Problem 27 - Objective Biology for NEET

Question

Lipids are (a) Compounds of carbon, hydrogen and oxygen (b) Compounds of glycerol and fatty acid (c) Insoluble in water (d) All of these

Step-by-Step Solution

Answer

The correct response is (d) All of these.

Step 1: Understanding the properties of lipids

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. They are typically composed of carbon, hydrogen, and oxygen atoms with some lipids also containing nitrogen and phosphorus.

Step 2: Checking each statement

(a) Compounds of carbon, hydrogen and oxygen: This is a characteristic of lipids; they are primarily composed of carbon, hydrogen and oxygen atoms. (b) Compounds of glycerol and fatty acid: This is another characteristic of some types of lipids, specifically fats and oils which are categorized as glycerol-based lipids. They are formed when one glycerol molecule combines with three fatty acid molecules to form a triglyceride. (c) Insoluble in water: This is also a common property of lipids. They are hydrophobic or ‘water-fearing’ molecules, thus they do not mix with or dissolve in water. Therefore, options (a), (b) and (c) are all correct.

Step 3: Conclusion

As all of the previous options are true, it's accurate to say that 'All of these' is the right answer as well, validating option (d).

Key Concepts

Fatty Acids

Fatty acids are fundamental building blocks of lipids. They contain long hydrocarbon chains with a carboxylic acid group at one end. This structure is key to their role in many biological functions. Fatty acids can be classified based on their saturation:

• Saturated fatty acids have no double bonds between carbon atoms. This means they contain the maximum number of hydrogen atoms possible.
• Unsaturated fatty acids have one or more double bonds. These can be further classified into monounsaturated (one double bond) and polyunsaturated (multiple double bonds).

The chain length and degree of saturation influence their properties and how they affect health. For example, unsaturated fats are usually liquid at room temperature and are considered healthier than saturated fats.

Glycerol

Glycerol is a simple polyol compound with three hydroxyl (OH) groups. It serves as the backbone for certain types of lipids, most notably triglycerides.
As a part of triglycerides, glycerol provides the framework to which fatty acids attach. It is colorless, odorless, and sweet-tasting, commonly found in many food products. Beyond its structural role in lipids, glycerol is also used in various industrial applications, including pharmaceuticals and cosmetics.
In the human body, glycerol is involved in metabolism and can be converted to glucose, providing energy for cellular processes.

Triglycerides

Triglycerides are a type of lipid formed by the combination of one glycerol molecule and three fatty acid molecules. They are the main form of stored energy in many organisms, acting as a fuel reserve.
Triglycerides can be found in most of the fat tissues in the body and are crucial for insulation and protection of organs. When energy is needed, these triglycerides are broken down into fatty acids and glycerol, which then enter metabolic pathways.
Being hydrophobic, they do not dissolve in water, which aids in their function as energy reserves since they don't draw excess water into cells, maintaining cellular integrity.

Water Solubility of Lipids

The water solubility of lipids is an essential factor that distinguishes them from other biomolecules. Lipids are predominantly hydrophobic, meaning they do not dissolve in water. This characteristic is due to the non-polar hydrocarbon chains present in fatty acids, which do not interact favorably with polar water molecules.
Lipids can, however, interact with water through emulsification, a process where lipids are dispersed into smaller droplets with the help of emulsifying agents like bile salts. This property is essential for digestion and absorption in the human body.
Despite their water insolubility, lipids play crucial roles in forming cellular membranes and acting as signaling molecules, exploiting their hydrophobic nature for structural and functional roles.