GCSE Paper 1 Revision Summary

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wall Ribosomes Page 3 -Nucleus -Cytoplasm Cell membrane DNA not in a nucleus Plasmid Flagella ● Cells may be specialised to carry out a particular function. Examples: A root hair cell has a large surface area to absorb water and minerals easily. ● A palisade cell has many chloroplasts for photosynthesis ● 1001010 0.0 O A white blood cell can change its shape to engulf microbes. Movement of molecules in and out of cells Summary The cells, tissues and organs in plants and animals are adapted to take up and get rid of dissolved substances. Different conditions can affect the rate of transfer. Sometimes energy is needed for transfer to take place. Dissolved substances Dissolved substances move by diffusion and by active transport. A nerve cell has a long nerve fibre to carry messages to other cells. A sperm cell has a tail to swim. Diffusion (covered in more detail in unit 2): The movement of particles in a liquid or gas from an area where they are in higher concentration to an area where they are in lower concentration. The greater the difference in concentration, the faster the rate of diffusion. 2 examples of diffusion through the cell membrane: o Oxygen required for respiration diffuses into cells. O Carbon dioxide produced by respiration diffuses out of cells. Membrane Osmosis: Water often moves across boundaries by osmosis. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. Page 4 ● ● Differences in the concentrations of the solutions inside and outside a cell cause water to move into or out of the cell by osmosis. If there is a higher solute concentration on one side of a membrane, water will move in that direction. Osmosis in animal cells: water Osmosis in plant cells: WATER ● Sports Drinks solute partially permeable If animal cells are placed in a solution that has a lower solute concentration than the cytoplasm, then water will enter the cell by osmosis until it bursts. Movement of water If animal cells are placed in a solution that has a higher solute concentration than the cytoplasm, then water will leave the cell by osmosis, until it shrinks and dies. This is why it is vital that we maintain the concentration of our body fluids at an equal solute concentration to our cells' cytoplasm. If plant cells are placed in a solution that has a higher solute concentration than the cytoplasm, then water will leave the cell by osmosis, and the cell membrane separates from the cell wall. This will cause a plant to wilt. 53 Page 5 WATER If plant cells are placed in a solution that has a lower solute concentration than the cytoplasm, then water will enter the cell by osmosis until it is fully turgid, and the cell wall prevents any more water entering. This is important in enabling plants to remain upright. ● ● Energy drinks Contain the same concentration of ions as the body fluids, and a high concentration of glucose. This enables rapid uptake of glucose. Most soft drinks contain water, sugar and ions. Sports drinks contain sugars to replace the sugar used in energy release during the activity. ● They also contain water and ions to replace the water and ions lost during sweating. If water and ions are not replaced, the ion / water balance of the body is disturbed and the cells do not work as efficiently. Rehydrating drinks These contain lower concentration of ions than in body fluids. This enables rapid uptake of water by osmosis. These drinks enable people to become quickly rehydrated after exercise. Active Transport: The process by which cells absorb substances against a concentration gradient. ● The substances being transported attaches to large protein molecules in the cell ● membrane. Energy released through respiration is used to change the shape of the protein. This releases the substance on the other side of the membrane. ● This process enables cells to absorb substances from very dilute solutions. 2 examples: o Absorption of mineral ions by the root hair cells in roots in plants. o Absorption of glucose by epithelial cells in the small intestine. 8=8 Membrane Carrie protein Page 6 Energy Specialised exchange surfaces Many organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by: o having a large surface area o being thin, to provide a short diffusion path O Animals can also maintain high concentration gradients: by having an efficient blood supply. for gaseous exchange by being ventilated. Gas and solute exchange surfaces in humans and other organisms are adapted to maximise effectiveness. ● ● The size and complexity of an organism increases the difficulty of exchanging materials. Larger organisms have more cells, so have greater requirement for exchange. ● However, the larger an organism, the smaller their surface area to volume ratio. ● Therefore, they require even more complex exchange surfaces to supply their requirements. Exchange systems in humans Absorption of nutrients in the small intestine Food in the small intestine has been digested into: Glucose Amino acids ● ■ O O o Fatty acids o Glycerol ● These nutrients need to be absorbed into the blood across the wall of the small intestine. They are absorbed by diffusion and active transport. The wall of the small intestine is covered with finger-like extensions called villi. ● ■ ● ● Epithelial cells Capillaries Small intestine -Epithelium Page 7 - Villi Many villi provide a large surface area. The wall is only one cell thick so the diffusion pathway is short. Villi have an extensive network of capillaries to absorb the products of digestion. Concentration gradients are maintained because the blood removes the absorbed nutrients. Topic 2 Cell Division Summary Characteristics are passed on from one generation to the next in both plants and animals. Simple genetic diagrams can be used to show this. There are ethical considerations in treating genetic disorders. Genetic material In the nucleus of a typical human body cell there are 23 pairs of chromosomes. We inherit one set of 23 chromosomes from each of our parents. ● ● ● ● ● ● ● Cell Division and Growth ● Chromosomes are made from a large molecule called DNA (deoxyribose nucleic acid). DNA consists of two strands coiled into a double helix structure. ● DNA has 2 main roles: 1. It can replicate prior to cell division (mitosis or meiosis). 