Answer

(c) All living organisms and non-living matter in our biosphere are made of similar elements and compounds. Several researches performed on plants, animals and microbes confirmed that a relative abundance of organic compound i,e., carbon, hydrogen and oxygen in living organisms than in the earth’s crust (non-living matter).

Whereas, the percent composition of other inorganic molecules like calcium and gold is more in earth’s crust as compared to living matter.

Representation of inorganic constituents of lining tissues.

• (a) Living organisms have more gold in them than inanimate objects: This is incorrect because gold is a very rare element in living organisms. The concentration of gold in the human body is extremely low compared to its presence in the earth’s crust.

• (b) Living organisms have more water in their body than inanimate objects: While it is true that living organisms contain a significant amount of water, the question is about elemental composition, not the presence of compounds like water. Therefore, this option does not address the elemental differences between living organisms and inanimate objects.

• (d) Living organisms have more calcium in them than inanimate objects: This is incorrect because the earth’s crust contains a higher percentage of calcium compared to living organisms. The human body has a lower percentage of calcium compared to the earth’s crust.

Answer

(a) Silicon is not found freely in nature, but it does occur as oxides and silicates, whereas magnesium, iron and sodium are present in living organisms as ions. Silicon is essential to plant life but is often found in minute quantities in human body and its function is still unknown.

• Magnesium is an abundant element. It is essential for a number of enzymes and their action, particularly those utilising ATP.

• Iron is an important constituent of haemoglobin and plays a vital role by taking part in $\mathrm{O}_{2}$ transport, and electron transport chain.

• Sodium plays a vital role in animals by regulating nerve impulse transmission and altering the membrane permeability. It also has indispensable role in osmoregulation.

Answer

(d) Glycine is the simplest amino acid with an amino group and a carboxyl group. Whereas formic acid is the simplest carboxylic acid, glycerol is a fatty acid and glycolic acid is carboxylic acid substituted with hydroxyl group.

• Formic acid is the simplest carboxylic acid and does not contain an amino group.
• Glycerol is a fatty acid and does not contain an amino group or a carboxyl group.
• Glycolic acid is a carboxylic acid substituted with a hydroxyl group and does not contain an amino group.

Answer

(d) A zwitterion is a neutral molecule having both the cationic and anionic charges on the same molecule. Amino acids are the best known examples of zwitterion.

In acidic solution’ amino group accepts a hydrogen ion to become positively charged. Whereas, in alkaline solution the carboxyl group donates a hydrogen ion to become negatively charged. The $\mathrm{pH}$ at which the amino acid is electrically neutral is called isoelectric $\mathrm{pH}$.

$\mathrm{NH}_3 -\underset{\substack{\text { Cation } \\ \text { (low pH) }}}{\stackrel{\mathrm{R}}{\mathrm{CH}}} - \mathrm{COOH} \rightleftharpoons \underset{\text { (Zwitterion at isoelectric pH) }}{\mathrm{^+H}_3 \mathrm{~N} - \stackrel{\mathrm{R}}{\mathrm{CH}} - \mathrm{COO}^{-}} \rightleftharpoons \mathrm{H}_2 \mathrm{~N} -\underset{\substack{\text { Anion } \\ \text { (high pH) }}}{\stackrel{\mathrm{R}}{\mathrm{CH}}} - \mathrm{COO}^{-}$

• (a) acidic form: An acidic form of an amino acid would have a net positive charge due to the protonation of the amino group and possibly the carboxyl group. It does not have both positive and negative charges simultaneously.

• (b) basic form: A basic form of an amino acid would have a net negative charge due to the deprotonation of the carboxyl group and possibly the amino group. It does not have both positive and negative charges simultaneously.

• (c) aromatic form: An aromatic form refers to the presence of an aromatic ring in the amino acid’s structure, such as in phenylalanine, tyrosine, or tryptophan. It does not describe the charge state of the molecule.

Thinking Process

Glucose is an aldohexose. Its carbon is attached to a hydrogen atom by a single bond and to an oxygen atom by a double bond.

Answer

(a) Fructose is a ketohexose. Its carbon is attached to an hydrogen atom by a single bond and to an oxygen atom by a double bond.

Erythrose is a tetrose carbohydrate $\left(C_{4} H_{8} O_{4}\right)$. Its a part of tetrose family and possesses one aldehyde group.

Ribulose is a ketopentose, containing five carbon atoms and includes ‘ketone’ as a functional group.

