1. An accelerated revision resource
B4 revision
Homeostasis
An accelerated revision resource
A.Blackford

2. 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!

3. 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.

4. Why is this important? Remember MRS. GREN?
Cells need to be looked after to work well!
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
Oxygen and glucose
Caron dioxide and urea
Glucose and other nutrients

5. 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

6. Incubator feedback control
Key words; Receptor, Processing Centre, Effector, Negative Feedback, Antagonistic Effectors
Receptor
Temperature sensor
Processing Centre
Thermostat
Effector A
Heater OFF
Rise in temperature
Fall in temperature
Required Incubator temperature 370C
Fall in temperature
Rise in temperature
Receptor
Temperature sensor
Processing Centre
Thermostat
Effector B
Heater ON

7. 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

8. 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

9. 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

10. Temperature control
Key words; Receptor, Processing Centre, Effector, Negative Feedback, Antagonistic Effectors
Receptor
Nerves in skin
Processing Centre
Hypothalamus
Effector A
Vasodilatation/sweat
Rise in temperature
Fall in temperature
Required body temperature 370C
Fall in temperature
Rise in temperature
Receptor
Nerves in skin
Processing Centre
Hypothalamus
Effector B
Vasoconstriction

11. 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?)

12. 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

13. Dangerously Hot Heat Stroke Treatment 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

14. Dangerously Cold Hypothermia Treatment
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

15. 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
Exhaled air
Sweat
Urine
Faeces
Inputs
Water in food
Water in drink
Water from respiration
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

16. 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

17. 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

18. 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

19. 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

20. 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)

21. Temperature and Enzymes
Optimum temperature enzyme stable maximum rate of reaction
Heat denaturing enzyme. Protein irreversibly damaged rate slows
Higher temperature, more kinetic energy rate increasing
Enzyme denatured active site irreversibly damaged no substrate can enter NO reaction
Low energy, less collisions, less energetic, low rate of reaction

22. pH and Enzymes This enzyme has an optimum pH of 8
A higher pH also causes the proteins in the enzymes to denature and the enzyme to stop workin
A pH lower than the optimum causes the proteins in the enzymes to denature
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)

23. 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

24. 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

25. 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

26. 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

27. Even More on Osmosis Compared to cell contents Animal Cells
Same as outside
Concentrated outside
Dilute outside
Animal Cells
Plant Cells
(Why don’t they burst?)

28. 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
ATP
Energy
Outside the cell

29. Diffusion, Osmosis and Active Transport
Oxygen into the lungs
Moving water into and out of cells
The last bit of glucose from the gut into the blood
Carbon dioxide and other waste out of cells
Water into freshwater animals
Potassium into nerve cells