Section 6 Response to stimuli Flashcards
What is stimuli?
A change in the internal and external environment
Why do organisms respond to stimuli?
For survival (For predator prey response and homeostasis)
How do “simple” respond to stimuli?
Taxis and kinesis
What are taxis?
A directional response to a certain stimuli
E.G. If and organism moves away from light it is known as a negative photo-taxis.
What is kinesis?
A non-directional movement from an unfavourable area to a favourable area.
Organisms move rapidly and randomly in an unfavourable area until they reach a favourable area where they slow down and move less randomly
This therefore means that they spend less time in an unfavourable area and more time in a favourable one.
What is the response to stimuli in plants?
Tropism
What is tropism?
A directional growth in plants in response to certain stimuli (Similar to the taxis in non-plant organisms)
E.g. a root would want to be far away from light therefore possessing a negative phototropism.
What is a plant growth factor?
The plant equivalent to animal hormones
The difference is that it is made within the cells and only affects those surrounding cells.
What is the effect of IAA on plants?
Promotes growth in the shoots and inhibits growth within the roots.
How does a positive phototropism occur within the shoot? (PROCESS)
The shoot tip produces IAA sending it down either side of the shoot to make it grow forwards (upwards)
If light is present on the one side the IAA redistributes to the opposite side (shaded side)
This causes the opposite side to grow faster
This then makes the shoot bend towards the light.
How does negative geotropism occur in the root? (PROCESS)
If gravity water is present on the one side, the IAA redistributes to the same side
This causes the same side to grow slowly, so the opposite side grows faster
So the root bends towards the gravity and water
What is the response to stimuli in animals?
Animals use the nervous system and the hormonal system
Job of the nervous system? (PROCESS)
STIMULI to the RECEPTOR to SENSORY neurone to the SPINAL CORD to the MOTOR NEURONE to EFFECTOR which causes a RESPONSE (e.g. muscle contraction/hormone response).
What do receptors do? (PLUS PROCESS)
They are the main detector of stimuli
They convert the stimuli into an nerve impulse
Each type of stimuli has a specific receptor
Uses stimuli energy to send sodium ions into the start of the sensory neurone.
What does a pacinian corpuscle do and what is its structure? (PLUS PROCESS)
Its a touch receptor found within the skin
Responds to the pressure of touch
Structure: Corpuscle wrapped around the start of the sensory neurone
Process: Pressure applied, corpuscle compressed, stretch mediated sodium channels opened, sodium ions move into the start of the sensory neurone.
How does the retina of the eye work? (PROCESS)
Detects light so the brain can generate an image
Detected by the retina (located at the back of the eye)
Made of cone and rod cells
Cone cells detect high light intensity only, produces colour image, with high visual acuity
Rod cells can detect low light intensity, producing black and white images, with a low visual acuity
Cone cells located in the centre of the retina (fovea) site of high light intensity
Rod cells located in the periphery of retina
What are the properties of cone cells in retina?
Made of Iodopsin pigment which is only broken down at high light intensity
One cone cell connects to the one bipolar neurone which connects to one sensory neurone
But because one cone cell connects to one bipolar neurone which connects to one sensory neurone each stimuli can be distinguished high visual acuity
What are the properties of rod cells in retina?
Made of rhodopsin pigment which can be broken down at low light intensity
A few rod cells connect to one bipolar neurone which connects to one sensory neurone
But because a few rod cells connect to one biopolar neurone which connects to one sensory neurone the stimuli will be merged together = low visual acuity
What is the central nervous system (CNS) and what is its function?
Made of the brain and spinal cord
Brain= analyses and coordinates response to stimuli
Spinal cord= connects brain to sensory and motor neurone
What is the peripheral nervous system (PNS) and what is its function?
Made of the sensory and motor neurone
A neurone transmits a nerve impulse
Sensory neurone takes nerve impulse from receptor to CNS
Motor neurone takes nerve impulse from CNS to effector
Sensory neurone has its cell body in the middle and has a dendron and axon
motor neurone has its cell body at the start and only has a long axon
What are the 2 different types of motor neurone and what are their function?
