Module 1 - Communication

8/6/2019 Module 1 - Communication

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Communication and Homeostasis

1) The need for communication

y Animals increase their chances of survival by responding to changes in their external environmentE.g. avoiding harmful environments such as places that are too hot or cold

y They also respond to their internal environment to make sure that the conditions are always optimalfor their metabolism

E.g. removing toxins from tissue fluid

y Plants also respond to changes in their environmenty Multicellular organisms are more efficient than single celled organisms as its cells can be differentiated

(specialised to perform particular functions)

y A good communication system willo Cover the whole bodyo Enable cells to communicate with each overo Enable specific communicationo Enable rapid communicationo Enable both short-term and long-term responses

y Cells communicate via a process called cell signallingo One cell releases a chemical that is detected by another cell which responds

y There are 2 ways cells communicate via cell signallingo Neuronal System etwork of neurones that signal to each over across synapse junctions they

can conduct a signal quickly enabling a rapid short term response

o Hormonal System Uses the blood to transport chemical messengers called hormones whichare recognised by specific target cells enabling a long term response

Syllabus statements:

4.1.1 (a),(b),(c)

Stimulus any change in the environment that causes a response

Response a change in behaviour or physiology as a result of a

change in the environment


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Co uni tion nd o ost sis

2

o

ost

sis

y Variousconditions inside the body need to be ke t constante o Body te eratureo Blood glucoseconcentrationo Water potential of the bloodo Blood pressureo Carbon dioxideconcentration

y Enzy es re uirecertain conditions to work efficiently and to prevent denaturingo Suitable pHo Suitable te peratureo Aqueousconditionso Freedom from toxins and inhibitors

y Theconditionscannot be kept perfectlyconstant they will deviate around the mean or optimum conditiony Aslong as that deviation isnt too large theconditions will remain acceptable

y Achange in the internalenvironment must be detected and signalled to other cells a response mustthen becoordinated to reversethat change

y For negative feedback to work effectivelythere must be a system coordinated bycellsignalling

y Positive feedback is not involved in homeostasisy Positive feedback is a lot lesscommon than negative feedback e g. oxytocin

o Oxytocin increases the uterinecontractions during pregnancy which stretches thecervix moreo As thecervix stretches the pituitary gland isstimulated to release more oxytocin

Optimum

condition Changeaway from

optimum

Receptordetectschange

Communicationsystem informs

effector (cellsignalling)

Effector reactsto reverse

change

Return tooptimum

conditions

Stimulus ReceptorCell

SignallingEffector Response

Syllbusst

t

nts:

41

1 (d

(e)

Ho

eost

sisis the maintenance of the internalenvironment in a constant despite

externalchanges

Negative Feedbackis a process that brings about a reversal of anychange in

conditions. It ensures that an optimum steadystatecan be maintained.

Positive Feedbacka process that increases anychange detected by the receptors it

tends to be harmful and does not lead to homeostasis


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Communication and Homeostasis

3) Maintaining Body temperature

Ectotherm Endotherm

Cant control their body temperature internally they

must alter their behaviour e.g. basking in the sun

Control their body temperature internally by

homeostasis and can also control their temperature bybehaviour

Internal temperature is dependent on external

temperature

Internal temperature is less affected by external

temperature

Their activity depends on the external temperature

(more active at higher temperatures vice versa)

Activity level is largely independent of the external

temperature

Variable metabolic rate generating very little heat Constantly high metabolic rate to generate a lot of heat

y Behavioural mechanisms to maintain body temperature in ectothermso Expose body to sun to absorb more heato Orientate body towards sun to expose larger surface areao Orientate body away from sun to expose less surface areao Hide in burrow to reduce heat absorptiono Increase breathing rate to evaporate more water reducing temperature

y The peripheral temperature receptors in the skin monitor the external temperature if externaltemperature changes too much it signals to the hypothalamus

y The hypothalamus in the brain monitors the temperature of the blood and signals to return tooptimum temperature if its not

