- When substances need to be moved against a concentration gradient or across a partially permeable membrane active transport is necessary.
- It allows cells to move substances from an area of low concentration to an area of high concentration (against the concentration gradient)
- Thus cells can absorb ions from very dilute solutions.
- Active transport requires energy, which comes from cellular respiration.
- If a cell is making lots of energy active transport can occur lots.
- Cells which are involved in a lot of active transport will usually have lotsd of mitochondria.
- Active transport is very important in plants - mineral ions in the soil are very dilute.
- It is also important in your gut and kidney to move out glucose into the blood.
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Exchange of gases in the lungs
- Your body needs a constant supply of oxygen for cellular respiration.
- Breathing brings oxygen into the body and removes waste carbon dioxide.
- When you breathe in your ribs move up and out and your diaphragm flattens pulling air into your lungs.
- When you breathe out the opposite happens, the diaphragm returns to its normal dome shape.
- The lungs are full of clusters of alveoli (tiny air sacs) which all together have a large surface area which is kept moist.
- The above characteristics help diffusion.
- The alveoli also have a rich blood supply which maintain a concentration gradient in both directions.
- Gaseous exchange occurs along the steepest gradients possible making it rapid and effective.
- Diffusion takes place over the shortest possible distance.
- Thin alveolus walls make diffusion easy
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Exchange in the Gut
- Your body cells need the molecules from food. Molecules move into bloodstream via a mixture of active transport and diffusion.
- Food needs to be broken down into soluble forms during digestion because diffusion can only take place when molecules are dissolved in water.
- The digested food molecules are then small enough to pass through the wall of the small intestine into the blood vessels.
- The move with the concentration gradient: there is a very low concentration of food in the bloodstream and a very high in the gut.
- The lining of the small intestine is folded into thousands of villi which greatly increase the uptake of digested food (increasing the surface area means there is more room for diffusion to take place).
- The lining has an excellent blood supply so that all the molecules are taken away once diffused maintaining the steep concentration gradient.
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Exchange in the gut (cont.)
- Glucose and other dissolved food molecules are moved from the small intestive into the blood by active transport.
- For other animals there are adaptations so that exchange can occur.
- There must be a large surface area, a rich blood supply, moist surfaces, and a thin membrane.
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Exchange of materials in other organisms
- Gills are made up of many thin layers of tissue so there is a only short distance for the gases to duffuse across, a rich blood supply and the surfaces are always moist as they work in water.
- Some fish have to keep swimming constantly so water keeps moving over their gills.
- Frogs and tadpoles can breathe in a out of water.
- The external gills dissapear and are reabsorbed into the body of the developing frog. The frog can breathe through its mouth and oxygen can diffuse through the skin.
- The spiracles on an insect open when they need pleanty of oxygen and close when they don't.
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Exchange in plants
- Plants need carbon dioxide and water for photosynthesis.
- The leaf shape increases surface area for the diffusion of carbon dioxide.
- They have thin leaves so that the distance for carbon dioxide to diffuse.
- Also, the air space in the leaves allow carbon dioxide to contact cells.
- When light is a limiting factor plants use carbon dioxide made by respiration for photosynthesis.
- Leaves are adapted to allow CO2 when it is needed: they are covered in a waterproof and gas proof waxy cuticle, all over there re stomata (small openings) which are controlled by the guard cells.
- The guard cells open them when air is needed and vice versa.
- Roots are also adapted for the intake of water and mineral ions.
- The shape gives them a large surface area, root hair cells also give a big surface area. The water has a short distance to diffuse.
- They are adapted to take in mineral ions using active transport as they have plenty of mitochondria.
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- When stomata are open to allow CO2 plants lose water vapour, this loss is called transpiration.
- As water evaporates from the surface of the leaves water is pulled up through the xylem to take its place.
- This constant movement of water is known as the transpiration stream.
- Conditions which increase the rate of photosynthesis increase the rate of transpiration as stomata are opened for carbon dioxide letting water out.
- Warm sunny conditions increase as this is when more water evaporation.
- In hot countries leaves will have a thicker cuticle for less water loss and most of the stomata will be found on the underside of the leaf where there is less sunlight for evaporation.
