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Biology by Mind Map: Biology

1. Microbiology

1.1. Growing Microbes

1.1.1. Microbiology is the study of micro-organisms, such as bacteria, viruses, fungi and protoctista, too small to be seen with the naked eye. They play a vital role in decay and the recycling of nutrient in the environment, as well as cause disease and be useful to people.

1.1.2. What do microbes need to grow? If you want to find out more, you need to culture them: Grow large numbers so you can see the colony as a whole. They need a culture medium containing carbohydrate as energy, as well as mineral ions and supplementary protein and vitamins are included. An Agar medium, which is a substance that dissolved and sets to form a jelly. Hot agar containing all neccessary nutrients is poured into a petri dish. It is cooled, and left before micro-organisms are added. Another way is as a broth in a culture flask. Warmth and oxygen need to be provided

1.1.3. Safety precautions in the lab There is always the risk that a mutation may take place, resulting in a new and dangerous pathogen. It may be contaminated by disease causing pathogens present in the air Pure strains of bacteria need to be kept free from other microorganisms.

1.2. Food production using yeast

1.2.1. One useful micro-organism is Yeast. They are single celled organisms, and has a nucleus, ctyoplasm and a membrane, surrounded by a cell wall. It mainly reproduces asexually- splitting in two to form new yeast cells.

1.2.2. With pleanty of oxygen, they respire aerobically, breaking down sugar to provide energy, produce water and CO2 as waste

1.2.3. Yeast can respire anaerobically, breaking down sugar to produce ethanol and CO2

1.2.4. The anaerobic respiration of yeast is called fermentation.

1.2.5. Yeast cells need aerobic respiration because it produces more energy than anaerobic. It allowes them to grow and reproduce. Once there are a large number of yeast cells, they can survive for a long time in low oxygen conditions. They'll break down sugar to form ethanol

1.2.6. We have used yeast to make bread and alchohol since human records bega. Yeast was used in bread 6000 years ago, and in wine 7000 years ago.

1.2.7. Making Alchoholic drinks When fruit falls to the ground and decays, wild yeasts break down the sugar to form ethanol and CO2. We use the same reaction in a controlled way to make beers and wine. Beer depends on a process called Malting. Barley grains are soaked in water and kept warm. Germination begins, and enzymes break down the startch in the barley into sugar. The sugary solution is extracted and used as an energy source for yeart. The Yeast and sugar mixture ferments to produce alcohol. Hops are added to give flavour. The beer clears and develops its flavour before being sold. Wine making uses natural sugar found in fruit as the energy source for year. The fruit is pressed, and mixed with yeast and water. The yeast respires anaerobiclaly until most of the sugar is used up. The wine is filtered to remove the yeast, and bottled. It is stored to mature before sold. Alcohol in large amounts is poisonous to yeast and people.

1.3. Food production using bacteria

1.3.1. People soon realised that female animal milk could be used as food for humans. One drawback in using milk is that it rapidly goes off, starts to smell and tastes disgusting.

1.3.2. Making Yoghurt Yoghurt is fermented whole/semi-skimmed/skimmed/soya milk, formed by the action of lactosse in the milk. A starter culture is added to warm milk, when bacteria grows, reproduces and ferments. Lactic acid is formed as the bacteria breaks down the lactose. This gives its sharp, tangy taste, and is known as lactic fermentation. The lactic acid causes the milk to clot and solidify into yoghurt.

1.3.3. Cheese Making Cheese depends on the reactions of bacterial with milk. These change the texture and taste, and preserve the milk. Some cheeses can survive for years without decay A starter culture of bacteria is added to warm milk. This is different to the yoghurt starter culture. The cheese-making bacteria converts lactose to lactic acid, but a lot more. The solid curds are much more sold than the yoghurt ones. Enzymes are added to increase the separation of the milk. When it has curdled, it can be seperated from the whey. The curds are used for cheese-making, and the whey as animal feed The curds are cut and mixed with salt and other bacterias, before being pressed and dryed out. The bacteria and mouls affect the development of the flavour and texture.

