which stimulates the hypothalamus to produce less ADH
140
role of posterior pituitary gland in osmoregulation
stores and secretes ADH into the capillaries and blood
141
role of ADH in osmoregulation
- increases permeability of the walls of the collecting duct and DCT to water
- means more water leaves the nephron
- more water is reabsorbed into the blood
- urine is more concentrated
142
what are aquaporins?
protein channels for water to pass through, with more aquaporins, more water leaves the nephron and is reabsorbed in the blood
143
fusing of aquaporins
when ADH binds to receptors on cell membrane of DCT and CD, it activates a phosphorylase enzyme in cells. phosphorylase causes vesicles containing aquaporins to fuse with the cell membrane and the aquaporins embed.
