3.1 WATER

POLARITY Oxygen exerts a greater pull on the electrons, so hydrogen and its electrons move closer to the oxygen This means that oxygen has an overall – charge (δ - ) The hydrogen end is therefore slightly positive (δ +)

HYDROGEN BONDS Hydrogen bonds are the attractions between polar molecules

Single hydrogen bond is not very strong Lots of hydrogen bonds are very strong Each water molecule binds with four others, resulting in a tetrahedral arrangement HYDROGEN BONDS

Because of the strength in the total hydrogen bonding and the tetrahedral arrangement, water is COHESIVE, meaning water molecules stick together. Water is also ADHESIVE, meaning that it sticks to other surfaces COHESIVE PROPERTIES

Water will move up a xylem against gravity CAPILLARY ACTION

The surface of water is strong enough to support insects and causes drops to form. SURFACE TENSION

High specific heat capacity- it takes a lot of energy to heat up water Due to the number of hydrogen bonds THERMAL PROPERTIES OF WATER

Temperature of water remains relatively stable Most organisms are adapted to a narrow temperature range The slow heating and cooling of water is an advantage to these organisms, as it produces less risk of extreme changes MEANING…

Because it takes a lot of energy for water to evaporate, it is an excellent coolant, as evaporating water removes a lot of heat energy from the organism WATER AS A COOLANT

High temperatures damage tissues and denature proteins- causing enzymes to cease to work It takes a lot of energy for water to change temperature It will heat and cool more slowly than air or land Can be used by organisms in water or mud to cool down When water evaporates it removes a lot of energy from the system Felt as a cooling sensation-excess heat energy is removed from body. Skin and blood vessels are cooled, and aquatic habitats remain at fairly constant temperatures in hot summers WATER AS COOLANT CONTINUED

Water makes up 70% of the body, including the blood Resistance to temperature change can cause cooler blood from some parts of the body to be circulated to warmer areas, causing the body to cool down. WATER AS COOLANT CONTINUED

GREAT solvent because it is polar; it will dissolve polar solutes easily. Ionic Solids dissociate in water (break down into ions) Polar attractions cause water molecules to surround and isolate the solute molecules The more soluble a solute is, the easier it is for the ions to be isolated from each other (they will end up in thicker water shells. WATER AS A SOLVENT

EXAMPLE PICTURE

Dissolved particles are able to move around and diffuse. Moving particles are likely to collide with one another, leading to a reaction. All metabolic reactions (reactions in living things) occur in solution- the reactants are dissolved. Membranes and biological surfaces are wet: This allows molecules to dissolve, including gases, so they can diffuse more easily. Ex. Alveoli MEDIUM FOR METABOLIC REACTIONS:

WATER AS A TRANSPORT MEDIUM

WATER IN HABITATS