The two types are:
Voluntary (SOMATIC)
Involuntary (AUTOMATIC)
Somatic supplies skeletal muscle under conscious control
Autonomic supplies cardiac muscles, smooth muscle, glands meaning they are under SUBCONCIOUS control.
Autonomic can be divided into sympathetic and parasympathetic (Having opposite effects)
What is a nerve impulse?
Movement of an action potential along a neurone
Action potential= change in membrane potential
Changes from negative (polarised) to positive (depolarised) back to negative (repolarised/ hyperpolarised)
What is a resting potential?
Membrane potential of neurone at rest
Is -65mV
Polarised
Caused by having more postive ions outside neurone compared to inside
Involves Na/K ions to be pumped (3 Na out, 2 K in)
What happens during and action potential? (PROCESS)
Stimuli causes Na ions to enter the start of the neurone
Makes membrane potential less negative
If it reaches a threshold (-50mV), Na channels open
Therefore more Na ions diffuse into the the neurone, therefore membrane potential becomes positive (depolarised)
The membrane potential reaches +40mV
Then the Na channels close, the K channels open
Therefore k ions diffuse out, therefore membrane potential becomes negative (repolarised)
Too many K ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)
one action potential= depolarisation, repolarisation and then hyperpolarisation
How does an action potential move across a neurone? (Process)
By local currents
If the stimuli energy is large enough and enough Na ions enter the start of the neurone
Na ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach a threshold and an AP to occur
This process continues across the neurone
How does the size of a stimuli effect the action potential?
The size must exceed a certain threshold known as the all or nothing threshold. If the stimuli is below a threshold nothing with activate. If it goes above it will give all.
What 3 factors affect the speed of a nerve impulse and how?
Temperature higher temp means a higher kinetic energy meaning a faster rate of diffusion (faster nerve impulse)
Axon diameter a wider diameter means the neurone is less leaky making the impulse faster
Myelination Schwann cells wrap around axon preventing an action potential with the ap only occuring within the gaps known as the node or Ranvier with the ap jumping from node to node =saltory conduction resulting in a faster nerve impulse.
What is a synapse and what is its function (PROCESS)?
It is the connection between 2 different neurones
Sends nerve impulses across the gap (synaptic cleft) using neurotransmitters
Action potential arrives at the presynaptic cleft
Calcium ions are released via the channels which enter the presynaptic neurone
Causes vesicles containing neurotransmitters to move to the presynaptic membrane
Vesicles bind to membrane releasing neurotransmitters into cleft
Neurotransmitter diffuses across cleft
Binds to complementary receptors on postsynaptic membrane
Sodium ion channels open and the sodium ions enter
If the threshold is reached the action potential occurs
What are the properties of a synapse?
Unidirectionality ap/ nerve impulses travel in one direction from pre to post pre contains the neurotransmitter and post has the receptors
FILTERS OUT LOW LEVEL OF STIMULI low level stimuli do not release enough neurotransmitters therefore not enough sodium ion channels are opened therefore not enough ions enter the postsynaptic neurone for the threshold to be reached and no AP PRODUCED.
SUMMATION low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial
INHIBITORY normal synapses are excitatory prevent action potential from occuring by making postsynaptic neurone hyperpolarised
What is a reflex?
A rapid involuntary response to a stimuli
Does not use brain
The sensory neurone connects directly to motor neurone
Ensures less damage done
How is the body’s heart rate controlled?
The heart is myogenic its heart beat is initiated by the SAN
The medulla oblongata in the brain can increase or decrease heart rate
Receives nerve impulse from chemoreceptors in the carteriod arteries and pressure receptors in the carotid arteries and pressure receptors in the carotid arteries and aorta
Sends impulse in sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR
How does exercise affect heart rate?
Exercise =muscle contraction which requires respiration
Therefore, waste product CO2 is released into blood
This lower pH of blood (acidic)
This is detected by the chemoreceptors in carotid arteries
Sends impulses to medulla oblongata
Then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase
Benefit increase blood flow to lungs to remove CO2 and take in O2
How does low blood pressure affect heart rate?
