Waxes lipids of plants:


The waxes found in lipids of plants are primarily composed of esters of fatty acids and long-chain alcohols. These waxes are important for plants as they provide protection against water loss, UV radiation, and environmental stressors. They also play a role in preventing microbial infections and preventing herbivory.

Some examples of plant waxes include cuticular wax, which is found on the surface of leaves and stems, providing a barrier against water loss and pathogens. Suberin is another type of plant wax that is present in the roots and outer cell walls of plants, acting as a protective layer against disease-causing microorganisms and enhancing resistance to waterlogging. 

Plant waxes are commonly extracted for various purposes, such as in the production of cosmetics, pharmaceuticals, food products, and industrial applications. They contribute to the smooth texture and sheen of many consumer goods and are often used as emollients in skincare products.

Overall, waxes in lipids of plants play a vital role in the growth and survival of plants, providing them with a protective layer and enabling them to adapt to a range of environmental conditions.

Composition: The waxes are lipids which are composed of long__ chain saturated fatty acids and a long__ chain saturated alcohol of high molecules weight instead of instead of glycerol. A few waxes are listed below__ 

(i) Beeswax:  It is a secretion of the abdominal glands of worker honeybees.It is a thick, tenacious material plastic ar room temperature. 

(ii) Lanolin or Wool Fat:It is a secretion of cutaneous glands and closely resembles the sebum.It is obtained from the wool of sheep. It consists of palmitic, oleic, or stearic acid and cholesterol. 

 ( iii) Sebum: It is a fatty secretion of the sebaceous glands of the skin ( L. sebum= tallow). 

( iv) Cerumen:  It is a soft, brownish, waxy secretion( a modified sebrum) of the ceruminous glands of the external auditory canal. It is commonly called earwax ( L. cera= wax). 

 (v) Plant Waxes: These form a coating on plant organs to prevent wetting and reduce transpiration. 

(vi) Paraffin  Wax:  A translucent,  waxy substance obtained from  petroleum. 

Function: The waxes form a water__ proof  protective coating on animal furs and feathers, on plant stem, leaves and fruits, and on insect exoskeletons. Bees wax is used by the worker bees for building hive. Cerumen lubricates the tympanic membrane. 
      The bacteria that cause tuberculosis and leprosy produce wax__ D that contributes to their pathogenicity.

Described the structure of phospholipid. How are they arranged in the cell membrane?

Phospholipids ( Phosphoglycerides):

Composition: The phospholipids are composed of a molecule of glycerol or other alcohol having 

(i) A phosphate group to one of its outer ___ OH groups ( never to the middle one), 

(ii) Two acid molecules linked to the other two __ OH groups, and 

( iii) A nitrogen __ containing base, such as choline molecule, bound to the phosphate group. The phospholipids are, thus, mixed glycerides.

Special Property: A phospholipid molecule has a strongly nonpolar and hydrophobic ( water fearing or water insoluble) " tail" consisting of fatty acid chain and a polar and hydrophilic ( water loving or water soluble), " head" comprising a negatively charged phosphate group and a positively charged base. Because of this dual solubility, the phospholipids are called amphipathic lipids. Due to this property, a phospholipid placed at the surface of water forms two_ molecules thick layer, called lipid bilayer, in a characteristic manner. The nonpolar fatty acid chains of the two layers associated together in the hydrophobic interior of the bilayer, and their polar phosphate __ base groups face the surrounding water molecules. Such lipid bilayers are the basic components of the cellular membranes. If a phospholipid is added to water, it forms droplets called micelles, in which phosphate heads are outside in contact with water and hydrocarbon tails are toward water __ free interior.


  Functions: The phospholipids form the framework of the cell, nuclear, mitochondrial, chlo__ replant and ER membranes .They are thought to control the passage of materials into and out of the cell and cell organelles. Some phospholipids ( lecithins) are a constituent of cytoplasm and some occur in storage fats  Certain phospholipids ( sphingomyelines) insulate the never fibres.


Composition:Glycolipids contain fatty acids, alcohol sphing sphingosine and sugar ( galactose). The latter replaces one fatty acid molecules. 

Function: The glycolipids are components of all membranes, particularly in myelin sheath of nerve fibres and on outer surfaces of nerve cells; and of chloroplast membranes. 


Composition:Lipoproteins contain lipids ( mainly phospholipids) and proteins in their molecules. 

Functions: Membranes are composed of lipoproteins. Lipids are transported in the blood plasma and lymph as lipoproteins. Lipoproteins occur in the milk and egg yolks.