Temperature Regulation in Endotherms

Component of body Response if core temp is too high Response is core temp is too low

Sweat glands in skin Secrete more sweat onto skinusing heat from blood to

evaporate water

Less sweat is secreted lessevaporation so less loss of latent

heat

Lungs, mouth and nose Panting increases evaporation

using latent heat

No panting ,less water evaporates

and less latent heat used

Hairs on skin Hairs lie flat providing little

insulation thus more heat can be

lost via convection and radiation

Hairs are raised to trap a layer of

insulating air reducing heat loss

from skin

Arterioles leading to capillaries in

skin

Vasodilatation allows blood i nto

capillaries near the skin thus

more heat can be radiated

Vasoconstriction reduces blood

flow to capillaries near skin so less

heat is radiated

Li!

er cells Rate of metabolism is reduced soless heat is produced from

exergonic reactions

Rate of metabolism is increasedso more heat is produced from

exergonic reactions

Skeletal muscles No spontaneous contractions Spontaneous contractions to

generate heat from respiring

muscles

y Endotherms also use behavioural mechanisms to maintain body temperature e.g.o Move into shade/ Move into the sunlighto Remain inactive / Move about to generate heato Decrease / Increase surface area


4.1.1 (f)

Ectotherm an organism that relies on external

sources of heat to regulate its body temperature

Endotherm an organism that can use internal

sources of heat to maintain its body temperature


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Nerves

1) Sensory Receptors andstructure ofneuronesy The nervoussystem is made up of a complex network ofcellscalledneuronesy There are 3 types of neurones

o Sensory Neuronestransmit nerve impulses from receptors to thecentral nervoussystem (CNS)o Motor Neuronestransmit nerve impulses from theCNS to theeffectorso Relay Neuronestransmit nerve impulses between sensory neurones and motor neurones

y Astimulus is detected by receptor cells and a nerve impulse issent along thesensory neuroney When a nerve impulse reaches theend of a neurone" chemicalscalled neurotransmitters take the

information across thesynapse to the next neurone which sends another nerve impulse.

y Different stimuli have different forms ofenergy (e.g. light energy)y Your nervoussystem onlysends the information in the form of nerves impulses (electricalenergy)y Sensory receptors act as transducers (energy form convertor)

Structure ofneurones

y Neurones areverylong so theycan transmit an action potential over a long distancey They havesodium / potassium pumpsy Surrounded by myelin sheath(Schwann cells) which insulates the neurone from other electrical activity

and there are gaps in-between called nodes of Ranvier

y Dendritesconnect neurones to other neuronesy Cell bodiescontain the nucleus # cytoplasm and other organellesy Axons carry nerve impulses away from thecell bodyy Dendronscarry nerve impulse to thecell body

Stimulus Receptors CNS Effectors Response

Syllabusstatements:

4$1

$2 (a), (b)

y This is a motor neuroney Cell body islocated in theCNSy Long axon carrying nerve impulse

to theeffectors

y This is a motor neuroney Cell body positionedjust outside

theCNS

y Long Dendron carrying nerveimpulse from sensory receptor to

cell body


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Nerves

2) Resting potentialsy When a neurone is at rest ( not conducting a nerve impulse)there is a potential difference across ity This is due to an accumulation of positive ions on the outsidey The inside of thecell has a charge of -70 mV compared to the outsidey The membrane issaid to bepolarisedas it has a potential difference across ity The resting potential is maintained bysodium-potassiumpumps and potassium ion channels

o Sodium potassium pumpsactively transport 3 Na+ out of a neurone for every2 K+ ino Potassium ion channels allow facilitated diffusion of K+ down their concentration gradient

y The membrane iseffectively impermeable to sodium ionsy This makes the outside of thecell more positive than the inside

Nerves3) Generating an actionpotential

Process

1) Astimuluscausessodium ion channels to open in thecell membrane which becomes more permeableto sodium