Ribose is a pentose which is a major component of DNA and RNA.

• (b) Erythrose: Erythrose is a tetrose carbohydrate, which means it contains only four carbon atoms. Glucose, on the other hand, is a hexose and contains six carbon atoms. Therefore, erythrose does not have the same number of carbon atoms as glucose.

• (c) Ribulose: Ribulose is a ketopentose, meaning it contains five carbon atoms. Since glucose is a hexose with six carbon atoms, ribulose does not have the same number of carbon atoms as glucose.

• (d) Ribose: Ribose is a pentose, which means it contains five carbon atoms. Glucose, being a hexose, contains six carbon atoms. Therefore, ribose does not have the same number of carbon atoms as glucose.

Answer

(d) Each nucleoside is made up of cyclic nitrogenous base, purine or pyrimidine and a pentose sugar.

On phosphorylation, it forms a nucleotide i.e., a molecule with nitrogenous base pentose sugar and three phosphate groups.

• (a) nitrogen base: A nitrogen base is a component of a nucleotide, but it is not formed by the phosphorylation of a nucleoside. Nitrogen bases are the building blocks that pair with each other to form the rungs of the DNA ladder, but they do not include the sugar or phosphate groups.

• (b) adenine: Adenine is one of the four nitrogenous bases found in DNA and RNA. It is a part of a nucleoside when combined with a sugar, but it is not the result of phosphorylation of a nucleoside. Adenine alone does not include the sugar or phosphate groups necessary to form a nucleotide.

• (c) sugar phosphate: A sugar phosphate is a component of a nucleotide, specifically the sugar (pentose) bonded to a phosphate group. However, it does not include the nitrogenous base, which is essential for forming a complete nucleotide. Therefore, it is not the correct answer for a compound formed by the phosphorylation of a nucleoside.

Thinking Process

Homogenisation is achieved by a mechanical device called homogeniser. The plant/animal tissues are homogenised for cytological/biochemical studies.

Answer

(a) On homogenising any tissue in an acid, the acid soluble pool represents cytoplasm. Homogenisation is a process whereby a biological sample is brought to a state such that all fractions of the sample are equal in composition.

• (b) Cell membrane: The cell membrane is primarily composed of lipids and proteins, which are not typically soluble in acid. Therefore, it would not be represented in the acid soluble pool.

• (c) Nucleus: The nucleus contains DNA, RNA, and various proteins, many of which are not soluble in acid. Thus, the nucleus would not be part of the acid soluble pool.

• (d) Mitochondria: Mitochondria contain their own DNA, proteins, and lipids, which are generally not soluble in acid. Hence, mitochondria would not be represented in the acid soluble pool.

Answer

(b) There is abundance of water in living matter. It is the only polar molecule in living organisms, that can diffuse through a cell membrane without active transport. It is vital for a number of metabolic reactions and one of the raw materials for photosynthesis.

• (a) protein: While proteins are essential macromolecules in living organisms, they are not the most abundant chemical. Proteins play crucial roles in structure, function, and regulation of the body’s tissues and organs, but they do not surpass water in terms of abundance.

• (c) sugar: Sugars, or carbohydrates, are important for energy storage and supply in living organisms. However, they are not as abundant as water. Sugars are primarily involved in energy metabolism and structural components, but their overall quantity is much less compared to water.

• (d) nucleic acid: Nucleic acids, such as DNA and RNA, are vital for genetic information storage and transfer. Despite their critical roles in heredity and protein synthesis, they are not the most abundant chemicals in living organisms. Their presence is significant but not as prevalent as water.

Answer

(a) Proteins are heteropolymers made of about 20 different kinds of monomer, i.e., amino acids. Each of these amino acids is made up of carbon, amino group, carboxyl group, hydrogen and a $R$-functional group. This variable $R$ - group is what that makes each monomer different from one another.

• (b) 40 types of monomers: Proteins are not made up of 40 different types of monomers. The standard set of amino acids that make up proteins is 20, not 40.

• (c) 30 types of monomers: Proteins are not composed of 30 different types of monomers. The correct number of standard amino acids that form proteins is 20.

• (d) only one type of monomer: Proteins are heteropolymers, meaning they are made up of more than one type of monomer. Specifically, they are composed of 20 different types of amino acids, not just one.

Answer

(d) Proteins can sometimes function as hormones, i.e., peptide hormones such as insulin, growth hormore etc. Other compounds such as antibiotics, florigen and melanin are non-proteineceous in nature.