Cutin and Suberin:

Cutin is found in the plant cell walls and cuticle. It binds epidermal cells and reduces transpiration. Suberin is present in the walls of.cork cells. It makes cell wall strong and impermeable to water.


Composition: The steroids do not contain fatty acids,but are included in the lipids because they have fat __ like properties. Unlike other lipids, they are not straight chain compounds. They are composed of four fused carbon rings. The various steroids differ in the number and position of double bonds between carbon atoms and in the side groups linked to the ring.

    Examples : The most common steroids are sterols. The latter have ___ OH groups in their molecules. They occur in both animal and plant cells. Common sterols are cholesterol and ergosterol. Other  steroids include bile acids,  vitamins D, sex hormones and adrenal cortical hormones.

     (a) Cholesterol: It is the most abundant steroid in the animal tissues. It is also formed in the liver itself. Its formula is C27H45 OH .It may occur free or as cholesterol ester  with a fatty acid. The cholesterol and its esters are insoluble in water. Therefore,they are deposited on the lining of the blood vessels if blood cholesterol level rises. This narrow the blood vessels ( atherosclerosis) and leads to high blood pressure and heart diseases. 

         Cholesterol may precipitate as crystals and combine with bile salts and bile pigments to form gall bladder stones.

     The cholesterol is useful also.

(i) Cholesterol is an essential component of animal plasma membrane. It also occurs in the cell membrane of mycoplasms.

(ii) The cholesterol is a parent compound from which many hormones are synthesized in cells. These include testosterone ( male sex hormone) estradiol and progesterone ( female sex hormones), aldosterone and cortisone ( adrenal cortex hormones) and ecdysone ( insect moulting hormones).

(iii) Cholesterol also produces bile salts that emulsify fat during digestion and also help in the absorption  of fats.

( iv) A cholesterol derivatives forms vitamin D by the action of ultraviolet rays of sunlight.

( b) Ergosterol: It is a plant sterols or phytosterol. Its formula is C28H43OH . It becomes vitamin D ( calciferol) when activated by ultraviolet rays. Ergosterol also occurs in cell membrane of fungi. 

Function: The steroids have the following functions ____ 

(i) They act as chemical coordinators.

( ii) Some steroids stimulate anabolism. They are called anabolic steroids. They are abused by athletes to increase muscle mass, strength and endurance.

(iii) Sterols are essential for growth and flowering in plants.

(iv) A steroid named diosgenin obtained from yam plant ( Dioscorea) is used in the manufacture of antifertility pills.

(v) Another steroid called digitalin prepared from the leaves of foxglove ¹is a heart stimulant. 


Terpenes are a major component of " essential oils" produced by certain plants. Camphor, eucalyptus oil, limonene, and menthol are the terpenes present in the oil of camphor, eucalyptus, lemon and mint respectively. They impart fragrance to plant parts. Vitamins A, E and K and pigment chlorophyll contain a terpenoid alcohol called phytol. Natural rubber and carotenoid pigments are also terpenoid compounds. Carotenoids are yellow and orange plant pigments. The group's  name is derived from the pigment compounds.Carotenoids are yellow and orange plant pigments. The group's name is derived from the pigment carotene found in carrots. This pigment is a precursor of vitamin A, and important molecule needed for vision. Hence, carrots are good for eyes, Lycopene, a pigment present in tomatoes, is also a terpenoid compound. Gibberelins, the plant growth substances, are also terpenes.


The prostaglandins are hormone__ like compounds derived from the 20__ carbon Polyunsaturated fatty acids such as arachidonic acid. They occur in many tissues.  Their richest sources are the secretion of seminal vesicles in males and menstrual fluid in the females . The prostaglandins have a variety of effects such as  vasodilation, vasoconstriction, stimulation of intestinal or bronchial smooth muscle, uterine such as vasodilation,  vasoconstriction,  stimulation of intestinal or bronchial smooth muscle, uterine such as vasodilation,  vasoconstriction, stimulation of intestinal or bronchial smooth muscle, uterine stimulation, and antagonism to hormones influencing lipid metabolism. They perhaps act by regulating the production of cyclic AMP by adenyl cyclase.

    Prostaglandins also function in inflammatory and allergic reactions, and in blood clotting. 

Q. Cholesterol is a crucial molecule in animals. Why? 

Ans: Cholesterol is a common compound in animal membranes, and is a source of many vertebrate hormones, and other steroids. 


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