2) Sodium ions (Na+) diffuse into the neurone down their electrochemical gradient making the inside ofthe neuroneless negative

3) Depolarisation occurs % this is when thethresholdpotential is reached (50mV) and voltage-gatedsodium ion channels open resulting in moresodium ions diffusing into the neurone. Thecell becomes

more and more positive

4) Repolarisationoccurs at a potential difference of around+30mV thesodium ion channels and thevoltage-gated potassium ion channels open

5) T

he membrane is then more permeabl

e to potassium ionsso more of them diffuse out of thecell

thisstarts to restore the membrane to itsresting potential

6) Hyperpolarisationthen occurs where the potassium ion channels areslow to closeso too many diffusein resulting in the potential difference becoming slightly more negative than the resting potential

7) Thesodium-potassium pumps then restore the membrane to its resting potentialy TheRefractory period is a period of time after an action potential when the neuronecannot beexcited

as the ion channels are recovering and cannot be made to open

-100

-80

-60

-40

-20

0

20

40

60

0 1 2 3 4

Syllabusstatements:

4&1

&2 (c), (d)

Syllabusstatements:

4&1

&2 (c), (d)

3)

4)

6)


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Ner es

4) Transmission of action potentials and mylenation

y The action potential moves along the neurone as a wave of depolarisationy During an action potential some of the sodium ions that enter diffuse sideways causing sodium

channels in the next region of the neurone to open and sodium ions diffuse in

y This results in an action potential and thus the wave of depolarisation travels along the neuroney The wave moves away from the parts in the refractory period because these parts cant fire an action

potential

y An action potential is an all or nothing response, the neurone either conducts or doesnt conduct an actionpotential and they are all of the same magnitude

y A bigger stimulus wont cause a bigger action potential but it causes them to be fired more frequentlyy A higher frequency of signal therefore means a larger stimulusy Some neurones are myelinated whereas some or noty Mylenation refers to the neurone being wrapped by an electrical insulator in the form ofSchwann cellsy In myelinated neurones there are gaps between theSchwann cells with bare membrane called nodes

of ranvier

y Depolarisation can only occur at the nodes of ranvier in myelinated neurones therefore the sodium ionchannels are concentrated at the node of ranvier

y The depolarisation jumps from node to nodey This is referred to as saltatory conduction and is very fasty In non myelinated neurones the action potential travels as a wave along the whole length of the axon

membrane

y This is slower than saltatory conductiony Cells that carry signals over long distances ( up to 1m) are usually myelinated


4.1.2 (e)(f)(g)(h)


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Ner es

5) Synapses Fundamentals

y A synapse is a junction between two or more neurones/effectors celly The tiny gap between the cells at the synapse is called the synaptic cleft (around 2nm)y Consists of a pre and post synaptic neuroney The pre-synaptic neurone has a swelling called the synaptic knoby This contains synaptic ' esicles which contains chemicals called neurotransmittersy Neurotransmitters are chemicals that diffuse across the cleft of the synapse to transmit a signal to the

postsynaptic neurone

y The most common neurotransmitter is acetylcholine and a synapse that uses this is called a cholinergicsynapse with cholinergic receptors

y When an action potential reaches the end of a neurone is causes neurotransmitters to be released intothe synaptic cleft

y They diffuse across to the post synaptic membra ne and bind to specific receptorsy This may cause an action potential, a hormone to be excreted from a gland or a muscle to contracty Neurotransmitters are removed from the cleft so the response doesnt keep happening

o Either taken back into pre synaptic neurone or broken down by enzymesy There are many different neuro transmitters e.g.

o Acetylcholine, Noradrenaliny Acetylcholine is broken down by the enzyme acetyl cholinesterase (AchE)y The synaptic knob has many specialised features