- Wilting is a protection mechanism; the leaves collapse and shrink so that there is less surface area for the evaporation of water.
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The Circulatory System
- Humans have a double circulatory system: one carries blood from the heart to the lungs and back again and the other carries blood all around the body and back again.
- This system is important for active, warm blooded animals as it is more efficient: the body can receive fully oxygenated blood more quickly.
- We have three blood vessels which are adapted for their functions.
- Arteries carry blood AWAY from the heart to the organs of the body, usually oxygenated blood. They stretch as the blood is forced through them and then go back into shape, this is your pulse.
- Veins carry deoxygenated blood TOWARDS the heart, they have no pulse but have valves to prevent back flow (because of gravity)
- Between the arteries and the veins are capillaries which are narrow with very thin walls so the useful substances can diffuse out and wastes like CO2 can diffuse in.
- The heart is made of two pumps beating at 70bpm. The walls os the heart are entirely muscle are supplied by the coronary blood vessels.
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Transport in the Blood
- The blood plasma carries red and white blood cells and platelets.
- White blood cells are part of the immune system, platelets are clotting agents and red blood cells help transport substances around the body.
- Blood plasma carries waste products around eg carbon dioxide produced in organs is sent back to the lungs and urea is carried to the kidneys.
- It carries digestion products to where they are needed.
- Red blood cells transport oxygen from the lungs to where it is needed.
- They are adapted by their bioconcave shape which gives them a bigger surface area : volume ratio for diffusion, they are full of haemoglobin which can carry oxygen, they have no nucleus so there is more haemoglobin.
- Haemoglobin is a large protein molecule folded around four iron atoms.
- In a high concentration of oxygen, haemoglobin reacts to oxyhaemoglobin.
- This is bright red.
- In low concentrations (cells, organs) reaction reverses to produce oxygen and haemoglobin, former diffuses to be used, latter is sent back to lungs.
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The Effect of Exercise on the Body
- Muscle tissue is made of proteins which contract with energy from respiration. So they contain many mitochondria.
- Muscles also contain glycogen stores, a carbohydrate which can be broken into glucose which in turn can be broken down for energy.
- glucose + oxygen ---> carbon dioxide + water (+energy)
- Even when resting muscles use up oxygen as some are constantly working against gravity and to keep your heart beating and you breathing.
- When exercising muscles contract harder and faster so they need more glucose and oxygen.
- They produce more carbon dioxide which needs to be carried away for the muscles to continue working properly.
- During exercise changes happen: heart rate increases and arteries dilate to increase the supply of oxygen and glucose and removal of CO2
- Breathing rate and capacity increases so oxygen and CO2 are sorted out.
- Heart and lungs become bigger through regular exercise and they develop more efficient blood supply.
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- During vigorous exercise muscle cells bay become short of oxygen.
- Anaerobic respiration is respiration is the absence of oxygen.
- Anaerobic respiration is less efficient than aerobic respiration as glucose molecules are not broken down completely so less energy is released.
- glucose ---> lactic acid (+energy)
- If you have been exercising hard you are still breathless after exercise.
- The length of time you are breathless depends on how fit you are.
- You cannot get rid of lactic acid easily (through breathing like with CO2).
- You need oxygen to break it down, the amount of oxygen needed is known as the oxygen debt.
- Your heart and breathing rates will remain elevated whilst you are paying off the oxygen debt.
- The equation for oxygen debt replacement is:
lactic acid + oxygen ---> carbon dioxide and water
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The Human Kidney
- Your kidneys are important for homeostasis eg. urea is poisonous but the kidneys filter it out of the blood.
- They are vital for the water balance. If the concentration of body fluids is wrong, water will move in or out of cells by osmosis and could kill them.
- You can lose water through breathing our and sweat but the kidneys remove it from the blood and it leaves the body as urine.
- If you are short of water the kidneys conserve it.
- Ion concentration is important, too much can be bad so kidneys remove it.
- They filter the blood then reabsorb useful substances.
