AS level biology AQA unit 1


Section 1 - disease and immunity

Learning objectives - Know that lifestyle can affect human health. Know the specific risk factors are associated with cancer and coronary heart disease. Know the changes made in lifestyle to reduce the risk.

Risk factors of coronary heart disease

  • poor diet - a diet high in saturated fat or salt increases the risk
  • smoking, lack of exercise and high alcohol intake - lead to high blood pressure


  • smoking
  • exessive exposer to sunlight
  • excessive alcohol intake

Reducing the risk

- reducing alcohol intake, exercise more, eat healthily

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Section 1 - disease and immunity 2

Learning ojectives - Pathogens include bacteria, viruses and fungi.

Disease can result from pathogenic microorganisms penetrating any of an organism’s interfaces with the environment.  These interfaces include the digestive and gas-exchange systems. The digestive system - eat or drink things that may contain pathogens, most of them killed by the acidic conditions of the stomach. However some may pass into the intestines where they can invade cells of the gut wall and cause disease.The gas exchange system - breath in air that contains pathogens, get trapped in mucus lining the lung epithelium. These cells have cilia that beat and move the mucus up the trachea where its removed. Some may pass and invade alveoli cells causing damage.The skin - if you damage it, pathogens on the suface can enter your bloodstream. The blood clots and forms a scab at the area of damage to preventpathogens from entering, but some may get in before a scab forms.

Pathogens cause disease by damaging the cells of the host and by producing toxins.

Toxins - Harmful molecules. Cell Damage can: repture them, break down nutrience inside the cell for their own use. This staves and kills the cell. Or it can replicate inside the cell, bursting them when they're released.

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Section 1 - disease and immunity 3

Learning objectives - Phagocytosis and the role of lysosomes and lysosomal enzymes in the subsequent destruction of ingested pathogens. The phagocyte reconises the pathogen is 'foreign'. It moves toward the pathogen by a process called chemotaxis. The arms of cytoplasm then enfulf the pathogen forming a phagosome containing the pathogen. A lysosome then fuses with the phagosome and empties its digestive enzymes into the phagosome, digesting the pathogen.

Definition of antigen and antibody. Antigen - Is a molecule found on the suface of cells, that are proteins and that may stimiulate an immune response. Antibody - proteins that bind to antigens, that are produced by plasma b-cells in a immune response.

Antibody structure and the formation of an antigen-antibody complex. Antibody structure - (see image) Varible region, constant region, light chain, heavy chain, hinge region, disulfide bridge and binding site. Antibodies bind to antigens that have a complimentary shape

The essential difference between humoral and cellular responses as shown by B cells and T cells. Humoral - B-cells and the production of antibodies. Cellular - T-cells

The role of plasma cells and memory cells in producing a secondary response. - Memory B- cells get activated and produce plasma cells which make the correct type of antibody to bind to the pathogens antigens. Memory T cells will produce the correct type of killer T-cell. (memory cells remain in the blood until infected again)

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Section 1 - disease and immunity 4

Learning objectives - The effects of antigenic variability in the influenza virus and other pathogens on immunity. - some pathogens change the antigens on their suface. So when you are infected for a second time your memory cells dont reconise the antigens and have to start a primary response against these new antigens, it takes time to get rid of the infection so you get ill again. Influenza - antigens change regularly creating new stains of the virus. Everytime your infected with a new strain you become ill again.

The use of vaccines to provide protection for individuals and populations against disease. - Vaccines contain antigens - these may be free or attached to a dead or weakened pathogen, that causes your body to produce memory cells against a particular pathogen, without the pathogen causing disease. You become immune without getting any symptoms.They protect the indervidual from the disease and reduce the occurence of it so unvaccinated people are also less likely to catch it. This is called herd immunity. If you take a vaccine orally, it could be broken down by enzymes in the gut because the antigens are proteins. Or the molecule coulbe to too large to be absorbed into the blood. Booster vaccines are offered to make sure that memory cells are produced.

The use of monoclonal antibodies in enabling the targeting of specific substances and cells. - are antibodies produced from a single group of genetically identical B-cells (plasma cells). This means they are identical in structure. They can only bind to one antigen. Can make the monoclonal antibodies bind to anything you want.

