IGCSE Biology Revision Guide Mock Exam PDF

Transport in plants Chapter 8 The transport system that carries water is made up of a tissue called xylem The transport system that carries water is made up of a tissue called phloem Xylem ○ It is made of many dead and hollow cells joined end to en...

Transport in plants Chapter 8 The transport system that carries water is made up of a tissue called xylem The transport system that carries water is made up of a tissue called phloem Xylem ○ It is made of many dead and hollow cells joined end to end. No end walls ○ It contains no cytoplasm or nuclei. ○ Its walls are made up of cellulose and lignin, it helps keep the xylem upright Phloem ○ Still have end walls, it has formed into sieve plates which have small holes in them. ○ Phloem transports sucrose and amino acids from the leaves to roots and flowers. ○ The cells are known as sieve tube elements, they contain cytoplasm but no nucleus and contain many other organelles ○ They don't have lignin in their cell walls ○ Sieve tube element’s companion cell has nucleus and many other organelles, it provides sieve tube elements with some of their requirements Vascular bundles ○ A group of xylem vessels and phloem tubes is called a vascular bundle ○ In the root, it’s found in the center while in the shoot, they are arranged in a ring near the outside edge Water uptake ○ Root cap is a layer of cells that protects the roots as it grows through the soil. They are present at the tip of the end of the root. ○ The rest of the root is covered by layer of cells called epidermis ○ Water moves into a root hair by osmosis The water in the soil is normally a more dilute solution therefore water diffuses into the  root hair, down its concentration gradient through the partially permeable membrane. ○ The pressure at the top is lowered and the pressure at the bottom stays high therefore water flows up, the pressure is lowered through transpiration. Root Hair Cells Root hairs are single-celled extensions of epidermis cells in the root They grow between soil particles and absorb water and minerals from the soil Water enters the root hair cells by osmosis This happens because soil water has a higher water potential than the cytoplasm of the root hair cell Structure of the root The root hair increases the surface area of the cells significantly This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport Transpiration ○ It is the evaporation of water from a plant. It mostly takes place from the leaves. ○ The mesophyll cells inside the leaf are each covered with a thin layer of moisture, some of this moisture evaporates from the cells, water vapour diffuses out of the leaf through the stomata. Water from the xylem vessels in the leaf travel to replace it. This constant process reduces the effective pressure at the top of the xylem vessels letting the water flow up. ○ This process is known as transpiration stream Cohesion ○ Water molecules have a strong tendency to stick together, this is called cohesion ○ When the water is pulled up the xylem vessels, the whole column of water stays together.  ○ Without cohesion the water column would break apart and the whole system would not work. The structure of the plant is adapted to help it take up water and move it up throughout the plant ○ The root hair cells provide a huge surface area through which water can be absorbed. This increases the quantity of water that can move into the plant at any moment. ○ The hollow, narrow xylem vessels provide an easy pathway for water to flow all the wat up from the roots to the very top of the plant ○ The many air spaces inside the lead mean that there is a large surface area of wet cells from which water can evaporate into the air. This increases the rate of evaporation, drawing more water out of the xylem ○ The stomata, when open, allow water vapour to diffuse easily out of the lead. This reduces the water potential inside the lead, which encourages more water to evaporate from the surfaces of the mesophyll cells Measuring Transpiration Transpiration can be measured by an instrument called a potometer. The diagram below shows the apparatus set up for a potometer. Vaseline is applied around the rubber bungs to ensure an airtight seal, thus the only water loss from the apparatus is via transpiration. The function of the reservoir is to allow the air bubble to travel back to the start of the measuring scale on repeating the experiment. As water moves up through the plant the air bubble moves along the scale giving a measure of water absorbed by the plant over time and hence the transpiration rate. Conditions that affect transpiration rate Temperature ○ On hotter days, water will evaporate more quickly, they are directly proportional. Humidity ○ The higher humidity, the less water will evaporate from the leaves, because there is not much of a diffusion gradient for the water between the air spaces inside and lead and the wet air around it. They are inversely proportional  Wind speed ○ Transpiration rate increases as wind speed increases. They are directly proportional Light intensity ○ Directly proportional Water supply ○ Directly proportional, less water supply, less water to transpire  Transport in animals Chapter 9 Circulatory system ○ The circulatory system is a system of blood vessels with a pump and valves to ensure one way flow of blood Single circulation ○ Single circulation means blood passes through the heart only once ○ E.g fish Double circulation ○ Double circulation means blood passes through the heart twice e.g mammals ○ Double circulation is advantageous because it maintains a higher blood pressure compared to a single circulation system. Blood flow around the body ○ Deoxygenated blood enters the right atrium (RA) ○ Deoxygenated blood enters the right ventricle (RV) ○ Deoxygenated blood is pumped by the right ventricle to the lungs to become oxygenated ○ Oxygenated blood enters the left atrium (LA) ○ Oxygenated blood enters the left ventricle (LV) ○ Oxygenated blood is pumped by the LV to the rest of the body ○ Body cells use the oxygen and cause the blood to become deoxygenated ○ Deoxygenated blood returns to the heart and the cycle repeats Vena cava → right atrium → atrioventricular valve → right ventricle → semilunar valve → pulmonary artery → lungs → pulmonary vein → left atrium → atrioventricular valve → left ventricle → semilunar valve → aorta → vena cava Functions of different structures Atrium ○ The right and left atrium contracts to pump blood into the right and left ventricles respectively Ventricles ○ The right ventricle contracts to pump blood to the lungs (to become oxygenated) ○ The left ventricle contracts to pump blood to the rest of the body. It has a thicker wall than the right ventricle because it needs to pump blood further and therefore needs more force Atrioventricular valves ○ The atrioventricular valves separate the atrium and ventricles on both sides of the