- Glucose, amino acids, mineral salts and urea move out of the blood into the kidney tubules by diffusion along a concentration gradient. Blood cells are left behind as they are too big to fit through the membrane.
- Then all of the sugar is reabsorbed back by active transport but the amount of water and mineral ions reabsorbed depends on the body needs.
- This is selective reabsorption.
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The Human Kidney (cont.)
- The amount of water reabsorbed depends on a very sensitive feedback mechanism.
- Urea is lost in the urine however some of it leaves the kidney and moves back into the blood by diffusion.
- Urine contains waste urea and excess mineral ions and water.
- Exact quantities depend on what you have taken in and given out.
- On a hot day if you drink little and exercise a lot you will produce little urine.
- On a cool day if you drink a lot and do little you will produce a lot of urine.
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- Kidneys can be damaged by infections, genetics and in accidents.
- Without kidneys toxins (urea) build up in the body which is fatal.
- In a dialysis machine we simulate the actions of the kidneys.
- Blood flows between partially permeable membranes, on the other side is dialysis fluid on which concentration of solutes makes sure unwanted substances diffuse out.
- However it makes sure that glucose and other useful substances remain.
- Dialysis fluid is controlled carefully it contains the same concentration of glucose and mineral ion as normal blood so that there is no net loss.
- It contains no urea to increase the concentration gradient;
- The process depends completely on diffusion, there is no active transport.
- The disadvantages are that you have to follow a strict diet and attend regular, long sessions.
- Also the balance of substances in the blood can be more difficult to control over the years, but the advantage is life.
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- Kidneys can be replaced by a single healthy donor kidney if they fail.
- The donor kidney is joined to the normal blood vessels in the recipient's groin.
- There is a problem that donor kidneys have different antigens on their surface, this means there is a risk that the recipient's body could reject it.
- When this happens your immune system destroys the new organ.
- To reduce the risk the match is made as close as possible and the recipient will be given immunosuppressant drugs.
- Unfortunately, these drugs make you more susceptible to disease.
- A new kidney will last for about 9 years before the body rejects it.
- A great advantage is that you no longer have to go through dialysis so you can eat what you like and don't have to go to hospital all the time.
- Disadvantages are you have to take medicine and have to have regular check ups.
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- Microbiology is the study of microorganisms (bacteria, viruses and fungi).
- Microbes play a vital role in decay and recycling nutrients in the environment
- They can cause disease but also can be very useful to people.
- To find out more they have to be cultured (grow very large numbers of them so that you can see the colony as a whole).
- To culture microorganisms you must provide them with everything they need to survive, this includes a culture medium with carbohydrate and minerals.
- The nutrients are contained in an agar medium, which is a substance which dissolves in hot water to form a jelly.
- There are safety measures that need to be taken when culturing microorganisms as there is always the risk of mutation and disease.
- You must sterilise petri dishes and the nutrient agar killing unwanted microorganisms using heat.
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Food Production Using Yeast
- Yeast are single celled microorganisms, each one has a nucleus, cytoplasm and a membrane surrounded by a cell wall.
- When they have plenty of oxygen they respire aerobically, breaking down sugar to provide energy and producing carbon dioxide and water as waste.
- Yeast can also respire anaerobically producing ethanol and carbon dioxide as waste. This is also referred to as fermentation.
- Aerobic respiration provide them with more energy than anaerobic does, allowing them to grow and reproduce.
- Once there are large numbers of yeast they can survive for a long time without oxygen.
- Wild yeasts on the skin of decaying fruits break down the fruit sugar forming ethanol and carbon dioxide.
- We use this reaction to create beer and wine.
- Beer making depends on a process called malting; you soak barley grains and as germination begins enzymes break down the starch into sugar which is then extracted by malting an used as an energy source for the yeast. It is then fermented to produce alcohol.
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Food Production Using Yeast (cont.)
- Wine making uses the natural sugar found in fruit as the energy source for yeast.
- You let the yeast respire anaerobically until most of the sugar has been used up.
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Food Production Using Bacteria
- To make yoghurt you add a starter culture of the right kind of bacteria to warm milk. The bacteria starts to grow, reproduce and ferment.
