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B4 revision
Homeostasis
An accelerated revision resource
A.Blackford
WARNING
This PowerPoint is not a
substitute for active
revision using notes, the
workbook and revision
guide.
You also need to do
plenty of past papers to
get exam practice.
Good luck!
What is Homeostasis?
• Homeostasis is keeping the
conditions inside your body constant
• In reality this means maintaining
these features within a narrow range
• Examples are body temperature,
water and salt, nutrients like glucose,
oxygen and removing waste.
Why is this important?
• Remember MRS. GREN?
• Cells need to be looked
after to work well!
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
Feedback Controls the Systems
• Incubator example
• There is an OPTIMUM (best)
temperature.
• If the temperature gets too high it must
be reduced.
• If the temperature gets too low it must
be increased
• This is NEGATIVE FEEDBACK
• Two systems needed with opposite
results; ANTAGONISTIC EFFECTORS
Incubator feedback control
• Key words; Receptor, Processing Centre,
Effector, Negative Feedback, Antagonistic
Effectors
Receptor
Temperature sensor
Rise in temperature
Processing Centre
Thermostat
Effector A
Heater OFF
Fall in temperature
Required Incubator temperature 370C
Fall in temperature
Receptor
Temperature sensor
Rise in temperature
Processing Centre
Thermostat
Effector B
Heater ON
Too Hot, Too Cold?
•
•
•
•
•
Human core temperature 370C
Hands /feet often cooler
Heat produced from respiration
Liver and muscle make loads of heat
Body temperature varies in the day
– Lower when we sleep
– Higher when we are awake, eat or
exercise
Just Right (1)!
• The HYPOTHALAMUS the processing
centre for body temp, water balance.
Sleep ++
• The cerebral hemispheres are where
we can make a conscious decision to
get warmer or cooler
Cerebral hemispheres
Hypothalamus
Just Right (2)!
• Temperature receptor
nerves in the skin are the
receptors
• The hypothalamus is the
processing centre
• The sweat glands, blood
capillaries and hair erector
muscles are the effectors.
When we shiver the muscles
are effectors as well
Temperature control
• Key words; Receptor, Processing Centre,
Effector, Negative Feedback, Antagonistic
Effectors
Receptor
Nerves in skin
Rise in temperature
Processing Centre
Hypothalamus
Effector A
Vasodilatation/sweat
Fall in temperature
Required body temperature 370C
Fall in temperature
Receptor
Nerves in skin
Rise in temperature
Processing Centre
Hypothalamus
Effector B
Vasoconstriction
Cooling Down When its Hot
• The body must LOSE energy
– Sweating; evaporation uses energy
– Vasodilation; more blood goes to the
surface of the skin, we look red and
energy is lost to the environment. You
can draw a feedback diagram for this.
– Fans, cool drinks, swimming or shade
can all help (remember the cerebral
hemispheres?)
Heating Up When Cold
• Our body must RETAIN heat
– Reduce sweating
– Vasoconstriction; less blood flows to the
surface so less energy is lost
– Erector muscles make our hair stand up to
trap an insulating layer of air (works better
for animals!)
– Also drink warm liquids, put on more clothes
etc
• We can also produce more energy to heat
us up by SHIVERING
Dangerously Hot
• Heat Stroke
– 420C
– hot dry skin (sweating has stopped)
– Rapid Pulse (dehydration, stress, increased
metabolic rate)
– dizziness and confusion
– Nerve cell damage to the brain
• Treatment
•
•
•
•
Sponge with water
Wrap in wet towel
Use a fan
Put ice into armpits and groin
Dangerously Cold
• Hypothermia
– The old and very young are most at risk
– Below 350C
Shivering , confusion, drowsiness,
slurred speech loss of
coordination, poor
judgement
– 300C
Coma
– 280C
breathing stops
• Treatment
–
–
–
–
–
Insulate the body esp head, neck armpits and groin
Handle gently to reduce blood flow to extremities
Use warm towels
Give warm drinks
DO NOT give alcohol, food or hot water bottles
Keeping our Water Balanced!
• We need to maintain our internal
liquids at a steady concentration. This
means balancing our water gain with
our water loss.
