Transcript Communication
Unit 1 Communication, Homeostasis and Energy
What effect does temperature change have on enzyme action?
What other environmental factors inhibit the action of enzymes?
List three changes to the external environment to which we might need to respond.
What is the main role of the Heart The lungs The kidneys
What is meant by cell signalling?
In what other process in the body is cell signalling particularly important?
Explain the role of cell surface receptors in cell signalling.
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 coordinate the activities of different organs.
Sensitivity Stimulus Internal communication Plants Animals Receptor Effector
All living things need to maintain a certain limited set of conditions inside their cells. Why?
Cellular activities rely on the action of enzymes Specific limited set of conditions Suitable temperature Suitable pH Aqueous environment No toxins / inhibitors
As the external environment changes it places stress on the living organism.
The environmental change is a stimulus and the way in which the organism changes its behaviour or physiology is its response to the stress.
Stimulus Any change in environment that causes a response Response A change in behaviour or physiology as a result of a change in the environment.
State that cells need to communicate with each other, which they do by a process called cell signalling.
State that neuronal and hormonal systems are examples of cell signalling
The internal environment of the cells in animals is tissue fluid. Activity of the cell alters its environment Use up substrates Produce products, some of which may be toxic Accumulation of excess waste acts as a stimulus to cause the removal of these wastes
Summary Composition of the tissue fluid is maintained by the blood Wastes accumulating in tissue fluid enter the blood Excretion prevents the accumulation of wastes in the blood Concentrations of all substances in the blood are monitored
In a multicellular organism cells become differentiated (specialised) forming tissues and organs.
A good communication system is required List the features of a good communication system
Whole body Cell communication Specific Rapid Short term and long term
How cells communicate with each other The neuronal system and the hormonal system work by cell signalling.
define the terms negative feedback, positive feedback and homeostasis; explain the principles of homeostasis in terms of receptors, effectors and negative feedback;
Maintaining a constant internal environment despite external changes Examples Body temperature Blood glucose concentrations Blood salt concentration Water potential of blood Blood pressure Carbon dioxide concentration
Reversal of any change in internal environment to return to an optimum steady state.
Optimum condition Return to optimum conditions Effector reacts to reverse change Change away from optimum Receptor detects change Communication system informs effector
Structures required for pathway to work Sensory receptors Communication system Effector cells
Control of room temperature Control of body temperature Control of blood glucose levels Control of body water concentration
Increases any change that is detected by receptors Does not lead to homeostasis
Optimum condition Effector reacts to increase change Change away from optimum Receptor detects change Communication system informs effector
If core temperature drops too low Dilation of the cervix at the end of pregnancy
Enzyme action and temperature regulation As core body temperature rises the increase will affect the activity of enzymes. This can lead to heat exhaustion and even death.
▪ ▪ Describe the effect of increasing body temperature on enzyme action.
Suggest what actually causes death as body temperature rises.
Temperature increase – rate of enzyme action increases 10 o C increase will double the rate of reaction Above 50 o C enzymes denature – rate of reaction falls quickly Death
The stress response The usual response to stress is to release the hormone adrenaline. This hormone has a wide range of target cells and prepares the body for activity. The activity may be to stay and fight or it may be to run away. The hormone is known as the “fight or flight” hormone.
The stress response When under stress women also release the hormone oxytocin. This results in a tendency to pacify or protect. It has been called the “tend and befriend” hormone. Oxytocin prompts a mother to protect her children.
Suggest how these responses to adrenaline and oxytocin may have evolved.
describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms
Changes in body temperature affects the structure of proteins Endotherms Maintain body temperature within strict limits Independent of external temperature Ectotherms Body temperature fluctuates with external temperature
Advantages Use less food in respiration Need less food Greater proportion energy used for growth Disadvantage less active in cooler temperatures May not be capable of activity in winter months
Increasing the heat exchange with their environment Expose body to sun Orientate body to sun Orientate body away from sun Hide in burrow Alter body shape Increase breathing movements
Design an A4 poster to summarise behavioural and physiological adaptions of ectotherms for temperature regulation.
