Gas and Solute Exchange: Diffusion, Osmosis and Ac
Life processes need gases or other dissovled substances before they can happen.
Waste substances also need to move out of the cells so that the organisms can get rid of them.
These substances move to where they need to be by diffusion, osmosis and active transport:
- Diffusion is where particles move from an area of high concentration to an area of low concentration.
- Osmosis is similar, but it only refers to water.
- Diffusion and osmosis involve moving from an area where there's a high concentration of it, to an area where there's a lower concentration of it. Sometimes substances need to move in the other direction - this is where active transport comes in.
Exchange surfaces are adapted to maximise effectiveness.
Gas and Solute Exchange: Structure of Leaves
Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. The leaf's structure is adapted so that this can happen easily.:
- The underneath of the leaf is an exchange surface. - it's covered in stomata, which the carbon dioxide diffuses in through.
- Water vapour and oxygen also diffuses in through the stomata.
- The size of the stomata are controlled by the guard cells. These close the stomata if the plant is losing water faster than itis being replaced by the roots. - Without the guard cell, the plant would wilt.
- The flattened shape of the leaf increases the area of this exchange surface so that it's more effective.
- The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the area of this surface so there's more chance for carbon dioxide to get into the cells.
The water vapour escapes by diffusion because there's a lot of it inside the leaf and less of it in the air outside. This diffusion is called transpiration and it goes quicker when the air around the leaf is kept dry. Transpirtation is best in hot, dry, windy conditions.
The Breathing System: The Lungs and parts of it
You need oxygen from the air into your bloodstream so that it can get to your cells for respiration. You also need to get rid of carbon dioxide in your blood. -This is all happens inside the lungs. Breathing is how the air gets in and out of the your lungs.
- The thorax is the top part of your body.
- It's seperated by the diaphragm.
- The lungs are protected by the ribcage.
- The air that you breathe in goes through the trachea.
- This splits into two tubes called 'bronchi, one going to each lung.
- The bronchi splits progressively, smaller tubes are called bronchioles.
- The bronchioles end at small bags called alveoli, where gas exchange takes place.
The Breathing System: Breathing in and out
- Intercostal muscles and diaphragm contract.
- Thorax volume increases.
- This decreases the pressure, drawing air in.
- Intercostal muscles and diaphragm relax.
- Thorax volume decreases.
- Air is forced out
Diffusion Through Cell Membrane: Gas Exchange in t
Different parts of the human body are adapted so that substances can diffuse through them most effectively.
The jobs of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it. To do this, the lungs contains millions of little air sacs called alveoli where gas exchange takes place.
The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. They have:
- An enormous surface area ( about 75 metres squared in humans).
- A moist lining for dissolving gases,
- Very thin walls.
- A copious blood supply.
Diffusion Through Cell Membrane: The Villi; exchan
The inside of the small intestines is covered in millions and millions of these tiny little projections called villi.
They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood.
Notice they have:
- a single layer of surface cells.
- a very good blood supply to assist quick absorption.
A large surface area is a key way that organisms' exchange surfaces are made more effective - molecules can only diffuses through a membrane when they're right next to it, and a large surface area means loads more molecules are close to the membrane.
Active Transport: Root hairs in plants
Sometimes substances need to be absorbed against a concentration gradient. This process is lovingly referred to as active transport.
Root hairs are specialised for absorbing water and minerals.:
- The cells on the surface of plant roots grow into long 'hairs', which stick out into the soil.
- This gives the plant a big surface area for absorbing water and mineral ions from the soil.
- Most of the water and mineral ions that get into a plant are absorbed by the root hair cells.
Active Transport: Root hairs take in minerals thro
Root hairs take in minerals using active transport:
- The concentration of minerals is usually higher in the root hair cell than in the soil around it.
- So normal diffusion doesn't explain how minerals are taken up into the root hair cell.
- They should go the other way, if they follow the rules of diffusion.
- The answer is active transport.
- Active transport allows the plant to absorb minerals against a concentration gradient. This is essential for its growth. But active transport needs energy from respiration to make it work.
- Active transport also happens in humans. For example taking in glucose from the gut and from the kidney tubules.
Active Transport: In the gut
We need active transport to stop us starving.
Active transport is used in the gut when there is a low concentration of nutrients in the gut, but a high concentration of nutrients in the blood.
- When there's a higher concentration of glucose and amino acids in the gut, they diffuse naturally into the blood.
- BUT - sometimes there's a lower concentration of nutrients in the gut than there is in the blood.
- This means that the concentration gradient is the wrong way.