1) Many mitochondria indicating that it is an active process requiring ATP 2) A large amount of smooth ER synthesising enzymes3) Vesicles containing Ach substance that will diffuse across synaptic cleft4) Voltage gated calcium ion channels in membrane


4.1.2 (i), (j)(k)


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Ner es

6) Synapses Process and role

y This is how neurotransmitters transmit nerve impulses between neurones:1) An action potential triggers calcium influx:

1)An action potential arrives at the synaptic knob of the pre-synaptic neurone2)The action potential stimulates the voltage -gated calcium ion channels in the pre -synaptic neurone to

open3)Calcium ions diffuse into the synaptic knob (they are pumped out afterwards by active transport)

2) Calcium influx causes Neurotransmitters to be released

1)The influx of calcium ions causes the synaptic knob causes synaptic vesicles to move to the pre -synaptic membrane

2)The vesicles fuse with the pre-synaptic membrane and release the neurotransmitter into the synapticcleft (exocytosis)

3) The neurotransmitter triggers an action potential in the post synaptic neurone

1)The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the post -synaptic membrane

2)This causes sodium ion channels in the p ost-synaptic neurone to open3)The influx of sodium ions into the post -synaptic membrane causes depolarisation4)This results in an action potential on the post -synaptic membrane to be generated if the threshold is

reached

5)The neuro transmitter is removed from the synaptic cleft so the response doesnt keep happening

Role of synapses in the ner(

ous system

1)When one neurone is connected to many the neurones signal can be dispersed to different parts ofthe body this is called synaptic di

)

ergence

2)When many neurones connect to one neurone information can be amplified this is called synapticcon

0

ergence

3)If a stimulus is weak only a small amount of neurotransmitter is released and may not be enough toexcited the post-synaptic neurone to threshold level

4)Summation is where the effect of neurotransmitter released from many neurones is added together toreach the threshold

5)Synapses make sure the impulses are transmitted one way

6)Receptors for neurotransmitters are only on the post -synaptic membranes therefore they can onlytravel in one direction


4.1.2 (j), (k)


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Hormones

1) Fundamentals

y Hormonal system is made up of endocrine glands and hormonesy The hormonal system sends information as chemical signalsy Hormones cause a specific response in target cells /tissue

o Target cells posses specific receptors that have a complimentary shape to the hormoney Hormones can be steroids (e.g. testosterone), protein (e.g. insulin) or amino acid derivatives (e.g. adrenaline)y Protein hormones and adrenaline bind to receptors on plasma membrane y Steroids and thyroxine pass through the plasma membrane and binds with the nucleus regulatingDNA

transcription

y Hormones are secreted when an endocrine gland is stimulatedo can be stimulated due to change in concentration of a specific substance or an electrical

impulse

y Endocrine glands is a gland that secretes hormones directly into the blood and has no ductso Hormones diffuse directly into the blood and are taken all over the body

y Exocrine glands secrete chemicals through ducts into cavities or on the surface of the bodyo Usually secrete enzymes (e.g. digestive gland)

y Some organs have both endocrine and exocrine tissue (e.g. pancreas)y A hormone is called a first messenger as it carries the chemical message the first part of the wayy When a hormone binds to its receptor it activates an enzyme in the cell membraney The enzyme catalyses the production of a molecules inside the cell called a signalling moleculey The signalling molecule is called a second messenger because it carries the chemical message the

second part of the way signalling to other parts of the cell to change how the cell works

y The second messengers activate a cascade (a chain of reactions) inside the celly The adrenal glands are endocrine glands found above the kidneyy The cortex secretes steroid hormones (e.g. cortisol for stress)y The medulla secretes catecholamine hormones (modified amino acids) e.g. adrenaliney The hormone adrenaline is a first messenger

o Adrenaline binds to specific receptors in the cell membranes of many cells (e.g. hepatocytes)o When adrenaline bind it activates an enzyme in the membrane called adenylate cyclaseo Activated adenylate cyclase catalyses the production of a second messenger called cyclic AMP

