Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Title: BIOLOGY OCR F214
Description: OCR Board A2 Level Biology F214 SECTION 1: COMMUNICATION AND HOMEOSTASIS
Description: OCR Board A2 Level Biology F214 SECTION 1: COMMUNICATION AND HOMEOSTASIS
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
BIOLOGY
F214: Communication, Homeostasis and Energy
1) Communication and Homeostasis
a) Communication
i) Outline the need for communication systems within multicellular organisms, with
reference to the need to respond to changes in the internal and external environment
and to co-‐ ordinate the activities of different organs
(1) Stimulus – any change in the internal or external environment that causes a response
(2) Response – any change in behaviour or physiology as a result of a change in the
environment
(3) Changes in external environment place stress on a living organism and need to be
accommodated for eg
...
build up of CO2
(5) All living things need to maintain a certain, limited set of conditions inside their cells
– their cells rely on enzymes
(6) Multicellular organisms are more efficient than single celled organisms
(a) Cells are differentiated à specialised tissues à specialised organs
(b) Good communication system – so different parts of the body work together eg
...
glucose and CO2
(c) Concentration of salts and other electrolytes
(d) Temperature of the internal environment
(e) pH of the internal environment
(3) Negative feedback – control mechanism/process essential for homeostasis reverses
any change in conditions so an optimum steady state is maintained
(a) Conditions change from the optimum/set point
(b) Change detected by receptors
(c) Change signalled to other cells (effectors)
(d) Corrective mechanism response of effectors to return conditions to set point
(e) When set point reached, corrective mechanism is switched off
(f) Continuous cycle of events with structures coordinated through cell signalling
(i) Sensory receptors eg
...
nervous or hormonal – transmits messages using
cell signalling from the receptor cells to the effector cells
(iii) Coordination centre eg
...
liver or muscle cells – will bring about a response that
reverses the change detected by the receptor cells
(g) NB: Conditions will never remain perfectly constant – always be some variation
(i) Conditions will always remain within a relatively narrow range
(ii) Conditions acceptable as long as variation isn’t too great
(4) Positive feedback – mechanism that increases any change detected by the receptors
(does not lead to homeostasis)
(a) Usually harmful as it destabilises the system
(b) Body gets too cold
(i) Below a certain core body temperature, enzymes become less active
(ii) Exergonic reactions (release heat) are slower and release less heat
(iii) Body cools further
(iv) Enzyme-‐controlled reactions slow down even more
(v) Body temperature spirals downwards
(c) Dilation of cervix – fully dilated cervix allows the baby to be born
(i) Cervix begins to stretch
(ii) Change is signalled to the anterior pituitary gland
(iii) Anterior pituitary gland is stimulated to secrete the hormone – oxytocin
(iv) Increases uterine contractions
(v) Cervix stretched more
(vi) So more oxytocin is released
(d) Breast feeding
vi) Describe the physiological and behavioural responses that maintain a constant core body
temperature in ectotherms and endotherms, with reference to peripheral temperature
receptors, the hypothalamus and effectors in skin and muscles
(1) Changes in body temperature
(a) Enzymes – globular proteins with a specific structures and functions
(b) Temperature can have a dramatic effect upon tertiary structure of such proteins
(c) Therefore activity of enzymes dramatically effected
(d) Overall level of activity that can be achieved by the organism affected
(e) Core temperature most important – all vital organs found in main part of body
(f) Peripheral temperature – allowed to increase or decrease in temperature without
affecting the survival of the individual
(2) Endotherms – organisms that can maintain the temperature of their body within
fairly strict limits (largely independent of external temperature), using internal
sources of heat eg
...
night, early in the
morning or during winter months
(iii) Wider geographical range – able to inhabit colder parts of the planes
(b) Disadvantages
(i) Significant part of energy intake used to maintain body temperature in cold
(ii) More food is required eg
...
snake can last several weeks between meals
(iii) Great proportion of the energy obtained from food can be used for growth
(c) Disadvantages
(i) Less active in cooler temperatures
(ii) Greater risk of predation – may need to warm up in the morning before can
be active eg
...
through less muscular contraction
(v) Less heat generated and more heat lost to the environment
(vi) Temperature falls
(b) Fall in core temperature
(i) Thermoregulatory centre (thermoreceptors) in hypothalamus detects change
(ii) Hypothalamus sends signals to reverse the change
(iii) Nervous system and hormonal system carry signal to skin, liver and muscles
(iv) Increased rate of metabolism eg
...