Temperature regulation in bee swarms Bees are ectothermic.
However, it has been shown that the temperature of a bee swarm can be maintained accurately to within one degree of 35 o C. This is achieved by bees moving to different parts of the swarm and by allowing passages for air flow through the swarm.
Suggest how movement of bees within a swarm and air movement through the swarm can help to maintain the temperature of the swarm.
Bees in the centre of the swarm will be warmer than those on the outside.
Warmer bees move towards the outer parts of the swarm while colder bees move toward the centre.
This transfers heat from the centre to the outer parts of the swarm.
In hot weather the bees create more passages for air flow; the passages are also wider Thus more air can pass through the swarm and carry heat away.
In cooler weather there are fewer air passages and they are narrower.
Why is it important to maintain body temperature?
Make a list of 5 ectotherms Explain how basking on a hot rock in the sun can help an ectotherm to regulate its body temperature.
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
Use internal sources of heat to maintain body temperature Many chemical reactions in the body are exergonic Endotherms also show behavioural and physiological adaptations
ADVANTAGES
Constant body temp.
Activity possible even when cool Inhabit colder parts of planet
DISADVANTAGES
Energy used up to maintain constant temp.
More food required Less energy used in growth
Sweat glands in skin Lungs, mouth and nose Hairs on skin arterioles Liver cells Too hot
Secrete more sweat panting Lie flat Vasodilation Reduce rate of metabolism
Skeletal muscles Too cold
Less sweat secreted No panting Raised vasoconstriction Increase rate of metabolism Spontaneous contractions (shivering)
TOO HOT
Move into shade Decrease exposed surface area Remain inactive / increase surface area
TOO COLD
Move into sunlight Increase exposed surface area Move about to generate heat in muscles Extreme cold – roll into a ball to decrease surface area
Change in core temperature
Thermoregulatory centre in hypothalamus detects change.
Nervous and hormonal systems carry signals to skin, liver and muscles ▪
Fall in core temperature
▪ Rise in metabolic reactions ▪ Release more heat from exergonic reactions ▪ Release heat through muscle contractions ▪ Decrease loss of heat, temperature rises
Skin temperature Core Temperature External
HYPOTHALAMUS
Thermoregulatory centre
TOO COLD
-Shivering -Increased metabolism -Vasoconstriction -Reduced sweating -Skin hairs erected
TOO HOT
-Reduce metabolism -Vasodilation - increased sweating
Thermoregulatory centre in the Hypothalamus Monitors blood temperature Detects changes in core temperature Peripheral temperature receptors “early warning” system Detect changes in temperature of the extremities Sends signals to the brain to initiate behavioural mechanisms to maintain core temperature.
Should mountain rescue dogs carry brandy?
In early part of the twentieth century St Bernard dogs were used for mountain rescues.
Traditionally they carried a small container of brandy for the lost or injured climber to drink.
Alcohol causes vasodilation.
Explain why drinking brandy is not a good idea for someone who is lost or injured and exposed to cold weather.
If the climber is unable to find shelter, the low temperature could reduce the body temperature to the point where enzyme activity is severely reduced.
Vasodilation caused by the alcohol in the brandy will increase the rate of heat loss from the body, because more blood carries heat from the body’s core to the surface where it can be lost.
Hypothermia and death will happen sooner in a person who has drunk alcohol.
Explain why a shrew has to eat almost its own body mass each day, but an elephant eats less than one percent of its body mass each day.
Suggest why the fairy penguin of Australia grows to about 25cm in height while the emperor penguin of Antarctica grows to a metre in height.
Shrew is very small with a large surface area to volume ratio. It loses heat through it’s skin A lot of food must be used to replace the heat lost Elephant is large with a small surface area to volume ratio Loses a smaller proportion of body heat.
Australia is warm – penguins do not need to be large to maintain their body temperature Antarctica is very cold – larger penguins have a smaller surface area to volume ratio – so can maintain body temperature more easily.
a huddle of penguins has a smaller surface area to volume ratio than a solitary penguin.
