3.6 Organisms respond to changes in their internal and external environments Flashcards
What is a stimulus?
Detectable change in the internal/external environment of an organism that leads to a response
What is a receptor?
Detects stimulus, specific to one type of stimulus
What is a co-ordinator?
Formulates a suitable response to a stimulus e.g. nervous system/hormal system
What is an effector?
Produces a response to a stimulus e.g. muscles/glands
What are the stages of a response to a change in the environment and why is it beneficial?
Stimulus
Receptor
Coordinator
Effector
Response
Organisms increase their chance of survival
What is tropism?
The growth response of a plant in response to a directional stimulus
What is positive tropism and negative tropism
Positive tropism: Growth towards the stimulus
Negative tropism: Growth away from the stimulus
Describe the responses in plants linking to growth factors
Growth factors move from growing regions where they a produced to other tissues, where they regulate growth in response to directional stimuli
What is IAA?
Indoleacetic Acid (IAA)
How does IAA result in phototropism in shoots?
Cell in the tip of shoot make IAA
Transported down the shoot
IAA conc increases on the shaded side
Promotes cell elongation
Shoot bends towards the light positive phototropism
How does IAA result in gravitropism?
Cells in tip of shoot produce IAA
Transported down the shoot
IAA conc increases on lower side of the root
Cell elongation
Root curve downwards towards gravity - positive gravitropism
What does a receptor do?
Detects a stimulus and converts stimuli energy into impulse
Describe the mechanism of the Pacinian Corpuscle?
Stimulus of Pressure deforms the lamellae and stretch mediated sodium channel
Sodium ion channels open and ions diffuse into sensory neuron
Greater pressure leads to more channels opening and greater ions
Depolarisation leading to generator potential as it reaches threshold triggering an action potential
What does the pacinian corpuscle illustrate?
Receptors only respond to a specific stimuli
Stimulation of a receptor leads to generator potential
Give the differences of a cone and rod cells
Rod
More at periphery of retina
One type of rod containing pigment
Connected in groups to one bipolar neuron
Sensitive to light
Low visual acuity
Black & White vision
Cones
Concentrated at fovea
3 types of cones containing different optical pigments
One cone joins one nuerone
Less sensitive
High visual acuity
Colour (trichromatic) visinon
Describe and explain the differences in sensitivity to light
Rods are more sensitive
One bipolar cell so spatial summation as cells connected in groups likely to meet threshold
Cones are less sensitive
One cone joins to one neurone
No spatial summation
Describe and explain differences in visual acuity
Cones give higher visual acuity
One cone to one bipolar nuerone to one sensory neuron
Each stimuli can be distinguished
Rods give lower
Connected in groups to one bipolar cell → spatial summation
Many neurons generate one impulse → can’t distinguish stimuli
Describe and explain difference in sensitivity to colour
Cones allow colour vision
Different optical pigments absorb different wavelengths
Stimulation of different combinations give range of colour perception
Rods offer monochromatic vision → one type of cone/pigment
How would you describe the cardiac muscle?
Myogenic
What prevents electrical waves from crossing directly to the ventricles?
A layer of non-conductive tissue
What is the AVN and its role?
Delays impulse allowing atria to fully contract and empty
Passes wave of electrical activity to the buncle of His → apex which cause ventricles to contract from bottom up
What are the names of the receptors involved with the control of the heart rate?
Baroreceptors
Chemoreceptors
Where are Baroreceptors and chemoreceptors located?
in aorta and carotid arteries
Describe what happens when low blood pressure occurs
Baroreceptors stimulated by LOW BP
More frequent impulses to the medulla
More impulses sent to the SAN along sympathetic neuron
More frequent impulses sent from SAN
Cardiac muscle contracts more frequently so heart rate increases
Describe what happens when there is LOW blood Carbon Dioxide Concentration/High PH
More frequent impulses sent to the medulla
More frequent impulses sent to SAN along parasympathetic neurons
Less frequent impulses sent from SAN
Cardiac muscle contracts less frequently so heart rate decreases
Describe how a resting potential is established within an axon
Sodium-Potassium ion pump actively transports 3Na+ ions out and 2K+ ions in
Electrochemical gradient created as higher concentration of potassium inside than outside
Membrane more permeable to potassium ions causing sodium ion channels to close
Potassium ion move out via facilitated diffusion
Inside of axon negatively charge relative to outside
Axon is polarised = resting potential
State the changes in membrane permeability in the generation of an action potential
Stimulus
Depolarisation
Repolarisation
Hyperpolarization
Resting Potential restored
Explain the changes in membrane permeability in a neuron in the generation of an action potential
Stimulus
- Membrane more permeable to sodium ions as sodium ion channels open
- Sodium diffuse into neurone down electrochemical gradient
-Depolarisation
- P.d. reaches threshold, action potential generated
- Because more voltage-gated sodium ion channels open and sodium diffuse rapidly
Repolarisation
- Sodium ion channels close (membrane less permeable to sodium ions) whilst (voltage-
gated) potassium ion channels open so potassium ions diffuse out of neurone
- Hyperpolarisation
- Potassium ion channels slow to close so there’s a slight overshoot – too many potassium
ions diffuse out of neurone
Resting potential restored
- By sodium-potassium pump
Why Is the Refractory Period important?
