Chapter 3- Exam 1: Biology Study Guide - Water

Describe pH Scale.

- An acid is a substance that donates hydrogen ions. Because of this, when an acid is dissolved in water, the balance between hydrogen ions and hydroxide ions is shifted. Now there are more hydrogen ions than hydroxide ions in the solution. This kind of solution is acidic. - A base is a substance that accepts hydrogen ions. When a base is dissolved in water, the balance between hydrogen ions and hydroxide ions shifts the opposite way. Because the base "soaks up" hydrogen ions, the result is a solution with more hydroxide ions than hydrogen ions. This kind of solution is alkaline.

Discuss the role of acids, bases, and buffers in homeostasis.

- Homeostasis: the ability of a cell or an organism to maintain stable internal conditions despite changes in its environment - Acids: a chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red; typically, a corrosive or sour-tasting liquid of this kind - Base: either of the nucleotide bases linked by a hydrogen bond on opposite strands of DNA or double-stranded RNA - Buffer: a solution that resists a change in pH when acids or bases are added

Provide examples of water's cohesive and adhesive properties.

1. Cohesion refers to the attraction of molecules for other molecules of the same kind, and water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another. - Cohesive: water molecules are attracted to other water molecules. For example, if you place a capillary glass tube open ended into a container with mercury, you will observe a concave down curve because the glass is polar which doesn't attract with mercury. 2. Adhesion is the attraction of molecules of one kind for molecules of a different kind, and it can be quite strong for water, especially with other molecules bearing positive or negative charges. - Adhesive: water molecules are attracted to other materials. For example, if you place a capillary glass tube open ended into a container with water, you will observe a concave up curve as a result of water molecules attracted to the polar glass capillary tube.

Describe the properties of water that are critical to maintaining life.

1. Water is polar. - Water molecules are polar, with partial positive charges on the hydrogens, a partial negative charge on the oxygen, and a bent overall structure. This is because oxygen is more electronegative, meaning that it is better than hydrogen at attracting electrons. 2. Water is an excellent solvent. - Water has the unique ability to dissolve many polar and ionic substances. This is important to all living things because, as water travels through the water cycle, it takes many valuable nutrients along with it! 3. Water has high heat capacity. - It takes a lot of energy to raise the temperature of a certain amount of water by a degree, so water helps with regulating temperature in the environment. For example, this property allows the temperature of water in a pond to stay relatively constant from day to night, regardless of the changing atmospheric temperature. 4. Water has high heat of vaporization. - Humans (and other animals that sweat) use water's high heat of vaporization to cool off. Water is converted from its liquid form to steam when the heat of vaporization is reached. Since sweat is made mostly of water, the evaporating water absorbs excess body heat, which is released into the atmosphere. This is known as evaporative cooling. 5. Water has cohesive and adhesive properties. - Water molecules have strong cohesive forces due to their ability to form hydrogen bonds with one another. Cohesive forces are responsible for surface tension, the tendency of a liquid's surface to resist rupture when placed under tension or stress. Water also has adhesive properties that allow it to stick to substances other than itself. These cohesive and adhesive properties are essential for fluid transport in many forms of life. For example, they allow nutrients to be transported to the top of a tree against the force of gravity. 6. Water is less dense as a solid than as a liquid. - As water freezes, the molecules form a crystalline structure that spaces the molecules further apart than in liquid water. This means that ice is less dense than liquid water, which is why it floats. This property is important, as it keeps ponds, lakes, and oceans from freezing solid and allows life to continue to thrive under the icy surface.

Explain why water is an excellent solvent.

Water has many properties that are critical to maintaining life. It is polar, allowing for the formation of hydrogen bonds, which allow ions and other polar molecules to dissolve in water. Therefore, water is an excellent solvent.