heart ○ These valves present the backflow of blood, thus ensuring a one way flow of blood form the atria to the ventricle Semilunar valves ○ Semilunar valves are found within the pulmonary arteries and the aorta. They prevent the backflow of blood and ensure unidirectional blood flow in the arteries. Pulmonary artery ○ The pulmonary artery carries blood from the right ventricle to the lungs Pulmonary vein ○ The pulmonary vein carries blood from the lungs to the left atrium Aorta ○ The aorta is a large artery which carries blood from the left ventricle to the rest of the body Vena cava ○ The vena cava is a large vein which carries deoxygenated blood from the body back to the heart (right atrium) Septum ○ The septum is a thick muscular wall which separates the right and left side of the heart. This separation is important to ensure that oxygenated and deoxygenated blood does not mix. Activity of the heart Physical activity increases heart rate ○ Heart rate is the rate at which the heart burns. The most common way to measure heart rate is by measuring the pulse rate ○ The pulse is exactly equal to the heart rate, as the contractions of the heart cause the increase in blood pressure in the arteries that lead to a noticeable pulse ○ Physical activity increases the energy demand in muscles such as the arms and legs. With an increased rate of respiration, blood must have to travel quicker to the muscles to supply them with oxygen/nutrients whilst removing waste products like carbon dioxide Electrocardiogram (ECG) ○ An electrocardiogram is a device which can track heart activity. It can accurately measure pulse rates via the opening and closing of heart valves  Coronary heart disease ○ The heart muscles too need a blood supply because they too are respiring muscles ○ The coronary artery is the very important artery which provinces the heart muscles with blood ○ Coronary heart disease is when the coronary artery becomes blocked, leading to blood(and oxygen) starvation in the heart muscles. This leads to an heart attack Causes of coronary heart disease ○ Blockage of the coronary artery begins by the narrowing of the artery due to cholesterol build up on the inner walls ○ Total blockage can occur when a blood clot gets stuck in these narrow arteries Risk factors ○ There are certain factors that increase the risk of an individual developing coronary heart disease Poor diet Stress Smoking Genetics Age Gender Treatment with medications ○ Blood thinning medications are used to reduce the chances of a blood clot forming Treatment with surgery ○ Stent is a tube-shaped device which is placed inside the coronary arteries to physically hold it open ○ Angioplasty is a stent with a balloon which can be inflated once the stent is inserted to even further increase the diameter to the artery ○ Bypass is the process of making a separate or new artery to allow for an alternate blood path that the heart can use to receive blood while the stent is being attached  Blood vessels ○ Blood vessels are tubular structures carrying blood through the tissues and organs. Starting from the heart, the pathway of blood is as follows ○ Heart → artery → arteriole → capillary → venule → vein → heart Arteries ○ Arteries take blood away from the heart. They have several important structural features Thick muscular walls to withstand blood being carried at high pressures Narrow lumen which expands as blood pulsates through to maintain blood pressure Valves absent since high blood pressures prevent backflow Arterioles ○ Arterioles are smaller branches of an artery. They eventually branch further to form capillaries Arterioles have muscular/elastic walls that can constrict and dilate in order to regulate blood flow Capillaries ○ Capillaries are fine branching blood vessels that form a network between the arterioles and venule ○ They allow for the nutrient and waste exchange between the blood and tissues of the body. The features of capillaries are as follows Walls are one cell thick to allow for quick diffusion of diffuse rates of nutrients/wastes Lumen has a diameter of just 1 red blood cell, to allow blood cells to pass closely to walls for faster diffusion rates Valves are absent since the narrow capillary lumen ensures unidirectional blood flow. Venules ○ Venules are small vessels formed from the joining of the capillaries. Venules combine to establish a vein. Veins ○ Veins take the blood towards the heart. Their structural features are as follows Thin walls with little muscles and elastic fibers (thick muscles are not required as the blood is carried at low pressure) Large lumen to reduce blood flow resistance Valves present to prevent blood backflow Blood ○ Blood is a mixture of several components such as Red blood cells White blood cells Platelets Plasma Plasma ○ Blood plasma makes up about 50% of the blood. It is a yellowish liquid that carries the other blood components such as RBC/WBC/platelets Red blood cells ○ Red blood cells contain hemoglobin which binds to oxygen for transportation around the body White blood cells  ○ White blood cells are part of the immune system that helps to destroy foreign organisms such as bacteria ○ There are 2 types of WBC cells Phagocytes are types which engulf and digest pathogens via phagocytosis Lymphocytes are white blood cells which produce antibodies Platelets ○ They are substances that form blood clots which is a protective mechanism to prevent blood loss during an injury ○ At the site of damage, platelets immediately stick together and release chemical signals which attract other nearby cells and clump them together ○ A series of chemical reactions take place. Fibrinogen is converted into fibrin, and this forms a thread which traps red blood cells to establish a thick clot. The clot seals off the site of damage.  Pathogens and immunity Chapter 10 A microorganism is a tiny organism that can only be seen with a microscope A pathogen is a microorganism that causes disease. Group to which pathogen belongs Examples of diseases which they cause Viruses Influenza. Common cold, poliomyelitis, AIDS Bacteria Cholera, syphilis, whooping cough, tuberculosistetanus Protoctista Malaria, amoebic dysentery Fungi Athlete’s foot, ringworm Diseases that are caused by pathogens can usually be passed from one person to another. They are called transmissible diseases How pathogens enter the body Direct contact ○ The passing of a pathogen to an uninfected person is called transmission ○ The entry of the pathogen into the body is known as infection. The person which pathogen lives and breeds is said to be a host ○ Viruses can be transmitted when an infected person’s blood comes into contact with another person's blood ○ The fungus that causes skin infection can be shared by sharing the same towel with an infected person. Indirect transmission ○ Through the respiratory passage Cold and influenza viruses are carried in the air in tiny droplets of moisture. Every time