1.4. Large-scale microbe production

1.4.1. Fermenters In ideal conditions, bacterial can double every 20 minutes. This is rare. As the numbers of micro-organisms rise, conditons change. Food is used up, metabolism of all the micro-organisms causes the temperature to rise, and oxygen levels fall due to respiration CO2 waste can alter the pH of the culture. This causes the activity of the enzymes in the culture to be affected, and may stop growing or die. Waste products may build up and poison the culture. In Industrial fermentations, problems like tthese can develop rapidly When microbes are grown industrially, vessels called fermenters are used. These overcome the problems which stop a culture from growing well, by reacting to changes, and keeping the conditions stable. This means we can get the maximum yield. Industrial fermenters usually have: An oxygen supply to provide oxygen for respiration A stirrer to keep the microorganisms in suspension, maintaining even temperature and making sure the oxygen and food are evenly spread throughout the culture. Water cooled jacket that removes excess heat produced by respiring organisms. A rise in temperature used to heat the water is removed and replaced with cold water. Measuring instruments monitor factors such as pH and the temperature Mycoprotein production Mycoprotein means 'protein from fungus'. This grows and reproduces rapidly on a cheap sugar syrup in large fermenters. It needs aerobic conditions to grow successfully. Then, it doubles its mass every 5 hours. The fungal biomass is harvested and purified. It is drived and processed to make mycoprotein. It has a faint taste of mushrooms, but can be given a range of tastes and flavours to make it similar to many foods. It is a high-protein, low-fat meat subsitute. When mycoprotein was first developed people thought there was going to be a world food shortage. This was a way of making protein cheaply and efficientlly. Fungus based food continues. It is versitile, high in protein and fibre, low in fat and calories, and is used widely in the developed world

1.5. Antibiotic production

1.5.1. The discovery of penicillin Fleming was a researcher. Lreaving some plates where he was culturing bacteria, he noticed spots of mould growing, surrounded by clear areas of agar. The bacteria had been killed. Fleming found Penicillium natatum in his dishes. It was almost impossible to extract the substance with the equipment at the time. He managed a tiny amound, and used it to treat an infected wound. It was named penicillin, and was very difficult to extract, as well as unstable. During WW2 the need for a bacterial drug was urgent. Two researchers managed to extract enough penicillin from Fleming's mould. After successful animal trials, a London policement made an amazing recovery. Once the supply of penicillin rang out, the man died. Months of work produced enough penicillin to save the life of a boy dying of a bacterial infection. Chain and Florey turned to the American pharmaceutical industry for help in deloping a manufacturing process. Fleming's mould was incredibly difficult to grow in large culture. Penecillin grew relatively easily in deep tanks, and by 1935 we were producing enough penicillin to treat 7 million people.

1.5.2. Modern penicillin production We now use modern strains of Penicillium mould to give higher yields. We grow it in a sterilised medium, contraining sugar, amino acids, mineral salts and other nutrients. It is called 'corn steep liqor', and a waste product from the food industry We use huge 10000 dm fermeters that have strong paddles to keep stirring the broth, as it required lots of oxygren to thrive. We control the temperature by a cooling jacket The first 40 hours of fermentation the mould grows rapidly. After most of the nutrients have gone, the mould makers penicillin. There is a 40 hour laf period from the start of fermentation to start of production. We have to provide the food to allow lots of mould to grow, then limit the supplied to produce penicillin Over 140 hours broth is removed and small amounts of nutrients are added. This allows a maximum yield, which is then extracted from the broth. It purifies and is tunred into medicine.

1.6. Biogas

1.6.1. What is biogas? Biogas is a flammable mixture of gases formed when bacteria breaks down plants of waste productions. It is mainly methane, but the composition varies on the reactants and bacteria

1.6.2. Biogas generators Bacteria involved in biogas production work best at 30c, so tend to work best in hot countries. The reaction generates heat, and so if initiated with heat energy, and insulate the generator, they will work anywhere. Under ideal conditioons, 10kg of dung can produce 3m of biogas, suppling 3 hours of cooking, 3 hours of lighting or 24 hours of refridgeration.

