1.1

• Inorganic ions


  A variety of inorganic ions is required for many cellular processes including muscle contraction and nervous coordination. Also known as electrolytes, some are needed in minute amounts (micronutrients) e.g. zinc, and some in larger amounts (macronutrients)
• Roles of inorganic ions


  • Magnesium (Mg2+): Constituent of chlorophyll, and therefore needed for photosynthesis. When lacking, leaves appear yellow (chlorosis)
  • Iron (Fe): Constituent of haemoglobin, so is involved in transport of oxygen. A diet deficient in iron can lead to anaemia
  • Calcium (Ca2+): Structural component of bones and teeth
  • Phosphate (PO4): Needed for making nucleotides including ATP. A constituent part of phospholipids in cell membranes
• Water


  • It is a dipolar molecule, i.e. has a positively charged end (hydrogen) and a negatively charged end (oxygen), but has no overall charge
  • Hydrogen bonds easily form between the hydrogen on one molecule and the oxygen on another, and although individually they are weak, collectively they make it difficult to separate molecules from each other
• Water as a solvent


  Due to its dipolar nature it attracts charged particles and other polar molecules allowing them to dissolve
• Properties of water


  • Solvent
  • High specific heat capacity
  • High latent heat of vaporisation
  • Metabolite
  • Cohesion
  • High density
  • Transparent
• Carbohydrates


  Small organic molecules containing carbon, oxygen and hydrogen. They act as: Building blocks for more complex molecules, Sources of energy, Energy storage molecules, Structural support
• Types of carbohydrates


  • Monosaccharides
  • Polysaccharides
• Monosaccharides


  Single sugars that all contain carbon, hydrogen and oxygen in the ratio 1:2:1, with the number of carbon atoms usually between 3 and 6. They are sweet tasting and soluble in water
• Polysaccharides


  When many monosaccharides combine together, the polymer formed is called a polysaccharide. Polysaccharides form a number of structural molecules and are also good energy storage molecules
• Polysaccharides


  • They are: unable to diffuse out of the cell, compact in shape so much glucose can be stored in a cell, insoluble in water, so they do not alter the water potential, and therefore have no osmotic effect, easily hydrolysed into their constituent monosaccharides which can be used in respiration
• Starch


  The main energy store in plants, found in starch grains which are seen in most plant cells and in chloroplasts. Sugars made in photosynthesis are stored as starch unless they are required immediately for respiration
• Starch


  • It is made up of many a-glucose molecules bonded together, and consists of two polymers, amylose and amylopectin. Amylose is linear (unbranched) with glycosidic bonds forming between the first carbon atom (C1) on molecule 1 and the fourth carbon atom (C4) on molecule 2. Amylopectin is a branched molecule and fits inside the amylose
• Cellulose


  A structural polysaccharide and is the most abundant organic molecule on Earth due to its presence in plant cell walls. Cellulose consists of many ẞ-glucose units bonded together with adjacent glucose molecules rotated by 180° forming long straight parallel chains that are cross-linked to each other by hydrogen bonds
• Chitin


  A structural polysaccharide found in the exoskeleton of arthropods (e.g. insects) and cell walls of fungi due to its strength, lightness and waterproof properties. It has a similar structure to cellulose with many long parallel chains of ẞ-glucose molecules (with added acetylamine group) cross-linked to each other by hydrogen bonds forming microfibrils
• Triglycerides


  Formed by the combination of one glycerol molecule and three molecules of fatty acids.

  via a condensation reaction 3 molecules of water are removed and an ester bond is formed between the glycerol and fatty acid.