- Bacteria break down the lactose in the milk and they produce lactic acid.
- This is known as lactic fermentation.
- Cheese making depends on the reactions of bacteria with milk.
- You add a starter culture of bacteria to warm milk. The bacteria is cheese making also convert lactose to lactic acid but they make much more of the lactic acid.
- Enzymes are also added to increase the separation of the milk.
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Large Scale Microbe Production
- In ideal conditions bacteria can double every 20 minutes.
- As the numbers of microorganisms begins to rise, conditions change as the food is used up.
- The metabolism of the millions of microorganisms causes a temperature rise
- Oxygen levels fall as it is used up in respiration.
- Carbon dioxide waste from respiration in creases the pH and if the pH changes the activity of the enzymes in the culture can be affected so it stops growing or dies.
- Other waste products can begin to build up and poison the culture.
- When we grow microbes on an industrial scale we use fermenters which are designed to overcome these problems: the react to changes and try to keep the conditions as stable as possible.
- They usually have and oxygen supply for respiration, a stirrer to keep microbes in suspension, to maintain an even temperature and make sure the food and and oxygen are evenly spread. A water cooled jacket to remove excess heat and measuring instruments.
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- Mycoprotein is a newly developed food produced using the fungus Fusarium which grows and reproduces rapidly on cheap sugar in large fermenters.
- It needs aerobic conditions to grow.
- The fungal biomass is harvested and purified the dried and processed to mycoprotein, a pale yellow solid with a faint taste of mushrooms.
- It can be given a large range of flavours to make it similar to many foods.
- It is a high protein, low fat meat substitute.
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- Alexander Fleming left some plates on which he was culturing bacteria near an open window, the next morning he saw bacteria growing but there were spots of mould surrounded by clear agar.
- Whatever has blown in was secreting a chemical which killed the bacteria.
- He set about trying to extract the substance but it was almost impossible with the technology at the time.
- Florey and Chain used the freeze dry process and tested it on animals then on the policeman.
- We grow the mould in a sterilised medium which contains sugar, amino acids, mineral salt and other nutrients.
- During the first 40 hours of fermentation the mould grows rapidly using up most of the nutrients.
- Over a period of about 140 hours broth is removed regularly and small amounts of nutrients added, allowing us to get the maximum yield of the drug.
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- Biogas is a flammable mixture of gases formed when bacteria break down plant material or the waste products of animals in anaerobic conditions.
- The percentages of the gas are: Methane - 50-80; Carbon Dioxide - 15-45; Water - 5; Hydrogen - 0-1; Hydrogen Sulfide - 0-3.
- The bacteria involved in biogas production work best at 30 degrees to generators usually work best in hot countries.
- The process is exothermic so if you put in some heat energy to get things started and have it well insulated they will work in any climate.
- In India there are religious and social taboos against using human dung so high quality gas is produced but less fertiliser.
- The design of generator chosen depends on local conditions, many are sunk into the ground for insulation.
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- In tropical countries sugar cane grows well. It has a juice high in carbohydrates, particularly sucrose.
- Maize also grow well and you can break down the starch to glucose using the enzyme carbohydrase.
- If these products from maize and cane are fermented anaerobically with yeast the sugars are broken down completely into ethanol and waterl
- Then you can extract the ethanol by distillation so it can be used as car fuel
- Engines need modifications to use ethanol as fuel.
- The advantages of ethanol as a fuel are: it is efficient, does not produce toxic gases when burnt, is much less polluting, you can mix it with petrol to make gasohol.
- Ethanol as a fuel is carbon neutral which means there is no overall increase in carbon dioxide in the atmosphere as the original plants removed carbon dioxide from the air during photosynthesis which is returned when burning.
- Disadvantages are that it takes a lot of plants to produce ethanol and that methods of ethanol production leaves large quantities of cellulose.
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More Biofuels (cont.)
- We need to find a way of using this cellulose to support ethanol production financially.
- We could develop a biogas generator that can break down excess cellulose into methane, another useful fuel.
- Genetically engineered bacteria or enzymes may be able to break down the cellulose in straw and hay to make it available for yeast to make ethanol.
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