someone with these illnesses speaks or coughs, millions of viruses are propelled into the air. If you breathe these droplets, you may be infected as well. You can also pick up viruses if you touch a surface on which they are present and put your hands on your face. ○ In food or water Bacteria such as Salmonella can enter your alimentary canal with the food that you eat. If you eat a large number of these bacteria, you may get food poisoning Fresh foods such as fruit and vegetables should be washed in clean water before you eat them. Cooking usually destroys bacteria so eating recently cooked food is generally safe. Many pathogens including viruses that cause poliomyelitis and the bacterium that causes cholera are transmitted in water. If you swim in water that contains these pathogens or drink water containing them, you run the risk of catching these diseases. ○ By vectors A vector is an organism that carries a pathogen from one host to another. Dogs, skunks, raccoons and bats are vectors for rabies Protoctista pathogen Plasmodium in their saliva Body defences Mechanical barriers ○ Mechanical barriers act as a physical obstruction to prevent pathogens from entering our body. For example, Skin Nose hairs Chemical barriers ○ Chemical barriers are chemical substances in the body which help to trap or destroy pathogens. For example, Mucus Traps bacteria that enter the respiratory system via air. The mucus is then beat upwards by the cilia and pushed up to the mouth Stomach acid The acidity kills pathogens that enter our digestive system via the food we eat. Food hygiene ○ Keep your own bacteria and viruses away from food. Always wash your hands before touching or eating food. ○ Keep animals away from food. Animals are more likely to have harmful bacteria on them. Some particularly dangerous things such as house flies have harmful bacteria on their feet. Rats or mice often carry pathogens. Covering food to keep flies and other animals is always a good idea ○ Do not keep foods at room temperature for long periods of time. Bacteria reproduction and temperature are directly proportional therefore higher the temperature, higher reproduction of the bacteria therefore it should be kept in the fridge after a short period of time ○ Keep raw meat away from other foods. Raw meat often contains bacteria. If the bacteria get into other foods that might be eaten raw, then they might breed there. Therefore foods such as salads and vegetables that are to be eaten raw should be washed in clear water before eating. Waste disposal ○ All rubbish from countries is usually dumped into a landsite, all kinds of rubbish are just piled up. Animals such as houseflies, rats and stray dogs forage for food in the rubbish ○ Bacteria breed in the waste food. Dangerous chemicals seep out of the rubbish polluting the ground and waterways. ○ Some of the rubbish in the landfill site is rotted by decomposers, especially bacteria. This produces a gas called methane which can cause explosions if it's allowed to build up. ○ Placing pipes in the rubbish can allow the methane to escape harmlessly into the air or it can be collected as fuel Sewage treatment ○ Sewage is waste liquid that has come from houses , industry and other parts of villages. Sewage is mostly water, but also contains many other substances, these include urine and faeces, toilet paper, detergents, oil and many other chemicals. ○ Raw sewage contains many bacteria and other microorganisms, some of which are likely to be pathogens especially if it gets into their mouths. ○ Poliomyelitis and cholera are just 2 of the serious diseases that can be transmitted through water polluted with raw sewage. The immune system There is one type of white blood cell called lymphocytes which produce chemicals called antibodies. These chemicals help to destroy pathogens Antibodies ○ There are thousands of different kinds of lymphocytes. Each kind is able to produce a different sort of antibody ○ An antibody is a protein molecule with a particular shape. Like an enzyme molecule, its shape is just right to fit into another molecule. ○ To destroy a particular pathogen, antibody molecules must be made which are just the right shape to fit into molecules on the outside of the pathogen. These pathogen molecules are called antigens. ○ When antibody molecules lock onto the pathogen, they kill the pathogen. One way is simple to alert phagocytes to the presence of pathogens, so that they come and destroy them. Another way is that the antibodies may start off a series of reactions in the blood which produce enzymes to digest the pathogens. ○ Most of the time, most of the lymphocytes do not produce antibodies. It would be a waste of energy and materials if they did. Instead, each lymphocyte waits for a signal that is a pathogen which can be destroyed by its particular antibody. ○ If the pathogen enters the body, it's likely to meet a large number of lymphocytes. The lymphocyte will start to divide rapidly by mitosis, making a clone of lymphocytes just like itself. These lymphocytes that secrete their antibody, destroying the pathogen Memory cells ○ When a lymphocyte clones itself, not all of the cells make antibodies. Some of them simply remain in the blood and other parts of the body, these are call ○ If the same kind of pathogen gets into the body again, these memory cells will be ready and waiting for them. They will kill the pathogens before they have time to produce a larger population and do any harm. The person has become immune to that type of pathogen. Vaccination ○ A vaccine contains weakened or dead viruses or bacteria that normally cause diseases. These pathogens have the same antigens as the normal ones but they are not able to cause fatal diseases  ○ When the pathogens are introduced into the body, they are recognised by the lymphocytes that can make memory cells, which give long term immunity. Active immunity ○ Defense against a pathogen by antibody production in the body. A person has active immunityto a disease if they have made their own antibodies and memory cells that protect against it ○ You can develop active immunity by Having the disease and getting over it Being vaccinated with weakened pathogens ○ Active immunity can be very long-lasting. Passive immunity ○ Short-term defense against a pathogen by antibodies acquired from another individual such as from mother to infant. ○ Babies get passive immunity by breastfeeding. Breast milk contains antibodies from the mother which are passed on to her baby. This is useful as a young baby’s immune system is not well developed, and so the mother’s antibodies protect it against any diseases to which she is immune. ○ Another way is to be injected with antibodies that have been made by another organism ○ Passive immunity only lasts for a short time as the antibodies eventually break down. No lymphocytes have been stimulated to make clones of themselves so no production of memory