1.1 Organic molecules

• Micronutrients are minerals needed in minute (trace) concentrations e.g. copper

  and zinc.
• Macronutrients are needed in small concentrations e.g. magnesium and iron.
• Magnesium Constituent of chlorophyll and therefore essential

  for photosynthesis
• Iron Constituent of haemoglobin, which transportsoxygen in red blood cells
• Nitrogen is needed for making nucleotides, including ATP, DNA and RNA. Nitrogen is also needed for amino acid formation.
• Phosphate Used for making nucleotides, including ATP, DNA and RNA. A constituent of phospholipids found in biological membranes. Hardens bones.
• Calcium Hardens bones and teeth (not strengthen). Also acomponent of plant cell walls.
• Organic – Molecules that have a

  high proportion of carbon and

  hydrogen atoms.
• Inorganic – A molecule or ion that

  has no more than one carbon

  atom.
• Water is a polar molecule; the oxygen end of the molecule has a negative charge

  and the hydrogen atoms have a positive charge. This uneven distribution of charge

  is called a dipole.
• When two water molecules are in close contact the opposing charges attract

  each other forming a hydrogen bond. Individually hydrogen bonds are weak, but

  many hydrogen bonds (between many water molecules) form a lattice-like

  framework which is much stronger. This attraction between water molecules is

  called cohesion.
• Dipole – A polar molecule which has a

  positive and negative charge,

  separated by a very small distance.
• Hydrogen bond – The weak attractive

  force between a hydrogen atom (with

  a partial positive charge) and an atom

  with a partial negative charge, usually

  oxygen or nitrogen.
• Water is a solvent

  The positive and negative parts of the water molecule

  attract other charged particles, such as ions and other

  polar molecules, such as glucose. Ions and polar

  molecules can dissolve in water. Non-polar molecules

  such as lipids do not dissolve in water.
• Water as a transport

  medium

  Blood is largely water and transports many dissolved

  substances around the body. Minerals dissolved in water

  are transported from the root to the leaves via the

  xylem in plants.
• Chemical reactions take

  place in water

  Transport of ions and polar molecules allows chemical

  reactions to take place when particles or molecules

  meet.
• Water has a high specific

  heat capacity

  A large amount of heat energy is needed to raise the

  temperature of water. This prevents large fluctuations

  in water temperature. This keeps the temperature of

  aquatic environments stable so that organisms do not

  have to endure extremes of temperature. This also

  allows enzymes within cells to work effectively.
• Water has a high latent

  heat of vaporisation

  Due to cohesion between water molecules (caused by

  hydrogen bonding) a large amount of heat energy is

  needed to change water from a liquid to a vapour state

  (gas). This process of evaporation transfers heat energy

  and is a very effective way of cooling the body e.g.

  sweating or panting. Evaporation of water from a

  surface causes cooling.
• Cohesion

  The attraction between water molecules allows water to

  be transported, in long columns, up the xylem vessels of

  even the tallest trees.
• Surface tension

  At ordinary temperatures water has the highest surface

  tension of any liquid except mercury. In a pond the

  cohesion between water molecules supports organisms,

  such as pond skaters, allowing them to walk on water.
• Density

  Water has a maximum density at 4C; ice is less dense

  and therefore floats on the surface and insulates the

  water beneath it. This reduces the tendency for large

  bodies of water to freeze completely allowing organisms

  to survive.
• The basic unit of a carbohydrate is a monosaccharide. Two

  monosaccharides form a disaccharide. Many monosaccharide molecules form a

  polysaccharide. A polysaccharide is a type of polymer.
• Monosaccharides have the general formula (CH2O)n and they can be grouped according

  to the number of carbon atoms they have. A triose sugar has three carbon atoms, a

  pentose sugar has five carbon atoms and a hexose sugar has six carbon atoms.
• Triose Important in metabolism. Triose sugars are intermediates in the

  reactions of respiration and photosynthesis.
• Pentose Constituents of nucleotides e.g. deoxyribose in DNA, ribose in RNA,

  ATP and ADP.
• Hexose

  Glucose is a hexose sugar. Glucose is a source of energy in

  respiration. Carbon-hydrogen and carbon-carbon bonds are broken

  to release energy, which is transferred to make adenosine

  triphosphate (ATP).
• At carbon 1 α glucose has a hydrogen atom above and a hydroxyl group (OH) below, β glucose molecules have a hydroxyl group

  above and a hydrogen atom below on carbon 1.
• Disaccharides are composed of two monosaccharide sub-units bonded with the

  formation of a glycosidic bond and the elimination of water. This is an example of a

  condensation reaction.
• When two α glucose molecules are joined by condensation reaction the disaccharide

  maltose is formed.
• The glycosidic bond can be broken by hydrolysis.
• Hydrolysis is the addition of 1 molecule of water to break a bond
• Maltose is made from 2 Glucose monosaccharides and found In germinating seeds
• Sucrose is made of Glucose and Fructose and is a product of photosynthesis which is transported in the phloem
• Lactose is made of Glucose and Galactose and Found in mammalian milk
• Benedict’s reagent is used to test for reducing sugars. Heat is needed for this reaction

  (80C or above). Reducing sugars reduce blue copper ll sulphate forming copper l

  sulphate, which is a brick red precipitate. Examples include all the monosaccharides and

  the disaccharides lactose and maltose.
• Sucrose is called a non-reducing sugar because it does not reduce copper ll sulphate.

  The Benedict’s test will not work; Benedict’s will remain blue. Sucrose must first be

  hydrolysed by boiling in dilute hydrochloric acid. Glucose and fructose are formed. The

  acid must be neutralised with dilute sodium hydroxide before testing with Benedict’s

  reagent. This should now give a positive result; glucose and fructose are reducing sugars

  which readily donate an electron to reduce copper II sulphate to form the brick-red

  precipitate copper I sulphate.
• Polysaccharides are large complex polymers. They are formed from very large numbers

  of identical monosaccharide units, which are their monomers, linked by glycosidic

  bonds formed by condensation reaction.
• Starch allows plants to store glucose. Starch is made up of α glucose monomers, added

  one at a time by condensation reaction.
• Starch

  has two types of polysaccharide, amylose and amylopectin.
• Amylose is unbranched and

  coiled; each α glucose monomer added forms a C1 – C4 glycosidic bond with the adjacent

  glucose molecule.