Biology AS



Biological Molecules

  • carbs - CHO 
  • Lipids - CHOP
  • Protein - CHONS 
  • nucleic acids - CHONP 


  • polysacharides - starch, glycogen and cellulose.
  • most important monosacharide - glucose C6H12O6
  • glycosidic bond plus water = condensation reaction.
  • maltose - glucose + glucose
  • sucrose - glucose + fructose
  • Lactose - glucose + galactose


  • triglycerides - glycerol + 3 fatty acid. forms ester bonds in condensations polymerisation reaction + 3 water molecules. 
  • no double bonds - saturated. double bonds - unsaturated. unsaturated - low melting point found in cold blooded animals. 
  • Phospholipids - phosphate replaces 1 fatty acid. hydrophobic tails.


  • C + H + carboxyl acid group ( COOH) + R group + amino group (NHH)
  • amino acid x2 = dipeptide + peptide bond + 1 water molecule
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  • the sequence of amino acids in polypeptide depends on the bases in DNA.
  • Protein structure - polypeptide -> alpha helix - hydrogen bonds -> globular structure - hydrogen, covalent and sulphur bonds -> more than one polypeptide chain + prosthetic. 


  • starch - iodine
  • reducing sugars - benedicts, shake and heat - brown/red
  • non reducing sugars - hydrolyised with dilute hydrochloric acid. 
  • lipids - shake with ethanol, add water - white precipitate
  • protein - buiret test. shake - purple/lilac.


  • enzyme substrate complex. lower activation energy by overcoming energy barrier. enzymes reduce the activation energy of reaction. Higher temp = more kinetic energy. too hot = hydrogen bonds broken. pH affects hydrogen bonds.
  • enzyme conc - increases linearly
  • substrate conc - curve. higher conc enzyme active site become saturated so fewer enzymes. 
  • competitive inhibitors - same shape. non competitive - binds to another part of enzyme. 
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  • cytoplasm - solution contains enzymes, sugars, salts, amino acids etc
  • nucleus - large holes for RNA and ribosomes.
  • Mitochondria - aerobic respiration site, highly folded cristae large surface area. matrix and strands of DNA inside. Stalked particles site of ATP synthase. 
  • Chloroplasts - photosynthesis takes place. 3rd thylakoid membrane folded into disks, stacks called grana. 
  • ribosomes - small, site of protein synthesis, manufactured in nucleus. found in cytoplasm. make proteins for export. 
  • ER - synthesis and transport materials. RER studded with ribosomes. Add carbs to proteins. SER - processes lipids. 
  • Golgi - transports proteins from RER to cell membrane. releases by exocytosis. 
  • Vacuoles - plants. contain water or solutions. keep cell turgid. 
  • lysomes - Contain digestive enzymes, breakdown toxins and chemicals so materials can be recycled. microvilli - epithelial cells of intestine, increase surface area for absorption. 
  • cell membrane - phosphlipids and proteins. 
  • cell wall - thick wall - strength.
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Prokaryotic cells

  • cytoplasm - contain enzymes for all metabolic reactions. 
  • ribosomes - smaller used for protein synthesis. 
  • nucleur zone - contain DNA
  • DNA - always circular 
  • Plasmid - small circles of DNA for exchange of DNA between cells.
  • Cell wall - murein - glycoprotein - protein/carb complex.
  • capsule - protection. 
  • Flagellum - tail 

differences between pro and EU

  • pro - unicellular EU - multicellular
  • pro - DNA circular EU - linear
  • pro - no nucleus EU - nucleus
  • Pro - asexual EU - asexual or sexual 
  • pro - small ribosomes EU - big

cell fractionation 

  • ice cold - enzymes buffer - PH isotonic - osmosis.
  • filter - remove insoluble tissue
  • centrifuge order - nucleus, mitochondria and chloroplasts, ER golgi and membrane lastly ribosomes. finish with cytoplasm.  
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Cell membrane 

  • 50% proteins - control the membranes properties. e.g transporters, receptors, enzymes, antigens and structure. 
  • protein + carb = glycoprotein phospholipid + carb = glycolipid. 