If a person moves from lying/sitting to standing blood pressure falls reducing the blood flow to the brain
This is detected by pressure receptors in the carotid and aorta
Sends impulses to medulla oblongata
The medulla oblongata sends impulses to the SAN via the sympathetic nerves causing the heart rate to increase
What are the different types of muscle?
Skeletal muscle
Smooth muscle
Cardiac muscle
Structure of skeletal muscle?
Basic structure sarcomeres
made up of actin and myosin, actin is thin and has tropomysosin wrapped around it, myosin is thick and has heads, when the sarcomere contracts the whole muscle contracts, contracts/shortens by the sliding filament mechanism
Many sarcomeres=myofibril
Many myofibrils= muscle fibre
Many muscle fibres= bundle
Many bundles= whole muscle
What are the 4 locations within the sarcomere and what changes occur within each part during contraction?
A band= location of myosin (no change in contraction)
I band= location between myosin (shortens in contraction)
H zone= location between actin (shortens in contraction)
Z line= end line of sarcomere (moves closer together in contraction)
What occurs in sliding fillament mechanism?
The sarcomere shortens
The myosin heads pull on the actin INWARD
The somatic motor neurone connects to the skeletal muscle via a neuromuscular junction
One motor neurone connects to a few muscle fibres motor unit
Releases acetylcholine that binds to complementary receptors on the muscle fibre membrane
Na+ channels open allowing sodium ions in causing depolarisation
Wave of depolarisation which travels through the sarcorplasmic reticulum
Causes release of Calcium ions into the sarcoplasm
This moves the tropmyosin on the actin exposing the binding sites
myosin heads now bind to the actin
A power stroke occurs the myosin pulling the actin inwards
ATP attaches to myosin head so it detaches
ATP breakdown by ATPase to release energy
Causes myosin heads to return to original position
So it therefore reattaches pulling the actin further inward
What is the role of calcium ions and ATP in muscle contraction?
Ca ions causes the tropomyosin to move exposing the binding sites on the actin
The calcium ions stimulate the enzyme ATPase
ATP causes the myosin heads to detach
The ATP releases energy so myosin head returns to original position
ATP actively transports calcium ions back into the sarcoplasmic reticulum
What are the 2 types of muscle fibres and how do they individually work (PROCESS)?
Fast twitch muscles
They provide powerful but short lasting contractions
Found in the biceps and sprinters
Adapted for anaerobic respiration
Has thicker myosin for powerful contractions
Contains more enzymes for anaerobic respiration
Contains phosphocreatine Provides phosphate to ADP to reform ATP
Slow twitch muscles
Provide less powerful but long lasting contractions found in thigh muscles Adapted for aerobic respiration Has a rich blood supply Contains many mitochondria Contains glycogen Contains myoglobin to store oxygen
What is the role of the hormonal system within the body?
Coordinates the response to certain stimuli
Involves chemical messengers (hormones) to affect or change a cell
What is diabetes?
A disease where a person loses control of their blood sugar levels
This usually results in having high blood sugar (Hyperglycaemia)
There are 2 types: type 1 and type 2
Type 1 starts at a young age and is due to the person not producing enough insulin hormone
Type 2 occurs at a later age and is due to cells becoming less sensitive to insulin that is produced due to diet high in simple sugars and or obesity.
Symptoms: Tiredness, increased urination and thirst
Diagnosis: high blood glucose levels on random testing & blood glucose levels remain high following a fasting blood glucose test
What is homeostasis?
Maintenance of the bodies internal environment
The control of the temperature of body along with pH blood glucose levels as well as blood salt and water levels and blood pressure.
What is positive and negative feedback in homeostasis?
Positive feedback is where the response to the change is to continue the change
Negative feedback is where the response to the change or bring levels back to normal
Why do organisms need to maintain constant body temperature?