2. Its code is used to synthesise proteins. A gene is a small section of DNA. Each gene codes for a particular combination of amino acids which make a specific protein. These proteins determine our characteristics. Some characteristics are controlled by a single gene. Nucleus Chromosome New body cells are produced: o When the animal is growing. o To repair damaged tissues. o To replace worn out tissues. 14004 DNA Mitosis occurs: o All of the chromosomes are replicated. O The nucleus is divided in 2. Cell DO00 This results in two genetically identical nuclei. The cell divides in 2 to form 2 genetically identical cells. Some cells undergo cell division again and again. Some cells carry out their function then die. Page 8 Gene ● ● ● ● ● Mitosis and cell division ● Cell prepares to divide ● DNA is copied ● G2 M Stem cells ● Stem cells can be made to differentiate into many different types of cells e.g. nerve cells. There are very few stem cells in an adult. There is currently a lot of research involving the use of stem cells to treat various diseases and injuries. Cells can be taken from human embryos, adult bone marrow and umbilical cords. Treatment with these cells may help cure conditions such as paralysis. However, many people are concerned about the use of human embryos to treat diseases. S New cell forms R Asexual reproduction The cells of the offspring produced by asexual reproduction are produced by mitosis from the parental cells. ● They contain the same genes as the parents. G1 Cell grows Cell differentiation Differentiation results when some genes are turned on, some are turned off. Once the cells are specialised they carry out their role. Most types of animal cells differentiate at an early stage. Many plant cells retain the ability to differentiate throughout life. In mature animals, cell division is mainly restricted to repair and replacement. Cell specialises and carries out its function If the cell goes past this point it will divide Page 9 They feel that all embryos have got the potential to become a baby, and that they should not be used in this way. Summary The cells of multicellular organisms may differentiate and become adapted for specific functions. Tissues are aggregations of similar cells; organs are aggregations of tissues performing specific physiological functions. Organs are organised into organ systems, which work together to form organisms. Multicellular organisms ● Large multicellular organisms develop systems for exchanging materials. During the development of a multicellular organism, cells differentiate so that they can perform different functions. ● ● A tissue is a group of cells with similar structure and function. Organs are made of tissues. One organ may contain several tissues. Organ systems are groups of organs that perform a particular function. Animal organs Examples of animal tissues include: ● ● ● Topic 3 Tissues, Organs and Organ Systems ● The stomach is an organ that contains: ● ● The digestive system is one example of a system in which humans and other mammals exchange substances with the environment. The digestive system includes: glands, such as the pancreas and salivary glands, which produce digestive juices the stomach and small intestine, where digestion occurs ● muscular tissue, which can contract to bring about movement glandular tissue, which can produce substances such as enzymes and hormones epithelial tissue, which covers some parts of the body. ● muscular tissue, to churn the contents glandular tissue, to produce digestive juices epithelial tissue, to cover the outside and the inside of the stomach. the liver, which produces bile the small intestine, where the absorption of soluble food occurs the large intestine, where water is absorbed from the undigested food, producing faeces. Page 10 Mouth ● Gall bladder Liver Plant organs Plant organs include stems, roots and leaves. Examples of plant tissues include: CO₂ in O₂ out Salivary gland Page 11 Oesophagus -Stomach -Pancreas -Large intestine -Small intestine epidermal tissues, which cover the plant mesophyll, which carries out photosynthesis xylem and phloem, which transport substances around the plant. -Anus epidermis Vein containing xylem and phloem palisade mesophyll spongy mesophyll moist air space stoma guard cells. Enzymes structure and function Enzymes are biological catalysts. Catalysts increase the rate of chemical reactions. ● ● ● ● Enzymes are protein molecules made up of long chains of amino acids. These long chains are folded to produce a special shape which enables other molecules to fit into the enzyme. ● This shape is vital for the enzymes function. Normally only one type of molecule (the substrate) will fit into the enzyme. The active site is the part of the enzyme which the substrate fits into. ● Glucose Enzyme available with empty active site Active site Fructose 4 Products are released Enzyme (sucrase) Activation Energy In order for a chemical reaction to take place, energy is required. This is called the activation energy. Enzymes reduce the activation energy of a reaction. Substrate (sucrose) Substrate binds to enzyme Effect of temperature on enzymes Like most chemical reactions, the rate of enzyme-controlled reactions increases as the temperature increases. Page 12 H₂O Substrate is converted to products The enzyme and substrates move around faster so they collide more often. The temperature when the enzyme is working fastest is called the optimum. This is true up to approximately 40°C, higher than this and the structure of the enzyme changes. As a result, the active site becomes a different shape and the substrate no longer fits. It is then described as denatured. ● ● ● ● The effect of pH on enzymes pH can also affect the shape of the active site. It does this by affecting the forces that hold the enzyme molecule together. A change in pH denature the enzyme. ● ● temperature and enzyme activity ● increasing enzyme activity ● 0 10 increasing enzyme activity 4 optimum temperature Different enzymes work best at different pH values. acidic conditions. Eg. Stomach enzymes work best Mouth enzymes work best in neutral conditions. 20 30 40 50 60 70 temperature (°C) T 5 pH and enzyme activity Digestion Some enzymes work outside the body cells. ● These are called extracellular enzymes. 