(cAMP)

o cAMP activates a cascade (e.g. makes more glucose avaliable)y Adrenaline has many function including

o Increase cardiac outputo Relax smooth muscle in bronchioleso Increase heart rateo Dilate pupilso stimulate conversion of glycogen to glucose etc


4.1.2 (a)(b)(c)


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Hormones

2) Pancreas

y Pancreas is an organ found below the stomach and has both exocrine and endocrine functions**LOOK AT DIAGRAMS PAGE 24 OCR TEXTBOOK**

y Exocrine functions of pancreas o Most of the pancreas is exocrine tissueo The exocrine cells are called acinar cellso Theyre found in clusters around the pancreatic duct (duct goes to duodenum)o The acinar cells secrete digestive enzymes which digest food (e.g. amylase break down starch)

y Endocrine functions of the pancreas o The areas of endocrine tissue are called the islets of Langerhanso They are found in clusters around blood capillarieso They secrete hormones directly into the bloodo They are made up of two types of cell

Alpha cells secrete a hormone called glucagon Beta cells - secrete a hormone called insulin

y Eating and exercise change the concentration of glucose in your bloodo Drops after exercise rises after eating

y When blood glucose concentration is too high insulin lowers it 1) Insulin binds to specific receptors on the cell membranes off hepatocytes and muscle cells2) it increases the permeability of cell membranes to glucose so cells take up more glucose3) Insulin activates enzymes that convert glucose to glycogen (glycogenesis)4)Cells are able to store glycogen in their cytoplasm as an energy source5) Insulin also increases the rate of respiration of glucose

y When blood glucose concentration is too low glucagon raises it 1)Glucagon binds to specific receptors on the cell membranes of liver cells2)Glucagon activates enzymes that break down glycogen into glucose (glyogenolysis)3)Glucagon also promotes the formation of glucose from fatty and amino acids ( gluconeogenesis)4)Glucagon decreases the rate of respiration of glucose in cells


4.1.2 (d) (e)


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Hormones

3) Insulin

y Beta cells secrete insulin when they 1 re depolarised y cells contain insulin stored in vesicles and they secrete insulin when they detect high blood glucose

concentration this is the process:

1)When blood glucose concentration is high, more glucose enters the cells by facilitated diffusion2)More glucose in cells causes the rate of respiration resulting in an increase of ATP 3)This increase of ATP triggers the potassium ion channels in the plasma membrane to close4)This means K+ ions cannot leave the cell and accumulate inside the cell making the cell less negative

and the cell membrane becomes depolarised

5)Depolarisation causes calcium ion channels in the membran e to open so calcium ions diffuse into the cells

6)This causes vesicles to fuse with the cells plasma membrane releasing insulin via exocytosisHormones

4) Diabetes mellitus

y Diabetes mellitus is a condition where blood glucose concentration cant be controlled properlyy There are two types Type 1 diabetes (insulin dependent) and Type 2 diabetes (non insulin dependent) y Type 1 diabetes

o The cells do not produce any insulin o After eating the blood glucose level rises and stays high (hyperglycaemia) which can result in death o The kidneys cannot reabsorb all this glucose so some of its excreted in the urine o Type 1 diabetes usually develops in children or young adults

y Type 2 diabeteso Type 2 is usually acquired later in life and often is linked with obesityo It occurs when cells do not produce enough insulin or when cells dont respond to insulin properly

y Benefits of insulin produced by genetically modified bacteriao Cheaper than extracting it from animal pancreasso Larger quantities of insulin can be producedo Less likely to cause an immune responseo Some people prefer it for ethical or religious reasons

y Stem cells could be used to cure diabeteso Stem cells could be grown into cellso cells would then be implanted into the persons pancreas and they would be able to make insulino The treatment is still being developed but if effective it will cure type 1 diabetes


4.1.2 (f)


4.1.2 (g) (h)


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Documents

Module 1 - Communication