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Section 1 - disease and immunity 4

Discuss ethical issues associated with the use of vaccines and monoclonal antibodies.Vaccines - tested on animals and contain animal based substances. Testing vaccines on humans can be risky, people may think they are protected and the vaccine doesnt work. Not all people have it becaus eof side affects but are still rpotected by herd immunity - seen as unfair. If a new epidemic - tough decisions for who will have the vaccine first. Monoclonal - animal testing

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Section 2 - the digestive system

Learning objectives - The gross structure of the human digestive system limited to oesophagus, stomach, small and large intestines, and rectum.  The glands associated with this system limited to the salivary glands and the pancreas. The mouth - teeth are used to break down food and the tongue is used to push food down into the oesophagus. Saliva (contains:mucus mineral salts and amylase) is secreted to make food easier to swallow and it contains enzymes which start the chemical digestion process. Oesophagus - a tube that takes food from the mouth to the stomach using waves of muscle contactions called peristalsis. Mucus is secreted from tissues in the walls to lubricate the foods passage downwards. The stomach - is a small sac, has lots of folds allowing it to expand. The stomach walls produce gastric juice, which helps break down food. It contains hydrocchloric acid, pepsin (enzyme) and mucus. pepsin hydrolyses proteins into small polypeptide chains. Only works in acidic conditions. Food now becomes an acidic fluid called chyme. The small intestine - Chyme moves along the small intesineby peristalsis. In the duodenum bile (alkaline) and pancreatic juices (amylase, trypsin,chymotrypsin and lipase, it also contains sodium hydrogencarbonate which...) neutralise the chyme and breaks it down into smaller molecules. In the ileum, the small, soluble molecules (e.g. glucose and amino acids) are absorbed through structures called villi (finger like projections) that line the gut wall. Yhey increase the surface area for absorbtion. (active transport, diffusion or facilitated diffusion) Large intestine - (colon) absorbs water, salts and minerals. It has folded walls which provides a large surface area.

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Section 2 - the digestive system

Digestion is the process in which large molecules are hydrolysed by enzymes to produce smaller molecules that can be absorbed and assimilated. - Physical digestion - broken down into smaller pieces by teeth and mouth. Moves to the stomach where broken down further by the churning movement of the stomach muscles. Making them smaller gives it a larger surface area, which makes chemical digestion quicker. Chemical digestion - the polymers in food are insoulble - they cant be directly absorbed into our bloodstream and made into new products. polymers have to be hydrolysed into smaller soluble molecules by adding water. Hydrolisis is catalysed by digestive enzymes (carbohydrases, proteases, lipases). It makes polymers into monomers.

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Section 2 - the digestive system 2

Proteins have a variety of functions within all living organisms. -  enzymes, antibodies and antigens, transport proteins and structual proteins.

The general structure of an amino acid as - has a carboxyl group, varbilbe group, an animo group


                           H2N            C           COOH


Condensation and the formation of peptide bonds linking together amino acids to form polypeptides.  The relationship between primary, secondary, tertiary and quaternary structure, and protein function. Primary - polypeptide chain Secondary - hydrogen bonds form between the amino acids in the chain. This makes it automatically coil into an alpha helix or a beta pleated sheet. Tertiary structure - it coils and folds further than the secondary, and more bonds form between different parts of the polypeptide chain. Its made from one single polypeptide chain. Quaternary structure - is several different plypeptide chains held together by bonds. 

The biuret test for proteins. - add some sodium hydroxide, then some copper sulphate and if a protein is present then the solution turns purple.

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Section 2 - the digestive system 3

Within this unit, carbohydrates should be studied in the context of the following

• starch, the role of salivary and pancreatic amylases and of maltase located in the intestinal epithelium - when starch is digested, its first broken down intomaltose by amylase - an enzyme released by the salivary glands and the pancreas. Maltose is then broken down into alpha glucose by maltase - released in the intestinal epithelium.

• disaccharides, sucrase and lactase. - sucrose is broken down into glucose and fructose by sucrase. Lactose is broken down into glucose and galactose by lactase.

