2.2 Properties of Water Biology A and C

Water’s unique properties allow life to exist on Earth Have you ever thought about why you need water to survive? Your cells and the cells of every living thing on the planet are mostly water. Why?

Properties of Water Water gives cells structure Water transports vital materials to and from organs in the body All of the processes of life take place in the watery liquid in the body Water’s unique properties and cellular structure are important for living things.

Properties of Water How do fish survive a cold winter if their pond freezes?

Properties of Water Because ice floats and covers the water’s surface, leaving the liquid underneath The ice acts as an insulator . Water expands when it freezes (That means it gets bigger) This is different from most liquids

Water Molecules Water is a polar molecule – because the hydrogen molecules are on opposite ends of the oxygen molecule (H2O) Oxygen is the nucleus (8 protons) Hydrogen (1 proton) Oxygen has a stronger pull Hydrogen gains small positive charges

Water Molecules The opposite charge of polar molecules interact to form hydrogen bonds A hydrogen bond is an attraction between a slightly positive hydrogen atom and a slightly negative atom, often oxygen or nitrogen. Water has a hydrogen bond Other liquids do too Hydrogen bonds are part of the structures of proteins and of DNA.

Water Molecules

Water Molecules Water has a strong bond in the molecule – this bond is the hydrogen bond With out this bond, water would act differently… Water would boil at a lower temperature Water would freeze at a higher temperature

Water Molecules High Specific Heat: Water resists changes in temperature Cohesion: Water sticks together (creates surface tension), such as when bugs land on water, or water beads up on a newly washed car Adhesion: Water sticks to things. Such as inside a test tube, a water bottle, or the way water can be transported from the roots of plants to leaves.

Water and its properties Most other liquids dissolve in water… Ice tea mix Kool aid Coffee Sugar Salt What else can you think of?

Water Properties When these things dissolve in water, we call it a solution Solvent – the substance that is the greater amount and that dissolves another substance (like water) Solute – is the item that gets dissolved (like Kool Aid)

Water Properties The reason many things will dissolve in water is because they are also polar molecules (things like sugar and proteins) Therefore, there is an attraction between the molecules

Water Properties Now, think about fats and oils. Do they dissolve easily in water? Why? Oils are nonpolar molecules