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Revision B2 - Disease Pathogens • Pathogens are microorganisms that cause infectious disease. Bacteria and viruses are the main pathogens. • Bacteria are living cells and can multiply rapidly in favourable conditions. Once inside the body, they release poisons or toxins that can make us feel ill. • Viruses can only reproduce inside host cells. Once inside, they make hundreds of thousands of copies of themselves. The first line of defence The first line of defence is the body’s natural barriers. These include: • skin • chemicals in tears • chemicals in sweat • stomach acid. • The skin The skin covers the whole body. It protects it from physical damage, microbe infection and dehydration. The skin's dry, dead outer cells are difficult for microbes to penetrate. White blood cells If a pathogen manages to get into the body, the second line of defence takes over. This is called active immunity. The white blood cells have key functions in this. Functions of the white blood cells White blood cells can: • ingest pathogens and destroy them • produce antibodies to destroy pathogens • produce antitoxins that neutralise the toxins released by pathogens. • The pathogens are not the disease - they cause the disease. • White blood cells do not eat the pathogens - they ingest them. • Antibodies and antitoxins are not living things - they are specialised proteins. Phagocytes There are several types of white blood cell, each with a different function. But there are two main groups: • phagocytes or macrophages • Lymphocytes Phagocytes can pass easily through blood vessel walls into the surrounding tissue and move towards pathogens or toxins. They then either: • ingest and absorb the pathogens or toxins, or • release an enzyme to destroy them. Lymphocytes Antibodies neutralise pathogens in a number of ways: • They bind to them and damage or destroy them. • They coat pathogens, clumping them together so that they are ingested easily by phagocytes. • They bind to the pathogens and release chemical signals to attract more phagocytes. • BBC News item from 2006 about a five-year- old girl who was born without an immune system. Vaccination Vaccination involves putting a small amount of an inactive form of a pathogen into the body. Vaccines can contain: live pathogens treated to make them harmless • harmless fragments of the pathogen • toxins produced by pathogens • dead pathogens. These all act as antigens. When injected into the body, they stimulate white blood cells to produce antibodies to fight the pathogen. • Because the vaccine contains only a weakened or harmless version of a pathogen, the vaccinated person is in no danger of developing a disease. If the person later becomes infected by the pathogen, the required lymphocytes are able to reproduce rapidly and destroy it. Viruses • Some common diseases like influenza (flu) and the common cold are caused by viruses. These mutate quickly, which changes their surface proteins. Policies • Vaccinations can never be completely safe because side- effect levels vary. A balance needs to be struck between the advantages and disadvantages. For example: • Using a vaccine may be much cheaper than treating a very ill person. • The chance of falling seriously ill or dying from the disease may be far greater than the chance of experiencing a serious side-effect. Antibiotics • Substances that kill bacteria or prevent their growth. They do not work against viruses. It is difficult to develop drugs that kill viruses without damaging the body’s tissues. • Over time, bacteria can become resistant to certain antibiotics. This is an example of natural selection. In a large population of bacteria, there may be some that are not affected by the antibiotic. Drug testing 1. The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work. 2. Drugs that pass the first stage are tested on animals. In the UK, new medicines have to be. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects. 3. Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check they are safe. The substances are then tested on people with the illness to ensure they are safe and work. The circulatory system • Arteries • thick outer walls • thick layers of muscle and elastic fibres. • Veins • thin walls • thin layers of muscle and Veins elastic fibres. The heart Blood vessels called the coronary arteries supply blood to the heart muscles. If they become blocked, a heart attack can happen. Causes of heart disease • genetic factors, which show as a family history of heart disease • lifestyle factors. • smoking • lack of regular exercise • stress leading to a fast heart rate • drinking a lot of alcohol • poor diet. A lack of exercise and a diet high in salt and saturated fat cause people to: • become overweight • have high blood pressure • have high levels of cholesterol in their blood C2 Polymers • Polymers are large molecules made by joining many smaller molecules