Ch 3: Water and Life

Question 1

When astronomers search the universe for “signs of life” they hope to find evidence of water. Why?

Answer 1

Water’s properties, such as its high specific heat, lower density as a solid, versatility as a solvent, and others make it crucial for life to thrive. It can help regulate the temperature of a planet, carry nutrients to organisms, and assists cells.

Question 2

Water is also very abundant. How is this abundance related to life, the planet and the state of matter

Answer 2

The abundance of water on the planet helps regulate Earth’s temperature and moderate climate, which in turn permits organisms to live. Many organisms living on Earth also depend on water for internal chemical reactions.

Question 3

Explain why the “poles” in water molecules exist (make sure to relate this to the electronegativity of the elements involved)

Answer 3

Oxygen atoms are highly electronegative, more than oxygen, so the electrons of covalent bonds are more attracted to the oxygen atoms. The electrons are distributed unequally between oxygen atoms and hydrogen atoms, thus creating the poles.

Question 4

What would hold two water molecules together?

Answer 4

Hydrogen bonds hold two water molecules together.

Question 5

How many other water molecules could form bonds with the one water molecule you drew? (include them in your picture)

Answer 5

4 other water molecules could form bonds

Question 6

Compare and contrast cohesion and adhesion. Use water transport in plants to provide an example of each

Answer 6

Cohesion is the linking of water molecules by hydrogen bonds, whereas adhesion is the clinging of water molecules to other substances. When water evaporates from the leaves of plants, it tugs on the water molecules below through cohesion. Adhesion helps water molecules hydrogen-bond to the walls of cells and counter the pull of gravity.

Question 7

Explain surface tension

Answer 7

Surface tension is a result of water molecules hydrogen-bonding to each other and the water below, but not to the air molecules, which causes surface tension

Question 8

Describe the difference between heat and temperature.

Answer 8

Heat is the transfer of thermal energy from one body of matter to another, where the cooler object absorbs the heat from the other until both are at the same temperature. Temperature is the average kinetic energy of the molecules.

Question 9

What is specific heat? How is the specific heat of water related to hydrogen bonds? Why is this important for life on Earth

Answer 9

Specific heat is the measure of energy put into a molecule to change the temperature, specifically the amount of heat lost or absorbed to change 1 g of substance by 1 C. Water has high specific heat because it takes a lot of heat to break hydrogen bonds, which water has a lot of. This is important for life on Earth because it helps regulate the planet’s temperature.

Question 10

What is the heat of vaporization? How does the high heat of vaporization facilitate life?

Answer 10

Heat of vaporization is the amount of heat required for 1 g of substance to become gaseous. High heat of vaporization helps moderate the Earth’s climate, such as the consumption of solar heat absorbed by tropical seas during surface water evaporation.

Question 11

Explain how evaporative cooling can moderate an organism’s temperature. Explain what happens to the structure of water as it freezes. How does this act as insulation?

Answer 11

Evaporative cooling can prevent an organism from overheating. The evaporation of sweat or any liquid on the skin can facilitate in dissipating body heat. As liquid water freezes, the hydrogen bonds stabilize and lock the water molecules in a crystalline lattice, causing the water to expand and take up more space.Heat must be absorbed to disrupt hydrogen bonds and melt the ice, so as ice remains on the surface of the water, it keeps the water below from freezing over.

Question 12

What would happen if ice sank?

Answer 12

The water at the surface exposed to freezing temperatures would continue freezing and sinking until entire bodies of water completely freeze. This would inhibit life in water.

Question 13

Summarize some of the effects of climate change on the species found in the Arctic

Answer 13

Organisms that rely on ice as hunting and feeding grounds, such as polar bears and walruses, would lose their habitat and source of food. On the other hand, the increased amount of sunlight reaching the depths of water would result in more phytoplankton, providing organisms like bowhead whales with more food

Question 14

Water is an excellent solvent for ionic and polar substances. Explain how water can dissolve a large water-soluble protein such as lysozyme.

Answer 14

The oxygen atoms in water molecules are attracted to the positive charge on the lysozyme molecule, and the hydrogen atoms are attracted to the negative charge on the molecule. The water molecules would dissolve the protein by surrounding and separating their components.

Question 15

What does “hydrophobic” mean? What types of molecules are hydrophobic?

Answer 15

Substances that are hydrophobic are nonionic and nonpolar, which causes them to seemingly repel water. The carbon and hydrogen atoms in oil molecules share electrons almost equally, making them nonpolar and are not attracted to water molecules

Question 16

The chemical reactions of life take place in an aqueous environment. What is an advantage of using molarity as a unit of concentration when carrying out experiments?

Answer 16

It is useful to measure quantities of chemicals in moles a mole of one substance has exactly the same number of molecules as a mole of any other substance, which makes it convenient to combine substances in fixed ratios of molecules.

Question 17

Describe what happens when water is dissociated. Include a chemical reaction for the dissociation.

Answer 17

A hydrogen atom, a part of a water molecule shifts to a different water molecule, leaving its electron behind. 2H2O → H3O + OH-

Question 18

What ions are formed? Why is dissociation so important in the chemistry of life? Give specific examples.

Answer 18

The dissociation of a water molecule forms a hydronium ion and hydroxide ion. Changes in the concentration of H+ and OH- can have a tremendous effect on a cell’s proteins and complex molecules. H+ and OH- are equal in pure water, but adding different acids and bases can disrupt this equilibrium.

Question 19

Contrast acids with bases. What happens to each of them in an aqueous solution?

Answer 19

Acids increase the hydrogen ion concentration in an aqueous solution, whereas bases decrease the hydrogen ion concentration. When acids dissolve, they donate H+ to the solution, and bases reduce H+ by accepting hydrogen ions

Question 20

Explain what is meant by pH. Why is a solution with a pH of 5 ten times more acidic than a solution with a pH of 6?

Answer 20

pH is the negative logarithm of the H+ concentration. Because the base of the log is base 10, and pH of 5 is 10^-5 compared to 10^6, a pH of 5 is ten times more acidic than a pH of 6.

Question 21

Why are buffers important to living things? Explain how a buffer system works.

Answer 21

Buffers are important to living things because they can minimize changes of H+ and OH- in a solution by accepting excess hydrogen ions in the solution and donating hydrogen ions to the solution when they have been depleted.

Question 22

Describe IN DETAIL the carbonic acid/bicarbonate buffer system.

Answer 22

Carbonic acid and bicarbonate acts as a pH regulator system, depending on whether the solution needs more or less hydrogen ions. When the amount of H+ in a solution decreases, more carbonic acid dissociates, which replenishes hydrogen ions. When the amount of H+ increases, HCO-3 removes them and becomes H2C-3. This keeps them in equilibrium.