2.3 Water Flashcards Preview

+ BIOL 112 > 2.3 Water > Flashcards

Flashcards in 2.3 Water Deck (36)
Loading flashcards...
1
Q

What is the most abundant molecule in cells?

A

water, so water is the medium in which the molecules of life interact

2
Q

What type of molecule is water?

A

polar

3
Q

What is a polar molecule?

A

a molecule that has regions of positive and negative charge

4
Q

What are polar covalent bonds characterized by?

A

an uneven distribution of electrons

5
Q

What do polar molecules tend to interact with?

A

other polar molecules, whereas nonpolar molecules tend not to interact with polar molecules

6
Q

What are the two general classes of molecules?

A

organized depending on how they interact with water

hydrophilic (water loving)
hydrophobic (water fearing)

7
Q

Describe hydrophilic compounds.

A
  • polar
  • dissolve readily in water
  • water is a good solvent
8
Q

Describe hydrophobic compounds.

A
  • nonpolar, these compounds don’t have regions of positive and negative charge so they arrange themselves to minimize their contact with water
9
Q

Give an example of a hydrophobic molecule.

A

oil molecules

when oil and water are mixed, the oil molecules organize themselves into droplets that limit the oil-water interface

10
Q

What is the hydrophobic effect?

A

the exclusion of nonpolar molecules by polar molecules, which drives biological processes such as the formation of cell membranes and the folding of proteins

11
Q

What is a hydrogen bond

A

a bond between a hydrogen atom in one molecule and an electronegative atom in another molecule

12
Q

How do water molecules orient themselves?

A

in a way that minimizes the repulsion of like charges so that positive charges are near negative charges because the oxygen and hydrogen atoms have slight charges

ie. because of its slight positive charge, a hydrogen atom in a water molecule tends to orient itself toward the slightly negatively charged oxygen atom in another molecule

13
Q

What can any hydrogen atom do?

A

covalently bound to an electronegative atom (ie. oxygen or nitrogen) will have a slight positive charge and can form a hydrogen bond

14
Q

Describe hydrogen bonds in the case of water.

A

the result of many such interactions is a molecular network stabilized by hydrogen bonds

hydrogen bonds are typically showed by a dotted line

*figure 2.10 textbook

15
Q

What are hydrogen bonds weaker than?

A

they are weaker than covalent bonds but hydrogen bonding is what gives water many interesting properties

16
Q

What can the presence of many weak hydrogen bonds do?

A

can help stabilize biological molecules, as in the case of nucleic acids and proteins

17
Q

What do hydrogen bonds influence?

A

the structure of both liquid water and ice

*figure 2.11 textbook

18
Q

What happens to hydrogen bonds when water freezes?

What happens when the temperature increases and the ice melts?

A

most water molecules become hydrogen bonded to four other water molecules, forming an open crystalline structure we call ice

as the temperature increases and the ice melts, some of the hydrogen bonds are destabilized and break, allowing the water molecules to pack more closely

this explains why liquid water is denser than ice

ie. ice floats on water, ponds and lakes freeze from top to bottom (and doesn’t freeze completely) which allows fish and aquatic plants to survive winter in the cold water under the layer of ice

19
Q

What is cohesion?

A

property of water given by hydrogen bonds; an attraction between molecules

20
Q

What is a consequence of cohesion?

A

high surface tension, a measure of the difficulty of breaking the surface of a liquid

21
Q

What does cohesion between molecules contribute?

A

water movement in plant

  • as water evaporates from leaves, water is pulled upward through the plant’s vessels
  • sometimes this water may rise as high as 100 meters above the ground in giant sequoia and coast redwood trees, which are among the tallest trees on Earth
22
Q

How do hydrogen bonds influence how water responds to heating?

A

molecules are in constant motion, and this motion increases as the temperature increases

when water is heated, some of the energy added by heating is used to break hydrogen bonds instead of causing more motion among the molecules

as a consequence, temperature increases less in these situations than if there were no hydrogen bonding

23
Q

What do the abundant hydrogen bonds do?

A

make water more resistant to temperature changes than other substances, a property that is important for living organisms on a variety of scales

24
Q

What does water resist in cells?

A

temperature variations that would otherwise result from numerous biochemical reactions

  • oceans minimize temperature fluctuations, stabilizing the temperature on Earth in a range compatible with life
25
Q

What is pH?

A

a measure of the concentration of protons in solution, which is important because the pH influences many chemical reactions and biological processes

26
Q

What is the formula for pH?

A

pH = -log [H+]

27
Q

Describe the pH scale.

A
  • ranges from 0-14

- logarithmic, a difference of one pH unit corresponds to a tenfold difference in hydrogen ion concentration

28
Q

What does acidic mean?

A

a solution in which the concentration of protons is higher than that of hydroxide ions (pH<7)

29
Q

What does basic mean?

A

a solution in which the concentration of protons is lower than that of hydroxide ions (pH>7)

30
Q

What does neutral mean?

A

a solution in which the concentrations of protons and hydroxide ions are equal (pH=7)

31
Q

What is an acid?

A

a molecule that releases a proton (H+)

32
Q

What is a base?

A

a molecule that accepts a proton in aqueous solution

33
Q

What is the pH of pure water>

A

7, it is neutral

34
Q

What is the pH of most cells?

A

~7 and is tightly regulated, as most chemical reactions can be carried out only in a narrow pH range

35
Q

What is the pH of blood?

A

~7.4, slightly basic

sometimes referred to as “physiological pH”

36
Q

What is the pH of freshwater lakes, ponds, and rivers?

A

tend to be slightly acidic because carbon dioxide from the air dissolves in the water and forms carbonic acid