Unit 1Communication, 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.

SensitivityStimulus Internal communication

Plants Animals

ReceptorEffector

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 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

Whole bodyCell communicationSpecificRapidShort 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

Change away from optimum

Receptor detects change

Communication system informs effector

Effector reacts to reverse change

Return to optimum conditions

Structures required for pathway to work Sensory receptors Communication system Effector cells

Control of room temperatureControl of body temperatureControl of blood glucose levelsControl of body water concentration

Increases any change that is detected by receptors

Does not lead to homeostasis

Optimum condition

Change away from optimum

Receptor detects change

Communication system informs effector

Effector reacts to increase change

If core temperature drops too lowDilation 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 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.

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 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.

3 Na+ leave the cell2 K+ enter the cell

Potential difference is created across the membrane

1

3

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 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.

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 openSodium ions enter neurone at a point

further along the membraneAction 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 tableAnswer 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.

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.

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 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

Outline the hormonal and nervous mechanisms involved in the control of heart rate in humans.

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

Adrenaline speeds up the rate of the SAN, increasing heart rate.