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| Question | Answer |
| Characteristics of living organisms |
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| Micro-organisms | Different types e.g. bacteria, viruses, some fungi and protoctista. Can be harmful [Pathogens]- Protoctistans e.g. plasmodium, a parasite carried by a certain kind of mosquito which causes maleria. |
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Bacteria- Single cell, no nucleus, coils of DNA. Cell wall [not cellulose] and membrane. Small = 1μm. Multiply quickly and release toxins. Used in Yoghurt, cheese. soap powder. Aids digestion. Causes food poisoning, tetanus, tuberculosis, tonsillitis. CAN be treated with antibiotics. |
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Virus - Strand of genetic info [DNA/RNA] surrounded by protein coat. No nucleus, non living [can only reproduce by invading other cells - parasite]. Very small = 1nm. They inject DNA into cells to make more viruses. Eventually cells burst. Used in genetic engineering. Some kill bacteria. Chickenpox, AID's, cold, influenza. CAN'T be treated by antibiotics. |
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Have Nuclei, and lack chlorophyll. Multi-cellular fungi are made up of tubular threads called hyphae. A dense mat of hyphae, called a mycelium, make up the body of the fungus. Aerial hyphae support the spores; feeding hyphae secrete digestive enzymes and then absorb soluble molecules. Grow longer and release poisons which attack cells. Used as a source of antibiotics . Used in the production of beer/bread. Athletes foot, ringworm. CAN NOT be treated by antibiotics. |
| Bacterial Growth | They grow by binary fission [splitting in half and x2] |
| Phases of Bacterial Growth |
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| Ways of spreading Disease | Air (droplet infection); direct contact between people (inc sexual); indirect contact (e.g. cough/ syringe); transferred via insects; passed through contamination (food/water) |
| Vaccines | Vaccines- contain a material which stimulates the body's defence (artificial active). A vaccine contains a dead or weakened (attenuated) form of a microbe which stimulates the body's white blood cells to make antibodies to kill the microbes. Some vaccines contain antibodies themselves (artificial passive) |
| Antibiotics | Antibiotics- used to kill bacteria or to prevent their growth inside the body; the full course of antibiotics must be taken to ensure that all the microbes are killed. |
| Antiseptics | Antiseptics- applied to living tissue/ skin to reduce the possibility of infection e.g. mouthwash |
| Disinfectant | Disinfectant- substances that are applied to non-living objects to try to destroy micro-organisms. |
| Diseases | Not all diseases that are caused by microbes can be easily treated by medicines; not all diseases are caused by microbes. |
| Preserving Food | ❖ Bacteria do not reproduce at temp below 0°c (e.g. in a freezer); they reproduce slowly at cold temp (e.g. fridge) and more quickly when it's warmer (e.g. room temp, 25°c, body temp - 37°c then even warmer). We refrigerate food to preserve it / stop it from going off by preventing the bacterial population from growing too large . Cooling/ freezing does not kill microbes, it just slows the enzyme activity to slow the reproduction. ❖ Bacteria are killed at high temp (enzymes/proteins are denatured). Food such as raw meat must be cooked to kill off microbes and prevent food poisoning. ❖ Examples of other ways of food preservation: smoking, pickling, irradiation, salting. |
| Growing Bacteria in lab | Bacteria need food, water, warmth, appropriate pH (acidity), absence of toxins and time in order to grow. Bacteria and fungi can be grown safely in the lab on agar plates, using aseptic (=sterile) techniques. Safety precautions are required in order to avoid contact with the microbes e.g. keep the lid on the dish, seal the dish, wear gloves/masks/goggles. |
| Immunity | Immune: Resistant to disease/having antibodies against a disease. Immunisation helps to protect against some diseases and can be natural or artificial and can active (an individual makes their own antibodies) or passive (an individual is given antibodies). e.g. natural passive immunity: antibodies can be passed to a foetus/baby via the placenta/breast milk. |
| 1st Natural defence mechanisms to prevent infection | 1st line: Preventing microbes from entering the body. Skin acts as a barrier and produces antiseptic oils; platelets in the blood cause clotting to close a cut; enzymes in tears can kill some microbes; stomach produces hydrochloric acid to kill microbes; trachea has mucus producing cells (mucus is sticky and traps the microbes/dust) and ciliated epithelial cells (have a band of cilia [hair] that move rhythmically to move mucus) |
| 2nd Natural defence mechanisms to prevent infection | 2nd line: phagocytes (non-specific white blood cells) respond to the presence of foreign bodies and engulf them and digest them. |
| 3rd Natural defence mechanisms to prevent infection | 3rd line: Natural active immunity. lymphocytes (specific white blood cells) produce antibodies in response to antigens (distinctive markers e.g. proteins on the surface of invading microbes). The antibodies stay in the blood ready to fight the infecting microbes if it returns. The antibodies are produced much more quickly the second time around, and much more are produced. The antibodies will only target specific antigens and no others. |
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