6. What are hydrophobic molecules (or hydrophobic molecular regions)? What are hydrophilic molecules? How can they be characterized in relation to their polarity?
Hydrophobic molecules are those that have little or no propensity to dissolve in water (hydro = water, phobia = fear). Hydrophilic molecules are those that have great propensity to dissolve in water (philia = friendship).
Water is a polar substance. Remembering the rule that “equal dissolves equal” one can conclude that hydrophobic substances are non-polar molecules while hydrophilic molecules are polar molecules.
7. Are organic solvents like benzene and ether polar or non-polar substances?
Benzene and the ethers are molecules without electrically charged portions and thus they are non-polar substances.
8. Regarding solubility, how are lipids classified?
Fats and oils are hydrophobic molecules, i.e., they are non polar and insoluble in water. Lipids in general are molecules with a large non-polar extension and so they are soluble in non polar solvents, like benzene, ether and chloroform.
There are some amphipathic lipids, i.e., lipids whose molecules have a hydrophilic portion, like the phospholipids, giving them the property of being dragged by water, and a hydrophobic portion (non polar).
9. What is meant by saturation or unsaturation of oils and fats?
When it is said that a triglyceride is saturated it means that in its molecule the carbon chain is bound in its maximum capacity to hydrogens, i.e., there are no double or triple bonds between carbons. These saturated molecules are generally solid fats at normal temperature.
Unsaturated triglyceride molecules are those in which there are double or triple bonds between carbons and so they do not accomplish their maximum capacity of hydrogenation. These unsaturated molecules in general are oils, liquid at normal temperature.
The terms saturated or unsaturated refer then to the saturation of the carbonic chain by hydrogen atoms.
10. Why do fats have thermal isolation properties?
Triglycerides are weak heat conductors and in addition they form thick layers of fat tissue when accumulated by the organism. That is why they are good thermal isolators.
In animals that live in cold climates, like polar bears, seals and whales, the adipose tissue helps the maintenance of the internal body temperature.
11. How are lipids used as an energy source by the organism?
Carbohydrates are the main energy source for aerobic cell respiration. In the absence or deficiency of such substances the organism can use lipid stores since fats (like proteins) can be degraded into acetyl-CoA to feed the Krebs cycle (a stage of the aerobic cellular respiration).
Compiled by My Preparation of Maharashtra Public Service Commission (MPSC) Examination for the blog http://maharashtrapublicserviceexams.blogspot.com
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