• Antibiotics: Antibiotics are typically small molecules or compounds that are not proteins. They are often derived from microorganisms and are used to kill or inhibit the growth of bacteria.

• Pigment conferring colour to skin: The pigment that confers color to the skin is melanin, which is not a protein but a complex polymer derived from the amino acid tyrosine.

• Pigments making colours of flowers: The pigments responsible for the colors of flowers are usually flavonoids, carotenoids, and betalains, which are not proteins but rather small organic molecules.

Thinking Process

In humans, glycogen is made and stored primarily in the cells of liver and the muscle, and functions as the secondary long term energy storage. Muscle glycogen is converted into glucose by muscle cells and liver glycogen is converted to glucose for entire body use including CNS, PNS and other body parts.

Answer

(a) Glycogen is the storage polysaccharide present in animals. Glycogen consist of glucose molecule linked together with $\alpha(1 \rightarrow 4)$ linkages with $\alpha(1 \rightarrow 6)$ branch points occurring every 8-12 residues.

Galactose, on the other hand is a monosaccharide, and combines with glucose through condensation reaction, resulting in the formation of disaccharide, lactose.

Ribose is a pentose monosaccharide which has all hydroxyl group on the same side in fisher projection. It forms a part of backbone in RNA and DNA. Amino acids are the monomers of proteins.

• Galactose is a monosaccharide, and combines with glucose through condensation reaction, resulting in the formation of disaccharide, lactose.
• Ribose is a pentose monosaccharide which has all hydroxyl groups on the same side in Fischer projection. It forms a part of the backbone in RNA and DNA.
• Amino acids are the monomers of proteins.

Answer

(a) Glycogen is the multibranched polysaccharide of glucose units popularly known as animal starch, as it is chemically similar to starch. It has 30,000 glucose residues and a molecular weight of about 4.8 million. Glucose residues in glycogen are arranged in a highly branched bush like chains.

There are two main linkage patterns, observed in glycogen, i.e., $\alpha$ 1-4 linkage in the straight part and $\alpha$ 1-6 linkage in the area of branching. The distance between two branching points is 10-14 glucose residues. Glycogen has as many non-reducing ends as branches plus one.

• (b) Equal to the number of branch points: This option is incorrect because each branch point in glycogen creates an additional non-reducing end. Therefore, the number of ends is actually equal to the number of branches plus one, not just the number of branch points.

• (c) One: This option is incorrect because glycogen is a highly branched molecule. If it had only one end, it would imply a linear structure without any branches, which is not the case for glycogen.

• (d) Two, one on the left side and another on the right side: This option is incorrect because it suggests a linear structure with only two ends. Glycogen is a branched molecule, and each branch creates an additional end, resulting in many more ends than just two.

Answer

(a) The primary structure of a protien refers to a linear sequence of amino acids in polypeptide chain, held together by peptide bonds. These are two ends of a polypeptide chain, carboxyl terminus (C-terminus) and the amino terminus ( $\mathrm{N}$-terminus) based on the nature of the free group on each extremity.

• (b) One end: The primary structure of a protein cannot have just one end because it is a linear sequence of amino acids, which inherently has two distinct ends, the N-terminus and the C-terminus.

• (c) Three ends: The primary structure of a protein cannot have three ends because it is a single, continuous polypeptide chain with only two termini, the N-terminus and the C-terminus.

• (d) No ends: The primary structure of a protein must have ends because it is a linear sequence of amino acids, which starts with an N-terminus and ends with a C-terminus.

Answer

(a) $\mathrm{CO}_{2}$ gets dissolved in water, a reaction which is not always catalysed by any enzyme. Unwinding and winding of the two strands of DNA is catalysed by the enzyme topoisomerase. Hydrolysis of sucrose is regulated by sucrase. Peptide bonds are formed by the action of enzyme peptidyl transferase.

• Unwinding the two strands of DNA is catalysed by the enzyme topoisomerase.
• Hydrolysis of sucrose is regulated by sucrase.
• Peptide bonds are formed by the action of enzyme peptidyl transferase.

Answer

(a) Penicillin is a group of antibiotics derived from fungi Penicillium and was initially used as a natural product.

(b) Sulphonamide is a synthetic chemical. It is an antimirobial agent is the basis of several groups of drugs.

(c) Vitamin-C or L-ascorbic acid or ascorbate is a natural product and an essential nutrient for humans. It is present in citrus fruits.