cells. Auto-immune diseases ○ Lymphocytes behave as though some of our own cells are foreign and react to them as they would to an invasion of pathogens ○ Diseases that result from this kind of malfunction of the immune system are called auto- immune diseases. For example, Type 1 diabetes Type 1 diabetes ○ One of the hormones produced by pancreas with insulin, this hormone is made when blood glucose concentration rises above normal, it causes the concentration to fall ○ Insulin is made by a particular type of cell in the pancreas called beta cells ○ In some people, the cells of the immune system attack the beta cells and destroy them. The loss of beta cells means that insulin is no longer produced so blood glucose concentration is not controlled. ○ This results in diabetes in which blood glucose levels fluctuate widely. ○ Most people with type 1 diabetes take insulin at regular intervals as well as taking great care over what they eat. IGCSE Chapter 10 Diseases and Immunity The chapter of "Diseases and Immunity" focuses on understanding how diseases are caused, how they are transmitted, and how the body defends itself against pathogens. This chapter provides a comprehensive understanding of the immune system, types of immunity, and the role of vaccination in disease prevention. 1. Pathogens and Disease  Pathogens are microorganisms that cause diseases in humans, animals, and plants. They include: o Bacteria (e.g., Salmonella, Tuberculosis), o Viruses (e.g., Influenza, HIV), o Fungi (e.g., Athlete's foot), o Protozoa (e.g., Malaria). Disease-Causing: These pathogens invade the body and cause illness by damaging tissues, producing toxins, or interfering with normal body processes. Transmissible Diseases: These diseases can be spread from one host to another, often through direct or indirect contact. Diseases like the common cold, malaria, and cholera are examples of transmissible diseases. 2. Transmission of Pathogens Pathogens can spread in a variety of ways, depending on the nature of the pathogen. Direct Contact Transmission: Pathogens can be transmitted when infected individuals come into physical contact with others. This includes: o Touching: Pathogens can spread through skin contact, e.g., herpes or warts. o Body Fluids: Transmission via fluids such as blood, semen, saliva, or mucus. Examples include HIV or Hepatitis. o Airborne Droplets: When an infected person sneezes or coughs, pathogens are released into the air and can be inhaled by others (e.g., flu, tuberculosis). Indirect Transmission: This type of transmission occurs without direct contact between individuals. It can happen through: o Contaminated Surfaces or Objects: Pathogens can survive on surfaces like doorknobs, utensils, or furniture and can infect individuals who come into contact with these contaminated surfaces (e.g., norovirus). o Contaminated Water or Food: Pathogens can contaminate water supplies and food sources, leading to diseases such as cholera or food poisoning (e.g., Salmonella). o Infected Animals: Certain diseases are transmitted through animal vectors. For example, Malaria is transmitted by mosquitoes, and Rabies can spread through animal bites. o Airborne Transmission: Some diseases, like tuberculosis or the flu, are transmitted via small droplets released when an infected person coughs or sneezes. 3. The Body’s Defences Against Pathogens The human body has several defence mechanisms that help prevent infections and fight pathogens that enter the body.  Skin: The skin acts as a physical barrier, preventing pathogens from entering the body. It also produces oils and sweat that contain chemicals that can kill certain pathogens. Hairs in the Nose: The hair inside the nose traps dust, pathogens, and other particles that are breathed in, preventing them from entering the respiratory system. Mucus: The respiratory tract and digestive system are lined with mucus that traps pathogens. Cilia (tiny hair- like structures) move the mucus, along with trapped pathogens, out of the body (through coughing or sneezing). Stomach Acid: The stomach produces hydrochloric acid that creates an acidic environment, killing many pathogens that enter the digestive system with food and water. White Blood Cells: These cells are the body's primary defence against infection. o Phagocytes: These are a type of white blood cell that engulf and digest pathogens. They are responsible for the process of phagocytosis. o Lymphocytes: These cells produce antibodies (proteins that specifically target pathogens) and can also destroy infected cells. Lymphocytes are crucial in the immune response to infections. How Lymphocytes Work in the Immune System? Lymphocytes are a type of white blood cell that play a crucial role in the immune system by recognizing and responding to specific pathogens (bacteria, viruses, fungi, etc.). They are part of the adaptive immune system, which means they are specialized to recognize and fight specific pathogens and provide long-term immunity. A. Activation of Helper T Cells When a pathogen enters the body, it is detected by the immune system. Helper T cells detect specific antigens Once a helper T cell encounters an antigen presented by an antigen-presenting cell, it becomes activated. This activation requires signals from the antigen-presenting cell and additional molecules. B. Role of Helper T Cells in the Immune Response Helper T cells enhance the immune response by producing antibodies and promoting the activation of other lymphocytes involved in fighting the infection. C. Formation of Memory T Cells After the initial immune response, some of the activated helper T cells do not die but instead become memory T cells. Memory T cells remain in the body for long periods, sometimes for years or even a lifetime, and "remember" the specific antigens they encountered during the initial infection. If the body is exposed to the same pathogen again, the memory T cells can recognize the antigen quickly and activate a faster and more effective immune response. D. The Role of Memory Cells in Immunity Memory T cells provide the basis for immunity. They allow the immune system to respond more rapidly and strongly if the same pathogen invades the body again.  Because memory T cells "remember" the antigens, they can trigger the activation of both helper T cells and B cells much more quickly upon subsequent exposures to the pathogen, leading to a faster production of antibodies. 