Lecture 3: Water in Life Flashcards
Why do astrobiologists look for water when looking for extraterrestrial life?
Water is the most abundant molecule in organisms and cells and essential for life on Earth.
What percentage of body weight is typically composed of water?
50-75%
Where is most of the body water located within organisms?
in cells, specifically in the intracellular fluid.
What percentage of the volume in a typical cell consists of water?
75%
How long can you survive without eating?
weeks
What is the likely maximum duration for survival without drinking?
You aren’t likely to live more than 3-4 days without drinking.
Why is water important for life?
because of its unique structure and properties.
What are the structure and unique features of water?
Water is unique due to its:
A. Small size
B. Bent shape
C. Highly polar covalent bonds
D. Overall polarity
What are the four major properties of water?
- Is a very good solvent
- Is cohesive (sticks to itself) and adhesive (sticks to other components)
- Has a high capacity for absorbing energy before changing (ex: high boiling point)
- Decreases in density when cooled below 4oC (stats to float)
Why does water have those four major properties?
due to its structure and its ability to form a network of hydrogen bonds with other water molecules or other substances.
What are hydrogen bonds?
weak electrical attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule.
Besides water molecules, where else can hydrogen bonds form?
between a water molecule and another polar/charged group of a molecule.
How do hydrogen bonds compare in strength to covalent or ionic bonds?
not as strong as covalent or ionic bonds.
Why are hydrogen bonds extremely important in biology?
because they are common, and a large number of these bonds can form between substances, resulting in an overall strong interaction.
Why is water polar?
Would hydrogen bonding
be affected if the structure
of water was linear?
it wouldn’t be polar anymore = all of its properties lost
What is the maximum
number of hydrogen bonds that water can make?
4
Why is water referred to as the “universal solvent”?
because it can dissolve almost any charged or polar molecule.
What keeps ions and polar molecules in solution in water?
due to their interactions with water’s partial charges, and they are termed hydrophilic.
How are nonpolar compounds described in their interaction with water?
Nonpolar compounds do not dissolve in water and are described as hydrophobic.
How do you relate the polarity and solubility of a compound in water?
the more polar a compound is, the more soluble it is in water
Why do polar or charged molecules dissolve in water and non polar ones don’t?
*because water molecules can form a hydration shell around charged or polar molecule through hydrogen bonding. (and get in between the molecules of the compound)
Are cells dissolved in water?
No since they are too big and else they wouldn’t be cells anymore
Which molecule is most soluble in water? explain
Vitamin C since its a more polar molecule
Give me three biological significance of water relative to “being a good solvent”
explain cohesion versus adhesion
Why is water cohesive and adhesive?
- Water molecules can interact with themselves or other polar molecules via hydrogen bonds.
What is water’s high surface tension? What does it result from?
Water’s high surface tension results from water molecules pulling on each other because of water’s cohesive nature.
- Cohesion minimizes the surface area of water not in contact with other water molecules.
*aka maximizes contact with itself
Give me three biological significance of water relative to “cohesion and adhesion”
Is cohesion or adhesion important for surface tension?
cohesion
Explain the transpiration in plants and what property of water allows this process.
Water can absorb a large amount of energy before it changes its ____ or ____.
temperature
physical state
Why can water resist change in temperature? aka absorb a lot of energy before it changes.
What is specific heat directly proportional to?
the molecule’s capacity for H-bonding
Define specific heat
the energy required to raise the temperature of 1 gram of a substance by 1oC.
Give me three biological significance of water relative to “water’s capacity to resist change”
At what temperature is water at its highest density?
4oC
Interpret the graph
Why is water’s highest density at 4oC?
- Between 4oC and 0oC: hydrogen bonding increases when molecules slow down as temperature decreases; density decreases.
- at 0oC: ice forms when molecules further slow down and maximum hydrogen bonding forms a crystal lattice.
Give me three biological significance of water relative to “water’s capacity to resist change”
Give two other roles of water in life (other than related to its properties)
What is the average pH of these three solutions?
Soln 1: pH 7
Soln 2: pH 6
Soln 3: pH 8
Why is pH important in bio? What does the change in ion concentration affect? (3)