  • lipid diffusion - lipid soluble, or very small eg H20 and 02. down conc gradient. 
  • Osmosis - water. down conc gradient. 100% pure water = 0 water potential.
  • facilitated diffusion - trans-membrane protein molecule. specific to one molecule. down conc gradient. channel proteins - gated, allow cell to control entry and exit. Carrier proteins have binding site and flip between 2 states.
  • active transport - trans-membrane protein pump. uses ATP. against conc gradient. 


  • rate of diffusion = surface area x conc difference / distance
  • large surface area, small distance, high conc gradient. 
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  • pathogen can be transmitted via water, food, breathing aaerosol droplets, animal bites or direct contact. 
  • tough skin. has to come through cuts, digestive system, gas exchange system, or sex. 
  • bodies defence - stomach acid, lysozyme enzymes and the immune system.
  • pathogens have to multiply, use up cells resources, burst cells, produce toxins that bind to enzymes, receptors and DNA.
  • risk = probability of event x impact

Digestive system

  • saliva contains lysosomes to kill bacteria and salivary amylase to digest starch. 
  • stomach - churn food into chyme. stomach wall secretes hydrocholric acid to kill bacteria and protease enzymes.
  • Small intestine - duedenum - pancreatic juice and bile secreted. contains amylase, protease and lipase enzymes. BIle secreted by liver to aid lipid digestion.
  • lleum - absorption. villi and microvilli - huge surface area. short diffusion distance - single layer of cells. high conc gradient by fluids on either side - blood low amount of nutrients. 
  • starch broken down by amylase to maltose broken down by maltase to glucose. 
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absorption of monosaccharides 

  • enzymes hydrolyze disaccharides into mono. 
  • absorbed by coupled active transport. sodium/ glucose cotransporters, move glucose into the cell and then the glucose diffuses out by facilliated diffusion  through glucose carrier proteins, it then diffuses into blood through gaps in capillary wall.
  • sodium is the pumped out of cell  by Na/ K pump and goes to either lumen or blood. 

lactose intolerance 

  • no lactase enzyme to digest lactose. fermented by bacteria in the colon, produces acids and gas. Acids lower water potential so water floods in from cells. 


  • Prokaryotic cell. causes vomiting and diarrhea. Bacterium attaches to epithelium cells and secretes toxin into in which opens chloride channels. Cl ions flood out into lumen reducing water potential so water floods out by osmosis causing Diarrhea. 
  • Oral rehydration therapy - salts glucose potassium and bicarbonate. salt and glucose activate Na/ glucose co transporter, so enter the cells causing the water potential in the cells to lower so water rushes in to rehydrate. 
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Immune System

  • lymph and blood vessels transport pathogens and white blood cells around body. 
  • lymph nodes and spleen contain phagocytes and lymphocyte cells to identify and remove pathogens.
  • Thymus is where blood stem cells differentiate to make T-cells.
  • B- cells are produced from bone marrow. 


  • first line of defense - tough skin 20-30 cells thick. sweat and tears contain lysosome enzymes. digestive tract - enzymes and stomach acid. Respiritory tract - sticky mucus containing lysosome enzymes secreted by bronchioles and trap microbes. cilia sweep the mucus up to throat where swallowed. 

Non specific 

  • phagocytes for phagocytosis using macrophages. Phagocytes are large white blood cells that remove bacteria dust etc. Flow over microbes, surrounding and ingesting them to form a phagosome which fuses with lysosomes which release lysosome enzymes into the phagosome killing the microbe. 
  • inflammation - Granulocyte cells release histamines which stimulate vasodilation to increase blood flow to area turning it red. Capillary leakage so phagocytes enter tissue fluid so swells. Blood clotting to seal wound so scab. dead phagocytes released as pus. 
  • fever - chemicals stimulate hypothalamus of brain to increase body temp. 
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Specific immune response

  • the lymphocytes (white blood cells) recognize self and non-self molecules using antigens which are molecules on the outside of a cell and specific to every different disease. 
  • B- cells make antibodies which is a protein molecule to binds to an antigen. Y shape held together by disulphide bonds and the stem is called constant region and the arms are the variable region. antigen- antibody complex
  • T-cells have receptor molecules on the surface which bond to antigens forming antigen-receptor complexes. T-cells do not secrete proteins. 
  • when non-self is recognized an immune response occurs:

1. antigen presentation. - Macrophages ingest pathogen and presents the pathogens antigens on its surface thus becoming an antigen presenting cell. It also secretes cytokine chemicals which stimulate the white blood cells.

