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General Biology II > lecture 3: water > Flashcards

lecture 3: water Flashcards

1
Q

Why is water abundant in organisms and where do we find most of the water in an organism?

A
  • 50-70% of body weight is water
  • in typical cell: 75% of volume consists of water
  • most of the water is in one’s cells (intracellular fluid)
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2
Q

Why is water important in life? + example

A

Because of its unique structure and properties
- can’t live more than 3-4 days without drinking

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3
Q

Structure of water (4)?

A
  1. small size
  2. bent shape
  3. highly polar covalent bonds
  4. overall polarity
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4
Q

Major properties of water (4)

A
  1. very good solvent
  2. cohesive and adhesive
  3. high capacity for absorbing energy before changing
  4. decreases in density when cooled below 4ºC
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5
Q

Why does water have these special properties? (2)

A
  • Its structure
  • Ability to form a network of hydrogen bonds with other water molecules or other substances
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6
Q

Explain the hydrogen bonds in water (where can we find them)

A
  • Weak electrical attractions between the partially negative oxygen of one water molecule & the partially positive hydrogen of a different water molecule
  • Can form between two water molecules AND between a water molecule and another polar/charged group of a molecule
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7
Q

Why are hydrogen bonds important in biology?

A
  • When as covalent/ionic bonds = not really strong
  • But, in biology: are really COMMON —> LARGE NUMBER of H bonds forming between substances = an overall STRONG interaction
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8
Q

Water can form hydrogen bonds because…

A

water is polar: large electronegativity difference between O and H

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9
Q

Why is water a good solvent? “universal solvent”

A
  • Can dissolve almost any charged or polar molecule bc of water’s partial charges —> these ions/polar molecules will stay in solution —> hydrophilic
  • Whereas non-polar compounds won’t dissolve in water and are said to be hydrophobic
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10
Q

How does water dissolve those hydrophilic molecules?

A
  • Polar molecules/ions dissociate
  • Water forms a HYDRATION SHELL around charged or polar molecule through hydrogen bonding

EX: partially negative O surrounds Na+ and partially positive H surrounds Cl- —> prevents them to come back together

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11
Q

Are cells dissolved in water?

A

No, bc of their phospholipid layer

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12
Q

What makes a molecule more soluble in water?

A
  • Presence of more polar groups —> more place for H bonds to occur
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13
Q

Why is water’s role as a good solvent biologically significant? (3)

A
  1. Most chemical reaction important for life take place in aqueous solutions
  2. Distribution of substances in body fluids of organisms (ex: antibodies in blood)
  3. Elimination of soluble wastes in organisms (ex: nitrogenous wastes in urine)
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14
Q

What is cohesion?

A

Binding with LIKE molecules (water molecule & another water molecule)

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15
Q

What is adhesion?

A

Binding between UNLIKE molecules (water molecule and an other polar molecule)

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16
Q

How can water be cohesive and adhesive?

A

With hydrogen bonds, water can interact with themselves and with other polar molecules

17
Q

Cohesion of water results in… (2)

A
  1. high surface tension
    - water molecules pull on each other
  2. a minimized surface area of water
    - little bubble of water on leaf
18
Q

Why is water’s cohesion & adhesion biologically significant? (3)

A
  1. Aids in transport of fluid within vascular tissue of plants (xylem + phloem)
  2. High surface tension (cohesion) allows some organisms to live on water
  3. Adhesion allows water to cling to surfaces and acts as a lubricant to resist friction (ex: joints)
19
Q

Why can water absorb a large amount of energy before it changes its temperature or physical state?

A

Large network of H-bonds = rly strong —> need lots of energy to first break the bonds AND then need lots of energy to get the molecules to move faster —> to change temp. or physical state

20
Q

What is the specific heat & its relation with the quantity of hydrogen bonding?

A
  • Energy required to raise the temperature of 1 gram of a substance by 1ºC
  • Specific heat increases as the quantity of hydrogen bonding increases (need more energy to break the bonds & get the molecules moving faster if there are more hydrogen bonding)
21
Q

Why is water’s high capacity for absorbing energy before changing biologically significant? (3)

A
  1. Most water on earth is in a liquid state necessary for organisms (need water to stay liquid)
  2. Helps buffer temp. changes in cells, organisms and environment
  3. Evaporation of water from an organisms dissipates heat as form of sweat —> to cool the body
22
Q

Like other substances, water become more dense as its temperature decreases. However, unlike other substances, water…

A

becomes LESS dense (EXPANDS) as its temp. decreases from 4ºC to 0ºC
- From liquid to solid (freezing point of 0ºC): water expands further and becomes even less dense

23
Q

Water has its highest density at…

A

4ºC

24
Q

Why is water less dense when cooled below 4ºC?

A

As temp decreases between 4ºC and 0ºC, H bonding INCREASES as molecules slow down —> density DECREASES (less compact)

At 0ºC: ice forms when molecules further slow down and MAX H bonding forms a CRYSTAL LATTICE (lighter bc the water molecules are equally pulling on one another —> molecules are further apart)

25
Q

Why is water’s smaller density below 4ºC biologically significant?

A
  • Ice floats which prevents bodies of water of aquatic habitats from freezing solid in cold temp
  • Ice forms a layer that can insulate the the body of water below from cooling and contribute to an organism’s habitat in some ecosystems
  • Maintains a water temperature of 4ºC in bodies of water during winter
26
Q

What are other roles of water in life (2)?

A
  1. Water directly participates in chemical reactions (dehydration and hydrolysis)
  2. Water can be used for support in organisms (turgor pressure and hydroskeleton)
27
Q

What is pH?

A
  • Measure of protons H+ in a solution
  • pH = -log[H+]
  • More H+ = Lower pH = More acidic
  • Less H+ = Higher pH = More basic/alkaline
28
Q

Why is pH important in biology?

A
  • Cells are EXTREMELY sensitive to changes in pH —> relatively big change in proton concentration is likely to kill you within minutes
  • Acids & other chemicals can be produced as part of organism’s metabolism —> can change pH of its fluids
  • Fluids in organisms are buffered to avoid drastic changes to pH
29
Q

Changes in pH affects… (3)

A
  1. Structure of proteins (then affect higher order of structure and protein’s functions)
  2. Interactions between molecules
  3. How likely key acid-base reactions in our metabolism are to occur
30
Q

What are pH buffers? Why are they important?

A
  • Compounds that minimize changes in pH —> prevent damaging effects of pH change
  • Important first line of defence in maintaining relatively constant pH in cells and other body fluids (homeostasis)
31
Q

What other 2 systems are also effectors in homeostatic mechanisms to regulate pH in blood?

A
  • Respiratory and urinary system
32
Q

How does a pH buffer work?

A
  • Buffer systems = weak acids & their conjugate bases such as carbonic acid and its conjugate base bicarbonate
    H2CO3 (base) —> HCO3- + H+ (acids)
  • Increase in H+ = countered by consuming excess H+ and producing H2CO3 (increase in metabolic acids or decrease in metabolic bases)
  • Decrease in H+ = countered by producing more H+ and consuming H2CO3 (decrease in metabolic acids or increase in metabolic bases)

General Biology II (7 decks)

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