respiration
(vi) Skeletal muscles – no spontaneous contractions
(c) Core body temperature is too low
(i) Less or no sweating – less sweat evaporates so less heat energy is taken away
with it (less loss of latent heat)
(ii) Hairs stand up – allows a layer of air to get trapped between the hair and skin,
which has an insulator effect and reduces loss of heat from the skin
(iii) Vasoconstriction – all the surface blood capillaries become narrower which
restricts the blood flow through capillaries at the surface, reducing the loss of
heat energy to the environment by radiation from the skin
(iv) No panting – less water evaporates
(v) Rate of metabolism (liver cells) increased – respiration generates more heat,
which is transferred to the blood
(vi) Shivering – muscles contracting and relaxing means muscle cells require
energy which comes from respiration, which also produces thermal energy as
a by-‐product
(6) Metabolic rate linked to energy release
(a) Endotherm
(i) Lower temperature
(ii) More heat is lost
(iii) Higher metabolic rate
(iv) Release more heat energy
(v) Replace heat loss
(b) Ectotherm
(i) Lower temperature
(ii) Enzyme action is lower
(iii) Lower metabolic rate
(iv) Stay still through inertia
(7) Behavioural mechanisms to maintain body temperature (ectotherms and endo
...
Horned lizard – expands rib cage to increase exposed surface area
(v) Locusts – increase their abdominal breathing movements to increase
evaporation of water and aid cooling
(b) Core body temperature is too low
(i) Move into sunlight – bask in the sun or lie on a warm surface
(ii) Orientate body side-‐on to increase surface area exposed to solar radiation
(iii) Move about to generate heat in muscles
(iv) Roll into a ball to reduce surface area and heat loss from skin
(v) Frilled lizard – uses its frill to help absorb heat in the form of solar radiation
b) Nerves
i) Outline the roles of sensory receptors in mammals in converting different forms of
energy into nerve impulses
(1) Central Nervous System – spinal cord and the brain
(2) Peripheral Nervous System – nerves that connect the CNS with sensory organs, other
organs, muscles, blood vessels and glands
(3) Sensory receptors – specialised cells which detect changes in our surrounding
(a) Energy transducers – convert energy from one form to another
(b) Each type is adapted to detect changes in a particular form of energy
(4) Stimulus – any disturbance in the internal/external environment which changes the
potential difference across a membrane (change in energy levels)
(5) Nerve impulse – form of electrical energy that sensory receptors are stimulated to
convert other forms of energy into
(a) When the resting potential across the membrane of a neurone has a stimulus
(b) Created by altering the permeability of the nerve cell membrane to sodium ions
(6) Action potential – depolarisation/complete reversal of charge across the membrane
so the potential difference across the membrane is +40mV, lasting 7ms
(a) Can be transmitted along the axon or dendron plasma membrane
(7) Summation – interaction of several small potential changes to combine and produce
one larger change in potential difference across the membrane that may pass the
threshold potential and create an action potential
(a) Temporal – a series of action potentials, not only one, is required to produce an
action potential in the post-‐synaptic neurone (small EPSPs act together)
(b) Spatial – several presynaptic neurones may each contribute to producing an
action potential in the post-‐synaptic neurone
(8) Six senses – sight, smell, taste, touch, hearing, balance
(a) Light sensitive cells (rods and cones) in the retina – light intensity and range of
wavelengths (colour)
(b) Olfactory cells lining the inner surface in the nasal cavity – volatile chemicals
(c) Taste buds in the tongue, hard palate, epiglottis and the first part of the
oesophagus – soluble chemicals
(d) Pressure receptors (pacinian corpuscles) in the skin – pressure on skin
(e) Sound receptors in the inner ear (cochlea) – vibrations in air
(f) Muscle spindles (proprioceptors) – length of muscle fibres
ii) Describe, with the aid of diagrams, the structure and functions of sensory and motor
neurons
(1) Function of a neurone – transmit impulses in the form of action potentials from one
part of the body to another
(a) Long – transmit action potential over a long distance
(b) Cell body containing the nucleus, many mitochondria and ribosomes –
metabolically active and carries out lots of protein synthesis
(c) Many voltage-‐gated ion channels in plasma membrane
(i) Allow the passage of charged particles or ions – Na+, K+ and Ca2+
(ii) Have a mechanism called a gate which can open and close the channel –
respond to changes in potential difference across the membrane
(d) Sodium/potassium ion pumps – use ATP to actively transport sodium ions out of
the cell and potassium ions into the cell
(i) Maintains a potential difference across their cell surface membrane
(e) Myelin sheath – fatty sheath consisting of a series of Schwann cells
(i) Insulates the neurone from electrical activity in nearby cells
(f) Nodes of Ranvier – gaps between sections of myelin sheath/Schwann cells
(g) Many dendrites – connect to other neurons
(2) Sensory neurons – carry out an action potential from a sensory receptor to the
central nervous system
(a) Cell body positioned just outside the CNS
(b) Short axon – carries the action potential into the central nervous system
(c) Long dendron – carrying that action potential away from the sensory receptor to
the cell body
(3) Relay neurons – connect sensory and motor neurons
(4) Motor neurons – carry an action potential from the CNS to an effector eg
...