Outline the roles of sensory receptors in mammals in converting different forms of energy into nerve impulses.
Describe, with the aid of diagrams, the structure and functions of sensory and motor neurones.
Specialised cells that detect changes in surroundings Energy transducers Convert one form of energy to electrical energy of a nerve impulse Stimulus Change in energy levels in environment
Receptors
Light sensitive cells Olfactory cells Taste buds Pressure receptors (pacinian corpuscles) Sound receptors Muscle spindles (proprioceptors)
Energy changes detected
Light intensity and wavelength Presence of volatile chemicals Presence of soluble chemicals Pressure on skin Vibrations in air Length of muscle fibres
Function To transmit the action potential Structure Very long Maintain potential difference across cell membrane ▪ Gated ion channels in cell membrane ▪ Sodium/potassium pumps Myelin sheath / schwann cells / node of ranvier Cell body contains nucleus, mitochondria and ribosomes.
Describe and explain how the resting potential is established and maintained. Describe and explain how an action potential is generated.
Gated channel proteins specific to either sodium or potassium ions Increase permeability when open reduces permeability when closed Carrier proteins Active transport Sodium-potassium pump ▪ Transports more Na 2+ out of cell than K + into cell.
Result is that inside cell is more negatively charged than outside the cell Cell membrane is polarised.
3 Na 2 K + + leave the cell enter the cell Potential difference is created across the membrane
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Summary of the sodium potassium pump!
Describe and explain how an action potential is generated.
Interpret graphs of the voltage changes taking place during the generation and transmission of an action potential.
Potential difference across the neurone cell membrane while the neurone is at rest Inside the cell is -60mv compared with outside the cell.
Cell membrane is polarised
The permeability of the cell membrane to sodium ions is increased Sodium ions move down a concentration gradient into the cell Creating a change in the potential difference across the membrane Inside the cell becomes less negative This is depolarisation
Generator potential
Small depolarisation caused by sodium ions entering the cell
Action potential
Potential difference +40mv
Threshold potential
Depolarisation of the cell membrane Inside is more positive than the outside Potential difference across membrane of 50mv
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Membrane is polarised at rest (-60mv) Sodium ion channels open Membrane depolarises (threshold value -50mv) Voltage-gated sodium ion channels open and many sodium ions flood in Potential difference across plasma membrane reaches +40mv
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Sodium ion channels close and potassium channels open Potassium ions diffuse out of the cell, this is repolarisation Hyperpolarisation = the potential difference overshoots slightly Resting potential restored
Resting potential – K + Na voltage-gated channels open, + voltage-gated channels closed Hyperpolarisation and repolarisation: sodium-potassium pumps restablish the resting potential Action potential established Repolarisation Sodium ions enter causing a greater influx of sodium ions (positive feedback) Na + voltage-gated channels open
Look at the animation For a narrated animation look at http://bcs.whfreeman.com/thelifewire /content/chp44/4402002.html
Allows the cell to recover after an action potential Ensures action potentials are only transmitted in one direction
Sensory receptors Are specific to a single type of stimulus Act as transducers Produce a generator potential Give and “all or nothing” response Become adapted
Describe and explain how an action potential is transmitted in a myelinated neurone, with reference to the roles of voltage-gated sodium ion and potassium ion channels.
Key ideas Local currents Voltage-gated sodium ion channels The myelin sheath Saltatory conduction
This is the movement of ions along the neurone During an action potential ▪ ▪ ▪ ▪ ▪ ▪ Sodium ion channels open Sodium ions diffuse across membrane Upsets balance of ionic concentrations Concentration sodium ions inside neurone rises Sodium ions diffuse sideways Movement of charged particles is a local current.