1.6.3. Scaling up the process What is put into a generator storngly affects what comes out. Biogas units are widely used in China, where there are 7 million biogas units producing the same energy as 22 million tonnes of coal. Waste vegetables, animal dung and human waste are mainly used. These produce excellent fertiliser, but poor biogas In India, there are taboos against human waste, so only cattle and buffalo dung is used, producing high quality fas but less fertiliser There are different sizes and designs of biogas, and depend on local conditions. Many fermenters are sunk into the ground, providing good insulation. Others are built above ground, meaning less insulation, but easier and cheaper. Many countries are looking at using biogas generators on a larger scale. The waste material we produce from sugar factories, sewage farms and rubbish tips could produce biogas.

1.6.4. More Biofules Ethanol based fuels Sugar rich products are fermented anaerobically with yeast, the sugars broken down give ethanol and water. The ethanol can be extracted from the products of fermentation by distillation, and used as a fuel Ad's/Disad's of ethanol as a fuel. It is efficient and does not produce toxic gases when burnt. It is less polluting than concentional fuels, which produce CO, SO2 and NO. You can miz ethanol with petrol to create gasohol, something done increasingly in the USA and reduces pollution considerably. Ethanol is carbon neutral- there is no increase in CO2 in the atmosphere when burnt. The original plants removed CO2 during photosynthesis The biggest difficulty is that it takes a lot of plants to produce the ethanol. The use of ethanol has been limited to countries with enough space and a suitable climate Brazil was the trailblazer for ethanol - growing their own green petrol and slashing the money paid on oil imports. In the 80s 90% of cars produced had ethanol-powered engines. When oil prices dropped, they began to move back to petrol cars People are now interested in clean alternatives. In America, Gasohol (90% petrol, 10% ethanol) is increasing all the town. A lot of it is fermentaed and distilled from maize fromt the USA. Ethanol use has meant the USA needs to import ethanol from Brazil and the caribbean. They imported 160 million gallons of ethanol fuel in 2004 The main problem is finding it. The methods of ethanol production leave large amounts of unused cellulose from the plant material. To make ethanol production work financially in the long term, we need to find a way to use this cellulose. We might devlop biogas genertors which can break down the excess cellulose into methane, another useful fuel. GM bacteria or enzymes may be able to break down the cellulose in straw and ahay, and make it into yeast

2. Exchange of Materials

2.1. Active Transport

2.1.1. Diffusion: Along a concentration gradient, in the right direction to be useful to cells.

2.1.2. Osmosis: Depends on a concentration gradient of water and a partially permeable membrane. Only water moves in Osmosis

2.1.3. Active Transport: Where substances are moved against a concentration gradient, or across a partially permeable membrane

2.1.4. Active transport allows cells to move substances from an area of low concentration to high concentration. Substances moving against the concentration gradient As a result, cells can absorb ions fro very dilute solutions. It makes it possible for them to move substances like sugars and ions frome one place to another through cell membranes

2.1.5. It takes energy for the active transport system to carry a molecule across the membrane, and return to its original position That energy comes from cellular respiration. Scientists have shows than the rate of respiration and rate of active transport are linked

2.1.6. If a cell is making lots of energy, it can carry out lots of active transport. These cells includine root hair cells and gut-lining cells. Cells involved in a lot of active transport usually have lots of mitochondria

2.1.7. Active Transport is widely used in cells. There are some situations where it is particularly important Mineral ions in soil are usually very dilute. By using active transport, plants can absorb these mineral ions Glucose is always moved out of your gut and kidney tubules into your blood, against a large concentration gradient.

2.1.8. Some marine birds have a problem - they take in a lot of salt, but their kidneys cannot get rid of it all. Special salt glands enable sodium ions to move out of the body into the salt glands. They then produce a very strong salt solution. The sodium ions have to be moved against a very big concentration gradient

2.2. Echange of gases in the Lungs

2.2.1. Breathing System The body requires a constant supply of oxygen for cellular respiration Breathing brings oxygen into the body and removes CO2 from the cells The lungs are protected by a bony rib cage. They are seperated from the digesive organs by a disphragm. The job of the breathing system is to move air in and our of the lungs When you breathe in, the ribs move up and out, and the diaphragm flattens from its normal domed shape. This pulls air into your lungs. When you breathe out, the ribs move down and in, and the disaphragm returnes to its domed shape, forcing air out.

