unit 1 communication, homeostasis and energy. what effect does temperature change have on enzyme...
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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.
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 responseResponse
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
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
Optimum condition
Change away from optimum
Receptor detects change
Communication system informs effector
Effector reacts to reverse change
Return to optimum conditions
Control of room temperatureControl of body temperatureControl of blood glucose levelsControl of body water concentration
Optimum condition
Change away from optimum
Receptor detects change
Communication system informs effector
Effector reacts to increase change
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 10oC increase will double the rate of
reaction Above 50oC enzymes denature – rate of
reaction falls quicklyDeath
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.
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 35oC.
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 ectothermsExplain 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
Too hot Too cold
Sweat glands in skin
Secrete more sweat
Less sweat secreted
Lungs, mouth and nose
panting No panting
Hairs on skin Lie flat Raised
arterioles Vasodilation vasoconstriction
Liver cells Reduce rate of metabolism
Increase rate of metabolism
Skeletal muscles
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
TOO HOT
-Reduce metabolism
-Vasodilation
- increased sweating
TOO COLD
-Shivering
-Increased metabolism
-Vasoconstriction
-Reduced sweating
-Skin hairs erected
Skin temperature External
Core Temperature
HYPOTHALAMUS
Thermoregulatory centre
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 skinA lot of food must be used to replace
the heat lostElephant is large with a small surface
area to volume ratioLoses 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 impulseStimulus
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 Na2+ out of cell than K+ into cell.
Result is that inside cell is more negatively charged than outside the cell Cell membrane is polarised.
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 negativeThis is depolarisation
Generator potential Small depolarisation caused by sodium
ions entering the cellAction potential
Depolarisation of the cell membrane Inside is more positive than the outside Potential difference +40mv
Threshold potential Potential difference across membrane of
-50mv
1. Membrane is polarised at rest (-60mv)
2. Sodium ion channels open3. Membrane depolarises (threshold
value -50mv)4. Voltage-gated sodium ion channels
open and many sodium ions flood in5. Potential difference across plasma
membrane reaches +40mv
6. Sodium ion channels close and potassium channels open
7. Potassium ions diffuse out of the cell, this is repolarisation
8. Hyperpolarisation = the potential difference overshoots slightly
9. Resting potential restored
Resting potential – K+ voltage-gated channels open, Na+ 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.
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 openSodium ions enter neurone at a point
further along the membraneAction potential moves along the
membrane
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
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
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
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.
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
1. An action potential arrives2. Calcium ion channels open3. Vesicles containing acetylcholine
move to the presynaptic membrane.
4. Vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft.
5. Acetylcholine diffuse across the synaptic cleft to the postsynaptic membrane
6. Acetylcholine binds to receptors in postsynaptic membrane
7. Sodium ion channels open – the membrane is depolarised and an action potential is produced.
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 unidirectionalAct as junctionsFilter out low level stimuliSummation
Amplification of low level signalsAcclimatisation
Prevent overstimulation and fatigueMemory 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
Endocrine cell
target cell
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
First Messenger
Second Messenger target of
second messenger inside the cell
4. Activation of a 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 pressureAdrenal 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/100cm3
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 cureType 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
Beating of the heart is myogenicEach 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