EPSP’s – excitatory post-‐synaptic potentials
(ii) Caused by some sodium ions entering the cell as one or two sodium ion
voltage-‐gated channels open
(iii) Will have no effect on the voltage-‐gated channels if too small
(c) Threshold potential – potential difference across the membrane of about -‐50mV
(i) Action potential only occurs when the depolarisation is large enough to reach
the threshold potential
(ii) The larger the stimulus, the more nearby gated channels will open
(iii) Large influx of sodium ions occurs – depolarisation reaches +40mV
(2) Depolarisation – temporary reversal of charge on the neuron surface membrane, loss
of polarisation across the membrane when sodium ions are entering the cell
(a) Arrival of a stimulus where stimulus is strong enough, exceeding threshold levels
of around -‐50mV
(b) In the generator region, receptor cells of sodium voltage-‐gated channels are
opened by energy changes in the environment
(c) Eg
...
from
sensory receptors to the CNS and from the CNS to effectors
(a) Myelinated – insulated by an individual myelin sheath
(b) Myelin produced by series of Schwann cells wrapped around the neuron
(c) Sheath consists of several layers of membrane and thin cytoplasm from the
Schwann cell
(d) Nodes of Ranvier (gaps in the myelin sheath) at 1-‐3mm intervals along the neuron
– 2-‐3 micrometres long
(e) Action potential moves along ion by ‘jumping’
(f) Where rapid response to a stimulus is necessary
(3) Speed of transmission of a nerve impulse is faster in a myelinated neurone than in a
non-‐myelinated neurone as action potentials can only occur at Nodes of Ranvier
(a) Saltatory conduction – jumping conduction whereby the action potential jumps
from one node of Ranvier to another
(b) Myelin sheath of fatty material acts as an electrical insulator
(c) Myelin sheath is impermeable to both sodium and potassium ions
(d) Therefore depolarisation can only occur at the Nodes of Ranvier where there is
no myelin – where ionic movements that create action potentials can occur
(e) Increase in concentration at one point causes faster diffusion away from the
region of higher concentration
(f) Longer local circuits are established – sodium ions diffuse along the neurone from
one node of Ranvier to the next
vii) Outline the significance of the frequency of impulse transmission
(1) Once it has been set up, a neuron will conduct an action potential from one end to
the other, without any change in size or intensity
(2) Higher frequency of signals means a more intense stimulus
(a) Stimulus is at a higher intensity
(b) The sensory receptor will produce more generator potentials
(c) More frequent action potentials in the sensory neurone
(d) More vesicles released at synapses
(e) (More) higher frequency of post-‐synaptic action potentials
(f) Brain can process this
(3) Factors affecting the transmission of action potentials
(a) Myelin sheath – speed of transmission of a nerve impulse is faster in a myelinated
neurone than in a non-‐myelinated neurone
(i) Electric insulator preventing an action potential from forming in part of the
axon covered in myelin
(ii) Action potential jumps from Node of Ranvier to Node of Ranvier by saltatory
conduction
(iii) Transmission is sped up by 60ms-‐1 from 30ms-‐1 to 90ms-‐1
(b) Diameter of the axon – the greater the diameter of the axon, the faster the speed
of transmission
(i) Leakage makes membrane potentials harder to maintain
(ii) Less leakage of ions from a larger axon so membrane potentials controlled
and maintained more effectively
(c) Temperature – the higher the temperature, the faster the speed of transmission
(i) Higher the temperature, the faster the rate of diffusion
(ii) Faster the movement of ions through the axon plasma membrane and along
axon, the faster the transmission of the nerve impulse
(d) Refractory period – the longer the refractory period, the slower the speed of
transmission
(i) Where the resting potential needs to be restored once an action potential has
been created
(ii) No movement of sodium ions into the neurone as the channels are closed
(iii) During this time, its not possible for a further action potential to be generated
viii) Interpret graphs of the voltage changes taking place during the generation and
transmission of an action potential
ix) Describe, with the aid of diagrams, the structure of a cholinergic synapse
x) Outline the role of neurotransmitters in the transmission of action potentials
(1) Neurotransmitter/transmitter substance – chemical that diffuses across the cleft of
the synapse to transmit a signal to the postsynaptic neurone
(2) Cholinergic – associated with the neurotransmitter acetylcholine
(a) Acetylcholine found in junctions between the muscles and those in the brain
(3) Synapse – junction between two or more neurones where one neurone can
communicate with, or signal to, another neurone
(a) Excitatory
(b) Inhibitory – noradrenaline neurotransmitter substance is found in synapses as
part of the sympathetic nervous system
(4) Synaptic cleft – small gap between two neurones, approximately 20nm wide
(5) Pre-‐synaptic knob – swelling that the pre-‐synaptic neuron ends in
(a) Many mitochondria – metabolically active eg
...