2. Clonal selection - The white blood cells encounter the matching antigen to which it can bind which stimulates the lymphocyte to divide repeatedly by mitosis. 

3. T-cells and cell mediated immunity - killer T-cells bind to antigens on pathogens and kill the cell by releasing proteins that burst the cell. Helper T-cells bind to antigens and secrete cytokines. Memory T-cells remain in the blood for decades. 

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4. B-cells nd antibody-mediated immunity - Plasma cells secrete free soluble antibodies which bind to the antigens of the pathogens. the antibodies prevent the bacteria from attaching to cells; change the shape of the active region of toxin proteins and link antigens together called agglutination which immobilises them and make phagocytosis easier. Memory B-cells continue to secrete antibodies for years.

Primary and secondary response

  • first infection - primary, symptoms shown and takes long time for immune response to work. 
  • second infection - memory T and B cells remain in the blood so immune response much faster. no symptoms as so fast. 
  • mutations cause antigens to change which causes new primary response. 


  • inject with an antigen to promote primary immune response. Non-virulent. The immune system then makes memory cells so a secondary immune response can occur quickly if ever infected.
  • active - antigens received. natural active immunity is without injection and is just the primary immune response .
  • Passive - antibodies received. used when already infected. the antibodies assist the bodies immune response. prepared from the blood serum of infected human called antiserum. naturally occurs when mother passes antibodies to child across the placenta and breast feeding.
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Monoclonal Antibodies

  • inject mouse with the antigens that you want anitbodies for and mouse will make an army of B-cells with antibodies for that antigen. 
  • extract B-cells from spleen and mix with myeloma cells which are cancer cells that will divide in vitro. the fuesd cells are called hybridoma cells.
  • Separate the cells into hundreds of wells in an immunossay plate, a different antibody in each well.
  • Then find the well which has the right antibody and grow it in a culture flask, where they multiply by mitosis.
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Gas Exchange System

  • alveoli - gas exchange surface - large surface area, small distance between source and destination - diffuse through just 2 epithelial cells, high conc gradient through blood flow on one side and ventilation on the other. o2 and CO2 can diffuse down the conc gradient. 
  • water loss - water diffues down conc gradient from tissue fluid and alveoli into the air. exhaled air contains more water than inhaled air. however, moist alveoli air means less of a diffusion gradient. 
  • epithelial cells secrete mucus which traps bacteria and is swept upwards by the cilia to the throat and then swallowed. 
  • Ventilation - thorax moves due to intercostal muscles and the diaphragm. Boyle's law - pressure change. ventilation in humans is tidal, means air flows in and out through the same route. air always flows from high pressure to low pressure. 
  • inspiration - diaphragm contracts and flattens, intercostal muscles contract pulling ribs up and out. pressure decreases, volume increases, air rushes in from high pressure to low. 
  • expiration - diaphragm relaxes, intercostal muscles relax, volume decreases, pressure increases, air flows out. 
  • breathing rate = 60 / cycle time. 
  • Pulmonary ventilation = ventilation rate x tidal volume.  
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Lung Diseases


  • symptoms - persistent cough, chest pains, tiredness, weight loss
  • transmitted by aerosol droplets which invade the epithelial cells of alveoli and bronchioles. 
  • they multiply into lumps called tubercles, but remain dormant. Which stimulate an immune response, resulting in scar tissue. 
  • After a delay the bacteria emerge from the tubercles multiplying and killing the lung epithelial cells, destroying the alveoli making gas exchange difficult
  • improved due to - improved diet, housing and hygiene, immunisation and antibiotics. 