6 optimum PH 7 pH 8 9 10 11 The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules. Page 13 They catalyse the breakdown of large molecules into smaller molecules. Digestion is the process where food is broken down into substances the body can absorb. Nutrition is the process of taking in and using food. The Human Digestive System ● ● Mouth ● Gall bladder Liver ● Digestion in the stomach Food enters the stomach from the oesophagus. The walls of our stomach produce juice. This juice contains: O A protease enzyme (called pepsin). ■ This digests proteins into amino acids. Digestion in the mouth Food is chewed to create a larger surface area for the action of enzymes. Saliva is released which contains amylase. Amylase digests starch into smaller sugars (maltose). Further chewing enables swallowing. The food enters the oesophagus. Oesophagus -Stomach -Pancreas -Large intestine Page 14 -Small intestine -Anus o Hydrochloric acid - this kills bacteria in our food. It creates pH3. O Mucus - this protects the wall of our stomach from acid and pepsin. The wall of our stomach is muscular, and churns our food. The food remains in our stomach for a few hours. The proteins are digested. Food leaves our stomach in small squirts into the small intestine. Digestion and absorption in the small intestine The small intestine has 2 main jobs: To complete the digestion of the food To absorb the soluble products of digestion into the blood. Digestion in the small intestine 3 juices are released: 1. Bile ● ● ● Produced by the liver. Stored in the gall bladder. Released into the small intestine. ● 2 main things in bile: o Alkali to neutralise the stomach acid O Bile salts which convert large fat droplets to small fat droplets - for a large surface area for the enzymes to act on. There are no enzymes in bile. O 2. Pancreatic juice and 3. Intestinal juice ● Both are released into the small intestine. Both contain 3 main enzymes: o Amylase to complete the digestion of starch into sugars. O Protease to complete the digestion of proteins into amino acids. o Lipase to break down fats into fatty acids and glycerol. Page 15 Summary Substances are transported around the body by the circulatory system (the heart, the blood vessels and the blood). They are transported from where they are taken into the body to the cells, or from the cells to where they are removed from the body. Modern developments in biomedical and technological research enable us to help when the circulatory system is not working well. Plants have separate transport systems for water and nutrients. The blood system The circulatory system transports substances around the body. ● ● ● Topic 4 Organising animals and plants ● ● High Pressure Vena cava Lowest Pressure Pulmonary artery Right atrium Right ventricle Left atrium Left ventricle Low Pressure -Pulmonary vein The heart is an organ that pumps blood around the body. Much of the wall of the heart is made from muscle tissue. O One to the lungs o One to all the other organs of the body. The blood passes through the heart twice in order to pass round both of these circulation systems. ● In one cardiac cycle: Page 16 Highest Pressure This muscle contracts to pump blood through the circulation systems. It is a double pump, because there are two separate circulation systems: O Blood enters the atria of the heart. O The atria contract and force blood into the ventricles. O The ventricles contract and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Blood flows from the heart to the organs through arteries and returns through veins. ● ● ● vena cava ● Right atrium Right ventricle Aorta outer layer muscle layer Blood is pumped to the lungs from the right ventricle through the pulmonary artery. The blood returns from the lungs to the left atrium through the pulmonary vein. Blood is pumped to the organs of the body from the left ventricle through the aorta. Blood returns to the heart from the organs into the right atrium through the vena cava. Blood vessels Blood flows from the heart to the organs through arteries and returns through veins. Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls. artery elastic layer valve Pulmonary artery inner layer Left atrium Page 17 Left ventricle vein ● Veins often have valves to prevent back-flow of blood. Valves Open In the organs, blood flows through very narrow, thin-walled blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood, and substances produced by the cells pass into the blood, through the walls of the capillaries. Wall is one cell thick Valves Closed Arteries Capillaries Carry blood away from the Carry blood away from heart to the organs. arteries into organs then back into veins. Decreasing blood pressure. High blood pressure. Elastic to withstand high blood pressure. Rarely contain valves. Substances diffuse through pores between the cells No elastic tissue - walls one cell thick. Muscular walls, to create a No muscle - walls one cell pulse, to maintain blood thick. pressure. No valves. Page 18 Veins Carry blood away from the organs back to the heart. Low blood pressure. Not elastic. Very little muscle. Contain valves to control the direction of blood flow. Blood ● Blood is a tissue. It consists of a fluid called plasma in which red blood cells, white blood cells, and platelets are suspended. ● Plasma: The liquid part of the blood. ● Blood plasma transports: o ● O ● Carbon dioxide from the organs to the lungs Soluble products of digestion from the small intestine to other organs: Glucose Amino acids Urea from the liver to the kidneys. Blood cells: White blood cell: Nucleus Dobe Red blood cells A red blood cell Cytoplasm Red blood cells transport oxygen from the lungs to the organs. A haemoglobin molecule (enlarged) An oxygen molecule Platelets Page 19 ● ● ● ● ● Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin. In the lungs: ● o Oxygen diffuses into the red blood cells. o Haemoglobin combines with oxygen to form oxyhaemoglobin. In the other organs: o Oxyhaemoglobin splits up into haemoglobin and oxygen. o Oxygen diffuses out of the red blood cell. ● White blood cells have a nucleus. They form part of the body's defence system against disease causing microorganisms (pathogens) They have a biconcave shape. This increases their surface area to increase rate of diffusion across the cell membrane. Some produce antibodies which help to destroy pathogens. Some engulf and digest pathogens. White blood cell produces antibodies Virus Other white