2.2.2. Exchange of gases in the lungs Specially adapted to make gas exchange more efficient. Made up of clusters of Alveoli Tiny air sacs with a large surface area, which is kept moist. This is important for effective diffusion of gases The Alveoli have a rich blood supply. This maintains a concentration gradient in both directions. Oxygen is removed into the blood and more CO2 is delivered to the lungs. Gas exchange takes place along te steepest concentration gradient possible; making it rapid and effective. The layer of cells between air in the lungs and blood in the capillaries is very thin. This lets diffusion take place along the shortest possible distance

2.3. Exchange in the gut

2.3.1. Absorption in the small intestine The molecules from food need to be made avaliable to body cells. In cells they provide food for respiration, and the building blocks of all tissues. For this to happen, they need to move from the inside of the small intestine into your bloodstream. This is done by diffusion and active transport Only when molecules are dissolved in water can diffusion take place When the digested food molecules are small enough, they pass freely through the walls of the small intestine into the blood vessels. They move because of the very high concentration of food molecules in the gut, to the lower concentration in the blood. The lining of the small intestine is folded into thousands of villi. These greatly increase the uptake of digested food by diffusion. Only a certain number of digested food molecules can diffuse over a given surface area of gut lining at any one time Increasing the surface area means there is more room for diffusion to take place The lining of the small intestine has an excellent blood supply.This carries away digested food molecules as soon as they have diffused. A steep concentration gradient is mainted all the time. This makes the diffusion as rapid and efficient as possible. Glucose and other dissolved food molecules are moved from the small intestine into the blood by active transport, against the concentration gradient.

2.3.2. Exchange of materials in other organisms Certain adaptations will be seen: A large surface area for diffusion A rich blood supply to remove the substances, maintaining a steep concentration gradient Moist surfasces for substances to dissolve A short distance between the two areas

2.4. Exchange of materials in other organisms

2.4.1. Gas Exchange in a fish Gills are made of many thin layers of tissue with a rich blood supply These gills are thin, and so there is only a short distance for the gases to diffuse across. They're always moist as in water In bony fish, the gills are contained in a special cavity. Water is pumped over them to maintain a concentration gradient. Fish have to keep swimming all the time to keep water moving over their gills Gills don't work in air. There isnt a big enough surface area to get the oxygen to survive

2.4.2. Tadpoles and frogs Frogs are amphibians and have a strange life history. Eggs hatch into tadpoles, which spend all their time in water. Young tadpoles have frilly external gills with a large surface area and a rich blood supply. They get all oxygen through diffusion from water. Carbon dioxide diffuses out along a concentration gradient When the tadpoles turn into frogs, they can breathe in and out of water The external gills disappear, and are reabsorbed into the body of the developing frog. This is metamorphosis An adult frog has moist skin and a rich blood supply, and so mostly takes place through the skin If the frog gets hot or active on land, it has a pair of very simple lungs. These increase the surface area avaliable for gas exchange.

2.4.3. Respiratory system in insects Insects have an internal respiratory system which supplies oxygen directly to their cells and removes CO2 There are spiracles along the side of an insect. They open when the insect needs oxygen, and close when they don't. This prevents water loss, like the guard cells of plants The spiracles lead into a system of tubes which run into tissue. Most gas exhcnage takes place in tracheoles: tiny tubes, permeable to gases. They are very moist, and air is pumped in and out of them to maintain a concentration gradient. There is no blood supply, but the tracheoles have a large surface area and come into close contact with indivudual cells in the body of the insect.

2.5. Exchange in plants

2.5.1. Gas exchange in plants They get the CO2 by diffusion through their leaves. The flattened shape increases the Surface area for diffusion. Most plants have thin leaves, making the distance for CO2 to diffuse from the outside air to the photosynthesising cells short Plants rely heavily on diffusion to gset the CO2 needed for photosynthesis. Osmosis takes water from the soil, and active transport to obtain minerals from the soil The air spaces in the leaf allows carbon dioxide to come into contact with lots of cells. Leaf cells constantly lose water by evapouration. Leaf cells do not need CO2 all the time. When it is dark, they are not photosynthesising. Leaves are adapted to allow CO2 in only when needed. They are covered with a waxy cuticle. All over the leaf surface there are small openings known as stomata. They can be opened when the plant needs air. They can be closed the rest of the time to control the loss of water. The closing and opening of stomata is controllbed by guard cells

