Biology Gcse Revision Essay Example for Free

Biology Gcse Revision Essay Small living organisms; there are 3 types * Bacteria – ecoli, salmonella * Fungi – mushrooms, athletes foot * Virus – influenza (flu), HIV * When they enter our body, they multiply and release toxins / harmful chemicals into our blood * They duplicate every 20 minutes Physical barriers: eyelashes prevent MO’s from entering through our eyes, nasal hairs reduce them, skin is a barrier to them (although they can enter through cuts), chemicals in tears and sweat, acid in the stomach kills most MO’s * Also called pathogens (microorganisms that cause disease) * Our body provides MO’s with ideal conditions to multiply in (warm and moist) The immune system: * All white blood cells are part of this system * Phagocyte – a type of white blood cell that will eliminate the virus by engulfing then digesting the bacteria, the process of this is called phagocytosis. Lymphocyte – a type of white blood cell that carry antibodies * Antigen – certain chemicals that are foreign to the body in pathogens * E. g. : 1. James is infected by some bacteria that cause a disease. 2. The bacteria reproduce and produce toxins that make James ill 3. A white blood cell detects the bacteria and it makes antibodies to attach to it. Other white blood cells engulf the labelled bacteria and destroy them 4. The white blood cells that produce the right antibodies reproduce meaning there are lots of them making antibodies 5. Most of the white blood cells that make this antibody die, but there are few that stay in the blood called memory cells 6. The bacteria are killed and James gets better 7. He is then infected by the same bacteria 8. The memory cells that stayed in James’ blood from last time respond quickly and kill the bacteria before he becomes ill * Memory cell – a type of white blood cell that stay in the blood after the infection has been fought off * They respond quickly when it meets a microorganism for the econd time and produce the right antibody for the particular microorganism and destroy it before you feel unwell meaning you become immune to a disease. Vaccinations: * Vaccination involves exposing the body’s immune system to a dead or inactive version of the pathogen in order to stimulate white blood cells to produce antibodies for a disease or group of diseases * People can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens * The vaccine contains only a weakened or harmless version of a pathogen, which means that the vaccinated person is in no danger of developing the disease * Epidemic – a widespread occurrence of an infectious disease in a community at a particular time * To prevent epidemics a large percentage of the population needs to be vaccinated Antimicrobials: Chemicals that inhibit the growth of MO’s or kill them, but don’t kill viruses * Antibiotics – type of antimicrobial that kill bacteria but don’t kill viruses * MO’s can sometimes become resistant to antimicrobials (leads to a gene for resistance being passed down to offspring) * Antibiotic resistance – when some of the bacteria are resistant to the antibiotics, this can be slowed down by finishing the course and only taking them when needed * The main steps in the development of resistance are: 1. Random changes or mutations occur in th e genes of individual bacterial cells 2. Some mutations protect the bacterial cell from the effects of the antibiotic 3. Bacteria without the mutation die or cannot reproduce with the antibiotic present 4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains * Mutations in bacteria can result in them becoming resistant to antibiotics, turning the bacteria into a ‘superbug’ * MRSA is a superbug resistant to almost all antibiotics Clinical trials: * When a new drug is tested on humans to find out whether or not it is afe and if it works * Groups are chosen at random to make sure that the results of the study are reliable * The control group is the group that will be given the same drug again, or a placebo * Placebo – a ‘fake’ drug in the form of a medicine that doesn’t do anything, it just dissolves in your system * In some trials where patients are seriously ill, placebos aren’t used because it is unethical not to allow them to get the potential benefits of the new drug * Blind trial – patients don’t know if they’ve been given a drug or placebo because a patient who knows they are being treated might feel better for psychological reasons even if there hasn’t been any improvement * Double-blind trial – as well as the patients, the scientists carrying out the research also don’t find out until the end which patients were given real drugs/placebos * Open-label trials – the patients and the scientists are both aware of the treatments that have been used because they can’t be masked, e. g. if one is a drug and the other is exercise Circulatory system: * Blood is circulated around the body in tubes called blood vessels * Oxygen and nutrients are carried in the blood to the body cells and waste substances (e. g. arbon dioxide) are carried away from the cells * Cell – a basic unit of life * The heart is a pumping organ that keeps the blood flowing through the vessels * The heart is a double pump * The right side pumps deoxygenated blood to the lungs to collect oxygen and remove carbon dioxide * The left pumps oxygenated blood around the body * Aorta – biggest artery in the body * Coronary arteries – branch from the aorta and provide the heart with oxygen, blood and nutrients * Lumen – the inside space of a vessel Blood vessel| Structure and adaptation| Arteries| * Carry blood away from the heart to the body cells * The blood comes out of the heart at a high pressure so the artery walls ave to be thick, strong and elastic| Veins| * Carry blood back to the heart * The blood is at a lower pressure so the walls are thinner * The lumen is bigger than arteries so the blood can flow more easily * The valves keep the blood flowing in the right direction| capillaries| * Carry blood really close to every cell in the body to exchange substances (the walls are permeable to substances diffuse in and out) * Branches of very small arteries (a microscope is needed to see them) * Supply nutrients and oxygen and remove wastes (e. g. carbon dioxide) * Walls are only one cell thick which increases the rate of diffusion| Heart rate / blood pressure: Blood needs to be under pressure to be able to travel around our body * The pressure is kept up by the heart continuously