(d) Growth hormone (GH or HGH) also known as somatotropin or somatropin is a peptide hormone occuring naturally in the body. It stimulates growth.

Answer

(a) Polysaccharide is linked by glycosidic bond. Glycosidic bond is a type of covalent bond joining simple or units carbohydrate molecules together to form a long chain polysaccharide.

(b) Protein are linked by peptide bonds. Peptide bond is a covalent chemical bond formed between two amino acids when the carboxyl group of one reacts with the amino group of other causing release of water molecule. Hence, called as dehydration synthesis reaction (condensation reaction).

Peptide bonds between a chain of amino acids results in the formation of protein.

(c) Ester bonds are formed by the reaction between carboxyl group of fatty acid and hydroxyl group of triglycerols to form fat. Water is eliminated during this reaction.

(d) Hydrogen bond is electrovalent interaction between polar molecules in which hydrogen is bound to a highly electronegative atom, such as N, O, S, F, etc. Water is the best known example

Answer

(a) Amino acid - Leucine

(b) Sugar - Lactose

(c) Nucleotide - Adenosine triphosphate

(d) Fatty acid — Palmitic acid

Answer

Oxidoreductase is an enzyme that catalyses oxidation and reductions reactions. This enzyme is associated in catalysing the transfer of $e^{-}$from one molecule (the reductant), also called as electron donor, to another molecule (the oxidant), also called as electron acceptor.

The complete reaction is

Answer

Prosthetic groups are organic compounds that are tightly bound to the apoenzyme, (an enzyme without cofaetor) by covalent or non-covalent forces, e.g., in peroxidase and catalase, which catalyse the breakdown of hydrogen peroxide to water and oxygen, haeme is the prosthetic group and it is a part of the active site of the enzyme.

Co-factor is small, heat stable and non-protein part of conjugate enzyme. It may be inorganic or organic in nature.

Co-factors when loosely bound to a enzyme is called coenzyme and when tightly bound to apoenzyme is called prosthetic group.

Answer

In both the amino acids the common substituent groups are $\mathrm{NH}_{2} \mathrm{COOH}$ and $\mathrm{H}$.

Answer

(a) Cotton fibre - Cellulose

(b) Exoskeleton of cockroach - Chitin

(c) Liver - Glycogen

(d) Peeled potato - Starch

Cellulose is a long chain of linked glucose molecules and is the main component of plant cell walls. Cotton is the purest natural form of cellulose. the cellulose content of cotton fibre is $90 %$.

Chitin is a long chain polymer that forms the hard part of the outer integument or exoskeleton of crustaceans and insects such as cockroach. It is also the main component of the cell walls of fungi.

Glycogen is a multibranched polysaccharide of glucose acting as a form of stored energy in the liver of animals. It is also found in some stored fungi.

Starch is a carbohydrate consisting of along chain of glucose units joined by glycosidic bonds. This polysaccharide is produced mostly by green plants for energy storage, e.g., peeled potato.

Answer

Enzymes, generally function in a narrow range of $\mathrm{pH}$. Most of the enzyme shows their highest activity at a particular $\mathrm{pH}$ called optimum $\mathrm{pH}$, and it declines below and above this value.

Extremely high or low $\mathrm{pH}$ values generally results in complete loss of activity for most enzyms. The graph above represents the maximum enzyme activity at the optimum $\mathrm{pH}$.

Answer

Rubber (cis 1, 4-polyisopyrene) is a secondary metabolite. Secondary metabolites are chemicals produced by plants for which no role has been found yet in growth, photosynthess, reproduction or other primary functions.

(i) Rubber is extracted from Havea brasiliensis (rubber tree).

(ii) It is a byproduct of the lactiferous tissue of the vessels that are in the form of latex.

(iii) It is the largest of the terpenoids because it contains over 400 isoprene units.

(iv) It is elastic, water proof and a good electrical conductor.

Answer

Proteins are the large-sized, heteropolymeric macromolecules having one or more polypeptides (chains of amino acid).

Primary Structure The primary structure of a protein is the linear sequence of amino acid structural units and partially comprises its overall biomolecular structures. The amino acids are linked together in a sequence by peptide bonds.

In the primary structure of protein initiate from an amino-terminal $(\mathrm{N})$ to the carboxyl terminal (C) end,

Secondary Structure It is a three dimensional form of local segments of bipolymers such as proteins. Secondary structure of proteins is defined by hydrogen bonds between backbone amino and carboxyl groups. Mainly secondary structure in proteins possess two forms, i.e., $\alpha$-helix and $\beta$-pleated sheet.