blood cells engulf and digest the marked pathogen Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound. Antibodies attach to pathogens eg viruses Medical treatment Artificial blood products may be used when a patient has lost a lot of blood and there is no donor blood available. Plasma can be used, but, without red blood cells and haemoglobin, the blood carries oxygen less efficiently. Haemoglobin-based oxygen carriers are made from sterilised haemoglobin, which can come from a variety of sources: Page 20 ● ● human blood ● O O cow blood o Genetically modified bacteria that can produce haemoglobin ● Stents are artificial tubes that can be inserted into blood vessels. They are made of metal mesh that does not corrode. If arteries begin to narrow and restrict blood flow stents are used to keep them open. Before After Human placentas It needs to be attached to another substance such as an artificial membrane to stop it breaking down. Synthetic oxygen carrying molecules have been also created that absorb oxygen. Artificial hearts are devices made of plastic or other man-made materials that can replace the ventricles and valves. Right Atrium Venae Cavae Right Ventricle Aorta Page 21 Pulmonary Artery Some work by using a pump carried externally in a backpack Other models use an internal pump and battery. -Left Atrium Left Ventricle ● ● ● ● ● ● They can only be used for short periods of time in emergencies where someone's heart stops working and there is no donor heart available. However, they are very expensive and not readily available. ● Artificial heart valves can be used to replace diseased valves. Diseased valves either restrict the flow of blood or the blood leaks backwards. Gaseous exchange The lungs are in the upper part of the body (thorax). • They are protected by the ribcage. ● They are separated from the lower part of the body (abdomen) by the diaphragm. Many different mechanical and tissue valves have been implanted in humans. The natural valve is cut out and the artificial valve is sewn into its place. However, no artificial valve is a perfect substitute for the natural valve. The life of the valve is limited by corrosion and damage due to its repeated use. right lung right bronchus muscles alveoli diaphragm -tracheal left lung The breathing system takes air into and out of the body. Oxygen from the air diffuses into the bloodstream. Carbon dioxide can diffuse out of the bloodstream into the air. Page 22 left bronchus. bronchioles. heart The alveoli provide a very large, moist surface, richly supplied with blood capillaries so that gases can readily diffuse into and out of the blood. ● ● blood plasma with a low concentration of carbon dioxide carbon dioxide diffuses out of blood plasma ● ● ● ● red blood cells with a high concentration of oxygen- oxgenated blood back to heart ↑ single cell walled blood capillary. O O O A 17 single layer of cells around alveolus oxygen diffuses into red blood cells Ventilation (breathing) The movement of air into and out of the lungs is known as ventilation. Breathing in (inhalation): air to and from rest of lung red blood cells with a low concentration of oxygen Gaseous Exchange in the Lungs Many small spherical alveoli provide a large surface area. The moist surface helps oxygen to dissolve so that it can diffuse into the cells. The capillaries are very close to the alveoli so that the gases have a short distance to diffuse. O The ribcage moves out and up. The diaphragm becomes flatter. This increases the volume inside the thorax. Concentration gradients are maintained by: O The blood removing oxygen from and bringing carbon dioxide to the lungs. o Breathing, which replenishes oxygen and removes carbon dioxide. Page 23 This reduces the pressure inside the thorax. Air enters the lungs. blood plasma with a high concentration of carbon dioxide O This increases the pressure inside the thorax. O Air leaves the lungs. deoxygenated blood from heart O Breathing out (exhalation): o The ribcage moves down and in. O The diaphragm moves upwards into a domed shape. O This reduces the volume inside the thorax. ● ● Rib cage expands as rib muscles contract ● Air inhaled INHALATION Lung ■ Diaphragm Artificial ventilators Artificial ventilation may be used when someone is unable breathe themselves. There are many possible risks with this process, including collapsed lungs, airway injury, damage to the airsacs (alveoli), and pneumonia. Therefore, care must be taken to do it properly. Manual ventilators: Diaphragm contracts (moves down) ■ Rib cage gets smaller as rib muscles relax O Often used for first aid to help someone breathe. A mask attached to a bag is placed over the mouth and nose. O The bag can be squeezed, pushing air into the lungs. Mechanical ventilators: o Machines can be used that enable air to move into and out of the lungs: o Negative pressure machines. ■ O Positive pressure machines. Air exhaled EXHALATION Diaphragm relaxes (moves up) Often referred to as iron lungs. These are used in cases of paralysis, for example, due to polio. ■ The patient's thorax is contained inside a metal box that can create a very low pressure outside the lungs. This causes the thorax to expand so air enters the lungs ■ These attach by a tube and mask to the mouth and nose. They are used during surgery or when a patient is unconscious. Air enters the lungs under high pressure. Page 24 Transport systems in plants Flowering plants have two separate transport systems: Xylem tissue transports water and mineral ions from the roots to the stem and leaves. ● ● ● ● The movement of water from the roots through the xylem and out of the leaves is called the transpiration stream. light energy photosynthesis Phloem tissue carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs. storage organy The transpiration stream pulls water up the stem Sugars -Water enters the root hairs by osmosis Some water is used for photosynthesis and some evaporates from the leaves sugars sugars Page 25 growing regions Exchange systems in plants Absorption of water by roots The surface area of the roots is increased by root hairs. Most of the water and mineral ions are absorbed by root hair cells. Water is absorbed by osmosis. Most of the mineral ions are absorbed by active transport. ● ● ● ● ● Water and mineral ions are absorbed ● Upper Epidermis soil particles Gas Exchange in the leaf