- The same process used in plant roots is used here.. active transport.
- Active transport allows nutrients to be taking into the blood, despite the fact that the concentration gradient is the wrong way.
An important difference between diffusion and active transport is that active transport uses energy.
The Circulation System
The circulation system's main function os to get food and oxygen to every cell in the body. As well as being a delivery service, it's also a waste collection service - it carries waste products like carbon dioxide and urea to where they can be removed from the body.
The double circulation:
- The heart is two pumps. The right side pumps deoxygenated blood to lungs to collect oxygen and remove carbon dioxide. Then the left side pumps this oxygenated blood around the body.
- Arteries carry blood away from the heart at high pressure.
- Normally, arteries carry oxygenated blood and veins carry deoxygenated blood.
- The pulmonary artery and pulmonary vein are the big exception to this rule.
- The arteries eventually split off into thousands of tiny capillaries which take blood to every cell in the body.
- The veins then collect the 'used' blood and carry it back to the heart at low pressure to be pumped round again.
Blood: Capillaries and the four main parts of bloo
Capillaries deliver food and oxygen to each cell:
- Capillaries use diffusion to deliver food and oxygen direct to the body tissues and take carbon dioxide and other waste materials away.
- Their walls are usually only one cell thick to make it easy for stuff to pass in and out of them.
- They are too small to see without a microscope.
Blood is made up of four main parts, blood consists of:
- white blood cells
- red blood cells
- platelets - these are small fragments of cells that help blood to clot a wound.
Blood: Red blood cells
Red blood cells carry oxygen:
- The job of red blood cells is to carry oxygen from the lungs to all the cells in the body.
- They have a doughnut shape, to give them a large surface area for absorbing oxygen.
- They don't have a nucleus - this allows more room to carry oxygen.
- They contain a substance called haemoglobin.
- In the lungs, haemoglobin combines with oxygen to become oxyhaemoglobin. In body tissue the reverse happens to release oxygen to the cells.
- The more red blood cells you've got, the more oxygen can get to your cells. At high altitudes there's less oxygen in the air - so people who live there produce more red blood cells to compensate.
Red blood cells are perfectly designed for absorbing plenty of oxygen and squeezing through capillaries. There's a condition called sickle-cell anaemia, in which the red blood cells are crescent-moon shapes. This causes problems because less oxygen is carried and the cells don't flow well through capillaries.
Plasma is the liquid that carries everything in blood, it's a pale straw-coloured liquid which carries just about everything:
- Red and white blood cells and platelets.
- Nutrients like glucose and amino acids. There are the soluble products of digestion which are absorbed from the gut and taken to the cells of the body.
- Carbon dioxide from the organs to the lungs.
- Urea from the liver to the kidneys.
- Antibodies and antitoxins produced by the white blood cells.
Exercise: Increase in the heart rate
When you exercise your body quickly adapts so that your muscles get more oxygen and glucose to supply energy. If your body can't get enough oxygen or glucose to them, it has some back up plans ready.
Exercise increases the heart rate:
- Muscles are made of muscle cells. These use oxygen to release energy from glucose - this is process is called respiration - which is used to contract the muscles.
- An increase in muscle activity requires more glucose and oxygen to be supplied to the muscle cells. Extra carbon dioxide needs to be removed from the muscle cells. For this to happen, the blood has to flow at a faster rate.
- This is why physical activity:
- increases your breathing rate and makes you breathe more deeply to meet the demand from extra oxygen.
- increases the speed at which the heart pumps.
- dilates the arteries which supply blood to the muscles.
Exercise: Glycogen and anaerobic respiration
Glycogen is used during exercise:
- Some glucose from food is stored as glycogen.
- Glycogen's mainly stored in the liver, but each muscle also has its own store.
- During vigorous exercise, muscles use glucose rapidly, and have to draw on their glycogen stores to provide more energy. If the exercise goes on for a while the glycogen stores get used up.
- When the glycogen stores run low, the muscles don't get the energy they need to keep contracting and they get tired.
Exercise: Anaerobic respiration
Anaerobic respiration is used if there's not enough oxygen:
- When you do vigorous exercise and your body can't take supply enough oxygen to your muscles, they start doing anaerobic respiration, instead of aerobic respiration.
- 'Anaerobic' means 'without oxygen'. It's the incomplete breakdown of glucose, which produces lactic acid.
- GLUCOSE -goes to-> energy + lactic acid
- This is not the best way to convert glucose into energy because lactic acid builds up in the muscles, which gets painful and causes the muscles to get tired.
