Atoms, Molecules and Life - General Biology | BIOL 1001, Study notes of Biology

Download Atoms, Molecules and Life - General Biology | BIOL 1001 and more Study notes Biology in PDF only on Docsity!

Chapter 2 (Part II)

Atoms, Molecules & Life

Importance of Water



Makes up 60-90% of most organisms body weight



Water molecules attract one another  (^) Hydrogen bonds form between water molecules  (^) Cohesion of water molecules produces surface tension  (^) Tendency for water surface to resist being broken  (^) Supports living organisms

 Ex: water skippers & basilisk lizard move across water surface

 Ex: plants pull water from the roots up to leaves



Adhesion = tendency of water to stick to surfaces  (^) Ex: Useful for plants to bring water up from roots

Fig. 2-

Basilisk Lizard

 Interacts with many other molecules



Water serves as an excellent solvent for molecules



Solvent= substance that dissolves other substances  (^) Water’s polar nature attracts it to other polar molecules & ions



Solution= solvent containing one or more dissolved substances



Molecules in solutions move around more freely to react with one another  Directly involved in many chemical

Importance of Water (cont)

Water as a Solvent

 (^) Ex: Table salt solution (NaCl + H 2 O)  (^) When salt is added to H

O:  (^) Positive H poles of H 2 O congregate around negative Cl ions  (^) Negative O poles of H 2 O attract the positive Na ions



Result: Salt dissolves  (^) H 2 O molecules block the Na & Cl ions from interacting

Fig. 2-

Salt crystal

Hydrophilic & Hydrophobic

Molecules



Hydrophilic molecules  “Water-loving”  dissolve readily in water  Polar molecules that electrically attract water molecules  (^) Water acts as a solvent  Ex: Salt (NaCl)



Hydrophobic molecules  “Water-fearing”  do not dissolve in water  (^) Large, non-polar molecules that clump together and repel water molecules (= hydrophobic interactions )  Ex: Oil molecules in water

What about small, non-polar

molecules?

 Still “dissolve” in water, but in a different way  Small size allows them to fit into spaces between water molecules



Don’t disrupt the hydrogen bonds between water molecules  Ex: Gases (e.g. oxygen or carbon dioxide)

Water-Based Solutions  Water has a slight tendency to form ions



Water molecule splits into:  (^) Hydroxide (OH-) ions

 Negatively charged due to gaining an electron

 (^) Hydrogen (H+) ions

 Positively charged fdue to losing an electron



This can cause a solution to be:  (^) Acidic  (^) Basic



hydrogen ion

(H  )

hydroxide ion

(OH  )

water

(H 2 O)

 (  ) (  ) O H H O H H

Fig 2-

Acidic Solution  When the H+ ions outnumber the OH- ions  Acid = substance that releases hydrogen ions when dissolved in water  Examples



Hydrochloric acid (HCl)



When added to water: HCl  H+ ions + Cl ions



Basic & Neutral Solutions



Basic Solutions



When the OH- ions outnumber the H+ ions  (^) Base = substance that combines with hydrogen ions thereby reducing their number



Example: Sodium hydroxide (NaOH)  (^) When added to water: NaOH  Na+ ions + OH- ions  Some OH- ions combine with H ions free in water  H2O  (^) Creates a basic solution since not all OH-^ ions are used up



Neutral Solutions  (^) When the H+ ions equal the OH- ions

pH Scale (Fig 2-12)  Each unit= tenfold change in H+ concentration 1 molar hydrochloric acid (HCI) stomach acid (2) lemon juice (2-3)^ "acid rain" (2-5–5-5) beer (4-1) tomatoes (4-5) black coffee (5-0) normal rain (5-6)^ milk (6-4) pure water (7-0) seawater (7-8–8.3) baking soda (8.4) antacid (10)^ household ammonia (11-9) washing soda (12)^ oven cleaner (13-0)^ 1 molar sodium^ hydroxide (NaOH) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH value H^ concentration in moles/liter 100 10 –1^10 –2^10 –3^10 –4^10 –5^10 –6^10 –7^10 –8^10 –9^10 –10^10 –11^10 –12^10 –13^10 – neutral (H ^  OH  ) (H ^  OH  ) (H ^ < OH  ) vinegar, cola (3-0) orange (3-5) urine (5-7) blood, sweat (7-4) chlorine bleach (12-6) drain cleaner (14-0) increasingly acidic increasingly basic

Buffer Solutions



Neutral pH levels are critical for cell & organism survival



Small increases or decreases in pH can cause damage to biological molecules & lead to the death of cells



Natural biological processes can alter pH levels



Buffer maintains a relatively constant pH in a solution  (^) Responds to changes in H+ ion concentration

 If H concentration rises  buffer accepts H+ ion

 If H+ concentration falls  buffer releases H+ ion



Common buffers in biological organisms:

Blood pH regulation by

Bicarbonate

 If blood becomes too acidic (= more H+ ions) HCO 3 -^ + H+  H2CO  If blood becomes too basic H 2 CO 3 + OH-  HCO 3 - + H 2 O Excess HCO 3 - released in urine

Bicarbonate Hydrogen ion carbonic acid

Carbonic acid hydroxide ion bicarbonate water

Water Moderates Effects of Temperature Change



Organisms can only survive within a limited temperature range



Ex: High temps can damage essential enzymes  (^) Ex: Low temps can slow down enzyme activity



Water keeps body temps within a tolerable range



Polar nature results in key properties to achieve this:  (^) High specific heat  (^) High heat of evaporation

Specific Heat of Water



Specific heat = energy required to heat 1 gram of a substance by 1 degree C



It takes a lot of energy to heat water  (^) Specific heat of water = 4.186 joule/gram C  (^) Higher than most other substances  (^) If applied to rock of same weight, temp of rock would increase by 50 degrees C



Most energy is used to break hydrogen bonds apart & not to raise water’s temperature  (^) Allows organisms (whose bodies are mostly water) to survive in hot environments without overheating

• Fig 2-

Heat of Vaporization of

Water



Heat of vaporization = amount of heat needed to cause a substance to evaporate



Water takes 539 calories/gram to evaporate  (^) One of the highest known  (^) Breaking of hydrogen bonds uses up energy

 A portion of water molecules break free & escape into

air

 Remaining water molecules are cooled due to loss of

energy



Organisms utilize processes involving evaporation of water to keep body temperature from rising

Evaporative processes that

cool body

 Perspiration  Panting  Dousing self with cool water

Water forms an unusual

solid: Ice



Most substances become more dense when in solid forms



However: Ice is less dense than liquid water



When water freezes:  (^) Each molecule forms hydrogen bonds with 4 other molecules



Forms an open, hexagonal arrangement of molecules



Molecules are kept further apart



When ponds & lakes freeze:



Surface water freezes & forms an insulating layer

Liquid Water Ice

Fig 2-14 Note the hexagonal

arrangement