The surface area of leaves is increased by the flattened shape and internal air spaces. Mesophyll Lower Epidermis root hair Air Space 20 Stoma nucleus vacuole cellulose cell wall Page 26 Wax Cuticle Guard Cell with Chloroplasts Most photosynthesis takes place in the palisade cells. Carbon dioxide needs to reach the palisade cells. ● Plants have stomata to obtain carbon dioxide from the atmosphere. This carbon dioxide is used in photosynthesis. Palisade Mesophyll Spongy Mesophyll Wax Cuticle The size of stomata is controlled by guard cells, which surround them. Stomata open during daylight hours, to enable carbon dioxide to diffuse in. ● ● ● Guard cell ● H₂Q Thickened inner cell wall Chloroplasts Epidermal cell Transpiration The process by which plants lose water vapour from the surface of their leaves. It evaporates into the air spaces in the leaf, and then diffuses out through the stomata. Water enters guard cells Stomata open guard cell •H₂O H₂O stoma GO EX C D G C O O O O O O ! UC CU SED High water vapour content Low water vapour content Water leaves guard cells Stomata close Nucleus stoma high CO₂ content Page 27 low CO₂ guard cell CO₂ Transpiration is more rapid in hot, dry and windy conditions: O Heat causes the water to evaporate quicker. o Dry conditions increases the water vapour concentration gradient. O Wind moves the water vapour away from the leaf, maintaining the concentration gradient. Most of the water lost by transpiration leaves through the stomata. Stomata close when it is dark, when carbon dioxide is not required. This reduces the amount of water lost by the plant at a time when it is not needed for photosynthesis. If plants lose water faster than it is replaced by the roots, the stomata can close to prevent wilting. Summary Our bodies provide an excellent environment for many microbes which can make us ill once they are inside us. Our bodies need to stop most microbes getting in and deal with any microbes which do get in. Vaccination can be used to prevent infection. Pathogens ● Bacteria ● ● ● ● ● Microorganisms that cause infectious disease are called pathogens. Disease occurs when large numbers of pathogenic micro-organisms enter the body. Viruses Viruses are much smaller than bacteria. All viruses are pathogens. ● Topic 5 Communicable Diseases Not all bacteria are pathogens. Pathogenic bacteria reproduce rapidly inside the body and may produce poisons (toxins) which make us feel ill. Example: E.coli produces toxins that cause fever symptoms when we have food poisoning. Viruses also produce toxins and they damage the cells in which they reproduce, leading to illness. How a Virus Invades a Cell Viruses replicate by invading cells, reproducing inside them and bursting them. This causes damage to tissues, leading to illness. viruses body cell 1. A virus enters a cell. 4. The nucleic acid gets into the cell's chemical manufacturing system. 2. Substances in the cell begin to strip off the virus's outer coat of protein. 5. The cell "ignores" its own chemical needs and switches to making new viruses. 3. The nucleic acid in the center of the virus is released. Page 28 6. The cell is sometimes destroyed in the process. Many of the new viruses are released to infect other cells. Examples: O HIV damages white blood cells, reducing immunity and leading to AIDS. O Influenza virus released toxins which cause aches and fever symptoms. Growing Microoganisms Microorganisms = organisms that can only be viewed with a microscope. Eg bacteria, viruses and fungi. Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics. It is important that the culture is not contaminated with other microorganisms that may compete for nutrients or produce toxins. Careful procedures are required to prevent potentially pathogenic microorganisms being released into the environment. ● ● ● ● Culturing microorganisms To study microorganisms, they need to be cultured. They need to be provided with the conditions they need to reproduce quickly: O Nutrients O O ● ● ● ● Warmth Moisture Bacteria and fungi can be grown in special media called agar. This provides them with: o Carbohydrate O ● Protein or amino acids O Water When agar is heated up it is liquid. It can be poured into a Petri dish. O A circular plastic or glass dish with a lid: The agar solidifies when left to cool. ● Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms • Inoculating loops are used to transfer microorganisms to the media. These must be sterilised by passing them flame: Page 29 through a ● ● ● o The lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture. ● In school and college laboratories, cultures should be incubated at a maximum temperature of 25°C. This greatly reduces the likelihood of growth of pathogens that might be harmful to humans. In industrial conditions higher temperatures can produce more rapid growth. The immune system ● The body has different ways of protecting itself against pathogens. White blood cells defend our internal environment from pathogens These form part of our immune system. There are various types of white blood cells: Cells that ingest and destroy microorganisms Bacteria White blood cell Bacteria are ingested Bacteria are digested Cells that produce antitoxins that destroy toxins released by pathogens Page 30 Cells that produce antibodies that destroy specific pathogens: o They produce specific antibodies to kill a particular pathogen. O This leads to immunity from that pathogen. O The body is able to rapidly produce large numbers of the specific antibodies if it is exposed to the same pathogen in the future. In some cases, dead or inactivated pathogens stimulate antibody production. This also leads to immunity. 