Unit 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 to form disaccharides and polysaccharides

  1. Condensation reactions - reactions that join 2 molecules together through the release of a small molecule (often water)

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


  Hydrolysis reaction - a water molecule is added, splitting a polysaccharide into 2 smaller molecules, or a disaccharide into 2 monosaccharides
• Monosaccharides


  The monomers of carbohydrates, they are 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
• Amylose


  An unbranched chain of glucose molecules joined by 1,4 glycosidic bonds, a very compact molecule that can store a lot of energy
• Amylopectin


  Branched and made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds, with many side branches, rapidly digested by enzymes so energy is released quickly
• Lipids


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


  Don't contain any carbon-carbon double bonds
• Unsaturated lipids


  Contain carbon-carbon double bonds and melt at lower temperatures than saturated fats
• 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, this is known as simple diffusion as it occurs only through the cell membrane
• For larger organisms, we have a low surface area to volume ratio, meaning diffusion would be too slow to supply all cells with the nutrients they need, so larger organisms 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 it to stretch, split into smaller blood vessels called 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, they are numerous and highly branched so have a large surface area, their walls are 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 (blood flowing in the wrong direction)
• Heart


  Comprised of 4 chambers: the left and right atria and the left and right ventricles, the atria receive blood into the heart from the veins, the 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 from the ventricles and into the atria, between the ventricles and the arteries leaving the heart are the semilunar valves which prevent backflow of blood from the arteries into the ventricles
• Double circulatory system


  The blood flows through the heart twice in each circulation, first entering the right atrium, going to the lungs to become oxygenated, then returning to the left atrium, and then being pumped out to the rest of the body
• Cardiac cycle


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

  2. Ventricular systole - the ventricles then contract, causing the 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 - the 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 in the aorta and pulmonary arteries to close, preventing backflow of blood
• Haemoglobin


  A water soluble globular protein found in red blood cells, which consists of two beta polypeptide chains, 2 alpha polypeptide chains and 4 haem groups, each of the 4 polypeptide chains is bound to a haem group (Fe2+ ion) to which 1 oxygen molecule can bind, meaning each molecule of haemoglobin can carry 4 oxygen molecules
• Oxyhaemoglobin


  The form of haemoglobin with oxygen bound to it
• Affinity of oxygen for haemoglobin

  The greater the concentration of dissolved oxygen in cells, the greater the partial pressure, and the greater the affinity of haemoglobin for oxygen, meaning oxygen binds to haemoglobin more readily
• Loading


  The process where oxygen binds to haemoglobin in the lungs
• Unloading


  The process where oxygen is released from haemoglobin in respiring tissues where it is needed
• Carboxyhaemoglobin


  The form of haemoglobin with carbon dioxide bound to it
• Dissociation curves


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


  Haemoglobin has high affinity for oxygen and is highly saturated
• Low partial pressure


  Haemoglobin has low affinity for oxygen and is less saturated
• Factors resulting in different affinities

  • Saturation - 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 higher 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
  • 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