- Another downside is that anaerobic respiration does not release nearly as much energy as aerobic respiration - but it's useful in emergencies.
- The advantage is that at least you can keep on using your muscles for a while longer.
Exercise: Oxygen Debt
Anaerobic respiration leads to an oxygen debt:
- After resorting to anaerobic respiration, when you stop exercising you'll have an 'oxygen debt'.
- In other words, you have to 'repay' the oxygen that you didn't get to your muscles in time, because your lungs, heart and blood couldn't keep up with the demand earlier on.
- This means you have to keep breathing hard for a while after you stop, to get oxygen into your muscles to oxidise the painful lactic acid to harmless carbon dioxide and water.
- While high levels of carbon dioxide and lactic acid are detected in the blood by the brain, the pulse and breathing rate stay high to try and rectify the situation.
Kidneys: Three stages - Ultrafiltration
The kidneys are really important organs. They get rid of toxic waste like urea, as well as adjusting the amount of dissolved ions and water in the blood.
Nephrons are the filtration units in the kidney. There are three stages of what happens in the kidneys:
- a high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule.
- The membranes between the blood vessels and the Bowman's capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. They stay in the blood.
Kidneys: Reabsorption and release of wastes
As the liquid flows along the nephron, useful substances are reabsorbed back into the blood:
- All the sugar is reabsorbed. This involves the process of active transport against the concentration gradient.
- Sufficient ions are reabsorbed. Excess ions are not. Active transport is needed.
- Sufficient water is reabsorbed.
3) Release of wastes:
The remaining substances (including urea) continue out of the nephron, into the ureter and down to the bladder as urine.
Kidney failure: The treatments
If someone's kidneys stop working, there are basically two treatments - regular dialysis or a transplant.
The kidneys remove waste substances from the blood:
If the kidneys don't work properly, waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body. Eventually, this results in death.
The kidneys are incredibly important - if they don't work as they should, you can get problems in the heart, bones, nervous system, stomach, mouth and many other places.
People with kidney failure can be kept alive by having dialysis treatment - where machines do the job of the kidneys. Or they can have a kidney transplant.
Kidney failure: Dialysis
Dialysis machines filter the blood:
Dialysis has to be done regularly to keep the concentration of dissolved substances in the blood at normal levels, and to remove waste substances.
In a dialysis machine the person's blood flows alongside a selectively permeable barrier, surrounded by dialysis fluid. It's permeable to things like ions and waste substances, but not big molecules like proteins, just like the membrane of the kidneys.
The dialysis fluid has the same concentration of dissolved ions and glucose won't be lost from the blood during dialysis.
Only waste substances, such as urea and excess ions and water diffuse across the barrier.
Many patients with kidney failure have to have a dialysis session three times a week. Each session takes three to four hours.
Kidney failure: Organ transplant
Transplanted organs can be rejected by the body. At the moment, the only cure for kidney disease is to have a kidney transplant. Healthy kidneys are usually transplanted from people who have died suddenly and who are on the organ donor register or carry a donor card. But kidneys can also be transplanted from people who are still alive - as we all have two.
The donor kidney can be rejected by the patient's immune system - treated like a foreign body and attacked by antibodies. To help prevent this happening, precautions are taken:
- A donor with a tissue type that closely matches the patient is chosen. Tissue type is based on antigens that are on the surface of most cells.
- The patient's bone marrow is zapped with radiation to stop white blood cells being produced - so they won't attack the transplanted kidney. They also have to take drugs that suppress the immune system.
- Unfortunately this means that the patient can't fight any disease that comes along, so they have to be kept in totally sterile conditions for some time after the operation.
Kidney failure: Advantages and Disadvantages of tr
Dialysis or transplant? Both treatments can be seen to have their down side.
The disadvantages of dialysis are:
- Kidney dialysis machines are expensive to run.
- The experience is not pleasant.
- Dialysis sessions have to be done regularly, roughly three times a week and take between three and four hours, consuming a lot of a patients time.
The disadvantages of a kidney transplant are:
- There are long waiting lists and kidneys have to be very specific, making them limited, but in high demand.
- There's the possibility it will be rejected.
- A person may become vulnerable to other illnesses as their immune system is suppressed.
Food and Drink from Microorganisms
Microorganisms, such as bacteria, cause changes in food. The theory of Biogenesis has been developed over the years: Evidence supports the theory that living things are created from other living organisms - this is the theory of biogenesis.
Most cheese is made using bacteria:
- A culture of bacteria is added to warm milk.
- The bacteria produces a solid curd in the milk.