EPSP is created
(e) If sufficient generator potentials combine, the potential across the post-‐synaptic
membrane reaches the threshold potential
(f) New action potential is created in post-‐synaptic neurone as depolarisation occurs
(g) Once an action potential is achieved, it will pass down the post-‐synaptic neurone
(9) Transmitter substance is then quickly broken down by acetylcholinesterase enzyme
(a) Acetylcholinesterase enzyme found in the synaptic cleft
(b) Acetylcholine is hydrolysed to choline and ethanoic acid
(i) Reabsorbed back into the pre-‐synaptic knob by diffusion
(ii) Recombined to acetylcholine using ATP from respiration in the mitochondria
(iii) Recycled acetylcholine is stored in the synaptic vesicles for future use
(c) Stops the transmission of signals so the synapse doesn’t continue to produce
action potentials in the post-‐synaptic neurone
xi) Outline the roles of synapses in the nervous system
(1) Connect two neurons together so a signal can be passed from one to another
(2) Ensure signals are transmitted in one direction only
(a) Only the pre-‐synaptic knob has acetylcholine
(b) Only the post-‐synaptic membrane has sodium channels
(3) Filter out low-‐level signals
(a) Action potential in the pre-‐synaptic neurone is unlikely to pass across the synapse
(b) Insufficient releases of acetylcholine will not create action potential in the post-‐
synaptic neurone
(4) Low-‐level signals can be amplified by summation
(a) A persistent low-‐level stimulus will generate several successive action potentials
(b) Many vesicles in pre-‐synaptic neurone will be released over a short period of time
(c) Enables generator potentials to combine together to produce an action potential
(5) Acclimatisation – due to a fatigued synapse
(a) After repeated summation, synapse may run out of vesicles containing the
transmitter substance
(b) Nervous system no longer responds to a stimulus
(c) People become accustomed to smells/noises
(d) Prevents over-‐stimulation of effectors which could damage them
(6) Signals from different parts of the nervous system can be registered together to
create the same response
(a) Several pre-‐synaptic neurons may converge to one post-‐synaptic neuron
(b) Several pre-‐synaptic neurones each release a small number of vesicles into one
synapse
(c) Eg
...
Reflex arc where one post-‐synaptic neuron elicits the response while another
informs the brain
(8) Creation of specific pathways by the synapses within the nervous system
(a) The basis of conscious thought and memory
(b) Enables the nervous system to convey a wide range of messages
(c) Brain ‘knows’ where the signals are coming from because the neurones from
specific receptors always connect to specific regions of the brain
(d) Eg
...
Salivary gland secretes saliva into a duct which then flows into the mouth
(4) Hormones – molecules that are released by endocrine glands directly into blood, act
as chemical messengers carrying a signal from the gland to a target organ/tissue
(a) Protein and peptide hormones eg
...
oestrogen, progesterone, testosterone – lipid soluble and
so can diffuse through the phospholipid bilayer, enter the cell and have a direct
effect on the DNA in the nucleus
(5) How hormones signal to the cell
(a) Target cells – cells receiving the specific hormone signal that possess a specific,
complementary receptor to the hormone on the cell surface membrane
(b) Target tissues – tissues receiving the specific hormone signal with cells that
possess specific, complementary receptors on their cell surface membranes
(c) Specific, complementary hormone binds to this receptor
(d) Response will be carried out
(e) – Why a hormone carried around in the blood will only affect specific cells
(f) If all the cells in the body possess such a receptor, then all the cells can respond
to the signal
ii) Explain the meaning of the terms first messenger and second messenger, with reference
to adrenaline and cyclic AMP (cAMP)
(1) Adenyl cyclase – enzyme found on the inner surface of the cell surface membrane
that is associated with the receptor for many hormones eg
...
