Biology unit 1

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Disease and immunity.

  • Pathogens can damage host cells by procuding toxins, rupturing them, breaking down their nutrients and replicating inside them.
  • Phagocytes recognise the surface antigens of pathogens and engulf them and forms a phagosome. A lysosome fuses with it and the hyrolytic enzymes within them break down the pathogen.
  • Phagocytes activate t-cells which have proteins that bind to the antigens presented to it by phagocytes. Some release substances to activate B-cells and some attach to antigens on a pathogen and kill the cell.
  • T-cells can activate B-cells, which are covered in antibodies- proteins that bind antigens to form an antigen-antibody complex. Each one has a different shaped antibody on its membrane so bind to different shaped antigens. B-cells divide into plasma cells.
  • Plasma cells are identical to the B-cell (theyre clones). They secrete loads of the antibody which is specific to the antigen.
  • Antibody functions include: coating the pathogen to make it easier for the phagocyte to engulf/to prevent it entering host cells.
  • Vaccines protect individuals who have them and because they reduce occurance, those not vaccinated are also less likely to catch the disease. This is called herd immunity.
  • Pathogens can change their surface antigens= antigentic variation. 
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The digestive system.

  • Oesophagus -> stomach -> small intestine -> large intestine -> rectum
  • The salivary glands: secrete saliva that consists of mucus, mineral salts and amylase. Salivary amylase breaks down starch into maltose.
  • The pancreas: releases pancreatic juice into the duodenum through the pancreatic duct. it contains amylase, trypsin, chymotrypsin and lipase. It also contains sodium hydrocarbonate to neutralise the acidity of the stomach.
  • Amylase= starch into maltose.
  • Trypsin= protein into peptides.
  • Maltase= maltose into glucose.
  • Sucrase= sucrose into glucose and fructose.
  • Lactase= lactose into glucose and galactose.
  • Polypeptides are formed in condensation reactions. A molecule of water is release and a peptide bond is formed.
  • Biuret test for proteins= test solution needs to be alkaline so you add sodium hydorxide and then you add some copper sulfate solution. A protein is present if a purple layer forms.
  • Primary structure= amino acids in polypeptide chain, Secondary= hydrogen bonds form between chains and it coils to form an alpha helix, Tertiary= coiled and folded further, more bonds, Quaternary= polpeptide chains assembled together.
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The digestive system. 2

  • Monosaccharides are joined together by condensation reactions. A molecule of water is released and a glycosidic bond is formed.
  • Reducing sugars= Add benedicts regent to a sample and heat it. If the sample contains a reducing sugar it will turn brick red.
  • Non reducing sugars= Break into monosaccharides by boiling solution with dilute hyrodchloric acid and the neutralising it with sodium hydrocarbonate. Then add benedicts regent and boil.
  • Iodine test for starch= add iodine dissolved in potassium iodide solution to the test sample. If there is starch present, the sample changes from browny-orange to bluey-black.
  • When a substrate fits into an enzymes active site and forms an enzyme-substrate complex- it lowers activation energy because if the two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily. Also, if the enzyme is catalysing a breakdown reaction, fitting into the active site puts strain on bonds in the substrate , so the substrate molecule breaks up more easily.
  • Competitive inhibitors- they compete with the substrate molecules to bind to the active site, but no reaction takes place. instead they block the active site so no substrate molecules can fit. high concentration of inhibitor means that almost all active sites will be taken up.
  • No competitive inhibitors- bind to allosteric site, causing the active site to change shape. 
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  • Plasma membrane- regulates the movement of substances into and out of the cells and also has receptor molecules to respond to chemicals like hormones.
  • Nucleus- chromatin controls the cells activites and the nucleous makes ribosomes.
  • Lysosome- contains digestive enzymes to digest invading cells or break down worn out components. 
  • Ribosome- the site where proteins are made.
  • Smooth ER- synthesises and processes lipids, Rough ER- folds and processes proteins made a ribsomes.
  • Golgi apparatus- processes and packages new lipids and proteins and also makes lysosomes.
  • Mitochondria- the site of aerobic respiration.
  • Epithelial cells in the small intestine are adapted to their functions- they have villi to increase surface area, microvilli to further increase surface area and lots of mitochondria to provide energy for the transport of digested food molecules.
  • Magnificaton is how much bigger an image is than the specimen.
  • Resolution is how well a microscope and distingish between 2 points that are close together.
  • Cell fractionation= homegenisation, filtration, ultra centifugation
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Plasma membranes

