B4 – Homeostasis

Overview of Topic• Diffusion & Active transport• Osmosis• Enzymes & optimum temperature• Control and Feedback systems• Homeostasis and temperature• What happens if you get too hot or too

cold?• Homeostasis and water balance• Hormones and water balance• Kidneys

Objectives• Explain how diffusion and active

transport work

Why does the colour of concentrated fruit drink change when it is added to water?

Why can you smell cooked food from a distance?

Smells and liquids spreading out

Why can you smell perfume or aftershave

when someone walks past you?

Diffusion• Diffusion is the net movement of

particles from a region of high concentration to a region of low concentration (concentration gradient).

• Only happens in gases or a substance in solution.

• It occurs because the particles move around and bump into each other and begin to spread out.

Changing concentrations

Molecules diffuse until they are evenly spaced apart and equilibrium is reached.

During diffusion molecules move from an area of high concentration to an area of low concentration often through a partially permeable membrane. Diffusion is a

passive process which means that no energy is needed.

highconcentration

lowconcentration

Concentration Gradient• The difference between the

concentration in each area is called the concentration gradient.

• The bigger the concentration gradient the faster the rate of diffusion will occur.

WHAT ELSE DO YOU THINK WOULD AFFECT THE RATE OF DIFFUSION?

Net Movement• At lower concentration gradients the

rate appears slower because particles from the other side may be moving too.

• Because particles may move from either side we must consider the net movement of particles.

• Net movement = particles moving in -

particles moving out

Diffusion

Why is diffusion so important?

Diffusion occurs in the organ systems that control your breathing, circulation, digestion and other life processes.

Diffusion is an essential process that is going on inside your body right now and keeping you alive!

Active Transport• Active transport is the opposite to

diffusion.• Its when particles move from a region

of low concentration to a region of high concentration.

• It requires energy to do this as it is going against the concentration gradient. high concentration

low concentration

diffusion active transport

What is active transport?Substances can move passively in and out of cells by diffusion until the concentration on both sides of the cell membrane reaches an equilibrium. Once they have reached equilibrium they will not appear to move anymore. Substances can continue to move in and out of a cell using a process called active transport.During active transport, protein carriers in the cell membrane ‘pick up’ particles and move them against the concentration gradient. As the name suggests, active transport requires energy from the cell, which is made available by respiration.

Questions• What is diffusion?• What is active transport?• What is the difference between

diffusion and active transport?• What is a partially permeable

membrane?• Why does oxygen diffuse into the blood

from the lungs?• Why does food diffuse into the blood

from the intestines?

Objectives• Explain how osmosis works

What is osmosis?Osmosis is a special type of diffusion. Diffusion involves gas or dissolved molecules, but osmosis only involves the movement of water molecules.

Osmosis occurs across a semi-permeable membrane which has tiny holes in it. These holes are small enough for water molecules to pass through but larger molecules cannot pass through.

watermolecule

What happens during osmosis?

Osmosis is the movement of water molecules from a region of high water concentration (dilute sol’n) to a region of low water concentration (conc sol’n) across a semi-permeable membrane.

watermolecule

semipermeable membrane

osmosis

Dilute vs. concentratedDuring osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions

Dilute solutions have a high concentration of water molecules.

Concentrated solutions have a low concentration of water molecules.

.

pure water dilute solution concentrated solution

Osmosis and animal cellsAnimal cells do not have a cell wall. This means they respond differently than plant cells to the gain and loss of water.

In concentrated solutions, water moves out from the cell from the cytoplasm, and causes the cells to shrivel and shrink.

In dilute solutions, water moves into the cell causing the cell to swell up and burst. This is called lysis.

Osmosis practical

Objectives• Describe what an enzyme is and

what conditions they work best in

What are enzymes?• Enzymes are proteins. They are biological catalysts – they speed up the chemical reactions that take place inside all cells, but without being used up in the process.

• There are many thousands of different types of enzyme, and each one catalyses (speeds up) a different reaction.

• They are specific to each reaction due to their ‘lock and key’ structure.

The ‘Lock and Key’ model• Each enzyme binds to a

specific molecule called the reactant or substrate.