Discrete and discontinuous impulses (no overlap)
Unidirectional action potential - cannot be propagated in a region that is refractory
Limits frequency of impulse transmission at a certain intensity
Define ‘Refractory Period’
The time to restore axon to resting potential
What factors affect the speed of conductance?
Myelination
Axon Diameter
Temperature
How does myelination affect speed of conductance?
Depolarisation at nodes by saltatory conduction (jumps from node to node)
Unlike non-myelinated that has to depolarise whole length of axon
Faster
How does Axon Diameter affect speed of conductance?
Bigger diameter means less resistance of ions
How does temperature affect speed of conductance?
Increases rate of movement of ions Na+ and K+ as more kinetic energy → active transport
Higher rate of respiration so ATP produced faster and energy released faster —> faster active transport
Proteins could denature at some point
Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon.
non-myelinated - next section of membrane depolarised / whole
Membrane = slower
myelinated - depolarisation / ion movement only at nodes;
impulse jumps from node to node /saltatory conduction;
Explain transmission across a cholinergic synapse?
- Action potential arrives causing calcium ion channels to open → calcium ions diffuse into pre-synaptic neurone
- Causing vesicles containing acetylcholine to fuse to pre-synaptic membrane → release acetylcholine into synaptic cleft (exocytosis)
- Neurotransmitters diffuse across synaptic cleft → bind to specific neurotransmitter receptors found only on post-synaptic membrane
- Sodium ion channels open → sodium ions diffuse into post-synaptic knob → depolarisation initiates action potential as threshold is met (excitatory synapse)
- Neurotransmitter removed from cleft so response doesn’t keep happening by
an enzyme called acetylcholinesterase
Compare transmission across cholinergic and neuromuscular junctions
Cholinergic:
Neuron to neuron
Neuromuscular:
Postsynaptic membrane has more receptors than other synapses
Lots of folds on postsynaptic membrane = clefts to store enzyme to break down neurotransmitter
Why do synapses result in unidirectional nerve impulses?
Neurotransmitter only made in/released from pre-synaptic nuroene
Nueroreceptors only on post-synaptic membrane
What is spatial summation?
Many presynaptic neurons share the same synaptic cleft
Collectively release sufficient neurotransmitter to reach threshold and trigger action potential
What is temporal summation?
One presynaptic neurone releases neurotransmitter many times over a short period
Sufficient neurotransmitter to reach threshold to trigger an action potential
What do inhibitory synapses do?
neurotransmitters that prevent the generation of an action potential in a postsynaptic neurone
How do inhibitory synapses cause inhibition?
Hyperpolarize the postsynaptic membrane
Inhibits the formation of action potential
- opening the gated potassium ion channels in the membrane so that potassium ions are able to diffuse out of the cell body
- both excitatory and inhibitory neurons forming synapses:
a. Sodium ions enter the cell body following stimulation by the excitatory synapse
b. The stimulation of the inhibitory synapse causes potassium ions to diffuse out of the cell body
c. This cancels out the effect of the sodium ions entering
d. The threshold potential is not reached so no action potential is generated
Describe the relationship of muscles
Antagonistic
What is the advantage of the muscle being antagonistic pairs?
- muscles can only contract/pull
- help maintains posture
Describe the structure of a muscle fibres
Sacrolemma
Sacroplasm
Myrofibirls
shared nuclei
many endoplasmic reticulum
What is Osmoregulation?
the control of water and salt levels in the body
How does the body respond to a decrease in water potential?
- Detected by osmoreceptors in hypothalamus
- Hypothalamus produces more ADH → posterior pituitary gland secretes more ADH into blood
- ADH travels in blood to kidney and attaches to receptors on collecting duct / DTC of kidney
- ADH increases permeability of walls of the DTC / collecting duct
- (more aquaporins fuse with
cell membrane) to water → more water absorbed from DCT/collecting duct by osmosis - (Less water lost in urine so) smaller volume of urine, more concentrated
How the body responds to an increase in water potential?