1. White blood cell produces antibodies Cell membrane. O O Nucleus White blood cell White blood cell 3. Antibodies destroy pathogens Antigen Pathogen (a bacterium) Antibodies Antibodies: O Antibodies are made of proteins. o They are released by white blood cells. o They have a specific shape that attaches to antigens. o Antigens are chemicals that pathogens carry or release. O The antibody prevents the pathogens from damaging our own cells. antibodies Antibody Page 31 2. Antibody attaches to specific chemicals on the pathogen Pathogen Antibodies bind to antigens on the bacteria Preventing transmission In the 1850s Semmelweiss recognised the importance of hand-washing in the prevention of spreading some infectious diseases. He insisted that medical students washed their hands before delivering babies. This resulted in doctors washing their hands before and after examining patients. This greatly reduced the number of deaths from infectious diseases in his hospital. This idea was not readily accepted - people were not aware of microorganisms. Nowadays, it is standard practice for people to wash hands after treating patients, to prevent disease being transmitted to other patients. ● ● ● ● Epidemics and Pandemics Epidemics diseases that spread widely through one country. Pandemics - diseases that spread through several countries. Eg Influenza ● ● Most people recover in a week. People who are old or very young or already ill can die. Different strains of influenza affect other animals. ● ● ● A viral disease. Immunisation If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced. ● Eg small pox was completely eradicated by the 1970s. People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). • Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogens. ● These rarely affect humans, because humans need to directly contact an infected animal. Humans that are infected may be more likely to die than if they had human influenza. Most of these viruses cannot be transmitted from human to human. However, there are concerns that the viruses could mutate and become able to be transmitted between humans. If it does this, it will start off by causing an epidemic, which may spread to become a pandemic. ● This makes the person immune to future infections by the microorganism. The body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease. An example is the MMR vaccine used to protect children against measles, mumps and rubella. ● Many people could die, particularly very old people, very young people, and people who are already ill. Topic 6 Preventing and treating diseases ● Antibiotic resistance Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic resistant strains of bacteria. Pathogenic bacteria mutate, producing resistant strains. Page 32 ● ● Antibiotics kill individual pathogens of the non-resistant strain. Individual resistant pathogens survive and reproduce, so the population of the resistant strain increases. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen. The new strain will then spread rapidly because people are not immune to it and there is no effective treatment. ● Many strains of bacteria, including MRSA, have developed resistance to antibiotics as a result of natural selection. These bacteria can enter the body through wounds and cuts. Healthy people's white blood cells would quickly destroy these bacteria. People who are ill in hospital are likely to have reduced immunity to bacterial disease, and become infected more easily. ● Exposure to bacteria occurs. Infection occurs and the bacteria spread. Non-resistant Bacteria 00 The bacteria multiply. Drug Resistant Bacteria The bacteria multiply. Drug treatment is used. What can be done? Doctor's should only prescribe antibiotics when necessary - and not for viruses. It is important that if you are prescribed antibiotics you take the whole course. o A lot of people will stop taking the antibiotic when they feel better. o If you do this, you leave a few bacteria inside your body. O These will reproduce, increasing the chance of some developing resistance. The bacteria die. The person is healthy again. ● Scientists are trying to develop new versions of the antibiotics. Some antibiotics are developed but not used - just in case. The bacteria continue to spread. The person remains sick. Page 33 Using drugs to treat disease Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogens. Antibiotics are medicines that help to cure bacterial disease by killing infective bacteria inside the body. Eg penicillin Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells. It is difficult to develop drugs which kill viruses without also damaging the body's tissues. It is important that specific bacteria should be treated by specific antibiotics. Antibiotics kill bacteria inside the body. ● The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. ● ● ● Summary Drugs affect our body chemistry. Medical drugs are developed and tested before being used to relieve illness or disease. Drugs may also be used recreationally as people like the effect on the body. Some drugs are addictive. Some athletes take drugs to improve performance. People cannot make sensible decisions about drugs unless they know their full effects. Types of drugs ● ● Drug trials Scientists are continually developing new drugs. ● ● ● ● Medical drugs: o Prescribed - a doctor must provide a prescription for these to be obtained. ■ Eg antibiotics and strong pain killers such as morphine. o Non-prescribed - these can be bought in a chemist without a prescription. Eg pain killers such as aspirin and paracetomol, and cough medicine. ● Recreational drugs: o Legal - eg alcohol, caffeine, nicotine o Illegal - eg ecstasy, cannabis and heroin ● Thalidomide Thalidomide is a drug that was developed as a sleeping pill. It was also found to be effective in relieving morning sickness in pregnant women. Thalidomide had not been tested for this use. Unfortunately, many babies born to mothers who took the drug were born with severe limb abnormalities. The drug was then banned. As a result, drug testing has become much more rigorous. More recently, thalidomide has been used successfully in the treatment of leprosy and other diseases. When new medical drugs are devised, they have to be extensively tested and trialled before being used. Drugs are tested in a series of stages to find out if they are safe and effective. New drugs are extensively tested for toxicity, efficacy and dose: O in the laboratory, using cells, tissues and live animals o in clinical trials involving healthy volunteers and patients. ▪ Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. In some double blind trials, some patients are given a placebo, which does not contain the drug. Neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete. Page 34 Statins Statins are a relatively new group of drugs used to lower blood cholesterol levels. ● A high cholesterol level increases a person's risk of having a heart attack or stroke. The long-term use of statins reduces the risk of such an event