Functions of lipids - class-XI

Adipose tissue, or fat, is an anatomical term for loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body.

 Lipids are the compound formed by alcohol and fatty acids ester linkage. They are characterized by solubility in the organic solvent. Sudan Red dye is used to stain lipids. It is water insoluble but dissolves with fats. Therefore, dye accumulates in the globules within the cells. Thus, the correct option is  D.

Lipids are technically micromolecules (low molecular weight), but they are extracted in the acid-insoluble fraction because they form vesicles that precipitate with cell debris.

Fats are an important class of biomolecules.They are compounds of carbon, hydrogen and oxygen where the ratio of hydrogen and oxygen is less than that of water. Lipids are a concentrated source of energy and serve for long term energy storage in body of animals and plants. Their respiratory quotient is less than one. Approximately 9 calories are provided by one gram of fat as compared to 4 by carbohydrates. Fats also act as insulating material because they are poor conductors of heat. Most of the animals have a layer of fat below the skin acting as insulating material. Lipids also serve as structural biomolecules for example conjugate lipid molecules like phospholipids, glycolipids, sphingolipids etc.

Vitamin A, testosterone and UV rays induce lysis of lysosomal membrane under acidic pH which makes options B, C and D incorrect. Cholesterol exhibit scavenging effect on free radicals as well as prevent osmotic rupture of lysosomal membrane which makes option A correct answer. 

Glycogen is also homopolysaccharide of D-glucose and serves as an energy storing molecule in animals as glucose as storage material can increase the osmotic pressure of storage cell enormously. Proteins do not serve as energy storage molecule. Fat and oil are storage lipids and are derivatives of hydrocarbon that produce enormous energy upon oxidation. Thus, the correct answer is B.

Lipids are broken down in the digestive tract to form fatty acids and cholesterol. Fatty acids and cholesterol are key components of cell membranes that regulate its fluidity and permeability. Lipids of the nervous system are localized in myelin sheaths thereby providing electrical insulation. Thus the correct answer is option D.

Lecithin is a group of yellow-brownish fatty substances present in animal and plant tissues.In the pharmaceutical industry, it is used in emulsifications and encapsulation of drugs and is a good dispersing agent. Thus the correct answer is option A.

Phosphatidylethanolamines are phospholipids found in all living cells, They are found mainly in the nervous tissue such as the white matter of the brain, nerves, neural tissue and in the spinal cord. 

Membrane biogenesis is structuring/rebuilding/repairing of the cell membrane. As the cell membrane is made of a bilayer of phospholipids embedded with proteins.It is a process carried out by the cell with the help of smooth endoplasmic reticulum (SER) and Golgi apparatus (GA). Where the SER synthesizes lipids which are added with phosphate group and modified to phospholipids by the process of phosphorylation in the GA and transported through vesicles to the cell membrane.

De novo synthesis of cholesterol from acetyl-CoA takes place in the liver. Cholesterol is an essential metabolite for the normal functioning of the endocrine system, regulation of cell membrane processes, and absorption of dietary lipids. They are important structural components of membranes. Cholesterol also serves as precursor for the synthesis of steroid hormones, vitamin D, and bile salts which are important in fat absorption from the small intestine into the blood circulatory system and secretion of liver waste products through feces. Thus the correct answer is option B.

Commonly candles are prepared from stearic acid and paraffin wax. Candles that made from paraffin wax only burn quicker than those made from paraffin wax and stearic acid together.

Turpentine oil is an oil which is a volatile oil which is mainly obtained from pines a gymnospermic plant. It is obtained by distillation of resin. Terpenes are the derivative of terpene oil. It is used for thinning oil based paints. It is a very good source of organic synthesis. It is highly viscous in nature. The solid material left behind after distillation is known as rosin.

Lipid bilayer of the cell membrane contains hydrophilic head groups facing outward and hydrophobic tails facing each other. The transport of phospholipids and lipid-linked oligosaccharides is difficult to achieve due to this bipolar nature. The transmembrane lipid transporter proteins called flippases transport lipids across cell membrane through transverse diffusion by flipping their orientation. Floppases transport in reverse direction. In mammals, this affects various processes such as blood coagulation, immune recognition, and programmed cell death.Most protein molecules do not flipflop due to their extensive polar regions, which are unfavorable in the hydrophobic core of the membrane.

The exine layer of a pollen grain is exceptionally hard and resistant to high temperatures, strong acids, and alkalis because it is chiefly composed of sporopollenin, a remarkably durable organic polymer. Cellulose and pectocellulose make up the intine layer, while lipids are found in various pollen coatings.

The tails of the lipids are made up of fatty acids. These are non-polar hydrophobic so they tend to arrange away from the cytoplasmic face as well as the extracellular face. So, they avoid aqueous medium by arranging themselves towards the inner part of the cell membrane.

Phosphoinositides make up a small fraction of cellular phospholipids, They play a fundamental role in controlling membrane-cytosol interfaces, regulation of membrane traffic and the permeability and transport functions of membranes. They are found in brain tissue in animals and soybean seeds. Thus the correct answer is option B.

Essential fatty acids (EFA) are those fatty acids that body cannot produce on its own and therefore must be supplied from the diet. Deficiency of EFA causes many disease conditions like dry and scaly skin, follicular keratosis (hard and dry skin around hair follicles), bumps on back of upper arms, color variation of skin, dry eyes, mouth and throat, menstrual cramps, dry vagina, excessive thirst, eczema, asthma, hay fever, painful joint. In severe cases, it may result in kidney failure and sterility.