• The part of the enzyme to which the reactant binds is called the active site. It is a very specific shape and the most important part of the enzyme.

• Only the substrate that matches the active site can bind to the enzyme. This is why we call it the lock and key model.

What happens at the active site?

enzyme

substrate+

enzyme-substrate complex

↔

products

enzyme +

↔

+ ↔ ↔ +

Lock and Key Model

Lock and Key Model

Why do enzymes speed up reactions?

Enzymes speed up reactions by lowering the activation energy (Ea) of a reaction. The activation

energy is the energy needed to start a reaction. Different reactions have different activation energies.

reaction (time)

ener

gy (

kJ)

Ea with enzyme

Ea without enzyme

How else can we speed up reactions?

Another way to speed up chemical

reactions is to increase the

temperature. If the temperature

gets too high though, the enzyme will

stop working.Human body Optimum Temp = 37°C

Factors affecting enzymesEnzymes work at an optimum temperature and

pH.If the temperature and pH changes from an

enzyme’s optimum level, the shape of the enzyme irreversibly changes.

This affects the shape of the active site and means that the enzyme will no longer work. When this

happens we call the enzyme denatured.

normal denatured

heat

pH

Enzyme Questions1. What are enzymes also known as?2. What do enzymes do to biological

reactions?3. What do we call the special shape on an

enzyme molecule?4. What are enzymes made of?5. What is created when an enzyme and

substrate combine together?6. What is lost when an enzyme is denatured?7. Write down two factors that can cause

denaturing.

Enzyme Practical• Put 5cm starch solution and 1cm

amylase (enzyme) in a boiling tube• Repeat this for 5 boiling tubes• Place each boiling tube in a different

condition and leave for 15 minutes• Conditions are:• Ice (0°C), Room temp (20°C), 40°C,

60°C and 80°C.CAUTION – VERY HOT WATER!!

Enzyme Practical• After 15 minutes remove the test tube

from the water bath and place in a test tube rack.

• Then add a few drops of iodine to each solution and observe the reaction.

• Record the results in a table.• See if you can draw any conclusions

about the temperature amylase likes to work at.

ResultsTemperatur

e

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6

0

20

40

60

80

Starter Activity1. List your senses

2. Tick which ones you used coming into the room

3. How would you tell the temperature of a cup of water without a thermometer?

Objectives• Describe how a control and feedback

system work

How does this greenhouse maintain its temperature?

• If its too cold...• A receptor detects the

temperature, which sends a message to a processing centre (computer), which triggers a response in the effector, which in this case turns heaters on

• And if its too hot... A receptor detects the temperature, which sends a message to a processing centre (computer), which triggers a response in the effector, which in this case opens ventilation flaps to allow cooling.

The same thing happens in the human bodyRECEPTORS in the body detect a change inside or outside of the body

CENTRAL NERVOUS SYSTEM (CNS) co-ordinates the body’s response, made up of brain and spinal cord

EFFECTORS cause a response by moving part of the body or secreting a hormone

RECEPTORIn your ears

EFFECTORMuscles contract so you turn to look at them

(CNS)STIMULUSFriend shouts you

STIMULUS is the change your body detects

Example...

Write a control and feedback flow diagram for each of these

situations• You touch a hot pan on a cooker• You prick your finger on something

sharp• Your friends shouts your name and

you turn round to look at them

The central nervous system (CNS) is made up of the

brain and

spinal cord.

What is the central nervous system?

cerebellum

cerebral hemisphere

spinal cord

Reflexes are fast, automatic protective biological control systems that link a stimulus to a response. Reflex reactions happen without you having to think about them – they are involuntary. This is because the central nervous system (CNS) sends electrical signals to the muscles before the brain can pick up the message.Many reflexes such as sneezing and focusing your eyes occur naturally, but other reflexes can be learned, i.e. conditioned responses.

What are reflexes?

What types of common reflexes do you know?