Biological molecules such as carbohydrates and proteins are often polymers and are based on a small number of chemical elements.  carbohydrates = hydrogen, oxygen and carbon. Protein = hydrogen, oxygen, carbon, nitrogen

Monosaccharides are the basic molecular units (monomers) of which carbohydrates are composed.

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Section 2 - the digestive system 3

The structure of a-glucose

The linking of a-glucose by glycosidic bonds formed by condensation to form maltose and starch. A disaccharide is formed when joining 2 monosaccharides together. A polysaccharide is formed when you join more than 2 monosaccharides together. water is removed in a condesation reaction.

Sucrose is a disaccharide formed by condensation of glucose and fructose. Lactose is a disaccharide formed by condensation of glucose and galactose.

Lactose intolerance. - lactose is the sugar found in milk, and its digested by lactase. If you dont have enough of this enzyme, you wont be able to break down lactose properly. Undigested lactose is fermented by bacteria and can cuase a whole host of intestinal complaints such as stomach cramps, wind and diarrhoea

Biochemical tests using Benedict’s reagent for reducing sugars and non-reducing sugars. Iodine/potassium iodide solution for starch. Reducing sugar - add benedicts soultion and heat. Non reducing sugar, you add hydrochloric acid and neutralsise with sodium hydrogencarbonate. Heat with benedicts solution. Should go brick red if sugar present. Starch - add iodine, should go blue-black colour.

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Section 2 - the digestive system 4

Enzymes as catalysts lowering activation energy through the formation of enzymesubstrate complexes. Enzymes lower the amount of activation energy thats needed often making the reactions happen at lower temperaturesthan they could withough an enzyme. This speeds up the rate of reaction. When a substrate fits into the active site it forms an enzyme substrate complex - its this that lowers the activation energy.

This is because - if two molecules need to be joined being attached to an enzyme holds them close together, reducing any repulsion between the molecules so they can hold more easily.

If an enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.

The lock and key and induced fit models of enzyme action. Lock and key - substrate fits the active site the same way a key fits a lock. The active site and the substrate have a complementary shape. Induced fit - Explains why enzymes are so specific, the substate doesnt only have to be the right shape to fit the active site, it has to make the active site change shape in the right way aswell.

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Section 2 - the digestive system 4

The properties of enzymes relating to their tertiary structure.  Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration. Temperature - as it increases, more heat means more kinectic energy so the molcecules move faster, making the substrate molecules more likely to collide with active sites, which is more likely for a reaction to occur. But if the temp gets to high it makes the enzymes molecules vibrate more, the vibrations break some of the bonds which holds to tertiary structure in place. The active site changes (denatures) so the substrate will no loger fit, no reaction can occur. pH - above and below the optimum pH, the H+ and the OH- ions found in acid and alkalines can disrupt the ionic and hydrogen bonds which hold the tertiary structure in place. The enzymes active site becomes denatured. Substrate - as substrate increases so does rate of reaction because collisions between the substrate and the enzyme are more likely. But after the saturation point, all the active sites are full so more substate makes no difference. Competitive - compete with the substrate molecules to bind with the acive site but no reaction occurs. They block the active site, so no reaction can occur. Depends on the conc of the inhibitors, if high then all active sites will be full. Non-competitive - binds to enzyme away from active site, changes shape of active site so substrate can no longer fit.

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Section 3 - cell structure and membranes

The appearance, ultrastructure and function of 

plasma membrane, including cell-surface membrane - Made of lipids and proteins and it regulates the movement of substances in and out of cells. It has receptors on it to respond to chemiclas e.g. horomones microvilli  - folds in plasma membrane , increases surface area nucleus - surrounded by a nuclear envelope, which contains many pores. It contains DNA and usally a nucleolus. DNA controls cell, envelop allows things in and out. nucleoulus makes ribosomes mitochondria - oval shaped, double membrane, inner one = cristae, inside there is the matrix which contains enzymes involved in respiration. Is the site of aerobic respiration which produces ATP. lysosomes - round organelle surrounded by a membrane, contains digestive enzymes which can digest unwanted material in cells. ribosomes - protein synthesis endoplasmic reticulumSER = a system of membranes enclosing a fluid filled space. syntheisies and processes lipids. RER the same but covered in ribosomes processes proteins made by the ribosomes. Golgi apparatus.- fluid filled flattened sacs, it processes and packages new lipidsand proteins it transports then elsewhere by vesicles and it also makes lysosomes.

