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Cell Theory Cells and Immunity (Grade 8) The basic units of all living things are called cells. Through centuries of observations scientists have identified two main ideas which together are called cell theory: All living things are composed of one ore more cells. All new cells originate from cells which already exist. Cell Structures Visible with a Light Microscope The Nucleus: The control center of the cell is called the nucleus. All of the cells activities are directed by the nucleus. For both plant and animal cells, the nucleus is surrounded by a membrane. Chromosomes: Chromosomes, which contain DNA or genetic material, are contained within the nucleus. DNA provides the “blue prints” or “construction plans” for all the pieces of the cell. Before being passed on to other identical cells, the genetic information of DNA must be duplicated. The Cell Membrane: The cell membrane holds all of the cell material in place; as well as, acting like a gatekeeper, controlling the movements of materials, like nutrients, and wastes in and out of the cell. The Cytoplasm: A watery fluid called cytoplasm holds everything inside the cell membrane but outside of the nucleus. Much of the cells chemical activity takes place within cytoplasm. Its fluid allows materials to steadily pass between different cell structures. As well, cytoplasm can store waste material until it can be disposed. The Vacuole: A vacuole has an appearance like bubble. It acts as a fluid filled storage area. Vacuoles can be used to store water and nutrients like glucose (sugar) and minerals. Excess cell waste may also be stored in a vacuole. Tiny Structures (organelles) of a Cell which can only be seen with an Electron Microscope Within the working of a cell, or cytoplasm, are tiny structures, which can only be seen with an electron microscope, called organelles. Mitochondria; Energy production: Mitochondria are the cells power source. They convert glucose (sugar) into energy by combining it with oxygen to produce carbon dioxide and water. This process is called cellular respiration. vacuole ribosomes Ribosomes: Protein Manufacturing: Ribosome’s use the information provided by the nucleus to build protein molecules. Different proteins are needed for the growth, repair and reproduction. Endoplasmic Reticulum: Material Transport: Endoplasmic reticulum may be “rough” if it has ribosomes attached or “smooth” if it has none. Both types of endoplasmic reticulum carry materials, like glucose, through the cell. “Rough” endoplasmic reticulums have more responsibility for moving amino acids (the small particles from which ribosomes manufacture proteins); whereas, “smooth” endoplasmic reticulums have more responsibility for moving fatty acids (for the manufacture of fats {lipids}). The Golgi Apparatus: Protein Storage: The Golgi apparatus (or Gogli body) is an organelle which stores proteins and releases them to the surface of the cell in packages called vesicles. Lysomes: Recycling: Lysomes are manufactured by the Golgi apparatus (or Gogli body) and sent out to clean and patrol the cytoplasm. They contain proteins, called enzymes, which chemically change large molecules into smaller molecules that can be used by the cell. Lysomes also play a role in destroying harmful substances (like alcohols) and invading bacteria. The difference between Plant and Animal Cells Two cell structures, the cell wall and chloroplasts, carry out functions in plant cell that are not needed by animal cells. The cell wall is tough material which surrounds the cell membrane giving the plant cell a box-like shape. This rigid outer wall, allows plant cells to support each other structurally as the plant grows. Plants contain green fluids called chlorophyll which capture sunlight to convert water and carbon dioxide into sugar (food) and oxygen in the process called photosynthesis. Chloroplasts are the organelles which house chlorophyll. Also note, the vacuole is much larger on a plant cell then an animal cell. Diffusion, Osmosis and Turgor Pressure. Did you know? Concentration usually refers to the amount of dissolved solid (like salt) packed into a liquid (usually water). Diffusion refers to the movement of molecules from an area of high concentration to low concentration. A drop of dye is actually mixture of dye molecules and water. In the dye, the concentration of dye molecules is high (the dye molecules are packed tightly together), so once a dye drop hits the water, the dye molecules will try to move away from each other - putting more and more water molecules between themselves and other dye molecules. As the dye spreads through the water, the concentration of dye in any one area is lowered. A similar thing will happen with sugar water. If you add a cup (250 ml) of sugar water to a liter of water, the sugar molecules will spread out in the water, lowering the overall concentration of sugar. Adding sugar at this point will increase the concentration of sugar; whereas, adding water will lower the concentration. Adding water always weakens or dilutes a solution so that certain properties like the “sweet taste” are less noticeable. Diffusion is one way in which molecules move in and out of cells. Oxygen, which a cell uses up continually, will be of low concentration in the cell and of high concentration outside the cell. Substances like oxygen which are of high concentration outside the cell will diffuse into the cell through the cell membrane. On the other hand, a waste product, like carbon dioxide, will be at