2.5.2. Uptake of water and mineral ions in plants Roots are adapted to enable plants to take water and minerals from the soil as efficiently as possible. Water is vital for plants. It is needed to maintain the shape of the cells, and photosynthesis. Minerals are needed to make proteins and other chemicals. Roots are thin, divided tubes with a large surface area. The cells on the outside of the roots have adaptions. They increase the Surface area for the uptake of substances. Root hair cells have tiny projections out from the cells which push out between the soil particles. The membranes of the root hair cells increase the surface area for diffusioon and osmosis. Water only has a short distance to move across the root to the xylem, where it is moved up and around the plant. Plant roots are adapted to take in mineral ions using active transport. They have pleanty of mitochondria for energy, a large surface area and short pathways for movement of water

2.6. Transpiration

2.6.1. Water Loss from leaves Plants have holes called stomata on the surfaces of their leaves. These open to allow CO2 into the plant for photosynthesis. All the time they're open, plants lose wated vapour from the surface of their leaves. This is known as Transpiration Stomata can be opened and closed by the guard cells around them. Losing water is a side effect of opening them As water evapourated from the surface, water is pulled through the xylem to take its place. This constant movement is known as the transpiration stream. It is driven by the evapouration of water from leaves.

2.6.2. Effect of the environment on transpiration Conditions which increase the rate of photosynthesis increase the rate of transpiration. Increased rated of photosynthesis mean more water is lost by evapouration through the open stomata. Conditions which increase the rate of evapouration of water when the stomata are open will make transpiration quicker. Hot, dry, windy conditions increase the rate of transpiration.

2.6.3. Controlling water loss Most leaves have a waxy waterproof layer to prevent uncontrolled water loss. This may be thick and shiny. This means they are not exposed to the Sun, and reduces the time they are open If a plant begins to lose water faster than it is replaced, it may wilt. Wilting is a protection against water loss. The leaves collapse so the surface area is greatly reduced. The stomata close, which stops photosynthesis and risk overheating. This prevents most water loss and further water loss.

3. Transporting Substances around the body

3.1. The Circulatory System

3.1.1. A Double Circulation The body has two transport systems One carried blood from the heart to the lungs, and back. This exchanges oxygen and CO2 with the air. The other carries blood all around the rest of the body and back again A double circulation is very important in warm-blooded, active animals like ourselves. It makes our circulatory system efficient. Fully oxygenated blood returns to the heart from the lungs and can be sent to the whole body. This means more areas of the body can recieve fully oxygented blood quickly.

3.1.2. Blood vessels Arteries Carry blood away from the heart to organs. Uusally oxygenated blood, and so bright red. Stretch as the blood is forced through them. You can feel this pulse near the surface. Thick walls Thick layer of muscle and elastic fibres Veins Carry blood torwards the heart; usually low in oxygen and so deep purple-red colour. No pulse, but have valves to prevent back flow. Relatively thin walls Often have valves Capillaries Huge network of capillaries between the artieries and veins. No cell in the body is more than 0.05mm away from a capillary. Have very thin walls, so the substances needed by the body cells can eaasily pass out of the blood into the cells through diffusion. In the same way substances produced by the cells (CO2) pass easily into the blood

3.1.3. The Heart as a pump Made up of two pumps, beating together about 70 times a minutre. Walls areentirely muscle, supplied with oxygen by the coronary blood vessels.

3.2. Transport in the blood

3.2.1. The blood is a complex mix of cells and liquid, which carries a huge range of substances around your body. The liquid part is called Plasma. It carries red and white bloodcells, and platelets

3.2.2. The White blood cells are part of the immune system, and is your defense against the disease. Platelets are involved in the clotting of the blood.