What are neurones? Neurones are specialised cells that conduct electrical impulses through the body.A nerve is a bundle of many nerve fibres enclosed within a protective sheath. Nerve fibres are the long axons of neurones together with any associated tissues.

nerve fibre

nerve

Definitions• Stimulus – Changes that receptor

cells detect.• Receptors – Cells that detect changes

inside or outside the body.• Sense organs – organs that contain

receptor cells.• Effectors – Organs in the body that

cause a response. They can be muscles or glands.

Interpreting signalsHow can you find your reaction time?

1. Extend your arm over the edge of a table and have a partner hold a ruler between your fingers at the 0 cm mark.

2. The partner drops the ruler – catch it between your fingers and thumb as quickly as possible.

3. Repeat the test 10 times, recording the results and calculate the mean (average) distance. Then convert the distance into a reaction time.

Converting distance to Reaction time

Distance on ruler Time• 5 cm 0.10 sec (100 ms)

• 10 cm 0.14 sec (140 ms)• 15 cm 0.17 sec (170 ms)• 20 cm 0.20 sec (200 ms)• 25.5 cm 0.23 sec (230 ms)• 30.5 cm 0.25 sec (250 ms)• 43 cm 0.30 sec (300 ms)• 61 cm 0.35 sec (350 ms)• 79 cm 0.40 sec (400 ms)• 99 cm 0.45 sec (450 ms)

Receptor detects change Stimuli

Information is sent as an

electrical signals called impulses

Impulse travels along nerve cells

called sensory neurone.

The brain or spinal cord co-ordinate a

response

Impulses send a message

along a motor neurone

to part of the body called an effector organ e.g. muscle or

gland Response

Receptor detects change

StimuliInformation is

sent as an electrical signals called impulses

Impulse travels along nerve cells

called sensory neurone.

The brain or spinal cord co-ordinate a

response

Impulses send a message

along a motor neurone

to part of the body called an effector organ e.g. muscle or

gland

Response

Saving energy?Sayid has decided to save energy by staying in bed all

day. How much of his energy do you think this will save? Surprisingly

the answer is only

about 30%.The other 70% keeps his body temperature at 37 °C, and

the solutions around his cells at just the right concentration. The body uses so much energy, even during sleep, because it must maintain a constant

internal environment.

Objectives• Explain how your body regulates

temperature

Homeostasis• The way our body keeps its internal

conditions constant is called Homeostasis.

• We have many different feedback systems to control the conditions of our body such as; temperature, water levels, blood sugar etc.

• We are constantly making and losing heat, and temperature levels have to be maintained at 37°C for our body to work properly.

Inside our body• The inside of our head and torso is known as

our core as it contains our vital organs such as brain, heart, lungs.

• Inside the core is where our body is the warmest because this is where most of the heat from respiration is produced.

• This heat is transferred to our arms and legs through our blood to keep the warm too.

• They often feel cold because they don’t make much heat themselves and lose heat easily because they have such a large surface area.

Finding the right balanceCore temperature is maintained by balancing heat gain and heat loss.

How can heat be gained?

How can heat be lost?

movement and exercise shivering

vasoconstrictionwearing extra clothing.

sweating vasodilation removing extra

clothing.

How is temperature controlled?

Body temperature is monitored and controlled by temperature receptors in the skin and brain.

These receptors detect changes in the temperature of blood flowing through those areas.The part of the brain that detects changes is called the hypothalamus.The skin has temperature receptors in its nerves.If body temperature changes from 37°C, the

hypothalamus and skin receptors send out electrical signals that trigger actions to change the temperature

back to 37°C

Body Temperature

Effectors (muscles and sweat glands) carry out the response

Temperature detectors in the skin detect the external temperature

Temperature detectors in the brain detect the blood temperature

The brain processes this information and coordinates a response

Diagram of skin

Keeping Warm• Your muscles cause you to

shiver (rapid contraction and relaxation of the muscles) to create heat.

• Goosebumps are caused by the tiny muscles at the base of body hairs pulling the hairs erect. The upright hairs trap an insulating layer of air, which helps reduce heat loss.

Keeping Warm• Blood vessels in the skin get

narrower. This is called vasoconstriction. (this is why you look pale)

• This is caused by contraction of the muscular wall of the blood vessels. This reduces the volume of blood flowing near the skin surface, and reduces the amount of heat lost from the body.