pumping * Heart rate – number of times the heart beats in one minute * Pulse rate  œ number of times an artery pulsates in one minute * The pulsation of an artery is caused by blood being pumped through it by a heart beat * When the heart muscle contracts, blood is forced out of the heart and increases blood pressure * When the heart muscle relaxes, the heart fills with blood and blood pressure decreases * Blood pressure measurements – e. g. 135/85 the higher value is the pressure when the heart contracts and the lower value is when it relaxes * Normal / average blood pressure – 80-110/60-80 * Normal / average heart rate – 60-100bpm High blood pressure increases the risk of heart disease * High blood pressure can damage the smooth and unbroken lining of an artery * Fatty deposits can build up in these damaged areas and they restrict blood flow, increasing the blood pressure to increase * If a fatty deposit breaks through the inner lining of an artery, a blood clot can form around it which could completely block the artery * If a coronary artery becomes completely blocked, an area of the heart muscle will be totally cut off from its blood supply, receiving no oxygen – this causes a heart attack * A heart attack can cause serious damage to the heart or cause death of the heart muscle Heart disease: * Heart disease can be caused by genes but is often linked to lifestyle factors * Poor diet – cholesterol makes up a large part of fatty deposits increasing blood cholesterol which increases the risk of heart disease, food with a lot of salt increases blood pressure * Smoking – carbon monoxide reduces how much oxygen the blood can transport and nicotine increases heart rate * Stress – increases blood pressure Drugs – ecstasy and cannabis increase heart rate which increases blood pressure * Excessive alcohol – increases blood pressure * Regular moderate exercise reduces the risk of developing heart disease * Heart disease is more common in industrialised countries (e. g. UK and USA) because they can afford high fat food and don’t need to be very active because they can afford cars, etc Epidemiological studies: * Epidemiology is the study of patterns of diseases and the factors that affect them * Lifestyle factors – studying a group of people who all died from heart disease to look for similarities in their lifestyle that may be linked to heart disease, e. g. hey were all smokers or they had poor diets * Genetic studies – studying the genetic makeup of a large group of people and looking out for genetic similarities between the people who affected by heart disease Homeostasis: * Balancing inputs with outputs to maintain a constant internal environment * Body temperature and water levels are both kept constant * The environment is constantly ch anging so the conditions inside the body need to be kept steady in order for cells to function properly * Automatic control systems maintain body temperature and water levels * The three main parts to maintaining homeostasis are: 1. The receptors – detect a change in the environment 2. Processing centres – receive information and determine how the body systems respond 3. Effectors – produce the response * Negative feedback – information that causes a reversal in a control system, e. g. when we get too hot our body responds by bringing our temperature back to normal (37 degrees) * Vasodilation – when blood vessels become wider and closer to the skins surface * When body temperature goes over 37 degrees, it is detected by the receptors and a message is sent to the processing centre in the brain (hypothalamus). The effectors produce the response and the blood vessels vasodilate so that heat is lost and temperature drops. The vessels then return to their normal diameter. The kidneys maintain levels of water, urea, salts and other chemicals in the blood * Urea comes from broken down proteins and needs to be excreted because it has poisonous chemicals that can get into the blood stream * Inputs – water can be gained from drinks, food an d respiration * Outputs – water can be lost through sweating, breathing and in faeces and urine * The kidneys balance water levels by producing dilute or concentrated urine * Blood plasma – the liquid that carries blood cells and dissolved substances * The concentration of urine depends on the concentration of blood plasma (which varies with external temperature, exercise levels and the intake of fluids and salt) External temperature| Exercise | Intake of fluids and salts| * Sweat contains water so sweating causes water loss * When it’s hot, the kidneys reabsorb more water back into the blood * A small amount of concentrated urine will be produced| * Exercise makes you hotter so you sweat to cool down * Same effect as heat produced * Small volume of concentrated urine| * Not drinking enough water or eating too much salt will produce concentrated urine * Drinking lots of water will produce lots of dilute urine| * The concentration of urine is controlled by a hormone called ADH (anti-diuretic hormone) * The pituitary gland releases ADH into the bloodstream * The process of water content regulation is controlled by negative feedback When the concentration of blood plasma falls†¦| When the concentration of blood plasma rises†¦| The pituitary gland secretes†¦| Less ADH| More ADH| The kidneys reabsorb†¦| Less water| More water| The urine volume†¦| Increases| Decrease s| The urine concentration†¦| Decreases| Increases| 1. A receptor in the brain detects that the water content is too high 2. The processing centre in the brain receives the information and coordinates a response 3. The pituitary gland releases less ADH so the kidneys reabsorb less water Or 1. A receptor in the brain detects that the water content is too low 2. The processing centre in the brain receives the information and coordinates a response 3. The pituitary gland releases more ADH so the kidneys reabsorb more water * ADH production can be affected by drugs * Alcohol suppresses (restrains or forcibly stops) ADH production so the kidneys will reabsorb less water * Drinking alcohol can result in a larger amount of more dilute urine being produced * More water passes out of the body as urine which can cause dehydration * Ecstasy is an illegal recreational drug * Taking it can result in a smaller amount of more concentrated urine being produced * Ecstasy causes the production of ADH to increase so the kidneys will reabsorb more water * Less water passes out of the body as urine