Outputs
Inputs
Water in food
Water in drink
Water from respiration
Exhaled air
Sweat
Urine
Faeces
We need to drink about 1.5 litres of water a day
Sweating a lot or drinking too little = small volumes dark yellow urine
In the cold or drinking a lot = lots of pale yellow urine
How the Kidneys Work
• Kidneys are made up of millions of
nephrons. These do the business of
cleaning our blood and regulating our
water content.
–
–
–
–
–
Blood high pressure filtered
Small molecules into capsule
Useful moles reabsorbed
Water controlled by ADH
Urea and other waste into bladder
down the collecting duct
Our Water Balance
• Kidneys regulate salt and water
• Caffeine and alcohol makes us produce
lots of dilute urine
• Ecstasy reduces the amount of urine
• ADH is a hormone and controls how much
water is absorbed back into the blood
– More ADH;
• more water reabsorbed = a little conc urine
– Less ADH;
• less water reabsorbed = lots of dilute urine
What are Enzymes?
• Enzymes are proteins produced by
living cells
• They are biological catalysts
• They (usually) increase the rate of
chemical reactions in a cell
• Most work best at 370C (optimum
temperature)
• They each have an optimum pH
How Enzymes Work 1
• Enzymes have a 3D shape
• A particular area is called the ACTIVE
SITE (a 3D hole)
• The SUBSTRATE fits into this (Lock and
Key)
• There is a change in shape of the enzyme
and PRODUCTS are produced
• Enzymes emerge unchanged from the
process ready to work again
How Enzymes Work 2
The reverse
is also true.
Two
substrate
molecules
can be linked
by an
enzyme
This is a 3D diagram of our old
friend catalase. Notice that is
made up of a ‘ribbon’ of amino
acids joined together. (B5
protein synthesis)
Temperature and Enzymes
Optimum temperature
enzyme stable maximum
rate of reaction
Higher
temperature, more
kinetic energy rate
increasing
Low energy, less
collisions, less
energetic, low
rate of reaction
Heat denaturing
enzyme. Protein
irreversibly damaged
rate slows
Enzyme denatured
active site
irreversibly damaged
no substrate can
enter NO reaction
pH and Enzymes
This enzyme has an
optimum pH of 8
A pH lower than
the optimum causes
the proteins in the
enzymes to
denature
A higher pH also
causes the proteins in
the enzymes to
denature and the
enzyme to stop workin
Pepsin in the stomach has an optimum pH of 2 (digests proteins)
Trypsin in the small intestine has an optimum pH of 8 (digests protein)
Salivary amylase has an optimum pH of around 7 (digests cooked starch)
Diffusion
• Random movement of molecules from
an area of HIGH concentration to an
area of LOW concentration until
evenly distributed
Potassium
permanganate
diffusing in
water
Changing the Rate of Diffusion
• Remember diffusion is a PASSIVE
process, it doesn’t need energy.
• Temperature changes the kinetic energy
of the molecules (hotter – they move
faster and collide harder)
• Concentration more molecules move in any
particular direction
• Small molecules diffuse faster than large
ones
Osmosis
• The diffusion of water
• Always takes place through a partially
permeable membrane
• Concentrated solutions have relatively
less water than dilute ones
• Water always moves from HIGH water to
LOW water i.e from DILUTE to
CONCENTRATED
• Also a PASSIVE process
More on Osmosis
• Can you explain what is going on in
this diagram?
Partially permeable
membrane small molecules
(like water) go through
larger ones do not
Water molecule
Sugar molecule
Even More on Osmosis
Compared to
cell contents
Animal Cells
Plant Cells
(Why don’t
they burst?)
Dilute outside
Same as outside
Concentrated
outside
Active Transport
• This needs ENERGY from
respiration in the form
of ATP
• Molecules move from a
LOW concentration to a
HIGH concentration
• Special carrier proteins
in the cell membrane are
responsible
Inside the
cell
Energy
Outside
the cell
ATP
Diffusion, Osmosis and Active
Transport
Diffusion
Oxygen into the
lungs
Osmosis
Moving water into
and out of cells
Active
Transport
The last bit of
glucose from the
gut into the blood
Carbon dioxide and Water into
Potassium into
other waste out of freshwater animals nerve cells
cells