aldosterone – help to control the concentration of sodium
and potassium in the blood
(b) Glucocorticoids eg
...
pain or shock (preparation for fight or flight)
(a) Relax smooth muscle in the bronchioles
(b) Increase stroke volume of the heart
(c) Increase heart rate
(d) Cause general vasoconstriction to raise blood pressure
(e) Stimulate conversion of glycogen to glucose
(f) Dilate the pupils
(g) Increase mental awareness
(h) Inhibit action of the gut
(i) Cause body hair to erect
iv) Describe, with the aid of diagrams and photographs, the histology of the pancreas, and
outline its role as an endocrine and exocrine gland
(1) Lies just below the stomach
(a) Pancreatic Acinar cells – cells that secrete enzymes
(b) Duct – tubule in centre of a group of enzyme-‐secreting cells
(2) Endocrine functions
(a) Islets of Langerhans – small patches of tissue in the pancreas
(b) Well supplied with blood capillaries as the islets are metabolically active and the
hormones are secreted directly into the blood
(c) Alpha cells – manufacture and secrete glucagon
(d) Glucagon – hormone, released from the pancreas, that causes blood glucose
levels to rise
(e) Beta cells – manufacture and secrete insulin
(f) Insulin – hormone, released from the pancreas, that causes blood glucose levels
to go down
(3) Exocrine functions
(a) Pancreatic Acinar cells – exocrine cells found in small groups surrounding tiny
tubules which secrete pancreatic juice which drains into the duct
(b) Manufacture and secrete digestive enzymes into these tiny tubules
(c) Triggered by nervous and hormonal stimulation
(d) Pancreatic tubules join to make pancreatic duct
(e) Pancreatic duct – main tube that collects all secretions from exocrine cells in the
pancreas and carries the pancreatic fluid to the duodenum
(f) Pancreatic fluid contains
(i) Amylase – carbohydrase
(ii) Tripsinogen – inactive protease
(iii) Lipase
(iv) NaHCO3 – alkaline to neutralise chyme (contents of the digestive system)
which has just left the acid environment of the stomach
v) Explain how blood glucose concentration is regulated, with reference to insulin, glucagon
and the liver
(1) Cells in the islets of Langerhans monitor the concentration of glucose in the blood
(2) Normal blood glucose concentration – 90mg100cm-‐3 or 4-‐6mmoldm-‐3
(3) High blood glucose concentration
(a) Detected by the beta cells
(b) Beta cells respond by secreting insulin into the blood stream
(c) Alpha cells respond by stopping glucagon secretion
(d) Target cells – hepatocytes in the liver, muscle cells, brain cells and other body
cells that possess specific membrane-‐bound receptors for insulin
(e) Insulin binds as the blood containing insulin passes the target cells
(f) Adenyl cyclase is activated inside the target cells
(g) Adenyl cyclase converts ATP to cAMP (cyclic AMP)
(h) cAMP activates a series of enzyme controlled reactions inside the target cell
(i) Effect of insulin on the cell
(i) More glucose channels placed into the cell surface membrane so more
glucose enters the cell
(ii) Glycogenesis – soluble glucose in the cell is converted to insoluble glycogen
for storage
(iii) More glucose is converted to fats
(iv) More glucose is used in respiration
(j) Blood glucose concentration is reduced
(k) Insulin secretion stops
(4) Low blood glucose concentration
(a) Detected by the alpha cells
(b) Alpha cells respond by releasing glucagon into the blood stream
(c) Beta cells respond by stopping insulin secretion
(d) Target cells – hepatocytes in the liver possess specific membrane-‐bound
receptors for glucagon
(e) Glucagon binds as the blood containing glucagon passes the target cells
(f) Adenyl cyclase is activated inside the target cells
(g) Adenyl cyclase converts ATP to cAMP (cyclic AMP)
(h) cAMP activates a series of enzyme controlled reactions inside the target cell
(i) Effect of glucagon on the cell
(i) Glycogenolysis – conversion of insoluble glycogen to soluble glucose
(ii) Gluconeogenesis – production of glucose by conversion of amino acids and
fats in hepatocytes
(iii) Use of more fatty acids in respiration
(j) Blood glucose concentration is increased
(k) Glucagon secretion stops