• This is when the blood vessels sink into the body to keep the blood warm.

Keeping Cool• You sweat and heat evaporates from

your sweat.• Hairs lie flat so air is not trapped.• Blood vessels in the skin get wider this

is called vasodilation. (this is why you go red)• This allows a larger volume of blood to flow near the skin surface, transferring heat to the environment.

Maintaining Temperature

Complete the TableIf your too hot you can do this to cool

down

If your too cold you can do this to warm

up

Diagram of skin

Objectives• Describe what happens if your body

gets too hot or too cold

What happens if your body is not 37°C

• If the temperature falls too low, reactions become too slow for cells to

survive.• If the temperature gets too high, the

body’s enzymes are at risk of denaturing.

If you get too hot - Heatstroke• If your temperature goes over 40°C

you can get heat stroke.• You will be dehydrated, dizzy, confused and

sick. You will look sweaty and pale, even though your skin is hot and dry and your not sweating much because your body is trying to conserve water.

• It happens easily to people who are ill (sickness and diarrhoea), people who have taken ecstasy and people who are not used to the heat.

If you get too hot - Heatstroke• To treat a person with heatstroke it is

important to cool them down as quickly as you can.

• Put them in a bath of cold water. If you cant do that cover them in a wet sheet and keep the sheet wet.

• Give them water to drink.• They must be seen by a doctor as

soon as possible.

If you get too cold - Hypothermia

• If your temperature goes below 35°C you have hypothermia. If it drops lower than 30°C you will pass out and be at risk of death.

• You will be shivering, confused, drowsy, have slurred speech, lose coordination and have cold, dry, pale skin.

• It doesn’t just happen in snowy places it can also happen in water, in wind and rain and even indoors! Elderly people are most at risk if their houses are cold and they don’t move around a lot.

If you get too cold - Frostbite• Your arms and legs don’t

generate as much heat as the core of your body. They also lose heat easier.

• When its cold the blood flow is less to those areas due to the body concentrating blood flow to vital organs, as well as due to vasoconstriction.

• This means they are more at risk of getting too cold, and can develop frostbite.

If you get too cold - Hypothermia

• To treat a person with hypothermia it is important to warm them up as quickly as you can.

• This can be done by taking them to a warm place and wrapping them n blankets and warm clothes. You can also give them something warm to drink.

• If they are wearing wet clothes, remove them and give them warm, dry clothes.

Task• Design an advice leaflet giving advice

to people who are off on a trekking expedition in the desert.

• Remember deserts are really hot during the day and really cold during

the night, so you will need to give advice on what to do to stay at the right temperature, and what to do if

you get too hot or cold.

Objectives• Explain how your body regulates

water balance

Why is water important?The human body is about 60-70% water.

Water is produced by the body during respiration, and absorbed from food and drink.

Water is lost from the body in exhaled air (breathing), sweat, urine and faeces.

Water molecules constantly move in and out of cells, and are essential for all life processes. Dehydration is the loss of too much water from the body and it damages cells.

How are water levels controlled?

Water levels are monitored by the receptors in the hypothalamus.Receptors inside the hypothalamus detect

changes in the concentration of salt

in the blood.

The higher the salt level the lower the water level. That’s why salty food makes you thirsty.

Dehydration and its causesJust a 1% decrease in body weight due to water loss is enough to cause mild dehydration. Mild dehydration can cause dizziness, a dry mouth and concentrated urine. Severe dehydration can cause death.

What causes dehydration?heavy sweatinglow water intakeeating salty foodbreathing dry aircaffeine and alcoholdiarrhoea.

Controlling water levels

Normal blood levelsDrinking,

Eating & respiration make you have more

water in your blood

Sweating, Excreting & breathing make you have less

water in your blood

To get back to normal blood levels you make lots of urine

and lose water by evaporation through sweat

To get back to normal blood levels you don’t make much

urine and need to take in more water through food and drink

Questions1. How do we gain water?2. How do we lose water?3. What do we do if our water levels are

too high?4. What do we do if our water levels are

too low?5. Which organ checks what our water

levels are?6. What are the symptoms of

dehydration?