These gates are operated by changes in the voltage across the membrane Movement of sodium ions alters the potential difference Depolarisation causes gates to open Sodium ions enter neurone at a point further along the membrane Action potential moves along the membrane
Is this an example of positive or negative feedback Give reasons for your answer
This speeds up the transmission of the action potential (up to 120ms -1 ) In a myelinated neurone Ionic exchanges can only occur at the nodes of Ranvier Local currents are elongated, sodium ions diffuse along neurone from one node of Ranvier to the next, a distance of 1 – 3 mm Action potential appears to jump from one node to the next
Transmission of an action potential
Outline the significance of the frequency of impulse transmission.
Compare and contrast the structure and function of myelinated and non myelinated neurones.
Action potentials are always the same size Strength of stimulus Frequency of action potentials ▪ ▪ Strong stimulus will generate more frequent action potentials Brain interprets a stream of closely spaced action potentials as a “strong stimulus” A strong stimulus is likely to stimulate more neurones than a weak stimulus
Nature of stimulus Deduced by the position of the sensory neurone bringing the information
The wider the axon the faster the speed of transmission Myelin insulates axons, speeding up transmission of an action potential along them Myelinated neurones 100 – 120 ms -1 Unmyelinated neurones 2 – 20 ms -1
Read through the handout on Multiple Sclerosis Complete the table Answer the question.
Describe, with the aid of diagrams, the structure of a cholinergic synapse.
Outline the role of neurotransmitters in the transmission of action potentials.
Outline the roles of synapses in the nervous system.
The Cholinergic Synapse A synapse is a junction between two or more neurones.
A synapse which uses acetylcholine as a neurotransmitter is called a cholinergic synapse.
The synaptic knob (bulb) is a swelling at the end of the presynaptic membrane. It contains: Many mitochondria Smooth endoplasmic reticulum Vesicles containing acetylcholine Voltage-gated calcium ion channels in the membrane
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An action potential arrives Calcium ion channels open Vesicles containing acetylcholine move to the presynaptic membrane.
Vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft.
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Acetylcholine diffuse across the synaptic cleft to the postsynaptic membrane Acetylcholine binds to receptors in postsynaptic membrane Sodium ion channels open – the membrane is depolarised and an action potential is produced.
On the worksheet Label the diagram of the synapse Sort out the sentences into the correct order
Acetylcholinesterase is an enzyme found in the synaptic cleft It hydrolyses acetylcholine into ethanoic acid and choline Choline is taken back to the presynaptic membrane to reform Acetylcholine
Transmit information between neurones Are unidirectional Act as junctions Filter out low level stimuli Summation Amplification of low level signals Acclimatisation Prevent overstimulation and fatigue Memory and learning
The cytoplasm in the synaptic knob has a high proportion of certain organelles. These include smooth endoplasmic reticulum, mitochondria and vesicles. Each organelle has a specific role to play in the functioning of the cell.
Describe the role of each of these organelles and explain why they are found in relatively large numbers in the synaptic knob.
Describe the roles of: Sodium ion channels Potassium ion channels Calcium ion channels In the transmission of information along and between neurones
20 marks = 20 minutes You should be able to complete this prep in 20 minutes Papers taken from OCR June 05 & 06
Compare the structure of a motor neurone to that of the “typical” animal cell. How does the specialised structure of a neurone relate to its function?
Define the terms endocrine gland, exocrine gland, hormone and target tissue. Explain the meaning of the terms first messenger and second messenger, with reference to adrenaline and cyclic AMP (cAMP).
Describe the functions of the adrenal glands.
Endocrine Gland Secretes it’s product directly into the blood or lymph.
Exocrine gland Secretes its product into a duct to take the secretions to the site of action.