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Section 3 - cell structure and membranes

The principles and limitations of transmission and scanning electron microscopes. Transmittion uses electromagnets to focus beams of elctrons through a specimen. They give the highest resolution, used on thin, dead specimens. Scanning - scan a beam of electrons across the specimen - thick specimens, 3D, dead specimens

The difference between magnification and resolution.  Magnification - is how many times bigger an image is than the actual specimen. Resolution - is how clear you can distinguish 2 neighboring objects. The clarity of the image.

Principles of cell fractionation and ultracentrifugation as used to separate cell components. Homogenisation - breaking up the cells (breaks cell membranes emptying organelles into solution) Filtration - get rid of connective tissue. Ultracentrifugation - seperating organelles (heaviest to lighest = nucleus, mitocondria, lisosomes, ER, ribosomes) Isotonic - no (reduces) net water movement via osmosis (prevents organelle damage). Ice cold - reduces enzyme action Buffered - to remain a constant pH

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Section 3 - cell structure and membranes 2

Glycerol and fatty acids combine by condensation to produce triglycerides. - ester bond

The R-group of a fatty acid may be saturated or unsaturated.  In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate group.

The emulsion test for lipids. - shake with ethanol then pour into water. If white and cloudy lipids are present.

The arrangement of phospholipids, proteins and carbohydrates in the fluid-mosaic model of membrane structure. - phospholipids form a continuous double layer (bilayer). This layer is fluid because the phospholipids are constantly moving. Protein molecules are scattered through the layer, like tiles in a mosaic


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Section 3 - cell structure and membranes 3

Diffusion is the passive movement of substances down a concentration gradient.  Surface area, difference in concentration and the thickness of the exchange surface affect the rate of diffusion.

The role of carrier proteins and protein channels in facilitated diffusion.

Candidates should be able to use the fluid-mosaic model to explain appropriate properties of plasma membranes.

 Osmosis is a special case of diffusion in which water moves from a solution of higher water potential to a solution of lower water potential through a partially permeable membrane. 

Isotonic - this means a solution has the same chemical concentration as the cell

Active transport The role of carrier proteins and the transfer of energy in the transport of substances against a concentration gradient.

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Section 3 - cell structure and membranes 4

Absorption of the products of carbohydrate digestion.  The roles of diffusion, active transport and co-transport involving sodium ions. Sodium is actively transported into the blood from the cell by a potassium and sodium pump. Makes the concentration of sodium lower in the cell than in the lumen so sodium and glucose are diffused into the cell by a co transporter. This makes the conc of glucose higher in the cell than in the blood so it diffuses out of the cell via a channel protein.

The cholera bacterium as an example of a prokaryotic organism.The structure of prokaryotic cells to include cell wall, cell-surface membrane, capsule, circular DNA, flagella and plasmid.

Cholera bacteria produce toxins which increase secretion of chloride ions into the lumen of the intestine.  This results in severe diarrhoea. This is because  more chloride ions are in the lumen lowering  the water potential so water enters to lumen from the cells via osmosis.

The use of oral rehydration solutions (ORS) in the treatment of diarrhoeal diseases. Contains Na and glucose, which increases the absortion of the into the cells, decreasing the water potential in cells which makes water eneter the cells vai osmosis.

the applications and implications of science in developing improved oral rehydration solutions - put people at risk because of blind trials - new one may not work and could risk a person dying. ethical issues associated with trialling improved oral rehydration solutions on humans. - affects children - testing on children is bad because its the parents which choose if they have it done

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Section 4 - The respiratory system

The gross structure of the human gas exchange system limited to the alveoli, bronchioles, bronchi, trachea and lungs.  

The essential features of the alveolar epithelium as a surface over which gas exchange takes place.  Thin exchange surface, large surface area.

