Biology revision notes (I)GCSE


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Biology revision notes (I)GCSE

  1. 1. Functions of the following: The mouth Mechanical digestion happens here- your jaw action. A bolus is created; this is a ball of food covered in saliva. This is help full as the food is lubricated to enable swallowing and enzymes in the saliva can begin to break down the food. (amylase) The oesophagus this tube connects you mouth and stomach. It is next to the trachea which is covered by the epiglottis when you swallow so the food only enters the oesophagus. Peristalsis- or muscular contractions- moves the food downward. The stomach Churning mechanically digests whilst enzymes do so chemically. Chime is the name for liquid food existing in the stomach. The small intestine this absorbs digested molecules into the blood stream. Villi cover the inside giving it a large surface area which many molecules can diffuse through into the blood. Large intestine this absorbs water from undigested food, producing faeces. Pancreas this produces the enzymes lipase, amylase and protease. Processes: Digestion: process in which large insoluble molecules of food are broken down into smaller ones. Absorption: the process by which soluble molecules produced by digestion are taken from the gut (occurs mostly in the small intestine.) The soluble products of digestion are then transported to the various tissues by the circulatory system. Assimilation: the cells of the tissues absorb the molecules for use. Egestion: removal of waste- undigested- products as faeces. Excretion: removal of waste products that have been in the body. Peristalsis: Food is moved through the gut by peristalsis. Muscles move food because mechanical action is needed to get food through the system. Digestive enzymes: Enzymes break down food into useful things that our bodies need. Different enzymes break down different components of our food. You should learn that:  amylase and maltase convert starch to glucose  proteases convert proteins to amino acids  lipases convert lipids to fatty acids and glycerol.
  2. 2. Bile: Bile is produce by the liver and stored in the gall bladder. Enzymes in the small intestine work best in alkaline conditions but the food is acidic after being in the stomach. Bile is alkaline and so when it is released into the small intestine it enables the enzymes to work. Bile also emulsifies fat; this gives it a larger surface area, which means that it is easier for lipases to work. Villi: The villi are in the small intestine. They are like lumps on this inside of the small intestine. They are the surface through which food diffuses into the blood stream. They have very thin walls, only one cell thick; this enables molecules to pass through easily. They also increase the surface area of the small intestine wall meaning that there is a lot of surface for diffusion to happen through. On the outside of villi there are capillaries which pick up the diffused food into the blood stream. What is respiration: Respiration is a reaction that occurs in living things to create energy. It breaks down glucose to release energy. Respiration is a continuous process in living things, so won't stop at any time. But photosynthesis depends on light and so will stop in the dark. This means that in the night carbon dioxide will be being given out by respiration but not taken in for photosynthesis, so the net exchange of carbon has an increased output. In the same way at night oxygen will not be being given out as there is no photosynthesis. Aerobic respiration Glucose + oxygen > carbon dioxide + water + energy C6H12O6 + 6O2 → 6CO2 + 6H2O (+ energy) In this form of respiration all of the energy is released from the glucose as it is fully broken down. It is used for day to day life processes- like movement and reproduction- and keeping warm. Anaerobic respiration Glucose > lactic acid + energy C6H12O6 > 2C3H6O3 + energy Anaerobic respiration takes place when the heart and lungs cannot work fast enough to provide to oxygen needed for aerobic respiration: for example when exercising The energy released is less in anaerobic respiration because the glucose cannot be fully broken down. The lactic acid produced accumulates in muscles; often making them feel soar. After this process 'excess post-exercise oxygen consumption' takes place. This process involves heavy breathing and fast heart rate to transport oxygen around the body so it can help break down lactic acid into carbon dioxide and water. Note that the time taken for the lactic acid to be removed and for the breathing and heart rate to return to normal is called the recovery period. Role of diffusion in gas exchange: Diffusion is the movement of particles from an area of high density to an area of low density. In this way gasses will move from an area dense with gas to an area of low density.