- Detected by osmoreceptors in hypothalamus
- Hypothalamus produces less ADH → posterior pituitary gland secretes less ADH into blood
- Less ADH travels in blood to kidney and attaches to receptors of collecting duct / DTC of kidney
- ADH decreases permeability of cells/walls of the DTC / collecting duct to water and urea to water
→ less water absorbed from/leaves DCT/collecting duct by osmosis
5. (More water lost in urine so) larger volume of urine, less concentrated
Describe the stages within the nephron in osmoregulation
Formation of glomerular filtrate
reabsorption of glucose and water by the proximal convoluted tubule
maintenance of a gradient of sodium ions in the medulla by the loop of Henle
reabsorption of water by the distal convoluted tubule and collecting duct
Describe the formaiton of glomerular filtrare in osomoregulation
- Build-up of hydrostatic pressure
in glomerulus - Water, glucose, mineral ions
squeezed out of capillary /
glomerulus into the Bowman’s
capsule to form
glomerular filtrate - Through pores in capillary
endothelium, basement
membrane act as filter - Large proteins / blood cells
aren’t pushed out as too large
Describe the reabsorption of glucose and water by the proximal convoluted tube
- Sodium ions actively transported out
of epithelial cell to capillary
- Lowers concentration of Na+ in
epithelial cell - Na+ moves via facilitated diffusion
from PCT into epithelial cell down
concentration gradient
- Co-transporting glucose / amino
acids / Cl-
- Increases concentration of
glucose etc. in epithelial cell - Glucose / amino acids / Cl- move into
capillary via facilitated diffusion down
concentration gradient (reabsorbed)
- Lowers water potential in
capillary - Water moves via osmosis down water
potential gradient into capillary
(reabsorbed)
Describe maintaining a gradient of sodium ions in the medulla by the loop of henle
- Loop of Henle acts as a counter current
multiplier → maintains water potential
gradient → water leaves collecting duct
/DCT by osmosis - Na+ actively transported out of
ascending limb and ascending limb is
impermeable to water so water remains
- Increases conc of Na+ in medulla →
lowers water potential - Water moves out of descending limbs /
collecting duct by osmosis into medulla
- Water reabsorbed by capillaries - Na+ diffuse into descending limb
- Recycles Na+ in loop of Henle
- Reduces water potential further
What factors influence blood glucose concentration
- eating food containing carbohydrates –> glucose absorbed from intestine to blood
- exercise –> increase rate of respiration of glucose
What factors influence blood glucose concentration
- eating food containing carbohydrates –> glucose absorbed from intestine to blood
- exercise –> increase rate of respiration of glucose
Describe action of insulin
Insulin binds to specific receptors on cell surface membranes of liver / muscle cells (target cells)
- Increases permeability of muscle cell membrane to glucose → by increasing number of
channel proteins (GLUT4) in cell surface membrane → cells uptake more glucose from
blood by facilitated diffusion - Activation of enzymes in liver / muscle cells that convert glucose to glycogen
(glycogenesis) → store glycogen in cytoplasm - Rate of respiration of glucose also increases
- DECREASES blood glucose concentration
When is insulin used?
when blood glucose concentration is too high
secretion by beta cells
When is glucagon used?
secreted by alpha cells
when blood glucose concentration is too low
Describe the action of glucagon
Binds to specific receptors on cell surface membranes of liver cells (target cells)
- Activates enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
- Activates enzymes involved in the conversion of glycerol / amino acids to glucose
(gluconeogenesis) - Rate of respiration of glucose also decreases
- INCREASES blood glucose concentration
When is adrenaline used?
secreted by adrenal glands when blood glucose concentration is low/stressed/exercising
Describe the action of adrenaline
Binds to specific receptors on cell surface membranes of liver cells (target cells)
- Activates enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
- Inhibits glycogenesis
- Activates secretion of glucagon
- INCREASES blood glucose concentration (more glucose for respiration)
Describe the staged of the secondary messenger model
- Adrenaline / glucagon bind to specific
complementary receptors on cell
membrane - Activate adenylate cyclase
- Converts ATP to cyclic AMP
(secondary messenger) - cAMP activates protein kinase A
(enzyme) - Protein kinase A activates a cascade to
break down glycogen to glucose
(glycogenolysis)
What is the cause of type 1 diabetes?
Gene mutation → Autoimmune
response on B cells of islets on
Langerhans →Body can’t produce
insulin
What is the cause of type 2 diabetes?
Poor diet / lack of exercise / obesity→
Glycoprotein / receptor loses responsiveness
to insulin (faulty) → cells less responsive to
insulin / don’t take up enough glucose
