topic 1

• Water


  Hydrogen atoms are more positive than the oxygen atom, causing one end of the molecule to be more positive than the other
• Permanent dipole


  Uneven distribution of charge within the water molecule, making water a polar molecule
• Dissolve


  Many substances, such as inorganic ions, can dissolve in water thanks to the positive and negative charges within the water molecule
• Chemical reactions


  When substances dissolve in water, they can move, allowing chemical reactions to occur
• Carbohydrates


  Molecules which consist only of carbon, hydrogen and oxygen, and they are long chains of sugar units called saccharides
• Types of saccharides


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Joining monosaccharides


  1. Monosaccharide monomers can join together through condensation reactions to form disaccharides and polysaccharides

  2. Glycosidic bond is formed between 2 monosaccharides, containing a single oxygen atom
• Breaking apart polysaccharides


  Glycosidic bonds have to be broken through hydrolysis reactions, where a water molecule is added, splitting a polysaccharide into 2 smaller molecules, or a disaccharide into 2 monosaccharides
• Monosaccharides


  Monomers of carbohydrates, soluble in water and small, simple molecules
• Disaccharides


  2 monosaccharides join together in a condensation reaction to form a disaccharide
• Polysaccharides


  Formed from many monosaccharides of glucose joined together, used as energy stores
• Lipids


  Biological molecules that have many different functions within an organism such as energy storage, organ protection, thermal insulation and making cell membranes, non-polar molecules so insoluble in water but soluble in organic solvents
• Types of lipids


  • Saturated lipids (no carbon-carbon double bonds)
  • Unsaturated lipids (contain carbon-carbon double bonds)
• Triglycerides


  Made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions, used as long term energy reserves in plant and animal cells

  
• Diffusion in single-celled organisms can occur directly between the external environment and the cell, known as simple diffusion, as it occurs only through the cell membrane
• Larger organisms have a low surface area to volume ratio, meaning diffusion would be too slow to supply all cells with the nutrients they need, so they have mass transport systems that supply all cells with vital substances
• Arteries


  Take oxygenated blood away from the heart, have thick walls containing muscles and elastic that expand and recoil with each heartbeat to withstand the high pressure of the blood, have a relatively small lumen, contain no valves, have a folded inner lining to allow stretching, split into smaller arterioles which split into capillaries, lined with smooth endothelium to reduce friction and ease flow of blood

  
• Capillaries


  Arterioles branch into these to supply cells with substances from the blood, are numerous and highly branched so have a large surface area, have walls one cell thick to allow quick diffusion, have a very narrow diameter to reach close to every cell
• Veins


  Carry deoxygenated blood back to the heart, carry blood at low pressure so have thin walls, have a wide lumen to maximise blood flow to the heart, have valves to prevent backflow

  
• Heart


  Comprised of 4 chambers: left and right atria, and left and right ventricles, atria receive blood into the heart from the veins, ventricles pump blood out of the heart via the arteries to the lungs or the body, between the ventricles and the atria are the atrioventricular valves which prevent blood flowing back, between the ventricles and the arteries leaving the heart are the semilunar valves which prevent backflow of blood

  
• Double circulatory system


  Blood flows through the heart twice in each circulation, first from the right ventricle via the pulmonary artery to the lungs where it becomes oxygenated, then returns to the heart via the pulmonary vein into the left atrium, second time the blood leaves the heart is from the left ventricle via the aorta where it flows to the rest of the body
• Cardiac cycle


  1. Atrial systole - atria contract, forcing atrio-ventricular valves open and blood flows out of the atria and into the ventricles

  2. Ventricular systole - ventricles contract, causing atrio-ventricular valves to close and semi-lunar valves to open, allowing blood to leave the left ventricle through the aorta and right ventricle through the pulmonary artery

  3. Cardiac diastole - atria and ventricles relax, elastic recoil of the heart lowers the pressure inside the heart chambers and blood is drawn from the arteries and veins, causing semilunar valves to close, preventing backflow of blood