4. Control of Disease Spread To prevent the spread of disease, certain practices and measures are necessary. Clean Water Supply: Ensuring that water is free from harmful pathogens is crucial in preventing waterborne diseases like cholera, typhoid, and dysentery. Hygienic Food Preparation: Proper handling, cooking, and storage of food prevent the contamination of food by bacteria or viruses. Practices such as washing hands, cooking meat thoroughly, and refrigerating food properly help reduce the risk of foodborne diseases. Good Personal Hygiene: Washing hands with soap and water, covering your mouth when coughing or sneezing, and maintaining general cleanliness reduce the chances of spreading pathogens. Waste Disposal: Effective disposal of human waste prevents contamination of water sources and helps control the spread of diseases such as cholera and dysentery. Sewage Treatment: Sewage treatment processes clean wastewater by removing pathogens and pollutants before it is released back into the environment. This reduces the chances of water borne diseases spreading. 5. Immunity: Body’s Defence System Immunity refers to the body’s ability to resist infections. There are two main types of immunity: active immunity and passive immunity. Active Immunity Active immunity occurs when the body produces its own antibodies in response to infection or vaccination. Antibodies: These are proteins produced by white blood cells (specifically lymphocytes) that can bind to specific pathogens. Antibodies neutralize pathogens by binding to their antigens or marking them for destruction by phagocytes. Antigens: These are molecules on the surface of pathogens that trigger an immune response. Each pathogen has a unique set of antigens, like a "name tag," which allows the immune system to recognize and respond to it. Complementary Shapes: Antibodies have shapes that are complementary to the antigens they target. This is like a lock and key mechanism, where only specific antibodies fit with their corresponding antigens. Vaccination Vaccination is a method of introducing weakened, dead, or inactivated pathogens or their antigens into the body to stimulate an immune response. How Vaccines Work: Vaccines expose the immune system to harmless antigens from a pathogen. This triggers an immune response where lymphocytes produce antibodies and memory cells that "remember" how to fight the pathogen in the future. Memory Cells: These cells are a type of lymphocyte that stays in the body long after an infection or vaccination. If the body is exposed to the pathogen again, memory cells can quickly respond, leading to a faster and stronger immune response. Vaccination helps to control the spread of diseases by providing immunity without causing the disease. It can be used to protect individuals and populations, reducing the prevalence of certain infections. Passive Immunity Passive immunity involves receiving antibodies from another individual, rather than the body producing them. Natural Passive Immunity: This occurs when antibodies are transferred from mother to child during pregnancy through the placenta or through breast milk. This provides infants with immediate protection against infections. Artificial Passive Immunity: This occurs when antibodies are given to an individual from an outside source, such as in the form of an injection of antibody-rich serum. No Memory Cells: In passive immunity, the body does not produce its own memory cells, so immunity is temporary and lasts only as long as the antibodies are present in the body. 6. Cholera is an infectious disease caused by the bacterium Vibrio cholerae. It primarily affects the intestines and leads to severe symptoms such as diarrhea and dehydration. Cholera is typically transmitted through contaminated water or food. Here's a detailed look at how cholera works, its symptoms, transmission, and treatment: Cause of Cholera Bacterium: Vibrio cholerae is the bacterium responsible for cholera. It is a gram-negative, comma-shaped bacterium that thrives in contaminated water, especially in areas with poor sanitation. Cholera Toxin: The bacteria release a potent toxin called the cholera toxin (CT), which plays a central role in the disease's pathology. This toxin is responsible for the symptoms associated with cholera. How Cholera Spreads Transmission: Cholera is mainly spread through oral transmission, meaning that the bacteria are ingested when a person consumes food or water contaminated with the faces of an infected person. o Contaminated Water: Cholera is often associated with drinking water that has been contaminated with human waste. In areas with poor sanitation or inadequate sewage treatment, the risk of cholera transmission is higher. o Contaminated Food: Food can also become contaminated with Vibrio cholerae through improper handling or when food is washed with contaminated water.  o Person-to-Person Spread: While less common, cholera can spread through contact with infected bodily fluids (e.g., faeces or vomit). How the Disease Develops After the cholera bacteria are ingested, they pass through the stomach and enter the small intestine. The cholera toxin binds to the cells of the intestinal wall, causing them to secrete excessive amounts of chloride ions into the intestine. This leads to the secretion of large volumes of water into the intestinal lumen by osmosis, resulting in profuse watery diarrhoea. The massive loss of water and electrolytes causes dehydration, leading to a decrease in blood volume, shock, and potentially death if not treated. Symptoms of Cholera Watery Diarrhoea: The hallmark of cholera is with the watery stools containing small particles of mucus. This diarrhoea can be profuse, often exceeding 1lt per hour. Dehydration: As a result of the diarrhoea, the body loses large amounts of water and electrolytes, leading to symptoms of dehydration: o Thirst o Dry mouth and skin o Rapid heartbeat o Low blood pressure o Sunken eyes o Muscle cramps Vomiting: Some people may experience vomiting in addition to diarrhoea, further contributing to the loss of fluids. Severe Cases: If left untreated, cholera can lead to severe dehydration, shock, kidney failure, and death within hours. Treatment for Cholera Rehydration: The primary treatment for cholera is to rehydrate the patient as quickly as possible. Oral Rehydration Salts (ORS) are used to replace lost fluids and electrolytes. In severe cases, intravenous (IV) fluids may be needed. Antibiotics: Antibiotics can be used in severe cases to reduce the duration and severity of symptoms, but the focus is on rehydration. Zinc Supplementation: Zinc is often given to children with cholera to reduce the duration of diarrhoea and prevent further complications. Prevention of Cholera Safe Drinking Water: Ensuring access to clean and safe drinking water is the most effective way to prevent cholera. o Use of chlorination or filtration systems to treat drinking water. Sanitation and Hygiene: Proper waste disposal and improving sanitation systems are critical in preventing the spread of cholera.  o Handwashing with soap and water, especially after using the bathroom, and before eating or preparing food. Vaccination: Oral cholera vaccines are available and can help reduce the risk of cholera, especially in areas where outbreaks are common. 