3.2.3. It is the blood plasma and the red blood cells which are involved in the transport of materials around the body

3.2.4. The blood plasma as a transport medium The blood plasma is a yellow liquid. The red colour comes from the red blood cells. Plasma transports all the blood cells and other things around the body CO2 produced in the organs of the body is carried in the plasma. Urea is carred in the plasma to the kidneys, where it is removed from the blood to form urine. Small, soluble products of digestion pass into the blood from the gut. They are carried around the body to the organs and cells that need them

3.2.5. Red Blood Cells There are 5 million blood cellls for every 1mm of blood. They pick up oxygen from the lungs and carry it to the tissues and cells where needed. Red blood cells have a number of adaptations that make them efficient: Bioconcave disks. Concave on both sides. Increased surface area for diffusion to take place. Packed full of haemoglobin No nucleus

3.2.6. Formation and breakdown of oxyhaemoglobin Haemoglobin is a protein molecule folded around 4 iron atoms. In a high concentration of oxygen, the haemoglobin reacts with oxygen to form oxyhaemoglobin. This is bright scarlet. Where the concentration of oxygen is lower, the reaction reverses. The oxyhaemoglobin splits to give Haemoglobin and oxygen. The oxygen diffuses into the cells. Because haemoglobin is based n iron, if your diet lacks iron, your body cannot make enough red blood cells and you suffer from anaemia. People who suffere from anaemia are pale and lack energy

3.3. The effect of excercise on the body

3.3.1. Muscle tissue is made up of protein fibres, which contract when supplied with energy from respiration. Muscle fibres need a lot of energy to contract. They contain many mitochondria to supply the energy

3.3.2. Muscles also contain clycogen stores. Glycogen is a carbohydrate which can be converted rapidly to glucose. This supplies the fuel needed to provide the energy for cellular respiration when your muscles contract.

3.3.3. Muscle fibres usually occur in big blocks as muscles. Your muscles contract to cause movement. They relax when their role is finished, which allows other muslces to work

3.3.4. The response to excercise When your muscles rest, they use up a certain amount of oxygen and glucose. This is because the fibres are constantly contracting to keep you in position against gravity. Muscles are used in breathing and circulating the blood When you excercise, the muscles contract harder and faster. They need more glucose and oxygen to supply their energy needs. They also produce increased amounts of CO2, which needs to be removed to working effectively. When muscular activity increase: Your heart rate increases and the arteries supplying blood to your muscles dilate. These increase the blood flow, and in turn increases the supply of oxygen and glucose, and the removal of CO2 The Breathing rate increases and is more deep. They make you breathe more often, but brings in more air every breath. This inceases the amount of oxygen brought into the body and picked up by the red blood cells. More CO2 can be removed

3.3.5. Benefits of excercise Your heart and lungs benefit from regular excercise. Both the lungs and heart become larger. They develop a bigger and efficient blood supply. They function effectively at all times

3.4. Anaerobic Respiration

3.4.1. During vigourous excercise, the muscle cells may become short of oxygen. The muscles can still obtain energy from glucose.

3.4.2. Muscle Fatigue When you have been using your muscle fibres for vigourous excercise for a long time, they become fatigued. This is when they stop contracting efficicently. Normally, they are very short of oxygen, and switch to anaerobic respiration Aneaerobic respiration isn't as efficient as aerobic respiration. In anaerobic respiration, the glucose molecules are not broken down completely, and so less energy is released. Glucose ---------> Lactic Acid (+Energy(

3.4.3. Oxygen Debt If you have been excercising hard, you breathe faster for some time after you stop. The length of this time depends on how fit you are The waste lactic acid produced in anaerobic respiration is a problem. You cannot get rid of lacti acid by breathing it out. As a result, when the excercise is over, lactic acid needs to be broekn down to produce CO2 na dwater. This requires oxygen. Even though your leg muscles have stopped, your heart rate and breathing rate stay high to supply extra oxygen untill you have paid off the oxygen debt. Oxygen Debt: Lactic Acid + Oxygen ---> Carbon Dioxide + Water

3.5. The Human Kidney

3.5.1. Functions of a kidney Very important for homeostastis. You produce urea in your kidney to break down amino acids, which come from protein in the food eaten and the breakdown of worn out body tissues. Urea is poisonous, but the kidneys filter it out and remove it in the urine Kidneys are also vital in the water balance of the body. If the concentration of the body fluids change, water will move in to or out of the cells by osmosis. This could damage of destroy the cells. You gain water when you eat and drink. You lose water from your lungs and during excercise. The kidneys remove any excess water, and remove it as urine. The kdineys conserve water, and produce little urine. Drink too much water, and the kidneys produce lots of urine. The ion concentration of the body is very important. You take in mineral ions with your food. The amount taken in varies. If you eat processed food (high in salt) you take in a load of minerals. Some are lost through sweat. The kidneys remove mineral ions (particularly salt) which are removed in the urine.