higher concentration inside the cell than outside, so they will diffuse out of the cell. Will glucose levels be higher inside the cell? Glucose is also known as (AKA) blood sugar because it is continually being added to the bloodstream as we digest carbohydrates. Inside the cell glucose is continually used up to supply energy. Hence, glucose levels are usually lower inside the cell than out. Did You Know? Carbohydrates are starchy foods like bread, cereals, potatoes, pastas and vegetables. Starch molecules must be cut into maltose and then into glucose before the reach the blood stream. Did You Know? A selectively permeable membrane is a material which allows some particles to pass through, but others are kept out. The lining of the small intestine is a selectively permeable membrane because - for example – glucose can pass through but similar sugars like maltose cannot. The cell membrane is also a semi-permeable membrane. This is especially important for skin cells, because we do not want everything we touch in the environment into absorb into our skin (especially bacteria). Osmosis refers specifically to the diffusion of water across a selectively permeable membrane (i.e. a cell membrane). If you were to surround a cell with salt water, the water in the cell would be of higher concentration, than the water surrounding the cell. (Wait a minute – Isn’t the salt water of higher concentration? It is if we Osmosis Example 1: Outward Flow were speaking in terms of salt, but in terms of water, fresh water has more water molecules in a volume then the salt water does). A cell in salt water H2O will send the water inside itself, diffusing out into the salt water. This H2O outward diffusion of water, or osmosis, is an attempt to dilute the salt water outside cell or increase its = water molecule water concentration. This is usually = salt particle not a good thing for a cell because the water moving out of the cell dehydrates the cell. Did You Know? There is good reason to salt a wound. Bacteria are everywhere and many are harmful. Any time you cut yourself bacteria can enter. All bacteria are singlecelled creatures. If you surround them with salt, the water on their insides will undergo outward osmosis until the bacteria dies of dehydration. Water can also diffuse into a cell (inward flow). A cell usually contains water with other molecules like glucose (sugar), so if a cell is surrounded by very pure water (of high water concentration), that water will attempt to move into the cell. This is fine if the cell was dehydrated to begin with, but if not, the inflow of water may overly swell up the cell. You can see this with certain fruits or vegetables like grapes, cherries or tomatoes. Overwatering tomatoes or cherries will Osmosis Example 2: Inward Flow cause them to split open as the cells within over expand. Wilted grapes on the other hand, can be rejuvenated to a plump state by sitting them in water for a while before eating them. H2O H2O Turgor Pressure: Water will enter a plant cell by osmosis if the water outside the plant cell is of higher concentration than inside the plant = water molecule cell. (Remember: The diffusion of = glucose (sugar) molecule water is called osmosis). A dehydrated plant is easy to spot, it will look wilted (picture a dried out piece of celery). In this situation the cytoplasm within the cells will shrink away from the cell wall. When fresh water reaches the cell, the cytoplasm and vacuoles will fill back up and once again push outward against the cell wall. This outward pressure is called turgor pressure. When the cell is full of water, and the turgor pressure highest, the cell wall begins to resist the push. The squeezing of the cell wall against the turgor pressure acts like a shut off valve, preventing more water from entering the cell. The Invaders and Immunity The Invaders There are a number of invaders which can enter our system to cause infections and illness. These include bacteria, viruses, protists, fungi, and parasitic worms. Bacteria There are over 5000 different types of bacteria (single bacterium) on the Earth inhabiting almost every conceivable environment, from hot springs to the undersides of glaciers. Bacteria are single-celled creatures or unicellular organisms – they may also be called microbes or microorganisms because they can only be seen under a microscope. They also have no nucleus, so they are prokaryotic cells. Did you know? Cells with a nuclear membrane are called eukaryotic cells. If the nucleus of a cell is not surrounded by a membrane, as is the case with bacteria, then the cells are called prokaryotic cells. Bacteria can wreak havoc on your system, but not all bacteria are bad. Some good bacteria are used to make cheese and yogurt. Healthy bacteria in the digestive system help to break down waste and release minerals. Bacteria can be harmful because they are little machines that consume other cells. If your body cannot fight them off (and your illness becomes too severe), you may need to take antibiotics. “Superbugs” are bacteria that are resistant to antibiotics, and as such, can cause extreme illness, even death. Did you know? Some harmful bacteria include salmonella which causes food poisoning, and E.Coli which causes diarrhea. Necrotizing fasciitis is a rare bacteria which causes flesh eating disease.