7. Food Hygiene involves practices that prevent contamination of food by harmful microorganisms (bacteria, viruses, fungi) that can cause food poisoning due to Salmonella bacteria. Key practices include: Proper Storage: Keep food at the correct temperatures (cold foods cold, hot foods hot). Handwashing: Always wash hands before handling food to avoid transferring harmful microbes. Cooking to Safe Temperatures: Ensure food is cooked thoroughly to kill harmful bacteria. Avoid Cross-Contamination: Use separate utensils for raw and cooked foods. Cleanliness: Keep food preparation areas clean and sanitize surfaces regularly. Use of Safe Water: Ensure that water used in food preparation is clean and safe. 8. Personal Hygiene: Personal hygiene is crucial for preventing the spread of infectious diseases. This includes: Washing Hands: Regular handwashing with soap and water to remove dirt and pathogens. Clean Clothing: Wearing clean clothes and ensuring that hair is clean and tied back when handling food. Covering Coughs/Sneezes: To prevent the spread of respiratory diseases. Dental Hygiene: Brushing teeth regularly to prevent infections like gingivitis and tooth decay. 9. Landfill Sites for Waste Disposal: A landfill site is a designated area for the disposal of waste materials, particularly solid waste. Proper management of landfill sites is important for environmental and health protection. The landfill should be designed to ensure that waste is compacted in layers. Waste is first shredded or crushed, then compacted and covered with soil at regular intervals to minimize air and water exposure. As organic waste decomposes in the landfill, it generates methane gas therefore pipes are used to release the gas to avoid explosion. Each day, a layer of soil, sand, or other material is applied to the surface of the waste to minimize odor, pests, and the spread of disease. This also helps to reduce wind-blown litter. Once it is completely filled then it is covered and plants are grown on top of it. Sewage Treatment: Sewage treatment is the process of cleaning wastewater (sewage) to remove harmful microorganisms and contaminants before it is released back into the environment. Importance of Sewage Treatment: Prevents the spread of waterborne diseases such as cholera, dysentery, and typhoid. Protects aquatic ecosystems from contamination. Ensures safe water quality for drinking and recreational use. 10. COVID-19: Implications for Public Health and Hygiene COVID-19, caused by the SARS-CoV-2 virus, emerged as a global pandemic in late 2019 and has significant implications for public health, hygiene, and disease prevention. The virus primarily spreads through respiratory droplets from coughing, sneezing, and talking, but can also be spread through fomite transmission (contaminated surfaces) and, to a lesser extent, airborne transmission in crowded or poorly ventilated spaces. Key Measures for Preventing the Spread of COVID-19 In the context of disease control and prevention, the following measures are critical to reducing the transmission of COVID-19: 1. Personal Hygiene: o Handwashing: Frequent and thorough washing of hands with soap and water for at least 20 seconds helps prevent the spread of the virus. If soap and water are not available, hand sanitizer with at least 60% alcohol is effective. o Face Masks: Wearing face masks helps reduce the transmission of respiratory droplets, especially in indoor or crowded settings. o Social Distancing: Maintaining physical distance (at least 1 meter) from others reduces the chances of airborne transmission in crowded spaces. 2. Quarantine and Isolation: o People who have been exposed to the virus or are showing symptoms should stay home and avoid contact with others to prevent further spread. 3. Vaccination: o Vaccines for COVID-19, such as the Pfizer-BioNTech, Moderna, and AstraZeneca vaccines, have been developed to protect individuals from severe illness, hospitalization, and death. Widespread vaccination is a critical strategy to achieve herd immunity and control the pandemic. 4. Surface Cleaning and Disinfection: o High-touch surfaces like doorknobs, handrails, and light switches should be regularly disinfected to prevent fomite transmission. This detailed overview provides a comprehensive understanding of the causes of diseases, how the body defends itself, and how immunity plays a critical role in disease prevention and control. Chapter 11 Respiration Respiration Respiration: Chemical reactions that break down nutrient molecules in living cells to release energy. Uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature. Respiration involves the action of enzymes in cells to speed up the reaction. Aerobic Respiration Aerobic Respiration: chemical reactions in cells that use oxygen to break down nutrient molecules to release energy Glucose+Oxygen→CarbonDioxide+Water C6H12O6+6O2→6CO2+6H2OC6H12O6+6O2→6CO2+6H2O Anaerobic Respiration Anaerobic Respiration: chemical reactions in cells break down nutrient molecules to release energy without using oxygen. In muscles (vigorous exercise): o Glucose→Lactic Acid In yeast (single-cell fungi): o Glucose→Ethanol+Carbon Dioxide o C6H12O6→2C2H5OH+2CO2C6H12O6→2C2H5OH+2CO2 Disadvantages of Anaerobic Respiration: o Only produces 1/20 of the energy per glucose molecule that aerobic respiration would o Produces poisonous lactic acid Lactic Acid: o Builds up in muscles and blood during vigorous exercise o The heart, liver and kidneys need extra oxygen to do this, which causes you to continue breathing heavily after exercise. o The extra oxygen is called the oxygen debt. Oxygen Debt is removed by: o continuation of fast heart rate to transport lactic acid in the blood from the muscles to the liver o continuation of deeper and faster breathing to supply oxygen for aerobic respiration of lactic acid o aerobic respiration of lactic acid in the liver  Gas Exchange in Humans Gas Exchange Surfaces Structure of the Lungs The lung contains a diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries. Cartilage (in the trachea): prevents the trachea from collapsing during the absence of air and protects it by keeping it open. Ribs: to protect vital organs and blood vessels and expand and contract (and efficient breathing). Intercostal (internal & external) muscles: situated between the ribs that create and move the chest wall. Diaphragm: produces volume and pressure changes in the thorax, leading to the ventilation of the lungs. Composition of Breathing Dry Air Physical Activity on Breathing Physical activity increases the breathing rate – more respiration - and higher CO2 concentration in the blood. This is measured with a spirometer to produce a spirogram. During exercise, tissues respire at a higher rate; the change in breathing volume and rate helps keep CO2 concentration and pH safe.  Internal intercostal muscles are used in coughing and sneezing. Mucus & cilia: goblet cells produce sticky mucus to trap and eliminate particulate matter and microorganisms. Ciliated cells have cilia, little hairs which sweep/beat back and forward in a coordinated way to brush mucus up the lungs into the mouth.  