Objectives• Explain how hormones regulate

water balance

How are water levels controlled?

Water levels are monitored by the receptors in the hypothalamus.

These receptors detect changes in the concentration of salt

in the blood.

Depending on the concentration, the hypothalamus instructs the pituitary gland to

secrete more or less of the hormone ADH (anti-diuretic hormone)

ADH and water regulation• Osmoreceptors in the hypothalamus detect

the low levels of water, so the hypothalamus sends an impulse to the pituitary gland which releases ADH into the bloodstream.

• ADH causes more water to be reabsorbed in the kidneys by making the wall of the collecting duct more permeable to water.

• This means less, more concentrated urine is made. It also increases thirst levels in the body, encouraging us to drink more.So, when ADH is present more water is

reabsorbed and less is excreted.

Not having enough waterLow blood water level causes a

high salt concentration

Receptors in the hypothalamus detect the high salt content

More ADH is secreted into the blood

The kidney becomes more permeable to water so more is

reabsorbed.The bladder fills with a small

quantity of urine

Normal blood water level is achieved.

Having too much waterHigh blood water level causes a

low salt concentration

Receptors in the hypothalamus detect the low salt content

Less ADH is secreted into the blood

The kidney becomes less permeable to water so more is

absorbed.The bladder fills with a large

quantity of urine

Normal blood water level is achieved.

Water regulation by ADHToo much water Too little water

Low blood water level causes a high salt

concentrationReceptors in the hypothalamus detect the

high salt contentMore ADH is secreted into the blood

The kidney becomes more permeable to water so more

is reabsorbed.The bladder fills with a small quantity of urine

Normal blood water level is achieved.

High blood water level causes a low salt concentrationReceptors in the

hypothalamus detect the low salt contentLess ADH is secreted into

the bloodThe kidney becomes less permeable to water so

more is absorbed.The bladder fills with a large quantity of urine

Normal blood water level is achieved.

Drugs and ADHSome drugs can affect the production of

ADH.• Alcohol acts as a diuretic by reducing the

amount of ADH secreted.• This results in increased amounts of urine

produced, which in turn can result in dehydration.

• Ecstasy is the opposite, it increases the amount of ADH secreted.

• This results in reduced amounts of urine produced, so the body is not releasing any water, yet users often drink lots.

Mark Scheme

Objectives• Describe what job the kidneys do and

explain how they work

The Kidneys• The blood contains many small

molecules such as water, glucose, salt and urea.

• The kidneys filter the molecules that are not needed out of the blood.

• Once they have done that they reabsorb any molecules that are needed back into the blood.

• This happens in the kidney tubules.

Amino Acids• Amino acids are used for growth and

repair. They come from proteins which we eat.

• They cannot be stored if they are not used though, and have to be broken down.

• The liver breaks them down into a substance called urea which is filtered out by the kidneys.

Kidneys

Blood in

Blood outUreter (tube that takes urine containing the

waste down to bladder)

Kidneys are responsible for controlling water, glucose, salt and urea content.

Inside the tubules

KidneysKidneys work in 3 stages:

1. ULTRAFILTRATION - Lots of water and products of digestion are

squeezed out of the blood and into tubules under pressure.

3. WASTE – excess water, excess ions and any urea are now removed

through the ureter

2. SELECTIVE REABSORPTION – the blood takes back the things it

wants (e.g. glucose and ions) even though this means going against a

concentration gradient.

Blood vessel

Tubule

Questions to answer1. Which part of the body monitors water

levels and how does it do it?2. How do we gain and lose water?3. How do we overcome not having

enough water?4. How do we over come having too

much water?5. How do the kidneys work?6. What effect do drugs and alcohol have

on water levels?

Objectives• Revise topic B4

Revision Brainstorm

Osmosis

Active

Transport

Diffusion

What do Enzymes

do?

What conditions

do Enzymes work best

in?

Responses

Can you write responses for each of these situations?

1. You knock an object off the table and go to pick it up

2. You have an itch on your head and scratch it

3. You feel warm so you take your jumper off

Stimulus

Receptor

Effector Response

CNS

Complete the revision diagram