vi) Outline how insulin secretion is controlled, with reference to potassium channels and
calcium channels in beta cells
(1) High blood glucose concentration
(2) Glucose concentration higher in the blood than in the beta cell
(3) Glucose moves by diffusion into the beta cell down the diffusion gradient
(4) Glucose is metabolised to produce ATP
(5) Potassium ion channels in the cell surface membrane stimulated to close by the ATP
(6) Potassium ions in the cells do not leave, but accumulate in the cell
(7) Accumulation of potassium ions alters the potential difference across the cell
membrane – usually potential difference across the cell membrane is about -‐70mV
(8) Inside of the cells becomes less negative compared to the outside than usual
(9) Change in potential difference opens the calcium ion channels
(10) Calcium ions enter the cell by facilitated diffusion
(11) Calcium ions cause the vesicles of insulin to move towards and fuse with the cell
surface membrane
(12) Vesicles of insulin release insulin by exocytosis
(13) Insulin counteracts the high blood glucose concentration
vii) Compare and contrast the causes of Type 1 (insulin-‐dependent) and Type 2 (non-‐ insulin-‐
dependent) diabetes mellitus
(1) Diabetes mellitus – disease in which the body is no longer able to control its blood
sugar concentration effectively
(a) Excess soluble glucose cannot be stored as insoluble glycogen
(b) Negative feedback mechanism, which maintains blood glucose concentrations
within certain limits, is not used effectively
(c) Hyperglycaemia – state in which the blood glucose concentration is too high eg
...
after exercise or fasting
(2) Signs and symptoms of diabetes
(a) Urinating often
(b) Feeling very thirsty
(c) Feeling very hungry or tired
(d) Losing weight without trying
(e) Having sores that heal slowly
(f) Dry, itchy skin
(g) Losing the feeling in your feet/tingling
(h) Blurry eyesight
(3) Type I Diabetes – insulin-‐dependent diabetes/juvenile onset diabetes
(a) Onset in childhood
(b) Symptoms develop quickly eg
...
pigs – close-‐match to human insulin
(2) Now produced by genetically engineered bacteria – bacteria with altered DNA ie
...
glucose, fatty acids and
amino acids
(b) Blood removes waste products eg
...
during vigorous exercise
(i) Detected by stretch receptors in the carotid sinus – small swelling in the
carotid artery
(ii) Stretch receptors signal to the cardiovascular centre
(iii) Heart rate tends to decline
(e) Less/stop exercise
(i) Less CO2 is produced
(ii) Activity of the accelerator pathway is reduced
(iii) Heart rate declines
(5) Hormonal and nervous control of the heart beat in humans
(a) Hormonal
(i) Release of adrenaline increases heart rate
(b) Nervous
(i) Increase in HCO3-‐ / H+ detected by chemoreceptors in the carotid arteries,
aorta and the brain
(ii) Increased frequency of impulses along accelerator nerves
(iii) To diaphragm and intercostal muscles – faster and deeper breathing
(iv) To SAN – heart beats faster
(c) Effect – negative feedback mechanism
(i) Stronger contractions by heart
(ii) Increased stroke volume of heart
(iii) Faster removal of CO2
(iv) More removal of CO2
(v) Blood CO2 falls and returns to set point
(6) Artificial pacemakers – device that delivers an electrical impulse to the heart muscle
when the mechanism controlling the heart rate in an individual fails
(a) Needle electrode inserted into the heart wall – not portable and needed to be
connected to a light fitting
(b) Deliver impulses via an electrode pad on the skin – complaints of pain and
needed mains circuit electricity to function (similar to functions of electric chairs)
(c) 1950s small plastic box with wires inserted through the skin to act as electrodes
on the heart muscle
(d) Now only about 4cm long, implanted under the skin and fat on the chest –
capable of responding to the activity of the patient
(e) Delivers impulses to the ventricle walls – deals with conditions where the SAN
functions but the AVN is not relaying the impulse from the atria to the ventricles
Title: BIOLOGY OCR F214
Description: OCR Board A2 Level Biology F214 SECTION 1: COMMUNICATION AND HOMEOSTASIS
Description: OCR Board A2 Level Biology F214 SECTION 1: COMMUNICATION AND HOMEOSTASIS