Coordination and response Chapter 12 The human nervous system The human nervous system is made up of two parts: Central nervous system (CNS) - brain and spinal cord: role of coordination Peripheral nervous system - nerves: connect all parts of the body tothe CNS. Together, they coordinate and regulate body functions. Sense organs are linked to the peripheral nervous system. They are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals. When exposed to a stimulus they generate an electrical impulse which passes along peripheral nerves to the CNS, triggering a response.  Peripheral nerves contain sensory and motor neurones (nerve cells). transmit nerve impules Motor neurone sense organs à CNS CNS à effectors Sensory neurone (muscles or glands) Motor and sensory neurones are covered with a myelin sheath, which insulates the neurone to make transmission of the impulse more efficient. The cytoplasm (mainly axon and dendron) is elongated to transmit the impulse for long distances. Structure Sensory neurone Motor neurone Cell body Near end of neurone, in a At start of neurone, ganglion (swelling) just indise the grey matter of outside the spinal cord the spinal cord Dendrites Present at end of neurone Attached to cell body Axon Very short Very long Dendron Very long None Fun fact: The human nervous system runs on electrical impulses that travel close to the speed of light.  Simple reflex arc A reflex action is an automatic response to a stimulus. A reflex arc describes the pathway of an electrical impulse in responseto a stimulus. Relay neurones are found in the spinal cord, connecting sensosy neuronesto motor neurones. On the picture below, the stimulus is a drawing-pin sticking in the finger. The response is the withdrawal of the arm due to contraction of the biceps. The sequence of events is: Reflex: automatically and rapidly integrating and coordinating stimuli withresponses Neurones do not connect directly with each other: there is a gap called asynapse. The impulse is 'transmitted' across the synapse by means of a chemical called acetylcholine. Video: Reflex Arc https://www.youtube.com/watch?v=Y5nj3ZfeYDQ  Effectors, biceps and triceps Effectors are muscles or glands which respond when they receive impulsesfrom motor neurones. Examples of effectors are the biceps and triceps muscles in the arm. Structure of the human arm When stimulated, muscles contract get shorter). The biceps and triceps areantagonistic muscles - they have opposite effects when they contract. The biceps is attached to the scapula (shoulder blade) and the radius. Contraction of the biceps pulls on the radius, moving the lower arm toward the scapula. This results in the arm bending (flexing) at the below - the armis raised. The triceps is attached to the scapula, humerus and ulna. Contractions of the triceps pulls on the ulna, straightening (extending) thearm. In doing so, the triceps pulls the biceps back to its original lengths.  Structure and function of the eye, rods and cones You need to be able to label parts of the eyeon diagrams. The eyebrow stops sweat running down into the eye. Eyelashes help to stop dust blowingon to the eye. Eyelids can close automatically (blinking is a reflex) to prevent dust and other particles getting ton to thesurface of the cornea. Blinking also helps to keep the surface moist by moving liquid secretions (tears) over the exposed surface. Tears also containenzymes that have an antibacterial function. Distinguishing between rods and cones Rods and cones are light-sensitive cells in the retina. When stimulated they generate electrical impulses, which pass to the brain along the optic nerve. The normal retina has rods that see only black, white,and shades of grey and tones and three forms of colorcones, red, green, and blue. Function Distribution Comments Rods Sensitive to low Found throught the retina, Provide us with night light intensity. but none in thecentrer of vision, when we can Detect shades of the fovea or in the blind recognise shapes grey spot but not colours Cones Sensitive only to high Concentrated in the There are three types, light intensity. fovea sensitive to red, green Detect colour and bluelight (don’t operate in poor light) Photos of rods and cones.  Accommodation - focusing on objects far and near The amount of focusing needed by the lens depends onthe distance of the object being viewed – light from near objects requires a more convex lens than light froma distant object. The shape of the lens needed to accommodate the imagecontrolled by the is ciliary body - this contains a ring of muscle around the lens. Distance objects The ciliary muscles relax, giving them a larger diameter. This pulls on the suspensory ligaments which, in turn, pull on the lens. This makes the lensthinner (less convex). As the ciliary muscles are relaxed, there is no strainon the eye. Near objects The ciliary muscles contract, giving them a smaller diameter. This removes the tension on the suspensory ligaments which, in turn, stop pulling on thelens. The lens becomes thicker (more convex). As the ciliary muscles are contracted, there is strain on the eye, which can cause a headache if a near object (book, microscope, computer screen etc.) is viewed for too long. Pupil reflex The reflex changes the size of the pupil to control the amount of light entering the eye. Inbright light, pupil size is reduced as too much light falling on the retina could damage it. In dim light, pupil size is increased to allow as much light as possible to enter the eye. The retina detects the brightness of light entering the eye. An impulse passes to the brain along sensory neurones and travels back to the muscles of the iris along motor neurones, triggering a response - the change in size of the pupil due to contraction of radialor circular muscles. Common misconceptions Students often confuse circular muscles and ciliary mucles. Remember that circular muscles affect the size of the iris, ciliary muscles affect theshape of the lens.  #91 Hormones, role of adrenaline Hormone is a chemical substance, secreted by endocrine gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver. 1. Chemical control of metabolic activity by adrenaline Adrenaline is a hormone secreted by adrenal glands. When you are frightened, excited, your brain sends impulses along a verve to your adrenalglands. This makes them secrete adrenaline into the blood. Adrenal gland is situated above each kidney. Adrenaline helps you to cope with danger: 1. ↑ heart rate → supply O2 to brain and muscle more quickly →↑ energyfor action (fighting, running…). Contract blood vessels in skin and digestive system → they carry very littleblood → supplies blood back to vital organs (brain and muscles). 