  
• Haemoglobin


  Water soluble globular protein found in red blood cells, consists of two beta polypeptide chains, 2 alpha polypeptide chains and 4 haem groups, each haem group can bind 1 oxygen molecule, so each haemoglobin molecule can carry 4 oxygen molecules
• Oxyhaemoglobin


  Oxygen binds with haemoglobin to form this
• Affinity of oxygen for haemoglobin

  Varies depending on the partial pressure of oxygen, the greater the concentration of dissolved oxygen in cells the greater the partial pressure, so as partial pressure increases, the affinity of haemoglobin for oxygen increases

  
• Loading


  Oxygen binds to haemoglobin more readily in the lungs due to the high partial pressure of oxygen
• Unloading


  Oxygen is released from haemoglobin in respiring tissues where the partial pressure of oxygen is low

  
• Carboxyhaemoglobin


  Carbon dioxide binds to haemoglobin in the low partial pressure of oxygen environment in respiring tissues

  
• Dissociation curves


  Illustrate the change in haemoglobin saturation as partial pressure changes, saturation is affected by the affinity of haemoglobin for oxygen

  
• Fetal haemoglobin has a different affinity for oxygen compared to adult haemoglobin, as it needs to be better at absorbing oxygen because by the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased
• Dissociation curves


  Illustrate the change in haemoglobin saturation as partial pressure changes

  
• Haemoglobin saturation


  Affected by its affinity for oxygen

  
• Partial pressure is high


  Haemoglobin has high affinity for oxygen and is highly saturated

  
• Partial pressure is low

  Haemoglobin has low affinity for oxygen and is less saturated

  
• Factors resulting in different affinities

  • Saturation - saturation can also have an effect on affinity. As after binding to the first oxygen molecule, the affinity of haemoglobin for oxygen increases due to a change in shape, thus making it easier for the other oxygen molecules to bind
  • Fetal haemoglobin - The haemoglobin present in foetuses has a different affinity for oxygen compared to adult haemoglobin, as it needs to be better at absorbing oxygen because by the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased. Therefore, fetal haemoglobin must have a higher affinity for oxygen in order for the foetus to survive at low partial pressure
  • The Bohr effect - The affinity of haemoglobin for oxygen is also affected by the partial pressure of carbon dioxide. Carbon dioxide is released by respiring cells, which require oxygen for the process to occur. Therefore, in the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases, thus causing it to be released

  
• Atherosclerosis


  The hardening of arteries caused by the build-up of fibrous plaque called an atheroma

  
• Atheroma formation


  1. The endothelium which lines the arteries is damaged, for instance by high cholesterol levels, smoking or high blood pressure

  2. This increases the risk of blood clotting in the artery and leads to an inflammatory response causing white blood cells to move into the artery

  3. Over time, white blood cell, cholesterol, calcium salts and fibres build up and harden leading to plaque formation

  4. The build-up of fibrous plaque leads to narrowing of the artery and restricts blood flow thus increasing the blood pressure which in turn damages the endothelial lining and the process is repeated

  
• Blood clots


  Formed to minimise blood loss from damaged vessels, and also to prevent pathogens entering the bloodstream

  
• Blood clot formation


  1. Platelets come into contact with a damaged blood vessel wall and change shape from flattened discs to spherical shapes with thin outward projections which form a temporary plug by clumping together

  2. The platelets and damaged tissues release clotting factors such as thromboplastin which causes prothrombin to change to thrombin

  3. This enzyme catalyses the conversion of fibrinogen to insoluble fibrin, whose strands form a mesh, trapping bundles of blood cells. More platelets attach to this, forming the clot
• Risk factors for cardiovascular disease

  • Genetics - certain genes can increase the risk, sometimes indirectly for instance by having genes for a higher blood pressure. Family history of the disease also increases your risk
  • Diet - diets high in cholesterol and certain fats increase the build-up of plaque on arteries
  • Age - prevalence of CVD increases with age
  • High blood pressure - this can narrow and damage arteries or cause an aneurysm, both of which increase the risk of CVD
  • Smoking - smoking damages the lining of arteries and can cause the formation of atheromas
  • Inactivity - has been linked with an increase in blood pressure