3A_Biomolecules

25 March 2010 What do I know about **HOMEOSTASIS**?


 * Homeostasis is the tendency to **maintain the equilibrium** (despite the **change in the external environment**) between the internal and external environments of **living organisms/systems** by regulating the inner environment to ensure its stability in response to the fluctuations of the external environment.
 * Osmosis: molecules move from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
 * Diffusion
 * Active Transport
 * The structure of the cell membrane

__DEFINITION. EXPLANATION. EXAMPLE TO ILLUSTRATE.__ The structure of a molecule always dictates its function. Example: Monosaccharides are the primary energy source for fueling cell metabolism while disaccharides act as building blocks for larger molecules.

E.g. In cells, the energy is generated from glucose in the mitochondria in the form of ATP molecules. We store energy in the form of fats that come from the food that we eat.
 * Energy** is stored in the organization of matter.

Living organisms use matter and energy to build and maintain body structures. E.g. Milk contains calcium that is used by young of mammals to help make teeth and bones stronger. Milk contains proteins that help build muscles and other structures in the body.

Communities of organisms depend on the cycling of matter and the flow of energy. Cannot use food chain for example because it does not involve a cycle. "According to the law of Physics, energy cannot be created or lost." Energy can be lost in the food chain in the form of heat energy and excretion or simply because it is indigestible, as it changes from one form to another form. Therefore, the statement is not true. Energy can be lost but cannot be DESTROYED. A lot of chemical energy is lost. A more appropriate example would be that of the water cycle and the carbon cycle. Why is the carbon molecule suitable for life as we know it? Why is the chemistry of water suitable for life? GO THROUGH ALL THE CHARACTERISTICS OF WATER.


 * The carbon molecule is suitable for life because it is the building block of matter. The carbon atom has a valency of 4, so there are 4 free electrons to form bonds with four other atoms, so it can form a macromolecule with its four electrons, with different properties and functions. Fats are stable because it has double carbon bonds so it is very hard to break fats down.
 * Carbon has the ability to combine with itself to form carbon backbone and macromolecules.

HOMEWORK: CARBOHYDRATES, LIPIDS and PROTEINS. 1. What is the structure? 2. What forms does it take? 3. How are these forms formed? 4. What is the function?