To provide the optimum conditions for enzymes and enzyme activity
What are endotherms and exotherms
Endotherms are animals that maintain a strict constant body temperature irrespective of the external environments temperature
Ectotherms animals internal body temperature maintained more generally and varies with changes in external environment temperature.
Benefit of being an endotherm?
Can maintain activity over a range of settings
Benefit of being an ecotherm?
Requires less food/ energy
How is internal body temperature controlled?
Anatomical, behavioural, physiological changes
Ecotherms mainly rely on behavioural changes
Endotherms mainly rely on physiological changes
Anatomical adaptations in organisms in warm areas?
Small body size means a large surface area to volume ratio
Less fur
Less fat
Large extremities
Anatomical adaptations in organisms in cold areas?
Large body size meaning a small surface area to volume ratio (Less heat given off)
More fur
More fat
small extremities (less heat loss)
Behavioural/physiological changes in ecotherms?
Warming up= exposure to sun or pressing on a warm surface, darker skin to absorb more heat, higher amounts of respiration in liver and less breathing
Cooling down= shaded from the sun pressing on a cold surface lighter skin colouration, less respiration in liver and more breathing.
Control of body temperature in endotherms?
Controlled by hypothalamus in the brain
Recieves nerve impulse from peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus
Peripheral thermoreceptors monitor changes in external environment temperature
Central thermoreceptors monitor changes in core body temperature
How an endotherm cools itself down?
Increase blood supply to skin surface
Sweating evaporation of water molecules from the skin surface using the heat in the blood
What is the structure of the kidneys?
Outer region called cortex and middle region called medulla
Role of kidneys?
Filter blood of urea, salts, excess water
Why must urea be removed from the blood?
It is a toxic substance and can harm the body
Why remove excess salts and water?
Maintain correct water potential and pressure in blood.
How do kidneys filter the blood?
Made up of millions of nephrons
Structure of nephron?
1st part bowmans capsules 2nd part proximal convoluted tubule 3rd part Loop of Henle 4th part of distal convoluted tubule 5th Collecting duct
Bowmans capsule
Site of nephron
Site of ultrafiltration
Occurs between specialised cappilaries called glomerulus and bowmans capsule
Glomerulus located in the middle of an arteriole
Affirent arteriole before glomerulus into bowmans capsule
small substances filtered glucose, amino acids , salts and urea
Only small substances can pass through the 3 layers
Glucose, and amino acids and some of the salts and water back into the blood (re absorption)
Proximal convoluted tube?
Second part of the nephron
Site of selective reabsorbtion
All glucose and amino acids and some of the salts and water are send back into the blood
Loop of henle?
Third part of the nephron
site of further water re absorption
occurs by hairpin counter current multiplier
sodium and chloride ions are actively transported out of the ascending limb of the loop of henle into the surrounding medulla of kidney
this lowers water potential of medulla
so water moves out of the descending limb of loop of henle (and collecting duct) by osmosis into the medulla
this water then moves into the blood
the sodium and chloride ions then diffuse into the descending limb of loop of henle so the above process can be repeated.
Distal convoluted tubule ?
Fourth part of the nephron
Site of further salt re absorption
Corrects required salt balance between blood and urine
Collecting duct? (LONG)
final part of nephron
site of further water reabsorption and osmoregulation
end up being left with urine that is sent into the ureter to the bladder
water reabsorption occurs by the hairpin countercurrent multiplier
amount of water being reabsorbed is controlled at this stage, this is known as osmoregulation
osmoregulation is the process by which the hypothalamus controls water potential of the blood (an example of homeostasis)
if water levels become low (dehydration):
osmoreceptors in hypothalamus shrink
this stimulates the release of ADH from the posterior part of the pituitary gland
ADH stimulates the cells lining the collecting duct to increase the number of aqauporins (water channels)
so more water moves from the collecting duct back into blood
so less water is lost in the urine
if water levels become high (overhydration):
less ADH released
l
ess aquaporins in collecting duct
less water moves from collecting duct into blood
more water lost in urine (reduces overhydration)
