AP Biology Chapter 3
Water and the Fitness of the Environment
47 flashcards · Biology · by Tommy Nguyen
Water makes up how much of the cell content in a living organism?
75 - 90%
Water covers 75 % of the Earth's surface.
In a water molecule 2 hydrogen atoms form single polar covalent bonds an oxygen atom.
Because oxygen is more electronegative, the region around the oxygen has a partial negative charge.
The reason near the two hydrogen atoms has a partial positive charge.
A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.
Water has a variety of unusual properties because of the attractions between these polar molecules.
When slightly negative regions are attracted to slightly positive regions in a water molecule, they form a hydrogen bond.
Water molecules can form hydrogen bonds with up to 4 neighbors.
Cohesion - water molecules attracted to other water molecules.
Cohesion is caused by the forming and re-forming of hydrogen bonds.
What does cohesion create in a liquid?
Creates a more structurally organized liquid.
Cohesion allows water to move against gravity in plants.
Water that evaporates from a leaf is replaced by water from vessels in the leaf.
Adhesion - water molecules attracted to different molecules.
Adhesion produces?
Surface tension
Water has a high surface tension.
Hydrogen bonds among surface water molecules resist stretching or breaking the surface.
Heat - is the measure of the total quantity of kinetic energy.
Heat is measured by the calorie (the amount of heat energy it takes to raise 1 g of water 1 c.
Water has a high specific heat due to hydrogen bonding.
At night the gradually cooling water can warm the air - this is the reason coastal areas generally have milder climates than inland regions.
Temperature - measures the average kinetic energy of the molecules in a substance.
Temperature is measured using a celsius scale. Water (at sea level) freezes at 0 C and boils at 100 C.
Heat of vaporization is the quantity of heat a liquid must absorb for 1 g of it to convert to a gaseous state.
As water cools below 4 C, it expands - each water molecule becomes bonded to four other water molecules forming a crystalline lattice.
Ice is less dense than liquid water therefore it floats. Ice insulates the liquid water below.
Solution - a liquid homogeneous mixture of two or more substances. Example: A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water.
Solvent - the dissolving agent. Solute - the substance that is being dissolved.
Aqueous solution - one in which water is the solvent.
Hydrophillic - "water loving" Have ionic or polar regions
Hydrophobic - "water fearing" Have nonpolar covalent bonds
Most chemical reactions that occur in organisms involve solutes dissolved in water.
Chemical reactions depend on collisions of molecules and therefore on the number of molecules available.
A water molecule can dissociate into a hydronium ion (H3O+) and a hydroxide ion (OH-)
Since hydrogen and hydroxide ions are very reactive, changes in their concentrations can drastically affect proteins and other molecules of the cell.
What increases hydrogen ion concentration in a solution? acid
What decreases hydrogen ion concentration in a solution? base
As pH decreases, [H+]? increases
Each pH unit represents a tenfold difference in H+ and OH- concentrations. A solution of pH 3 is a thousand times more acidic in a solution with a pH of 6.
To maintain cellular pH values at a constant level, biological fluids have buffers.
Buffers resist changes to pH of a solution when H+ or OH- is added to the solution.
Buffers accept hydrogen ions from the solution when they are in excess, and donate when they have been depleted.
Buffers consist of weak acids and its corresponding base.
One important buffer in human blood is carbonic acid
The chemical equilibrium between carbonic acid and bicarbonate acts as a pH regulator
Uncontaminated rain has a slightly acidic pH or 5.6