- The curds are separated from the liquid whey.
- More bacteria are sometimes added to the curds, and the whole lots is left to ripen for a while.
- Moulds are added to give blue cheese its colour and taste.
Yogurt is made using bacteria too:
- The milk is heated to kill off any bacteria, then cooled.
- A starter culture of bacteria is then added. The bacteria ferment the lactose sugar to lactic acid.
- The acid causes the milk to clot and solidify into yogurt.
- Sterilised flavors are then added.
Using Yeast: Anaerobic and Aerobic respiration
Yeast is a single-celled fungus; yeast is a microorganism. A yeast cell has a nucleus, cytoplasm, a vacuole, and a cell membrane surrounded by a cell wall.
Yeast can respire with or without oxygen: Anaerobic respiration of glucose by yeast is called fermentation. The equation for this is glucose goes to ethanol, carbon dioxide and energy. Yeast can also respire aerobically, with oxygen. This produces much more energy, and is needed to grow and reproduce. The equation for aerobic respiration is glucose and oxygen goes to carbon dioxide, water and energy. This is the same respiration process that releases energy in animals and plants.
Yeast is used to make bread:
- Yeast is used in dough to produce nice, light, bread.
- The yeast converts sugars to carbon dioxide and some ethanol. It is the carbon dioxide that makes the bread rise.
- As the carbon dioxide expands, it gets trapped in the dough, making it lighter.
- Holes on the bread, which makes it nice and light are made by carbon dioxide bubbles in the dough.
Using Yeast: Making alcoholic drinks
Beer is brewed through the following process:
- Beer is made from grain - usually barley.
- The barley grains are allowed to germinate for a few days, during which starch in the grains is broken down into sugar by enzymes. Then the grains are dried in a kiln. This process is called malting.
- The malted grain is mashed up by and water is added to produce a sugary solution with lots of bits in it. This is then sieved to remove the bits.
- Hops are added to the mixture to give the beer its bitter flavour.
- The sugary solution is then fermented by yeast, turning the sugar into alcohol.
Microorganisms in Industry: Fermenters
Shedloads of microorganisms are grown in huge vats called fermenters to make things like antibiotics, fuels, and proteins. It's really important to control the conditions in fermenters, so that just the stuff you want grows as fast as possible.Microorganisms are grown in fermenters on a large scale:
A fermenter is a big container full of liquid culture medium which microorganisms can grow and reproduce in. The fermenter needs to give the microorganisms the conditions they need to grow and produce their useful produce. In a fermenter:
- Food is provided in the liquid culture medium. More can be pumped in if needed.
- Air is piped in to supply oxygen to the microorganisms.
- The microorganisms need to be kept at the right temperature. The microorganisms produce heat by respiration, so the fermenters must be cooled. This is usually done with water in a water-cooled jacket. The temperature is monitored by instruments.
- The right pH is needed for the microorganisms to thrive. Instruments will monitor this.
- Sterile conditions are needed to prevent contamination from other microorganisms.
- The microorganisms need to be kept from sinking to the bottom. A motorised stirrer keeps them moving around and maintains an even temperature.
Microorganisms in Industry: Mycoprotein
Mycoprotein - food from fermenters:
- Mycoprotein means protein from fungi. It's a type of single-celled protein.
- Mycoprotein is used to make meat substitutes for vegetarian meals - for example Quorn.
- A fungus called Fusarium is the main source of mycoprotein.
- The fungus is grown in fermenters, using glucose syrup as food. The glucose syrup is obtained by digesting maize starch with enzymes.
- The fungus respires aerobically, so oxygen is supplied, together with nitrogen, as ammonia and other minerals.
- It's important to prevent other microorganisms growing in the fermenter. So the fermenter is initially sterilised using steam. The incoming nutrients are heat sterilised and the air supply is filtered.
Microorganisms in Industry: Penicillin
Penicillin is made by growing mould in fermenters.
Penicillin is an antibiotic made by growing the mould penicillium chrysogenum in a fermenter.
The mould is grown in a liquid culture medium containing sugar and other nutrients.
The sugar us used up as the mould grows.
The mould only starts to make penicillin after using up most of the nutrients for growth.
Alexander Fleming discovered Penicillin accidently in 1928. A culture of bacteria became contaminated with a mould. This mould wiped out areas of bacteria. No one took much notice Fleming's findings until the Second World War, when the hugh number of injuries made it important to find something that would heal infected wounds.