(Note: Flesh eating disease may also be called Necrotizing Fasciitis) Protists unlike bacteria are eukaryotic unicellular organisms – the single cell that makes up their being contains a nucleus. Like a bacteria, protists are neither animal nor plant. One type of protist that is close to a plant is called a diatom. These one-celled organisms contain chlorophyll and can produce food by photosynthesis. A protist that is both plantlike and animal-like is the euglena which propels itself with a whip-like tail called a flagellum. The euglena can use chlorophyll to make food if sunlight is available (plantlike) or consume feed on smaller cells if necessary (animal-like). Two of the most common animal-like protists are the amoeba and the paramecia which both feed on smaller cells and bacteria. The amoeba is a blob-like, shape changing, unicellualar oraganism that moves itself by stretching out and anchoring its pseudopod (false foot). The paramecium (plural is paramecia), moves with use of hair-like oars called cilia. Did you know? Some single-celled animals will have a flagellum or whip-like tail which they use to propel themselves with. Others will be covered with cilia or tiny hairs which work together to move surrounding fluid. Fungi Bread moulds, mushrooms, puff balls and yeasts are all fungi (singular is fungus). Some fungi like mushrooms are multicellular, while others, like yeast, are unicellular. Fungi like yeast will grow on any piece of decaying plant or animal matter. Some harmful fungi include those that cause ring worm (named for the shape the fungi grows in), and athelete’s foot Did you know? Fruit flies circle fruit because they eat the yeast that grows on fruit. Viruses If bacteria are the most primitive organisms – existing as prokaryotic cells (without a nuclear membrane) – then viruses are one stage below. Viruses are not considered living because they have no cell; they are just strands of DNA (chromosomes) which puncture through cells of living things. When virus invades a cell, it takes over the nucleus, reprogramming it to replicate (or clone) the virus over and over until the cell explodes. The most deadly viruses destroy organs; less deadly ones produces skin pustules like those of chicken pox or cold sores; while others irritate breathing tracts and mucus membranes too mimic the common cold. Did you know? Deadly viruses include the avian flu virus which originally wiped out flocks of birds, but has made its way into humans, and Ebola which quickly destroys internal organs. The Immune System “Germs” or disease causing invaders like bacteria and viruses are called pathogens. Pathogens never stop attacking your body. To prevent infections your immune system has powerful defenses against pathogens. The first line of defense is a physical barrier of skin, organ linings, mucus, tiny hairs, and acidic fluids. In addition to its texture – which is difficult to for pathogens to penetrate – skin is covered by a slightly acidic oil which traps and kills off pathogens. Of course many invaders can get around the skin by entering your body through your mouth. Luckily stomach acid is an effective killer of most pathogens. To trap air borne pathogens your nose and lungs are lined with mucus and cilia (small hairs). Let’s say a pathogen like a bacteria does get past the bodies physical barriers. All foreign organisms release a chemical signal which identifies white blood cell them as invaders to our own defense cells, the white blood cells. Once the chemical signals from an invader are detected, an increased blood flow to the pathogen infected area will bring in white blood cells. The white blood cells capture, engulf and destroy the invading pathogens. Did you know? You can detect an invading organism in your system by how your body responds. When the increase in blood flow reaches the infected area, swelling, and redness will occur – this known as inflammation. In addition to inflammation you may also experience a fever. You can also recognize when you white blood cells are effectively destroying the invader by the presence of pus. Pus is the waste product of destroyed pathogens and dead white blood cells. Sometimes an invader is so aggressive that your white blood cells cannot stop it before its starts entering tissue and organ cells, this is when your bodies last line of defense will take over. The last line of defense is called the acquired immune system. The key defenders in the immune system are chemical agents called antibodies. When an invader, like bacteria , breaches our physical defenses its chemical signals identify it as an invading cell. The chemicals signals given off by an invading organism are called antigens. Antigen is short for “antibody generator”, because, as the name suggests, these chemicals cause the body to start to produce or “generate” antibodies. Essentially, the work of antibody is simple; it finds the chemical signal and attaches itself, chemically, to site of that signal. This binds up the organism so that it can no longer attack the body’s cells. The problem for the immune system is that every invader has a different chemical signal - a different antigen – so your body must have antibody ready, or make new one for every invader. Worse, the invaders, especially viruses and bacteria are always evolving and changing, so our immune system must continually change to stop the onslaught of invaders. antibodies antigens (chemical signals) "bound up" pathogen pathogen Did you know? Non-living things like toxins (harmful chemicals compounds and metals), and pollens (and other allergens), also give off chemical signals. Antibodies also bind to the sight of these signals, preventing them from entering cells. Allergens like pollens are actually harmless substances which your body mistakes