The exchange of gases in the lungs. Oxygen diffusesnout of the alveoli, across the alveolar epithelium and the cappillary endothelium into haemoglobin in the blood. Carbon dioxide diffuses into the alveoli and is breathed out. The circulation of blood means that blood high in oxygen is continually replaced with blood low in oxygen in the alveoli. Air low in oxygen is continually replaced with air high in oxygen as you breathe. 

Pulmonary ventilation as the product of tidal volume and ventilation rate. PV = T x V

The mechanism of breathing. As the intercostal and diaphragm muscles contract the ribcages moves up and out and the diaphragm flatterns increasing the volume of the thorax. As the volume of the thorax increase the pressure of the lungs decrease. this causes air to flow in. Its an active process which requires energy.

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Section 4 - The respiratory system 2

The course of infection, symptoms and transmission of pulmonary tuberculosis. Droplet infection (when an infected person coughs, sneezes, tiny dropleta of saliva and mucus containing the bacteria are realsease and may be breathed in by and uninfected person) Infection - when someone becomes infected by the bacteria, immune system cells build a wall around the bacteria in the lungs. This fors a tubercle (hard lump). Infected tissue in the lump the dies and gaseous exchange surface is damaged, so tidal volume is reduced. TB can also cause fibrosis and if enters the blood can infect other parts of the body. Symptoms - persistant cough, cough up blood and mucus, chest pain, shortness of breath and tiredness

The effects of fibrosis, asthma and emphysema on lung function. Fibrosis - scar tissue - thicker and less elestic. less able to expand and repel air. diffusion is slowere across a thicker membrane, less oxygen being recieved so less aerobic respiration so less ATP. Asthma - allergic reaction to pollen or dust. Smoth muscle lining in the bronchioles contract and large amounts of mucus is produced. it constricts airway making it difficult to breath. less oxygen enters the alveoli, less body cells recieve oxygen so less aerobic respiration, so less ATP. Emphysema - foreign particles of smoke get trapped in alveoli, causes inflamatio which attracts phacocytes which produce an enzyme which digests elastin in alveoli. Can repel air as well. It also leads to destruction of alveoli walls, which reduces surface area. Reduces gaseous exchange, so less ATP, so tired.

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Section 5 - The circulatory system

The gross structure of the human heart and its associated blood vessels in relation to function.  Vena cava (from body), right atrium, right atrioventricular valves, right ventrical, semi luna valve, pulmonary artery (to lungs). Pulmonary vein (from lungs), left atrium, left atrioventricular valve, left ventricle, semi lunar valve, aorta.

Pressure and volume changes and associated valve movements during the cardiac cycle.If there is a pressure higher behind the valve it is forced open. But if the pressure is higher in front of the valve its forced shut. pressure higher in atrium than ventricle - valve open. pressure higher in ventricle than blood vessle - valve open

Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity.  

Roles of the sinoatrial node (SAN), pace maker - it sets the rhythme of the heart atrioventricular node (AVN) responsible for passing the electrical activity down the bundle of his, but makes a slight pause to allow the atria to empty and bundle of His. leads to the purkyne fibers which amke sure the ventricals contract from the bottom up.

Cardiac output as the product of heart rate and stroke volume. C = H x S

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Section 5 - The circulatory system 2

Atheroma as the presence of fatty material within the walls of arteries. lumen narrows resulting in high blood pressure.

The link between atheroma and the increased risk of aneurysm and thrombosis.  atheroma leads to any of these. It increases blood pressure which may rupture the endothelium causing a blood clot. Or it (the high pressure blood) may push the inner through the outer elastic layer to form a aneurysm

Myocardial infarction and its cause in terms of an interruption to the blood flow to heart muscle. blood clot has reached the coronary arteries. cuts of circulation in a part of the heart which may cause damage or death to the muscles in that region starved of oxygen.

Risk factors associated with coronary heart disease: diet, blood cholesterol, cigarette smoking and high blood pressure. All cause an atheroma formation which will lead to a blood clot. Smoking - CO combines with haemoglobin reduces the amount of oxygen transported around the body - heart muscle doesnt recieve enough oxygen - leads to a heart attack. It also decreases the amount of antioxidants  which are important for protecting cells from damage. means cell damage in coronary artery walls is more likely leading to an atheroma.

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charlotte milburn


Thank you this was very helpful and detailed. :) 

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