In some developing countries, it is difficult to find enough protein. Meat is a big source of protein, but animals need lots of space to graze, plenty of nice grass. Single-celled protein grown in a fermenter is an efficient way of producing protein to feed people. The microorganisms grow very quickly, and don't need much space. And they can even feed on waste material that would be no good for feeding animals.
Fuels from microorganisms: Fermentation and Ethano
Food and antibiotics aren't the only things microorganisms can be used for - the stuff they produce can also be used as fuel.
Fuels can be made by fermentation:
- Fuels can be made by fermentation of natural products - luckily enough, waste products can often be used.
- Fermentation is when bacteria or yeast break sugars down by anaerobic respiration.
- Anaerobic respiration does not use oxygen.
Ethanol is made by anaerobic fermentation of sugar:
- Yeast make ethanol when they break down glucose by anaerobic respiration.
- Glucose goes to ethanol, carbon dioxide and energy.
- Sugar cane juices can be used, or glucose can be derived from maize starch by the action of carbohydrase (an enzyme).
- The ethanol is distilled to separate it from the yeast and remaining glucose before it's used.
- In some countries, cars are adapted to run on a mixture of ethanol and petrol - this is known as 'gasohol'.
Fuels from microorganisms: Biogas and fuel product
Biogas is made by anaerobic fermentation of waste material:
- Biogas is usually about 70% methane and 30% carbon dioxide.
- Lots of different microorganisms are used to produce biogas. They ferment plant and animal waste, which contains carbohydrates. Sludge waste from sewage works or sugar factories, is used to make biogas on a large scale.
- It's made in a simple fermenter called a digester or generator.
- Biogas generators need to be kept at a constant temperature to keep the microorganisms respiring away.
- There are two types of biogas generators - batch generators and continuous generators.
- Biogas can't be stored as a liquid, as it needs too high a pressure, so it has to be used straight away - for heating, cooking, lighting or to power a turbine to generate electricity.
Fuel production can happen on a large or small scale:
- Large-scale biogas generators are now being set up in a number of countries. Also, in some countries, small biogas generators are used to make enough gas for a village or a family to use in their cooking stoves and for heating and lighting.
- Human waste, waste from keeping pigs, and food waste can be digested by bacteria to produce biogas.
- By-products are used to fertilise crops and gardens.
Fuels from microorganisms: Different biogas genera
Not all biogas generators are the same, there are two main types of biogas generator - batch generators and continuous generators.
Batch generators make biogas in small batches. They're manually loaded up with waste, which is left to digest, and the by-products are cleared away at the end of the session.
Continuous generators make biogas all the time. Waste is continuously fed in, and biogas is produced at a steady rate. Continuous generators are more suited to large-scale biogas produced.
Whether a biogas generator is continuous or batch, it needs to have the following:
- An inlet for waste material to be put in.
- An outlet for the digested material to be removed through.
- An outlet so that the biogas can be be piped to where it is needed.
Fuels from microorganisms: Factors to consider
When biogas generators are being designed, the following factors need to be considered:
Cost: Continuous generators are more expensive than the batch ones, because waste has to be mechanically pumped in and digested material mechanically removed all the time.
Convenience: Batch generators are less convenient because they have to be continually loaded, emptied and cleaned.
Efficiency: Gas is produced most quickly at about 35 degrees celcius. If the temperature falls below this the gas production will be slower. Generators in some areas will need to be insulated or kept warm, for example, by solar heaters. The generator shouldn't have any leaks or gas will be lost.
Position: The waste will smell during delivery, so generators should be sited away from homes. The generator is also best located fairly close to the waste source.
BIogas makes a great fertiliser and provides energy. Biogas isn't new though - before electricity, it was drawn from London's sewer pipes and burned in the street lights.
Fuels from microorganisms: Economic and environmen
Using biofuels has economic and environmental effects:
- Biofuels are a greener alternative to fossil fuels. The carbon dioxide released into the atmosphere was taken in by plants which lived recently, so they're carbon neutral.
- The use of biogas doesn't produce significant amounts of sulfur dioxide or nitrogen oxides, which cause acid rain.
- Methane is a greenhouse gas and is one of those responsible for global warming. It's given off untreated waste, which may be kept in farmyards or spread on agricultural land as fertiliser. Burning it as biogas means it's not released into the atmosphere.
- The raw material is cheap and readily avaliable.
- The digested material is a better fertiliser than undigested dung - so people can grow more crops.
- In some developing rural communities women have to spend hours each day collecting wood for fuel. Biogas saves them this drudgery.
- Biogas generators act as a waste disposal system, getting rid of human and animal waste that'd otherwise lie around, causing disease and polluting water supplies.