3.1.1 State that the most frequently occurring chemical elements in living things arecarbon, hydrogen, oxygen and nitrogen. Review ionic, covalent and hydrogen bonds Some fun with elements http://en.wikipedia.org/wiki/File:CHONPS.
3.1.2 State that a variety of other elements are needed by living organisms, includingsulphur, calcium , phosphorus, iron and sodium http://commons.wikimedia.org/wiki/File:Electron_shell_020_Calcium.svg http://commons.wikimedia.org/wiki/File:Electron_shell_016_Sulfur.svg http://commons.wikimedia.org/wiki/File:Electron_shell_015_Phosphorus.svg http://commons.wikimedia.org/wiki/File:Electron_shell_026_Iron.svg http://commons.wikimedia.org/wiki/File:Electron_shell_011_Sodium.svg
3.1.3 State one role for each of the elements Sulphur is an important element in some amino acids. It allows disulphide bonds to form in proteins, influencing the protein’s shape see HL 7.5 Proteins What about iron? http://commons.wikimedia.org/wiki/File:Granulated_sulphur02.jpg
Iron is inhaemoglobin, tocarry oxygen inblood. Calcium? http://www.flickr.com/photos/csutka/3956855512/
And, of course, in phospholipids in cell membranes. Here in Italian, just for a change.See: Structure of the membrane 2.4.1 http://commons.wikimedia.org/wiki/File:Fosfolipide.svg
…and in DNA, amongs t other things. Also… CHON!http://commons.wikimedia.org/wiki/File:DNA_Structure%2BKey%2BLabelled.png
3.1.4 Draw and label a diagram showing the structure of water molecules to show their polarityand hydrogen bond formation. Water is a weird and freaky substance. It is this way because of its polar nature. http://commons.wikimedia.org/wiki/File:Water_drop_animation_enhanced_small.gif
The oxygen atom has 8Revisit the Crash Course positive charges (protons)Biology video “Carbon” (on at its nucleus.slide 2) at the 8:08 mark Therefore it attracts the shared electrons more strongly and they spend more time orbiting the O -ve than the H. O Thus water molecules are polar, i.e. they have a negatively charged pole+ve H (the oxygen) and a positively charged pole (the hydrogens) H +ve
Hydrogen bonds form when the negatively charged oxygen on one molecule is electrostatically attracted to the positive hydrogen on anotherhttp://commons.wikimedia.org/wiki/File:Liquid_water_hydrogen_bond.png
3.1.5 Outline the thermal, cohesive and solvent properties of water Thermal: You know about the phases (states) of water: Solid, Liquid and Gas. Water changes from solid to liquid and gas progressively as more energy (heat) is added. The weird thing about water is that it takes more energy than it “should” to change from one state to the next. Why do you think that might be? http://www.flickr.com/photos/westy559/328563694/
Extra energy is requiredto overcome thehydrogen bondsWe say that water has avery high specific heatcapacityIt absorbs a lot ofenergy before changingstate http://commons.wikimedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.svg
CohesiveThe polar nature of water makes it “sticky”The molecules themselves stick together dueto hydrogen bonds (cohesion)Water molecules stick to othersubstances, e.g. glass (adhesion) for the samereason If water did not have this cohesive nature then it would not form into drops like in the background. Drops form because the cohesive forces are trying to pull the water into the smallest possible volume, a sphere.
SolventWater is sometimes called the “universal solvent”Again, this is to do with the polar nature of waterConsider the sodium chloride below. The sodium andchloride atoms are held together by ionic bonds. NaCl Dissolving NaCl http://commons.wikimedia.org/wiki/File:Sodium-3D.png http://commons.wikimedia.org/wiki/File:Sodium-chloride-3D-ionic.png
Chlorine WaterSolvent SodiumThe polar water molecules have a stronger affinity forboth Na+ and Cl- than those ions do for each other.So the Na and Cl “dump” each other and drift off withthe water molecules NaCl Dissolving NaCl
The polar water molecules have a stronger affinity for both Na+ andCl- than those ions do for each other.So the Na and Cl “dump” each other and drift off with the watermolecules.Note how on the right of the diagram the oxygen in each watermolecule is close to the Na+ and the hydrogen in the watermolecules is close to the Cl- NaCl Dissolving NaCl
All your ion are belong to us!!! Also, the relatively small size of Check out the animation the water molecules means that they can “gang up” on the ions (not to scale)http://commons.wikimedia.org/wiki/File:Water_molecule.svg
3.1.6 Explain the relationship between the properties of water and its uses in living organisms asa coolant, medium for metabolic reactions and transport medium Water’s thermal properties, its high specific heat, means that it can cool us. Evaporating sweat (water changing phase from liquid to gas) takes heat away from the body Water is also the main component of blood plasma. It transfers heat from the internal organs to the skin. http://www.flickr.com/photos/bukutgirl/205304794/
Cohesion allows plants to pull water up their xylem via transpirationAdhesion aidscohesion indrawing waterup due tocapillary action See HL Plant Science 9.2.6 http://www.flickr.com/photos/jaxxon/37559138/
Water’s solvent propertiesmean that waste and nutrientscan be moved around by blood in the veins and arteries. It enables trees to transport gases and solutes as well http://www.flickr.com/photos/roughgroove/3554305017/
Water’s nature as a solventmeans substances dissolved in it can react with one another. The main component of cytoplasm, where many reactions occur, is water. http://www.flickr.com/photos/cambridgeuniversity-engineering/5431155934/
Extension: Water as habitat These water striders rely on the cohesive nature of water resulting in surface tension http://www.flickr.com/photos/alexyo1968/4985953786/
Liquid water IceWhat are the implications of ice being less dense(due to it’s highly organised crystalline structure) than liquid water? http://commons.wikimedia.org/wiki/File:Liquid-water-and-ice.png
Back to the bear… I have somewhere to stand and hunt. See 5.2.6 to see why you hoomans are worrying me! http://commons.wikimedia.org/wiki/File:Eisb%C3%A4r_1996-07-23.jpg
Lakes at high latitudes would freeze from the bottomup. Solid. And remain so for most if not all of the year at high latitudes. The seas would be similarly affected. The water that is usually insulated by the ice, at above freezing temperatures, would not exist. There would be no habitat for the bottom dwellers.In fact, the pressure of the overlying water would make the water at the bottom freeze. Even in the tropics.