for harmful invaders. The body’s response to allergens has symptoms like an infection – itchy redness and inflammation – which can make an allergy sufferer very uncomfortable. As you get older, you are exposed to more and more pathogens. Every time your body builds a new antibody to destroy a new pathogen, it keeps some of the antibody around in case the same pathogen returns. This is why you only get the chicken pox once – you will be exposed to the chicken pox virus many times in your life, but once you have the chicken pox antibody, your immune system easily fights it off future invasions. The accumulation of antibodies is called an acquired immune response – it is called such because you acquire the immunity by building antibodies as you go. Did you know? The cells that keep your antibody memory roam freely in the blood and are called B-cells. They also manufacture antibodies when needed. A vaccination is an injection of blood plasma containing dead or weakened pathogens. The chemical signals (antigens) carried by these “compromised” pathogens stimulate the immune system to develop antibodies. Did you know? A “flu” shot is a vaccine which targets the various strains of the influenza virus. Influenza causes symptoms of the common cold, but with severe body and head aches, extreme tiredness and fever. A breakout of influenza in 1918, killed more people than World War I. Before vaccinations were invented the only way to acquire antibodies, was to get a disease, get really sick, and let your system make the antibodies while you suffer. With a vaccination, you get to acquire the antibodies, but you do not need to get really sick in the process. Did You Know? You can acquire immunity to toxins or even poisons. Antibodies will develop to bind up toxins and poisons (provided they do not kill you first). At the turn of the 19th Century, Russian politicians tried to kill the “Tsar influencing Monk” Rasputin with poison. Rasputin did not die from the poison, much to his adversary’s dismay. Historians believe that Rasputin had the antibody for the poison in his system because he had taken small amounts throughout his life, thus, he had acquired immunity to it. Disease Carriers If a person with HIV (the virus that causes AIDS) is bitten by a mosquito it is unlikely that the virus will be transferred to another human. For one thing, a drop of HIV infected blood contains (maybe) one virus and that virus is easily destroyed by the mosquito’s digestive systems. (Recall, that a virus is not a cell, but a strand of DNA protected only by a thin layer of protein). The single-celled parasite that causes malaria is, on the other hand, difficult to kill. The mosquito acts like a hypodermic needle injecting a half billion people with the malaria parasite each year causing over one million deaths. Did you know? The Black Plague, or Black Death, or Bubonic Plague occurred in Europe the late 1340s when biting fleas (living on rats) carried the disease to humans. The “Black Death” was known as a “pandemic” which essentially means severe “epidemic” or severe breakout in disease. The “Hygiene Hypothesis” Many scientists believe that North American’s are just too clean. By not exposing children to enough “uncleanly” microbes, the immune system which is supposed to be busily attacking invaders does not have enough to do. As overcompensation harmless allergens are attacked instead, causing unnecessary allergy symptoms well into adulthood. This is known currently as the “hygiene hypothesis”. Notice that the word “hypothesis” is used here instead of “theory”. To be accepted as a scientific theory, a notion like the “hygiene hypothesis” must tested and re-tested over and over while the world’s brightest scientific minds examine every aspect of the hypothesis in detail. In other words, a scientific theory is the most thoroughly examined statement of explanation we humans offer to explain our observations. An extension of the “hygiene hypothesis” is the idea that it’s okay for young children to eat dirt once in a while. In fact this would be good thing, because the microbes (microscopic pathogens like bacteria) in dirt will give the immune system something worthy to attack. (A Mr. G Note: If “hygiene hypothesis” does become a scientific theory some day, then I suggest they call it the “Happy Kids Eat Dirt Theory”.). Superbugs In the fight against infectious disease the term antibiotic means any substance that can kill bacteria (singular: bacterium). Penicillin (discovered by Alexander Fleming in 1928) was the first antibiotic used by doctors. There are several variations of penicillin – including tetracycline – which are used as bacteria killers today. Antibiotics are not the only killers of bacteria. Disinfectants like soap and bleach will kill bacteria. Bacteria will also kill themselves off – a feat they accomplish by developing and releasing toxins. White blood cells and the production of antibodies by the immune systems of animals also kill bacteria. To survive all these threats, bacteria must mutate – this means their genes or DNA programs must change. Thankfully – for the sake of bacteria – their cell design makes it easy for a mutation to occur. A bacterium does not have a nucleus to house its chromosomes; instead a thin layer of protein protects a tangle of chromosomes – the group of which is called a plasmid. With no nucleus to interfere, gene segments are easily exchanged with other bacteria. In fact, bacteria are always exchanging genes with each other in search of a life-saving advantage. Sometimes, a