Biology topic 1

• Water


  • It is a solvent - some substances dissolve for biological reactions to take place in a solution
  • It transports substances - easier if substance dissolved in a solvent
  • The specific heat capacity is very high to maintain homeostasis
• Water molecule


  One oxygen, two hydrogen - shared hydrogen pulled towards oxygen so the other side of hydrogen has a slight positive charge. Unshared electrons on the oxygen give it slight negative charge - dipolar molecule
• Hydrogen bonding


  Slight negative oxygen atoms attract slightly positive hydrogen atoms of other water molecules
• Water's dipole nature


  • Water is very cohesive - attraction between water molecules allows water to flow
  • Water is a good solvent - can surround ionic substances
• Single celled organisms


  Materials can diffuse directly across cell membrane due to shorter distance and larger SA;V ratio
• Multicellular organisms


  Carry raw materials from specialised exchange organs to body cells and remove metabolic waste
• Left ventricle


  More muscular walls to contract more powerfully and pump blood round body
• Atrioventricular valves


  Stop blood flowing back into the atria when the ventricles contract
• Semilunar valves


  Link ventricles to arteries and stop backflow when the ventricles contract
• Valves


  Only open one way depending on pressure behind to help blood flow in one direction
• Artery


  • Carry blood to the rest of the body
  • Thick walled, muscular and elastic tissue to cope with high pressure
  • Folded endothelium to allow expansion
  • Contains collagen to avoid rupture
  • Smooth endothelium to reduce resistance
  • Elastic fibres stretch to accommodate high pressure and recoil to maintain
• Vein


  • Take blood back to the heart
  • Wider with less elastic and muscle tissue
  • Contain valves to prevent backflow
• Capillary


  • Where metabolic exchange occurs
  • Networks increase surface area for exchange
  • Walls only one cell thick to allow fast diffusion
• Atrial systole


  1. Atria contract to decrease chamber volume and increase pressure

  2. Blood pushed into ventricle to cause slight increase in ventricle pressure and volume due to passive filling
• Ventricular systole


  1. Atria relax and ventricles contract to increase pressure and decrease volume

  2. Pressure higher in ventricles to force AV valves shut and also higher than the arteries so SL valves are forced open so blood forced into arteries
• Cardiac diastole


  1. Ventricles and atria relax. Higher pressure in arteries closes SL valves

  2. Blood returns to heart and atria fill again due to higher pressure in vena cava and PV. pressure in atria increases and ventricular pressure falls below so AV valves open and blood flows passively into ventricles before atria contract
• Adjustment knobs


  • Coarse - Changes the height of the objective lens
  • Fine - adjust focus to see clearer image
• Ethical issues of using invertebrae
• Atheromas develop


  1. Damage occurs to the endothelium and an inflammatory response occurs - white blood cells accumulate

  2. White blood cells and lipids clump to form fatty streaks

  3. Over time more cells, calcium salts and fibrous tissue build up and harden to form a fibrous plaque (atherosclerosis)

  4. The plaque partially blocks the lumen and restricts blood flow which causes blood pressure to increase - positive feedback
• Atheromas


  • Can rupture through the endothelium and damage the artery wall to leave a rough surface
  • This triggers thrombosis
• Blood clot formation


  1. Thromboplastin protein is released from the damaged vessel that exposes collagen

  2. Along with calcium ions, thromboplastin catalyses conversion of prothrombin into thrombin (an enzyme) in the presence of vitamin K and calcium ions

  3. Thrombin then catalyses the conversion of fibrinogen to fibrin (insoluble fibres) which tangle together in a mesh and trap platelets
• Heart attack


  • Coronary arteries supply oxygen for heart muscle cell respiration
  • If it becomes blocked, supply is cut off and heart muscle respires anaerobically
• Stroke


  Rapid loss of brain function due to disruption of blood supply to the brain
• Deep vein thrombosis


  Formation of a clot in a vein caused by prolonged inactivity
• Saturated fats


  Increase blood cholesterol which increases atheroma formation which leads to thrombosis
• High salt


  Increases blood pressure
• High blood pressure


  Increases risk of damage to the artery walls and atheroma formation, caused by alcohol, stress and diet
• Smoking


  • Carbon monoxide combines with haemoglobin and reduces amount of oxygen transported
  • Nicotine makes platelets sticky so increases blood clot formation
  • Decreases antioxidants in the blood - responsible for cell protection
• Inactivity


  Increases blood pressure
• Genetics


  Inheritance of alleles that increase likelihood of high bp or cholesterol
• Age


  Risk increases as plaque builds over time
• Gender


  Different hormonal levels e.g. oestrogen increases levels of HDL to lower risk
• Antihypertensives


  • Reduce blood pressure
  • Beta blockers - reduce strength of heartbeat
  • Diuretics - reduce sodium reabsorbed in blood to reduce water absorbed
  • Vasodilators - widen blood vessels
• Advantages of antihypertensives


  • Can be used in combination
  • Can monitor blood pressure at home to see if drugs are working
• Risks of antihypertensives


  Side effects: fainting, headaches, palpitations
• Statins


  Reduce blood cholesterol by reducing LDL produced in the liver
• Advantages and disadvantages of statins

  • Reduce atheroma formation
  • Muscle and joint pain, digestive issues, increased diabetes risk, nausea
• Anticoagulants


  Reduce blood clotting so less chance of blockage of a vessel
• Advantages and disadvantages of anticoagulants

  • Can prevent existing clots from growing and new ones from forming
  • Can't get rid of existing ones
  • Can cause excessive bleeding, tissue swelling, osteoporosis
• Platelet inhibitory drugs


  Prevent platelets clumping together so reduce clot formation