2. Stimulate liver to convert glycogen to glucose, ↑ glucose release into theblood by liver → extra glucose for muscle →help muscle to contract. Examples of situations in which adrenaline secretion increases Adrenaline is needed and secreted in a “fright, fight or flight” situation. E.g.: When you are facing danger, for example, amasked man with a gun is approaching you. - Your brain sends a signal to the adrenal glands, to startsecreting and pumping adrenaline into the bloodstream. - the actions of the adrenaline is listed above - this gets you ready to either stand and fight or run away from the man. 2. Comparison of nervous and hormonal control systems  Voluntary and involuntary actions Knee jerk is an involuntary reflex Two types of action controlled by the human nervous system are: voluntary and involuntary actions. The peripheral nerves transmit both. Comparison of voluntary and involuntary ations Feature Voluntary action Involuntary action Nature - Conscious thought - Does not involve thought (make decision about making action). - Not under the control of thewill - Free will - Cannot control the - Consciously control activities. skeletal muscles Speed of Slow response, as the brain Rapid response, as the brain action needs time to is not involved. “think” before an action is carried out. The same stimulus may The same stimulus always Response produce various results in the same response to the responses. (stereotyped response), e.g. same E.g. when you are the knee jerk reflex. stimulus hungry, you may decide to eat or not to eat, or just need to drink water.  Coordination in plants – tropism Tropism are responses by part of a plant toward of away from a stimulus comingfrom one direction. The movement is always a growth movement. Like animals, plants are able to response to their environment, although usually with much slower responses than those of animals. In general, plants respond to stimuli by changing their rate ordirection of growth. They may grow either towards or away from a stimulus. These responses are called tropisms. Two important stimuli for plants are light and gravity. Shoots normally grow towards light. Roots do not usually respond to light,but a few grow away from it. Shoots tend to grow away from the pull of gravity, while roots normally growtowards it. Pictures are taken from: Tropism slideshow  Control of plant growth by auxins, weedkillers Auxins are plant growth substances, produced by the shoot and root tipsof growing plants. - Auxins in the shoot → stimulate cell growth, by the absorption of water. - Auxins in the root → slow down the cell growth. Auxin in phototropism 1. If a shoot is exposed to light from one side More auxins are moving in the shaded side (from the tip of the shoot) On this side, cells are stimulated to absorb more water, plant growsmore Shoot bends toward the light. This is called positive phototropism. 2. If a root is exposed to light in the absence of gravity More auxins are moving in the shaded side (from the tip of theroot) → On this side, cells are stimulated to absorb less water, plant growsless Root bends away from the light. This is called negative phototropism. When exposed to light from one side Fetures Shoot Root More auxins are moving in the shaded side (+) (+) Cell are stimulated to absorb (on more less the shaded side) water water Stem bends toward away the light from the light Process Positive Negative phototropism phototropism. Auxin in geotropism 1. If a shoot is placed horizontally in the absence of light: Auxins accumulate on the lower side of the shoot, due to gravity. Cells on the lower side grow more quickly The shoot bends upwards. This is called negative geotropism. 2. If a root is placed horizontally in the absence of light: Auxins accumulate on the lower side of the shoot, due to gravity. Cells on the lower side grow more slowly The shoot bends downwards. This is called positive geotropism. When is placed horizontally in the absence of light Fetures Shoot Root More auxins are moving in the lower side (+) (+) Cell growth (on the lowerside) more quickly more slowly Bending upwards downwards Process Negative Positive geotropism phototropism. Darwin did the first experiments to study the effects of Auxin Credit: plantphys.info Shoots and roots that have their tips removed will not respond to light or gravity because the part that produces auxins has been cut off. Shoots that have their tips covered with opaque material grow straight upwards when exposed to one-sided light,because the auxin distribution is not influenced by the light. Effects of weedkillers Weedkillers (herbicide) are synthetic plant hormones, like auxins. If these chemicals are sprayed on to plants they can cause rapid, uncontrolledgrowth and respiration, resulting in the death of the plant. Some plant species are more sensitive than others to synthetic planthormones, so weedkillers can be selective. Many weedkillers kill only broad-leaved plants (dicotyledons), leavinggrasses (moncotyledons) unharmed. Summary of coordination and response All organisms can sense changes in their environment, called stimuli and respond to them. The part of the body that senses the stimulus is a receptor, and the part that responds is an effector. The human nervous system contains specialized cells called neurons. The brain and spinal cord make up the central nervous system (CNS), which coordinates responses to stimuli. Reflex actions are fast, automatic responses to a stimulus. They involve a series of neurons making up a reflex arc. A sensory neuronetakes the impulse to the CNS and a motor neurone takes it from the CNS to an effector. Receptors are generally found within sense organs. The receptors in the eye are rod and cone cells, found in the retina. Rods respond to dim light and cones to bright light. Cones give colourvision. The cornea and lens focus light rays onto the fovea, the part of theeye where cone cells are most densely packed. The shape of the lens is changed by the contraction or relaxation of the ciliary muscle. When focusing on a distance subject, the muscle relaxes so that the suspensory ligament are pulled taut and the lens ispulled into a thin shape. When focusing on a near object, the muscle contracts and the lens falls into its natural, more rounded shape. Muscles can pull when they contracts, but they cannot push. A pair ofmuscles is therefore needed to pull in different directions, e.g. at the elbow joint. They are antagonistic muscles. Hormones are chemicals made in endocrine glands and carried in the blood plasma. Adrenaline is secreted by the adrenal glands and bring about changes that supply the muscles with extra glucose. This gives the energy for contraction for ‘fight or flight’. Plant response to some stimuli by growing towards or away from them. These responses are tropism. Auxins are mostly made in the tips of the shoots and roots and candiffuse to other parts of the shoots or roots. It collects in the shady side of the shoot, making the side grow faster so the shoot bends towards the light. Auxins are used as selective weedkiller.