3.5.2. How the kidneys work The kidneys filter the blood and take back everything the body needs. Sugar, amino acids, mineral salts and urea move outof the blood into the kidney tubules by diffusion along a concentration gradient. Blood cells are left behind, as they are too big to pass through the membrane. All the sugar is reabsorbed back into the blood by active transport. The amount of water and dissolved mineral ions reabsorbed varies. It edepnds on selective reabsorption Sugar and dissolved mineral ions move back into the blood by active transport and diffusion. Active treansport is used to move them against a concentration gradient. It makes sure no sugar is left in the urine, and the right quantity of dissolved mineral ions is reabsorbed The amount of water reabsorbed depends on what the body needs. It is controlled by a feedback mechanism. Urea is lost in the urine. However, some of it leaves the kidney into the bloody by diffusion. The kidneys have a rich blood supply, and produces urine all the time.

3.5.3. What does urine contain Waste urea Excess mineral ions and water not needed by the body. The quantitys vary depending on what is taken in and given out.

3.6. Dialysis- An artifiicial kidney

3.6.1. Dialysis The machine which carries out the functions of the kidney is known as a dialysis machine. It relies on the process of dialysis to clean the blood. In a dialysis machine a person's blood leaves their body and flows between partially permeable membranes. On the other side of these membranes is dialysis flud. The concentration of the solutes in the dialysis makes sure unwanted substances pass out by diffusion. These include urea and excess mineral ions. Glucose and other useful substances remain in the blood Without functioning kidneys, the concentration of urea and mineral ions builds up in the blood. Treaement restored the concentrations of these substances to normal levels. The dialysis has to be repeated at regular intervals. It tkaes 8 hours for dialysis to be complete. People with kidney failure have to remain attatched to a dialysis machine for many hours several times a week. They have to manage their diets carefully.

3.6.2. How Dialysis works It is vital that patients lose excess urea and mineral ions built up in their systems. It is also important they do not lose vital substances like glucose and mineral ions The loss of these substances is contrlled by the dialysis fluid. It contaisnt he same concentration of glucose and mineral ions as blood plasma, so there is no net movement. It also contains normal plasma levels. Dialysis fluid contains no urea, creating a strong concentration gradient. Dialysis depends on diffusion along concentration gradients maintained by flow of fluid. There's no active transport Some people with kidney failure can set up dialysis in their own home. They're still quite large. Dialysis has some disadvantages. There needs to be a carefully controlled diet, and long sessions with the machine. Many people with kidney failure see dialysis meaning life rather than death.

3.7. Kidney Transplants

3.7.1. What is a kidney transplant? If kidneys fail, they can be replaced in a transplant operation by a healthy kidney from a donor. It is joined to normal blood vessels in the groin of the recipient. It will function normally to clean and balance the blood. One kidney is capable for a lifetime The main problem is that as the kidney is from a different person, the antigens on the cell surfaces are different. There is a risk thsat the kidney will be rejected by the immune system. When this happens, the kidney is destroyed. There are anumber of ways of reducing the risk of rejection: Having the donor and recipient as close as possible. May have a similar tissue type, with similar antigens. People from the same blood group Given drugs that suppress their immune response and stop it working for the rest of their lives. As immunosuppressant drugs get better, the need for a tissue match is less important

3.7.2. Dialysis v Transplants The advantage of a kidney transplant is that you no longer have to live like someone with kidney failure. You can eat whatever you like, and are free from restrictions with dialysis sessions. The disadvantages are because of rejection. Medicine needs to be taken every day, and needs regular check-ups. You may never get the chance of a transplant at all. Dialysis is much more avaliable than donor organs. It enables a normal life, although needs a special diet and regular sessions

3.7.3. Finding the donors Lack of donor kidneys. Main source is those who unexpected deaths. In the UK, organs can only be taken from those with donor cards or the online register, or if the relatives give consent As many of us do not carry donor cards, there are little kidneys going around. As cars become safer, fewer people die in accidents and become donors.