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General Biology

This article explores the importance of water in biology, including its role in the evolution of life, its abundance in living cells, and its unique molecular interactions. It discusses the polarity of water, its cohesive behavior, resistance to temperature changes, high heat of vaporization, and versatility as a solvent. The article also touches upon water's regulation of temperatures on Earth and its role as a solvent of life.

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General Biology

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  1. General Biology Properties of Water

  2. I. Water is an important topic to biologists • Life on earth probably evolved in water. • Living cells are 70% or more water. • Water covers about 75% of the earth. • In nature, water naturally exists in all three physical states of matter. • Water has very special molecular interactions.

  3. II. Water is Polar A. Water and Hydrogen Bonding • The polar molecules of water are held together by hydrogen bonds. • Positively charged H of one molecule is attracted to the negatively charged O of another water molecule. • Each water molecule can form a maximum of four hydrogen bonds with neighboring water molecules.

  4. Water has special properties as a consequence of its polarity. 1. Has cohesive behavior 2. Resists changes in temperature 3. Has a high heat of vaporization and cools surface as it evaporates. 4. Expands when it freezes 5. Is a versatile solvent.

  5. 1. Cohesion • Phenomenon of a substance being held together by hydrogen bonds. • Enough water molecules are hydrogen bonded together to give water more structure than other liquids. • Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid.

  6. 2. Water helps regulate temperatures on Earth • Heat and Temperature have a Relationship • Kinetic Energy – The energy of motion • Heat – Total kinetic energy due to molecular motion in a body of matter • Temperature – Measure of heat intensity due to the average kinetic energy of molecules in a body of matter.

  7. 3. Water’s High Specific Heat • Water has a high specific heat, it resists temperature changes when it absorbs or releases heat. • Specific Heat – Amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by one degree Celsius. • For water – One calorie per gram per degree Celsius.

  8. Because of hydrogen bonding – takes a large heat loss or gain for each 1C change in temperature. • Hydrogen bonds must absorb heat to break, and they release heat when they form. • Keeps temperature fluctuations within a range suitable for life.

  9. Evaporative cooling • Vaporization (evaporation) – transformation from liquid to a gas. • Molecules with enough kinetic energy to overcome the mutual attraction of molecules in a liquid, can escape into the air. • Heat of vaporization – Quantity of heat a liquid must absorb for 1 g to be converted to the gaseous state.

  10. To evaporate water, hydrogen bonds must break which requires heat energy. • Evaporative cooling – cooling of a liquid’s surface when a liquid evaporates. • Great example is when you get out of the shower.

  11. Water has a high heat of vaporization which; • Moderates the Earth’s climate • Stabilizes temperature in aquatic ecosystems. • Helps organisms from overheating.

  12. 5. Water is the solvent of life • Solution – A liquid that is a completely homogenous mixture of two or more substances. • Solvent – Dissolving agent of a solution. • Solute – Substance dissolved in a solution. • Aqueous Solution – Solution in which water is the solvent

  13. Hydrophilic • Water loving, property of having an affinity for water. • Ionic and polar substances • Hydrophobic • Water fearing, not water-soluble. • Nonpolar compounds

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