  • allergic response - causes difficulty breathing wheezing, tight chest and coughing. 
  • white blood cells produce histames, causing the bronchioles to contract narrowing the airways. the epithelial cells also secrete mucus.

Pulmonary Fibrosis

  • inhalation of dust particles. stimulates inflammatory response in lungs, fibrous scar tissue grows around alveoli, reducing the elasticity and compresses them.
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  • caused by smoking. tar in fag smoke stumlates white blood cells to release protease enzymes which digest the protein forming the alveoli. reduced elasticity so cant expand and recoil. much smaller surface area.

TB - bacterial. chest pain, coughing, death. bacteria from tubercles in lungs reproduce and consume tissue. overcrowding, poor diet, AIDS.

Asthma - allergens. wheezing, tight chest, breathing difficulty. bronchiole muscles contract, mucus. pollen, dust

Pulmonary Fibrosis - dust. breathing difficulty. fibrous tissue. coal dust, mould spores

Emphysema - smoking. permanent breathing difficulty, coughing, wheezing. protease enzymes digests elastic tissue, reduces elasticity in alveoli. smoking.

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The circulatory system

  • atria receive blood from veins, ventricles pump blood away into arteries. between atria and ventricles = atrioventricular valve. left valve bicuspid right valve tricuspid. 
  • semilunar valves between ventricles and arteries. left and right divided by septum. right side walls 3 times thinner as it produces less force and pressure. internal volume is the same though
  • the heart is made of cardiac muscle composed of myocytes cells, which are fed by numerous capillaries from 2 arteries. 

the cardiac cycle

  • cardiac muscle is myogenic so contracts on its own. the impulse originates at the sinoatrial node in the right atrium. 
  • atrial systole - the SAN causes the atrias to contract pumping blood into the ventricles. The blood cant flow back due to the valves. 
  • Ventricular systole - the impulse passes to the atrioventricular node, the bundle of his and purkinje fibres. short delay of 0.1s to make sure all the blood is in the ventricles. ventricles contract forcing blood into the arteries. (Pulmonary artery and aorta) artioventricular valves close. 
  • Diastole - atria and ventricle relax while atria fill with blood. semilunar valves close. 
  • heart rate = 60 / cycle time
  • cardiac output = heart rate x stroke volume  
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cardiac output increases during exercise to 

  • get oxygen and glucose to the muscles faster
  • to get CO2 and lactate away from the muscles faster
  • to get heat away from muscles

Coronary Heart Disease

  • heart incapable of anaerobic respiration so need O2 and glucose. a blockage in a coronary artery can restrict supply of O2 to the cardiac cells, killing them.
  • cholesterol and other insoluble lipids collect in the artery called an atheroma which narrows the lumen restricting blood flow. this can become hardened to form rough plaque
  • the plaque weakens the wall so the pressure causes a swelling called an aneurism which may burst causing death.
  • the plaque can also cause a blood clot called thrombus which grows until it blocks the artery. 
  • myocardial infarction - heart attack when starved of oxygen.

atheroma -> plaque -> aneurism -> myocardial infarction

atheroma -> plaque -> thrombosis -< myocardial infarction

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risk factors and microscopy

  • blood cholesterol - carried in large complexs with proteins called lipoproteins. High density lipoproteins remove cholesterol. low density deliver cholesterol to tissue. 
  • Blood pressure - high blood pressure stimulates thickening of artery wall, increasing the risk of thrombus. 
  • Genetics
  • Diet - high levels of saturated fats increase amount of cholesterol.
  • Smoking - carbon monoxide and nicotine in **** cause increase in blood pressure. 


  • mm = 10x-3     micro = 10x-6     nano = x10-9
  • resolution - smallest separation at which 2 separate objects can be distinguished. 
  • light microscope - can be living or dead, illuminated by light, colored stain used, cant see details of cell organelle.
  • electron microscope - much better resolution and magnification, but much more expensive. uses electrons so needs vacuum so must be dead, specimins must also be very thin and can be destroyed. 
  • Transmission electron micrscope - best resolution, in colour
  • Scanning electron microscope - 3-D image 
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This is amazing, really, really helpful!  Thank you

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