Chapter 2. Molecular Biology Flashcards
What caused water molecules to be polar?
Unequal sharing of electrons between atoms. Electrons are more attracted to the oxygen end, giving the oxygen atom a partially negative charge and the hydrogen atoms partially positive charges.
Water molecules are dipola. Define ‘dipola’.
Partial charges are different at each pole.
What are hydrogen bonds?
They are intermolecular forces between opposite partial charges in polar molecules (e.g. water, ammonia).
Hydrogen bonding gives water its special properties. Outline 5 properties of water which are resulted directly from hydrogen bonding.
- High specific heat capacity
- High latent heat of vaporization
- High boiling point
- Cohesion and adhesion
- Solvent property
Define what is the specific heat capacity (of water etc.).
The amount of thermal energy in joules required to increase the temperature of 1g (1cm3) of water by 1 degree Celsius.
Define what is the latent heat of vaporization.
The heat needed to separate a molecule from other molecules to form a vapor during evaporation.
Define the terms cohesion and adhesion.
Cohesion refers to the binding together of molecules of the same type (e.g. water).
Adhesion is when hydrogen bonds form between one molecule to other molecules of a different type (e.g. water to other polar molecules), causing the molecules to stick together.
Outline an example of cohesion in real life phenomena.
Useful for water transport in xylem vessels in plants. Water is pulled from the roots to the top of the plant by its cohesive forces. Even though xylem vessels have very low pressure, cavitation is unusual with water (molecules cannot be separated easily).
Outline an example of adhesion in real life phenomena.
As water adheres to polar cellulose cell walls, adhesive forces cause water to be drawn out of the nearest xylem vessel when water is loss by evaporation through stomata in plants. This keeps the walls moist so they can absorb carbon dioxide needed for photosynthesis.
The theory that hydrogen bonds form between water molecules –> explains –> water’s special properties is an example of …
Theory –> explains –> natural phenomena
Why it is essential for water to have a high specific heat capacity?
- To avoid any rapid changes in organisms’ internal temperature and to enable them to maintain a stable temperature even when the temperature in the surroundings varies considerably.
- To provide a thermally stable habitat for aquatic organisms.
Application of water’s high latent heat of vaporization.
A good evaporative coolant (sweating, panting).
Why water’s high boiling point is essential?
The high boiling point gives the water a wide temperature range at which it remains as a liquid (0 ~ 100 degree Celsius), which is the temperature range found in most habitats on the Earth.
Define the term boiling point.
The boiling point of a substance is the highest temperature that it can reach in a liquid state.
Define the solvent property of water.
The polar nature of water molecules means that they form shells around charged and polar molecules, preventing them from clumping together and keeping them in solution.