and can increase the life expectancy of people with a history of heart disease. People are concerned that these drugs could encourage people to lead an unhealthy lifestyle in the belief that they can reduce their cholesterol levels. ● ● ● Drug Abuse Some people use drugs recreationally. Some of these recreational drugs are more harmful than others. Some of these drugs are legal, such as alcohol and nicotine. Some of these drugs are illegal such as ecstasy, cannabis and heroine. Some of these drugs are prescribed but are not taken sensibly, such as sleeping tablets, antidepressants and strong pain killers such as morphine. ● ● ● ● Addiction and Withdrawal Drugs change the chemical processes in people's bodies. Drugs work by affecting synapses. ● ● ● ● ● ● ● ● ● ● The overall impact of legal drugs on health is much greater than the impact of illegal drugs, because far more people use them. ● Effects of drugs Alcohol affects the nervous system by slowing down reactions. o It helps people relax. ● Some drugs make them work faster (eg, caffeine). Some drugs make them work slower (eg. cannabis). Drug abusers may become dependent or addicted to the drugs. They may suffer withdrawal symptoms without them. Heroin and cocaine are very addictive. There are concerns about the possible progression from people taking non-addictive recreational drugs to addiction to hard drugs. For example, cannabis is referred to as a gateway drug; it is thought that it leads to people taking cocaine or heroin. Too much may lead to lack of self-control, unconsciousness or even coma. o Long term abuse eventually damages the liver and brain. Nicotine is the addictive substance in tobacco smoke. O This makes it difficult for people to stop smoking. o Nicotine patches and nicotine chewing gum can be used to help people stop smoking. Tobacco smoke contains carcinogens, which are chemicals that cause cancer: O The link between smoking tobacco and lung cancer has been known about for about 100 years. o However, this was only gradually accepted. Tobacco smoke also contains carbon monoxide which reduces the oxygen-carrying capacity of the blood. O In pregnant women this can deprive a fetus of oxygen and lead to a low birth mass. Ecstasy, cannabis and heroin may have adverse effects on the heart and circulatory system. Cannabis smoke contains chemicals which may cause mental illness in some people. Page 35 Drugs in sport There are several types of drug that an athlete can use to enhance performance. Some of these drugs are banned by law and some are legally available on prescription. All are prohibited by sporting regulations. Examples include: ● ● ● Summary A combination of a balanced diet and regular exercise is needed to help keep the body healthy. ● Healthy Diet A healthy diet contains the right balance of the different foods you need and the right amount of energy. These foods should provide the following nutrient groups: ● Stimulants that boost bodily functions such as heart rate; O Anabolic steroids which stimulate muscle growth. ● Athletes in major sporting events have to be willing to give a blood or urine sample so that they can be tested for these drugs. Some scientists work to develop drugs that cannot be detected by these tests. Malnourishment A person is malnour hed if their diet is not balanced. This may lead to a person being overweight or underweight. An unbalanced diet may also lead to diseases. Lack of essential nutrients in the diet can lead to deficiency diseases. ● ● Topic 7 Non-Communicable diseases O Carbohydrates for energy and to make cell structures O Fat for energy and insulation and cell structures O Protein to control cell reactions (as enzymes) and to build cell structures O Vitamins and minerals to help our bodies function well. Excess intake of high energy foods can lead to type 2 diabetes. O Exercise O Slimming programmes A person gains mass when the energy content of the food taken in is more than the amount of energy expended by the body. A person loses mass when the energy content of the food taken in is less than the amount of energy expended by the body. An effective slimming programme advises people to reduce the energy content of their food, and to increase the amount they exercise. This is a disease where the person is unable to control the levels of sugar in their blood. This is very dangerous, and the person must carefully control their diet and monitor their blood sugar levels regularly. Some slimming programmes encourage people to consume a low proportion of one of the nutrient groups in their diet. This may enable them to lose weight, but it will not necessarily be a sensible, healthy diet. Page 36 Exercise increases the amount of energy expended by the body. ● People who exercise regularly are usually healthier than people who take little exercise. • They expend more energy and their circulatory system becomes more efficient. They are likely to have lower blood pressure, and less likely to be overweight. Metabolic rate This is the rate at which all the chemical reactions in the cells of the body are carried out. ● ● ● ● ● Inheritance Inherited factors can influence our health. We can inherit genes from our parents which can influence our metabolic rate. We can also inherit genes which influence our cholesterol level. Cholesterol is a substance that our body creates from fat that we consume in our diet. Cholesterol is needed to make cell membranes. ● ● ● One major set of metabolic reactions is respiration. The rate of these reactions vary with the amount of activity you do. The more activity, the more energy is required by the body. Metabolic rate also varies with respect to the proportion of muscle to fat in your body. The higher the proportion of muscle to fat, the higher the metabolic rate. Exercise increases the proportion of muscle to fat. ● Summary Green plants and algae use light energy to make their own food. They obtain the raw materials they need to make this food from the air and the soil. The conditions in which plants are grown can be changed to promote growth. ● However, too much cholesterol can increase the chance of cardio-vascular diseases, such as strokes, heart attacks and thrombosis. Photosynthesis Photo light Synthesis = making of (glucose) Photosynthesis = making glucose using light Topic 8 Photosynthesis During photosynthesis: • light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and algae. ● This energy is used by converting carbon dioxide (from the air) and water (from the soil) into sugar (glucose). Oxygen is released as a by-product. Photosynthesis is summarised by the equation: carbon dioxide + water light energy Where does photosynthesis happen? Leaves are the main site of photosynthesis. Page 37 glucose + oxygen ● ● ● Photosynthesis mainly in occurs in the mesophyll cells. These cells contain lots of chloroplasts. Chloroplasts contain chlorophyll. A palisade mesophyll cell: Cellulose Cell Wall Cell Membrane Vacuole Membrane Vacuole ● '90 the l W Chloroplast (contains chlorophyll) Nucleus Cytoplasm Factors that limit the rate of photosynthesis 1) Temperature A low temperature will limit the rate as the molecules will move less and therefore the reaction happens slower 2) Carbon dioxide A shortage of CO2 will limit the rate as fewer molecules will be available for the reaction. 3) Light intensity A shortage of light means there is less energy to power the reaction. Limiting factors explained: Light, temperature and the availability of carbon dioxide interact and in practice any one of them may be the factor that limits photosynthesis. If one of these factors is closest to its minimum value it will limit the rate. Increasing this factor will increase the rate. The rate will continue to increase until another factor becomes limiting. Any further increase in the original factor will now not increase the rate. With no limiting factors, increasing a factor above a certain level will not increase the rate. All chlorophyll molecules are being used. Farming practices Farmers artificially manipulate the environment in which they grow plants. They grow plants in greenhouses or in polythene tunnels. They can control the temperature in greenhouses using heaters and ventilation. Page 38 They can artificially increase the carbon dioxide levels. They can control the light using fluorescent lamps. By doing all of this, their plants grow faster and certain plants can be grown in this country out of their natural growth season. Eg tomatoes can be grown all year round. Therefore, they increase their profits. How do plants and algae use glucose? The glucose produced in photosynthesis may be converted into insoluble starch for storage Plant cells use some of the glucose produced during photosynthesis for respiration. Some glucose in plants and algae is used: to produce fat or oil for storage • to produce cellulose, which strengthens the cell wall to produce proteins: o To produce proteins, plants also use nitrate ions that are absorbed from the soil. ● ● ● ● Summary Respiration in cells can take place aerobically or anaerobically. The energy released is used in a variety of ways. The human body needs to react to the increased demand for energy during exercise. ● Respiration Definition: The process of transferring energy from food molecules in every living cell. Aerobic respiration - uses oxygen ● ● ● ● Topic 9 Respiration Aerobic respiration Glucose reacts with oxygen, producing carbon dioxide and water as waste products. This takes place continuously in animals and plants. Word equation: Glucose + Oxygen Chemical equation (do not need to learn!): C6H12O6 + 602 ● Anaerobic respiration - uses no oxygen All chemical reactions inside cells are controlled by enzymes. Carbon dioxide + Water + Energy 6CO2 + 6H₂O ● Respiration actually involves a series of many small reactions. Each reaction is controlled by an enzyme. Mitochondria Most of the reactions in respiration happen in the mitochondria. The inner surface of the mitochondria is highly folded to increase the surface area for enzymes. Page 39 ● ● Cell Energy use The energy that is released during respiration is used: ● To build up larger molecules using smaller ones. In animals, to enable muscles to contract. MU ● Mitochondrion -Outer membrane -Enzymes In mammals and birds, to maintain a steady body temperature in colder surroundings. In plants, to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins. The role of respiration during exercise Muscles contract to move the bones in our bodies. Respiration releases energy, which is used to contract the muscles: O The heart rate increases. Highly folded inner membrane ● When we exercise, our muscles contract more quickly and with more force. This requires more energy. This requires more glucose and oxygen. Also, more carbon dioxide is created which needs to be removed. The human body needs to react to the increased demand for energy during exercise. Changes during exercise ● During exercise a number of changes take place: O The rate and depth of breathing increases. I This increases the rate of gaseous exchange. ■ More oxygen is taken into the blood. ■ More carbon dioxide is removed from the blood. Page 40 ■ This increases rate of blood flow to the muscles All of these changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen and increase the rate of removal of carbon dioxide. Glycogen Glucose is stored as glycogen is in the muscles. During exercise, glycogen is broken down into glucose in the muscles. This increases the amount of glucose that can be respired. Anaerobic respiration During exercise, if insufficient oxygen is reaching the muscles they use anaerobic respiration to obtain energy. ● ● ● glucose ● ● Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid. As the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration. One cause of muscle fatigue is the build up of lactic acid in the muscles. Blood flowing through the muscles removes the lactic acid. During and after exercise, we breathe heavily to take in extra oxygen to oxidise the lactic acid: lactic acid + oxygen • The extra oxygen is called the oxygen debt. ● The heart continues to pump faster. ● lactic acid + small amount of energy released However, lactic acid is poisonous. We can only tolerate small amounts in our body. If muscles are subjected to long periods of vigorous activity they become fatigued, ie they stop contracting efficiently. ● The breathing rate remains high. This delivers the extra oxygen to the muscles. This pays back the oxygen debt. Oxygen uptake / litres per minute 2 1 0 0 Ideal rate of oxygen uptake 1 carbon dioxide + water Oxygen uptake during exercise Resting oxygen uptake L 3 Page 41 5 Oxygen debt 7 Exercise duration / minutes