  3. 3. In the circulatory system oxygen enters the blood and carbon dioxide leaves the blood via gaseous exchange. Gasses move across the walls of alveoli to an area of lower density than they are in: Oxygen moves into the blood as there is a low density of oxygen in the blood; Carbon dioxide moves into the lungs as it is an area of lower density. How a leaf is adapted for gas exchange: Leaves are thin which allows gasses to diffuse quickly through them. In addition the stomata at the bottom of the leaf allow the diffusion of gasses in to the leaf- when a guard cell is shrunk gasses can enter the leaf. Stomata: Stomata are minute holes in the lower epidermis of the leaf. Guard cells regulate the opening and closing of the stomata; allowing carbon dioxide and oxygen to be exchanged between the leaf and the atmosphere. The guard cells absorb water and become turgid- opening the stomata- during the day. At night the guard cells are flaccid and so close the stomata. Breathing: Breathing in The intercostal muscles contract The ribs move up and out The diaphragm contracts and moves down The trachea carries air towards the lungs; it splits into two bronchi- one leading to the left lung, and one of the right- which then split into even smaller tubes, called bronchioles; these end in alveoli where gas exchange takes place. The pleural membranes prevent friction. Breathing out The intercostal muscles relax The ribs drop down The diaphragm also relaxes and moves upward These things reduce the space inside the lungs, pushing the air out. The intercostal muscles and diaphragm control ventilation in the lungs. When they contract the create more space in the lungs: drawing air in. When the relax the constrict the rings: pushing air out of the lungs. Alveoli: The alveoli have are thin, this allows gasses to diffuse through them easily. They are small and there are many of them meaning there is a large surface area through which much gas can diffuse at once. It also means there is a lot of surface in contact with the blood stream for gasses to diffuse into. Alveoli have a moist lining for gasses to dissolve into. Consequences of smoking: Tar can cause cancerous mutations in the lungs. Smoke removes the cilia- tiny hairs- which keep the lungs clean. Smoking also hardens the arteries, constricting the blood flow and putting strain on the heart, resulting in coronary heart disease. Phloem: Phloem tissue has tube like cells which carry dissolved substances like sucrose and amino acids around the plant. The phloem is made up of columns of living cells. Xylem: Xylem transport nitrates, phosphates, water and other mineral salts from the roots to other parts of the plants, like the leafs, flowers and buds. Xylem consists of columns of hollow, dead cells. Substances are carried up the tube dissolved in water.
  4. 4. Root hair cells > up taking water: Roots branch to increase the surface area and to increase the chances of finding a water source. Root hairs are epidermal cells on the surface of the root: they also increase the surface area for absorption. They absorb minerals by active transport and water by osmosis. These substances then move to the xylem. Transpiration: Transpiration is the name given to the process by which water is evaporated from the surface of a plant. Heat- from sunlight- is absorbed into the leaf which turns liquid water into gas, the gas then leaves the leaf through the stomata. Effects on rate of transpiration: Humidity Increased humidity decreases transpiration. This is because high water content outside the leaf will mean there is little difference in concentration, so the water will not be able to move- as it naturally does- from an area of low concentration to an area of high concentration. Wind speed Increased wind speed will increase transpiration. Because if the wind blows away the water vapour being produced there will be a greater difference in water concentration, meaning water will be able to continue leaving the leaf. Temperature Increased temperature increases transpiration, as increased heat makes evaporating easier. Light intensity Increased light intensity increases transpiration, as more heat is absorbed by the leaf meaning more water will be evaporated, also there is more photosynthesis meaning more water is being transported through the leaf (so more will need to leave the leaf.) Blood: The blood has several different components. 55% of the blood is plasma: yellow liquid containing water with different things dissolved in it. There are many red blood cells (Erythrocytes.) There is less white cell: Phagocytes; lymphocytes. Platelets (dead red blood cells) which play an important role in clotting. Red blood cells: Red blood cells carry oxygen around the body. In order to do this they have haemoglobin- which is made from iron- that can bond to oxygen. Red blood cells are enucleate (they have no nucleus) to make room for the haemoglobin. There are no mitochondria as the cells respire anaerobically so the cells don't use any oxygen. They are biconcave; they are a flat disk with a dip in the middle. The shape of a flat disk enables them to pass through narrow capillaries They have a dip in the middle to increase the surface area and decrease the distance for diffusion meaning that diffusion of oxygen happens quickly. White blood cells: White blood cells are specialised cells which can stop pathogens in your body. Phagocytes they can detect the presence of pathogens because of chemicals they give off. The cell then engulfs the pathogen. If then destroys the cell with digestive enzymes. Lymphocytes they release anti-bodies that are specific to the pathogen. When a lymphocyte meets its specific pathogen it divides: one cells it creates being a memory cell; the other being the cell which will create anti-bodies. One type of anti-body will attach to the pathogen to attract phagocytes. The other type will disable
