An accelerated revision resource 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 Oxygen and glucose Caron dioxide and urea Glucose and other nutrients

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 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

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 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

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 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

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

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

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 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

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)

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 Same as outside Concentrated outside Dilute outside Animal Cells Plant Cells (Why don’t they burst?)

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

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