AP Biology Unit 1 Topic 1: Water and Life

What does it mean that water is a polar molecule? Why is water a polar molecule?

• Water being a polar molecule means that it has an uneven distribution of electrical charge. 

• Oxygen and hydrogen have different electronegativity values, with the oxygen side having a more negative pole and the hydrogen side having a more positive pole.

What are hydrogen bonds? What do they have to do with the properties of water?

• Weak chemical bonds that form when hydrogen atoms(already covalently bonded to a highly electronegative atom) are attracted to another nearby electronegative atom; i.e hydrogen to oxygen, hydrogen to nitrogen etc. 

• These bonds cause water molecules to “stick” together.

What is specific heat capacity and heat of vaporization? How is water compared to other substances? Why is it important for biological systems?

• Specific heat capacity is the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by one degree celsius. Heat of vaporization is the amount of heat a liquid must absorb for one gram to be converted to gas

• Water has a high specific capacity/ heat of vaporization due to its strong hydrogen bonds that take a lot of energy(heat) to break. 

• These properties are important in water for climate regulation, temperature regulation in organisms, cooling systems, and for protecting aquatic ecosystems. It does this through its ability to hold copious amounts of heat without raising its temperature.

What is cohesion, adhesion and surface tension with regards to water? What causes these properties?

• Cohesion is the attraction between two water molecules(hydrogen to oxygen). Adhesion is the attraction between one water molecule and another molecule(hydrogen to another electronegative atom). Surface tension of water is induced by cohesion when water molecules stick together minimizing its area. (Think of a water droplet on a penny).

• These properties are caused by the forming of hydrogen bonds.

What are the structures involved in the transport of water in plants?

• The xylem(a specialized tissue) is responsible for transporting water and dissolved minerals from the roots to the stems in plants. The stomata(multiple pores on the surface) control the amount of water released from the leaf; transpiration. 

What is transpiration? What environmental factors influence it?

• A process where plants release water vapor into the atmosphere through stomata. 

• Temperature, humidity, air movement, and light intensity can influence it.