AP Biology Mind Map: Water and Life

Polar Covalent Bonds in H2O Molecules
1. Polar Covalent Bonds: Polar covalent bonds are bonds where the electrons are not shared equally. In water molecules, oxygen is more electronegative than hydrogen, so the electrons of the covalent bonds will linger closer to oxygen than to hydrogen.
2. Polar Molecule: A polar molecule is one that its charges are unevenly distributed. In a H2O molecule, the oxygen is partially positive, and the hydrgens are partially negative.
3. Water's properties arise from the attractions that exist between oppositely charged atoms of different water molecules. The slightly positive hydrogen atom of one molecule is attracted to the slightly negative oxygen of a nearby molecule. As a result, H2O molecules are held by hydrogen bonds.
4. When water is in liquid form, the hydrogen bonds are really fragile causing H2O molecules to form, break, and then reform hydrogen bonds again. This means that in water, H2O molecules are constantly forming, breaking, and reforming hydrogen bonds with each other.
Water's Emergent Properties
1. Cohesion of Water Molecules
  1. Cohesion: Water molecules are linked by hydrogen bonds. These linkages make water more structured than most other liquids. This process is also known as the phenomenon named cohesion.
  2. Cohesion contributes to the transport of water and dissolved nutrients as it resists gravity in plants. Water from the roots reaches the leaves through a system of water-conducting cells.
  3. Adhesion: This is the clinging of one substance to another. Similarly, as cohesion, adhesion of water to cell walls helps counter the downward pull of gravity.
  4. Surface Tension: Related to cohesion, surface tension is a measure of how difficult it is to stretch or break the surface of a liquid. Water compared to other liquids, has greater surface tension. The section between water and air is an organized arrangement of water molecules bonded to each other with hydrogen bonds, and they are also bonded to the water below. This makes the water behave as though covered with an invisible film.
2. Moderation of Temperature by Water
  1. Heat and Temperature
    1. Kinetic Energy: Kinetic energy is energy in motion. As a result, atoms and molecules have kinetic energy because they are constantly moving. The faster a molecule moves, the greater its kinetic energy.
    2. Heat: Heat is a form of energy. The amount of heat is a measure of the matter’s total kinetic energy. As a result, heat depends in part on the matter’s volume.
    3. Temperature: It is the measure of heat intensity that represents the average kinetic energy of the molecules, indifferent of volume.
    4. When two objects of different temperature are brought together, heat passes from the warmer to the cooler object until the two are the same temperature.
    5. Celsius Scale: This is a scale that can indicate the temperature.
    6. Calorie and Kilocalorie: It is the amount of heat it takes to raise the temperature of 1 g of water by 1°C. A kilocalorie is the quantity of heat required to raise the temperature of 1 kilogram of water by 1°C.
    7. Joules: It is a unit of energy and one joule equals 0.239 cal and one calorie equals 4.184 J.
  2. Water's HIgh Specific Heat
    1. Specific Heat: The specific heat of a substance can be determined by amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C. Compared to others, water's specific heat is 1 calorie per gram and per degree Celsius, when most other substances have a much lower specific heat. Because of the high specific heat, water will change its temperature less when it absorbs or loses a given amount of heat.
    2. To break hydrogen bonds, heat must be absorbed, and to form hydrogen bonds heat must be released. A calorie of heat doesn't influence a lot the temperature of water because the majority of the heat disrupts hydrogen bonds before the water molecules begin to move faster. When the temperature of water drops slightly, additional hydrogen bonds are formed, releasing a considerable amount of energy in the form of heat.
    3. The high specific heat of water also serves to stabilize ocean temperatures, creating a favorable en- environment for marine life.
  3. Evaporative Cooling
    1. Heat of Vaporization: It is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to a gas. Asides from the high specific heat, water also has a high heat of vaporization compared to most other liquids. This is also another factor that helps with the global temperature.
    2. Evaporative Cooling: This is the process where a liquid evaporates, then the surface of the liquid that remains behind cools down. This occurs as the hottest molecules, those with the greatest kinetic energy, are more prone to leave as gas.
3. Floating of Ice on Liquid Water
  1. Water is one of the few liquids that becomes less dense when turned into a solid. This means that water the solid-state will float on liquid water. The reasoning behind is that when temperatures drops and liquid water turns into a solid, the hydrogen bonds keep the molecules at “arm’s length,” this makes ice about 10% less dense than liquid water at 4°C.
  2. This is important as if ice sank, eventually all ponds, lakes, and even oceans would freeze solid, making life as we know it impossible on Earth.
4. The Solvent of Live
  1. Solute Concentration in Aqueous Solutions
    1. Molecular Mass: Molecular mass is the sum of the atom's atomic mass in a molecule.
    2. Mol: It is a unit for measuring how much of a substance is there. The benefit of measuring a number of chemicals in moles is that a mole of one substance has exactly the same number of molecules as a mole of any other substance.
    3. Molarity: It is the number of moles of solute per liter of solution. It is the unit of concentration most often used by biologists for aqueous solutions.
  2. Hydrophilic and Hydrophobic Substances
    1. Hydrophilic: Any substance that has an attraction for water. In some cases, substances can be hydrophilic without actually dissolving.
    2. Colloid: A stable suspension of fine particles.
    3. Hydro Phobic: Substances that are nonionic and nonpolar, not being able to form hydrogen bonds, and seem to repel water)
  3. Solution, Solvent, and Solute: A liquid that is a completely homogeneous mixture of two or more substances is called a solution. The dissolving part of a solution is the solvent, and the substance that is dissolved is the solute
  4. Aqueous Solution: In solutions where water is the solvent, the name for the solution is an aqueous solution.
  5. Water is a great solvent as water it is a very versatile solvent. The reason behind this is water's polarity.
  6. Hydration Shell: It is the sphere of water molecules around each dissolved ion.
  7. A compound does not need to be ionic to dissolve in water, such compounds dissolve when water molecules surround each of the solute molecules, forming hydrogen bonds with them.
Acids and Basic Conditions
1. Buffers
  1. The internal pH of most living cells is close to 7. Even the smallest change in pH can be harmful, due to the chemical processes of the cell are very sensitive to the concentrations of hydrogen and hydroxide ions.
  2. Buffer: It is a substance that minimizes changes in the concentrations of H+ and OH- in a solution. It does so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted.
2. pH Scale
  1. pH: The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration:
  2. pH declines as H+ concentration increases. Also, the pH scale is based on H+ concentration, it also implies OH- concentration.
3. Acid and Bases
  1. Acid: An acid is a substance that increases the hydrogen ion concentration of a solution.
  2. Base: A substance that reduces the hydrogen ion concentration of a solution is called a base.
4. Acidificatoin
  1. When CO2 dissolves in seawater, it reacts with water to form carbonic acid, which lowers ocean pH, a process known as ocean acidification.
  2. Acid precipitation refers to rain, snow, or fog with a pH lower (more acidic) than 5.2. (Uncontaminated rain has a pH of about 5.6, which is slightly acidic due to the formation of carbonic acid from CO2 and water.)
5. Hydrogen Ion (H+), a single proton with a charge of 1+.
6. Hydroxide Ion: The water molecule that lost a proton is now a hydroxide ion (OH-), which has a charge of 1-.
7. Hydronium Ion: The proton binds to the other water molecule, making that molecule a hydronium ion (H3O+).

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