A1.1 Water

• Water is a solvent

  • Water can dissolve a variety of molecules 
  • Water's role as a solvent helps a multicellular organism transport molecules around a body and acts as the medium in which chemical reactions occur.
• Water is a metabolite 

  • Chemical reactions take place in all cells 
  • Collectively these reactions are called metabolism 
  • Chemicals involved are called metabolites 
• Condensation Reaction 


  When water is formed as one of the products when two molecules join together.
• Hydrolysis Reaction 


  When water reacts with a chemical to break it into smaller molecules.
• Water is temperature buffer

  • Water helps to buffer temperature changes in cells because of its relatively high specific heat capacity
• Water maintains biological structures 

  1. Water contributes to the formation of cell membrane 
  2. Water impacts the folding of proteins 
  3. Water surrounds DNA to support the double helix
• how does Water contributes to the formation of cell membranes. 

  • Phospholipid heads interact with water wile the heads try to avoid water 
  • Seeking favourable interactions, phospholipids spontaneously form bilayers, with the heads facing outwards towards the surrounding water and tails facing inwards.
• how does Water impacts the folding of proteins. 

  • Water drives the folding of amino acids chains as different types of amino acids seek and avoid interacting with water 
  • Without the proper shape proteins would be unable to perform there functions
• how does Water surrounds DNA to support the double-helix.

  • Without this shape, cells would be unable to follow the careful instructions encoded by DNA or to pass the instructions onto future cells. 
• Covalent bond


  A bond which holds together two atoms that share one or more pair of electrons between atoms
• Ionic Bond 


  A bond is an attraction between a positively charged ion and a negatively charged ion. 
• Hydrogen bonds


  an attraction between two polar molecules.
• hydrogen bond - polar molecule 


  a molecule in which one end of the molecule is slightly positive while the other end is slightly negative.
• water structure 


  consists of 2 hydrogen and 1 oxygen atom, hence…H2O
• Water molecules are polar 

  Because the oxygen atom has more protons, it attracts the shared electrons more of the time creating an unequal distribution of charge.
• Hydrogen bonds form between water molecules

  The 1 proton in the nucleus of the H-atom has less pull on the shared electrons.

  • The partially positive hydrogen atoms of one water molecule are attracted to the partially negative oxygen atom of a different water molecule, forming a hydrogen bond. 
  • Each water can form up to H-bonds with up to 4 other water molecules
• cohesion 


  Water’s ability to make hydrogen bonds with itself causes water molecules to stick together
• The cohesion of water molecules:

  • Allows plants to move water under tension in xylem 
  • Retains water on Earth’s surfaces to serve as habitats 
  • Contributes to the physical properties of water important to living organism
• Transport of water under tension on xylem

  Xylem tissue are long tubular vessels in vascular plants that form a continuous tube from the roots to the leaves 
• Longitudinal cross section of xylem

  There are parallel tubes of xylem with rings of “lignin” that provide extra support for the plant as it grows up against gravity.
• The cohesion-tension hypothesis is the most widely-accepted model for movement of water in vascular plants. The cohesion-tension model works like this:

  1. Transpiration (evaporation) occurs because stomata are open to allow gas exchange for photosynthesis. As transpiration occurs, it creates negative pressure (also called tension or suction).
  2. The tension created by transpiration “pulls” water in the plant xylem, drawing the water upward .
  3. Cohesion pulls up water molecules in a chain as the top-most water is pulled up and out of the stomata.
• Water surfaces as habitats due to surface tension, what is surface tension?

  a property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules.  Water has a very high surface tension
• At the surface, there are fewer other water molecules to bond to since there is air above (thus, no water molecules).


  This results in a stronger bond between those water molecules that actually do come in contact with one another.
• Polar and charged molecules are called ---- because they are attracted to water

  hydrophilic
• The attraction of water to other polar or charged molecules is called


  Adhesion
• The adhesion of water molecules to other molecules:

  • Allows plants to move water using capillary action. 
  • Permits water to move through soil, even against the force of gravity
• cation

  has a positive charge because it has more protons than electrons (Na+)
• anion

   has a negative charge because it has more electrons than protons (Cl-)  
• Cellulose 


  is a polymer made of glucose units that is present in plant cell walls.
• Capillary action 


  is the movement of water in through a narrow space, often in opposition to external forces like gravity
• Water solvent properties allow it to be used as a medium for

  metabolism 
• Cytosol

   is the liquid part of the cytoplasm, a structure common to all cells. It is composed of about 80 percent water and also contains dissolved salts, fatty acids, sugars, amino acids, and proteins such as enzymes.
• Water solvent properties allow it to be used as a medium for

  transport
• Water solvent properties allow it to be used as a medium for transport

  • vascular plants
  • Dissolved mineral ions are transported in the xylem from roots to leaves.
  • Dissolved sugars produced in photosynthesis are transported in the phloem from source to sink.
• Water solvent properties allow it to be used as a medium for transport -Animal blood plasma transports 

  • Salt ions such as Na+ and Cl-
  • Amino acids 
  • Proteins such as antibodies (C3.2.6) and those used in blood clotting (C3.2.3)
  • Glucose which is used in cellular respiration (C1.2.4) and whose concentration must be regulated (D3.3.3)
  • Waste products of metabolism such as urea which is later removed from the blood at the kidney (D3.3.8)
  • A small amount of dissolved gasses such as CO2 and O2
• Not everything will transport in water 

  Because they are hydrophobic, lipids can not be directly transported in solution around the body of an organism (B1.1.8).  In order to be transported in blood, fat droplets are first coated in proteins and phospholipids to form a structure called a “lipoprotein.”
• Buoyancy

  • Aquatic organism are supported by water from effects of gravity 
  • The tissue of living organism have similar density to water = organism don't immediately sink
  • Buoyancy depends on density.  
• Buoyancy depends on density:

  • If the density of the object is lower than the density of the fluid, the buoyant force will be greater than the force due to gravity and the object will float.
• Viscosity

  • Water has a higher viscosity than air, greater resistant to flow 
  • Aquatic organs must therefore develop more streamlined bodies and other adaption to help move through water 
• Thermal conductivity 


  is  a measure of a material's ability to move heat across a temperature gradient.  The thermal conductivity of the material is determined by how easily energy transfers through the material.