  • Triglycerides are formed by condensation reactions. A molecules of water is released and a ester bond is formed. 
  • Phospholipids are similar to triglycerides but one of the fatty acids is replaced with a phosphate. The phosphate group is hydrophylic (attracts water) and the fatty acid tails are hyrdophobic (repel water).
  • Emulsion test for lipids-> Shake the test substance with ethanol for about a minute and the pour the solution into water. Any lipid will show as a milky emulsion.
  • Diffusion= the net movement of particles from an area of higher to lower concentraion. Particles diffuse down a concentration gradient. It is a passive process, no energy is needed. 
  • The rate of diffusion depends of the concentration gradient (higher= faster), thickness of exchange surface (thinner=faster) and surface area (bigger=faster)
  • Osmosis= the diffusion of water molecules from an area of higher to lower water potential. 
  • Facilitated diffusion= The diffusion of larger molecules, down a concentration gradient, through carrier proteins.
  • Active transport= the net movement of particles, against a concentraton gradient using ATP.
  • Membrane is a barrier against water-soluable sunstances, controls what enters and leaves the cell and allows cell recognition. 
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The respiratory system

  • Oxygen diffuses out of the alveoli, across the alveolar epithelum and the capillary endothelium and into the haemoglobin in the blood.
  • Cardon dioxide diffuses into the alveoli from the blood and is breathed out. 
  • The alveoli are adapted for efficient gas exchange- they have a thin exchange surface (epithelium is one cell thick) and there is a large surface area because there is lots of them.
  • Pulmonary tuberculosis-> transmitted by droplet infection, tiny droplets of saliva and mucus are breathed in when an infected person coughs or sneezes. The immune system cells build a wall around the bacteria in lungs, forming hard lumps called tubercles. infected tissue within tubercles dies and the gas excange surface is damaged so tidal volume is decreased.
  • Fibrosis-> formation of scar tissue. scar tissue is thicker and less elastic. this means that the lungs are less able to expand and cant hold as much air- tidal volume is decreased. diffusion is slower across scar tissue.
  • Emphysema-> foreign particles become trapped in the alveoli, cauing inflammation and attracts phagocytes to the area. the phagocytes produce an enzyme that breaks down elastin. loss of elastin means that the alveoli cant recoil to repair as well. it also leads to the destruction of alveoli walls, which reduces surface area so the rate of gas exchange decreases.
  • Asthma-> during an asthma attack, the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced, causing constriction of the airways.
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The circulatory system

  • The left ventricle of the heart is thicker and more muscular because it needs to contact powerfully to pump blood all around the body. The venticles are thicker then the atria because the atria only pump blood a short distance compared to the venticles.
  • The cardiac muscle is myogenic it can contract and relax without recieving signals from nerves. starts with the SAN, atria contract, slight delay so the atria can emoty, AVN, bundle of his, purkyne fibres, then venticles contract.
  • Cardiac output = heart rate X stroke volume
  • Atheroma-> if damage occurs to the endothelium white blood cells and lipids from the blood clump together to form fatty streaks, over time more build up and form a fibrous plaque called an atheroma. This partially blocks the lumen and restricts blood flow increasing BP
  • Aneurysm-> ateroma plaques damage and weaken arteries and also increase blood pressure. when blood travels through a weakened artery at high pressure it can push the inner layer our through the elastic layer to form a balloon like swellin called an aneurysm.
  • Thrombosis-> An atheroma plaque can rupture the endothelium damaging the wall and leaving a rough surface. platelets and fibrin accumulate and from a blood clot (thrombus).
  • Mycardial infarction-> if the coronary artery becomes completely blocked an area of the heart muscle will be completely cut off from its blood supply, recieving no oxygen. This causes mycardial infarction and damage or death to an area of the heart muscle.
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