A hormone Is a protein or steroid molecule which acts as a chemical messenger Causes a specific response in target cells Target cells Possess a specific receptor on cell surface membrane complementary to the hormone
First Messenger
1. Protein hormone secreted from a cell in an endocrine organ 2. Hormone circulates in body fluids 3. Hormone binds to receptor on the plasma membrane of a target cell
Second Messenger
4. Activation of a second messenger inside the cell Endocrine cell target cell target of second messenger inside the cell
Adrenaline is released by the adrenal glands Binds to glycoprotein receptors on the plasma membrane of target cells The enzyme adenyl cyclase becomes active Concentration of cAMP in the cell increases cAMP activates the first of a “cascade” of enzymes
The last enzyme in the cascade is kinase Kinase binds to glycogen phosphorylase This catalyses the breakdown of Glycogen into glucose in the liver cells
Adrenal Cortex Uses cholesterol to produce steroids ▪ Glucocorticoids stimulate the synthesis of glycogen in the liver ▪ Mineralocorticoids increase the uptake of Na + in the gut and raise blood pressure Adrenal Medulla Secretes Adrenaline in response to stress Preparing the body to fight or take flight
The role of adrenaline is to prepare the body for action, list as many of the effects of adrenaline as you can, and explain how the effect prepares the body for action.
Relax smooth muscle in bronchioles Increase stroke volume of the heart Increase heart rate Cause general vasoconstriction Stimulates breakdown of glycogen Dilates the pupils Increase mental awareness Inhibit the action of the gut
Describe, with the aid of diagrams and photographs, the histology of the pancreas, and outline its role as an endocrine and exocrine gland.
Explain how blood glucose concentration is regulated, with reference to insulin, glucagon and the liver.
The islets of langerhans are patches of endocrine tissue scattered throughout the exocrine tissue of the pancreas Islets make up 15% of the pancreas A-cells secrete glucagon B-cells secrete insulin These hormones help to regulate blood glucose concentrations
Islets of Langerhans Groups of cells which carry out the endocrine functions
Alpha cells (α cells)
▪ Secrete glucagon which stimulates glycogen glucose
Beta cells (β cells)
▪ Secrete insulin which stimulates glucose glycogen These two types of cells work antagonistically
Blood glucose concentration in a healthy human 80 – 120mg/100cm 3 A decrease in blood glucose Cells may run out of blood glucose for respiration An increase in blood glucose May upset the normal behaviour of cells Blood glucose levels never remain constant they oscillate above and below a required level due to the time delay between the change and the onset of corrective actions.
Glucagon leads of activation of enzymes to: Convert glycogen to glucose Increase the rate of gluconeogenesis
Insulin
Rate of respiration increases Rate of conversion glucose to glycogen increases Rate at which glucose is converted to fat and stored in adipose tissue increases
Compare and contrast the causes of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus.
Discuss the use of insulin produced by genetically modified bacteria, and the potential use of stem cells, to treat diabetes mellitus.
Type I diabetes Insulin-dependent diabetes or juvenile onset diabetes Beta cells do not make insulin Type II diabetes Non-insulin dependent diabetes Insulin is produced, but target cells do not respond to it adequately
Hyperglycaemia High blood glucose levels Associated with ketoacidosis Hypoglycaemia Low blood glucose levels
Type 1 Insulin dependent diabetes Viral infection Autoimmune response ? Genetic?
Type 2 non-insulin dependent diabetes Obesity Genetic link – family history A diet high in sugars Asian or afro-Caribbean origin Apple –shaped BMI > 27
There is no cure Type 1 Patients monitor blood glucose levels, take insulin injections Most common form of insulin is now GM insulin Type II Well-controlled diet / weight loss diet
Stem Cell An undifferentiated cell capable of cell division and forming specialised cells Transplant stem cells into a pancreas that has no functioning beta cells Persuade these cells to form new beta cells that can secrete insulin.
Use stem cells to produce white blood cells that do not attack the beta cells in the pancreas
Outline the hormonal and nervous mechanisms involved in the control of heart rate in humans.
Beating of the heart is myogenic Each contraction is initiate by the sino-
atrial node
Information can be transferred through the body and to the SAN by nerves and hormones to increase the pace set by the SAN.
SAN receives nerve impulses along two nerves Vagus nerve (parasympathetic nerve) ▪ Slows down the rate of the SAN Sympathetic nerve ▪ Speeds up heart rate Both these nerves arise from the cardiac centre in the brain
Adrenaline speeds up the rate of the SAN, increasing heart rate.