together, end to end. The smaller molecules are called monomers. Crude oil • Short hydrocarbon molecules with only a few carbon atoms are gases. • Hydrocarbon molecules with between five and 12 carbon atoms are usually liquids. • Longer hydrocarbon molecules are solids. • The separation of crude oil into different fractions through a process called fractional distillation. • The production of shorter hydrocarbon molecules from longer ones by cracking. Synthetic polymers • Monomers can join together to form polymers Lycra Gore-Tex Modifying polymers Life Cycle Assessments Recycling can include: • Melting down metals, plastics or glass so they are ready to make new objects. • Using chemical reactions to break polymers down into simpler substances that are ready for use. Problems with polymers • One of the useful properties of polymers is that they are unreactive, so they are suitable for storing food and chemicals safely. Unfortunately, this makes them difficult to dispose of. • Biodegradable Most polymers, including polyethene and polypropene, are not biodegradable • Incineration Polymers can be burnt or incinerated. They release a lot of heat energy, which can be used to heat homes or generate electricity. • Recycling Many polymers can be recycled. This reduces disposal problems and the amount of crude oil used. P2 • An object can affect another object that is some distance away from it using electromagnetic radiation. The flow chart summarises how this happens. The intensity of a beam • the number of photons arriving and • the energy each photon delivers. The effect of distance The intensity of a beam of electromagnetic radiation decreases with distance from its source. This is because the energy is spread over a larger surface area. Ionising radiation • Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage. Ionising radiation includes: • ultraviolet radiation (found in sunlight) • X-rays (used in medical imaging machines) • gamma rays (produced by some radioactive materials). Infrared light Information such as computer data and telephone calls can be converted into infrared signals and transmitted by optical fibres Microwaves Microwave radiation can be used to transmit signals such as mobile phone calls Radio waves Radio waves are used to transmit television and radio programmes. Longer wavelength radio waves are reflected from an electrically charged layer of the upper atmosphere. Non-ionising radiation • radio waves • microwaves • infrared light • visible light. Microwave ovens protect users from the radiation by using: • a metal case • a metal mesh in the glass window of the door. Mobile telephones communicate with their base stations using low-intensity microwave radiation Microwaves from the phone can penetrate body tissues to a depth of a few centimetres. They are absorbed and give up their energy to body tissues. This can cause a small amount of heating, about 0.1°C - much less than if you were standing in sunshine. Ultraviolet light is part of the Sun’s spectrum of electromagnetic radiation. It does not penetrate very far into the body’s tissues, so its effects are seen mainly in the skin and eyes. The eyes can develop cataracts, which damage your sight. There are two main dangers to the skin: • short-term acute effects - sunburn • long-term chronic effects – skin cancer • Oxygen Plants use the energy in sunlight to make their own food by photosynthesis: • carbon dioxide + water → glucose + oxygen • Photosynthesis releases oxygen into the atmosphere, and removes carbon dioxide. This reverses the effect of respiration • Absorbing ultraviolet light (Higher Tier) Ultraviolet light splits oxygen molecules, O2, into separate oxygen atoms. These react with other oxygen molecules to make ozone molecules, O3. This is a reversible process. • Ozone absorbs ultraviolet radiation. This prevents it from reaching the ground and harming living organisms, especially animals. • The Earth emits infrared radiation. This is absorbed by gases in the atmosphere called greenhouse gases: methane, water vapour and carbon dioxide. These absorb the radiation and prevent it from escaping into space. This greenhouse effect keeps the Earth warmer than it would otherwise be. Processes that remove carbon dioxide from the air: • photosynthesis by plants • dissolving in the oceans. Processes that return carbon dioxide to the air: • respiration by plants, animals and microbes • combustion (burning wood and fossil fuels such as coal, oil and gas) • thermal decomposition of limestone (for example, in the manufacture of iron, steel and cement). • Global warming • For thousands of years, the concentration of carbon dioxide in the atmosphere remained much the same. But during the past 200 years it has increased steadily • Effects of global warming Global warming could cause: • climate change • extreme weather conditions in some areas • rising sea levels.
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