1A

• ionic bonding - electrons are transferred from one atom to another for a full outer shell
• covalent bonding - sharing of electrons between atoms for a full outer shell
• dissociation - splitting of a molecule into smaller molecules, atoms, or ions
• Water is a polar molecule, so it forms hydrogen bonds. This is when the delta negative oxygen is attracted to the delta positive hydrogen from another molecule, due to electrostatic attraction.
• Water is a polar solvent so ionic and covalently bonded substances dissolve
• Water is a good transport medium.
• Ice is less dense than water, so it creates an insulating layer at the top which stops the rest of the water from freezing, allowing organisms to live in the water.
• Water is most dense at 4 °C.
• Water has a high specific heat capacity so the temperature is not easily changed, making a stable environment for organisms.
• Water is a liquid so it can't be compressed.
• Water molecules are cohesive due to hydrogen bonds, so they stick together, e.g. for transpiration in plants.
• Water molecules are adhesive so they stick to other polar molecules, e.g. meniscus
• Organic compounds always contain carbon, and hydrogen and oxygen, and sometimes nitrogen, sulphur, snd phosphorous. Carbon atoms make 4 bonds, particularly in a tetrahedral shape. Some carbon compounds are polymers made of many small monomers. Carbon can make macromolecules.
• Carbohydrates are used in cells as energy sources, energy stores, and for cell walls.
• There are 3 main groups of carbohydrate:

  1. monosaccharides
  2. disaccharides
  3. polysaccharides
• Monosaccharides are simple sugars, with the general formula (CH2O)n.
• Monosaccharides examples:

  • triode sugars (C3H6O3) are made when glucose breaks down in respiration
  • pentose sugars (C5H10O5) are in DNA and RNA
  • hexose sugars (C6H12O6) are sweet, and include glucose and fructose
• Disaccharides are double sugars, formed by 2 monosaccharides joining together in a condensation reaction. They are covalently bonded with a glycosidic bond, e.g. sucrose, lactose, maltose.
• oligosaccharides - molecules with 3 to 10 sugar units
• true polysaccharides - molecules with 11 or more sugar units
• Polysaccharides can be broken into monosaccharides by adding water in hydrolysis.
• Chemical reactions in cells need energy, which comes from respiration making ATP. Simple sugars have to be used immediately because they affect the water potential of cells due to their solubility.
• Polysaccharides form compact molecules, are inactive, and are insoluble so they can be energy stores in cells.
• Starch is used as an energy store in plants from photosynthesis. It breaks down into glucose easily. It is made of alpha glucose in 2 compounds: amylose, amylopectin
• Amylose:

  • spiraled
  • unbranched
  • 200 - 500 glucose units
  • only 1,4 - glycosidic bonds
• Amylopectin:

  • branched
  • easily broken terminal units
  • 1,4-glycosidic bonds and 1,6-glycosidic bonds
• Glycogen is the only carbohydrate energy store in animals. It is similar to amylopectin molecules but it has more 1,6-glycosidic bonds. It is very compact and has lots of branches for a rapid release of energy.
• Fats are solid at room temperature, but oils are liquid.
• Triglycerides are made from glycerol and 3 fatty acids, in a condensation reaction where the molecules are bonded with ester bonds.
• Fatty acids have a long hydrocarbon chain, with a carboxyl group (-COOH) at the end.
• saturated fatty acids - a fatty acid in which each carbon atom is joined to the next one with a single covalent bond
• unsaturated fatty acid - a fatty acid in which the carbon atoms have one or more double covalent bonds
• monounsaturated fatty acid - a fatty acid with one double bond
• polyunsaturated fatty acid - a fatty acid with two or more double bonds
• Proteins are macromolecules made up of amino acid monomers, joined in a condensation reaction.
• There are 20 different naturally occurring amino acids.
• All amino acids have the same basic structure of an amino group (-NH2), a carboxyl group (-COOH) and a R group. The R group varies depending on the amino acid.
• Amino acids join together in a condensation reaction, to form a peptide bond between the amino group of one amino acid, and the carboxyl group of another amino acid.
• Two amino acids joined together are a dipeptide.
• Between 100 and 1000s of amino acids form a polypeptide chain.