bacterium acquires a gene which allows it to survive an encounter with an antibiotic. If this happens, the new gene segment provides the bacterium with instructions for building an enzyme. The enzyme is an energized protein which acts chemically to chop the antibiotic molecule into smaller pieces, effectively destroying it. A bacterium that is able to destroy an antibiotic without dying off in the process is called resistant. This type of bacterium has an advantage over other bacteria when exposed to antibiotics. Antibiotics are not selective – they destroy all different types of bacteria. Only resistant bacteria can survive in the presence of antibiotics. This is where the trouble begins; if the gene mutation allows a bacterium to survive an antibiotic attack; then the resistant bacterium will go on to multiply (by the billons) and thrive. A place that uses a lot of antibiotics is a hospital. Due to overexposure to antibiotics, hospitals tend to have more resistant bacteria then other places. This makes sense because the bacteria in hospitals will fight for survival by mutating (exchanging genes); eventually some will become antibiotic resistant. Most bacteria do not cause lifethreatening diseases (most in fact are harmless), but if the resistant gene is passed to a disease-causing bacterium then a “superbug” occurs. The term superbug is synonymous with the terms “super germ” or “super pathogen” and “super bacteria”. A “super” bacterium is “super” because it causes disease and it can survive antibiotics. In other words, a superbug is an infectious, resistant, bacterium. What is the bad news? The only disease fighting defense we have against resistant infectious bacteria is the immune system. Recall, that the immune system relies on white blood cells and the production of antibodies to kill invaders like our “superbug”. Without antibiotics to help, how fast our immune system reacts to a “superbug” will be the only factor which will determine of how sick we get or whether we will survive at all. The H1N1 Flu Vaccine A virus is an infectious biological agent. Many are simply strands of DNA with no cell housing them. Often described a “pre-life form” or an “organism on the edge of life”, a virus cannot replicate (reproduce or clone itself) without taking over the cells of another organism. The process of replicating within a host cell usually results in the death of that cell. The influenza or “flu” virus is well known for causing disease in humans. Symptoms of a flu infection include chills, fever, muscle pains, headache, and a sore throat. The modern “flu” is a relative of the Spanish Flu that killed over 50 million people in the 1918 pandemic. (The term pandemic refers to the spread of disease on a world-wide scale). With no cell to contain their DNA strands a virus can easily evolve or mutate by exchanging DNA with another virus (or simply changing the links in its own DNA strands). Hence, the flu we catch today is often similar to the Spanish flu. Anytime you catch the flu and survive, your B-Cells develop an antibody that fights off any further attack by that particular virus. However, since a virus will strive to live on, the “flu” you catch next year will likely be a slightly different version (a mutation) of the one you caught in years prior. If the flu virus is only slightly different than those previously encountered, your B-Cells will easily manufacture new antibodies to ward of the infection. It is when the flu virus is significantly different from previous ones that trouble arrives in the form of a pandemic. A virus is usually specific to a species. Stated differently, a flu virus that infects humans will generally not harm pigs and vice versa. However, if a flu virus does make the jump from pigs to humans there is a good chance that the virus will be significantly different from other human flu viruses. This is the case with H1N1 or “swine flu”. Samples of circulating influenza viruses are routinely sent to the World Heath Organization. The virus sample for H1N1 was identified as having pandemic potential because it differed significantly from other samples (this was not to surprising, since it jumped form pigs to humans). A vaccine is actually a “cheat” in the infectious process – it allows you to develop antibodies without suffering the full effects of the disease (which may include death). Manufacturing a vaccine flu virus is complicated because the vaccine virus is most easily grown in chicken eggs. To make sure the vaccine virus is safe and easy to mass produce the H1N1 virus is first mixed with other standard lab viruses. Any mix of two influenza viruses will eventually grow together to produce a hybrid virus. The most important task is to find a hybrid virus that is both similar to the real H1N1 virus and able to grow quickly in a hen’s egg. Once isolated the hybrid virus is injected into thousands of eggs, where it multiplies. The harvested virus, now called the vaccine virus is killed – a process which breaks the vaccine virus into proteins. These proteins give off the same chemical signals or antigens as the live virus. Once purified, the virus proteins are ready for injection. Upon injection into humans, the virus proteins, or antigens, will signal the B-cells to begin constructing new antibodies. These antibodies will bind to the antigen site effectively tying up the virus protein. Full immunity takes about 8 days to develop. After the vaccine injection, B-Cells loaded with many of the correct antibodies will easily bind up any invasion by the real H1N1 virus.