  5. 5. the cell. A third type will group the pathogens together so that phagocytes can engulf them all. If the memory cells every meet the pathogen again they will create the anti-bodies very quickly. Vaccination: Vaccination is when a harmless or inactive form of a pathogen is injected into the body. It stimulates a response from the immune system without putting the body at risk. The pathogen will meet the lymphocyte that has the ability to get rid of it, it will be disposed of. The key thing is, though, that when the lymphocyte divides it will create memory cells. If the same pathogen is ever in the blood stream again (in the case of a real harmful infection) the memory cells will meet it and produce the appropriate anti-bodies making the immune reaction occur sooner and faster meaning a greater quantity of anti-bodies will be produced from when the pathogen enters the body. Platelets: When you have a wound you are at risk of losing blood and Platelets are produced in the bone marrow- they are fragments of cells. The chemicals in platelets turn fibrin in the blood into a solid called fibrin. A network of fibrin creates inherits red blood cells and platelets; it will then dry over to form a scab, beneath which the tissue can begin to repair. Structure of heart: The heart can be thought of in four sections: the right atrium; the right ventricle; the left atrium; the left ventricle. A description of the workings of the heart: The right atrium fills with blood (from the vena cava) and the valve is closed; This area is squeezed forcing the blood through an atria-ventricular valve into the right ventricle; This area contracts forcing the blood through the pulmonary artery where it is oxygenated at the lungs; the pulmonary vein fills the left atrium with blood; This contracts forcing the blood into the left ventricle; when the left ventricle contracts the blood is forced out through the aorta. Things to remember: Veins lead to the heart; arteries lead away. Atrium means entrance hall in Latin; hence the atrium is where blood enters the heart. The left side is bigger than the right as it has to pump blood through the whole body. You talk about the heart from right to left, as if you were examining someone's heart and using their own left and right. Heart rate different with exercise: During exercise muscles require more energy which is created by respiration that requires more oxygen to be brought to cells and more carbon dioxide to be taken away; this means the heart needs to increase its speed so that more blood is sent to muscles. Adrenalin- produced in the adrenal glands in top of the kidneys- stimulates adrenergic receptors in the heart which increase the rate that your heart cells work at. Arteries Take blood away from the heart Blood in them is under high pressure They are delivering blood to an organ Thick, muscle wall; small lumen (to give high blood pressure) Folded endothelium Veins Take blood to the heart Blood is under low pressure Their blood is returning from an organ Relatively thin wall; large lumen Valves stop blood flowing back in the wrong direction Open endothelium
  6. 6. Capillaries Exchange is taken place Very thin cell walls (one cell thick) so that substances can diffuse easily Circulation system: Vein- to the heart Artery- away from heart Lung- pulmonary Liver- hepatic Kidney- renal Stomach- gastric between the gut and liver is the hepatic portal vein. Lungs Carbon dioxide- a waster product from respiring cells- is diffused into the lungs and then breathed out. Kidneys Excess water, urea (amino acids) and salts are diffused into the kidneys. Skin Water and salts are excreted through the skin. Excretion amino acids contain nitrogen- which is toxic to the body- the liver converts it into urea. The kidneys filter urea from the blood stream and combine it with water to create urine which then moves into the bladder. Osmoregulation the kidneys react to ADH hormone released by the pituitary gland. If there is too little water ADH will be released and the kidneys won't absorb any water, but if there is too much water then less ADH is released and the kidneys absorb water from the blood stream. Nephrons: Nephrons are tubular structures within the kidneys which carry out filtration. The blood enters into the glomerulus in the Bowman’s capsule; this is where the blood is filtered to create a filtrate of water, glucose, salts and urea (among other things). This then travels through convoluted tubules; here some components are reabsorbed into the blood stream. The loop of Henle s where water is where water and sodium chloride and reabsorbed into the blood stream. The filtrate then travels down the collecting duct which transports it to the 'renal pelvis' after which it goes down the ureters to the bladder. Ultra filtration: Blood arrives in Bowman's casual under the high pressure of an artery, it travels it to the glomerulus where the pressure is further increased (as the tubes are smaller). Components of the blood are forced out of the blood vessel into the glomerulus due to the high pressure, creating glomerulus filtrate (water, slats ect.) Glucose is a component of glomerular filtrate. Some of the glucose in this filtrate is reabsorbed into the blood stream as it is needed by the body. The first section of convoluted tubules (before the Henle loop) is the proximal convoluted tubule, in this area glucose is removed from the nephron and taken back into the blood.