$\alpha$-helix is a polypeptide chain spirally coiled to form a right handed helix. This helix may be coiled regularly at places and at some places randomly coiled. The helix is stabilised by many hydrogen bonds which are formed between $\mathrm{CO}$ of one amino acid and $\mathrm{NH}$ group of next fourth amino acid.

$\beta$-pleated sheets two or more polypeptide chains are joined together by intermolecular hydrogen bonds to produce a sheet like structure instead of fibre as in $\alpha$-helix. The polypeptide strands in a sheet may run parallel in same direction, e.g., keratin or in opposite direction called antiparallel $\beta$-sheet, e.g., fibroin.

Tertiary structure involves interactions that are caused by the bending and folding of $\alpha$-helix or $\beta$-sheets leading to the formation of rods, spheres of fibres. Such interactions are typically conferred by $\mathrm{H}$-bonds, ionic bonds, covalent bonds, van der Waat’s interactions and hydrophobic interactions or disulphide linkages. It gives the protein a three dimensional conformation.

Answer

Nucleic acids are polymeric macromolecules or large biological molecules, essential for all known forms of life. The secondary structrure of a nucleic acid molecule refers to the base pairing interactions within a single molecule or set of interacting molecules.

DNA and RNA represent two main nucleic acids, however their secondary structures differ e.g., the secondary structure of DNA comprises of two complementary strands of polydeoxyribonucleotide, spirally coiled on a common axis forming a helical structure.

This double helical structure of DNA is stabilised by phosphodiester bonds (between $5^{\prime}$ of sugar of one nucleotide and 3 of sugar of another nucleotide), hydrogen bonds (between bases, i.e., hydrogen of one base and nitrogen of oxygen of other base) and ionic interactioins.

Answer

Living organism are not in equilibrium because system at equilibrium cannot perform work. The living organisms exist in a steady state characterised by concentration of each of the biomolecules.

These biomolecules are in a metabolic flux. Any chemical or physical process moves simultaneously to equilibrium. As living organisms work continuously, they cannot afford to reach equilibrium. Hence, the living state is in a non-equilibrium steady-state to be able to perform work. This is achieved by energy input provided lay metobolism.

Answer

Each enzyme molecule has an active site for specific binding of substrate molecules. The enzyme work by altering the activation energy of the reaction.

The catalytic site of an enzyme can be described as follows

(i) The substrate process to the active site of the enzyme, fitting into it.

(ii) Binding of the substrate induces the enzymes to alter its shape leading to formation of the Enzyme Substrate (ES) complex.

(iii) The active site of the enzyme, now is in close proximity with the substrate and break its chemical bonds and a new enzyme product complex is formed.

(iv) The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of substrate and run through the catalytic cycle once again.

Answer

Enzymes are divided into six classes each with 4-13 sub-classes and named accordingly by a four-digit number.

(i) Oxidoreductases/dehydrogenases These enzymes take part in oxidation and reduction or transfer of $e^{-}$.

$$ S(\text { reduced })+S^{\prime} \text { (oxidised) } \rightarrow S \text { (oxidised) }+S^{\prime} \text { (reduced) } $$

(ii) Transferaes These enzymes transfer a functional group from one molecule to another (other than hydrogen). The chemical group transfer does not occur in free state.

$$ S-G+S^{\prime} \quad \text { Transferase } \rightarrow S+S^{\prime}-G $$

(iii) Hydrolases These enzymes catalyse the hydrolysis of bonds like ester, ether, peptide, glycosidic C-C, C-halide, P-N etc.

$$ C_{12} \underset{\text { Maltose }}H_{22} O_{11}+H_{2} O \quad \xrightarrow{\text { Maltase }} \underset{\text { Glucose }}{2 C_{6} H_{12} O_{6}} $$

(iv) Lyases These enzymes causes cleavage, removal of groups without hydrolysis and addition of groups to double bonds or removal of groups producing double bond.

(v) Isomerases These enzymes cause rearrangement of molecular structure to effect isomeric changes. They are of three types, i.e., isomerases, epimerases and mutases.

$\underset{\text{(Aldose to ketose group or vice-versa)}}{\text{Glucose - 6 - phosphate} \xrightarrow{\text{Isomerase}} \text{Fructose 6 - phosphate}}$

$\underset{\text{(Shifiting the position of side group)}}{\text{Glucose - 6 - phosphate} \xrightarrow{\text{Mutase}} \text{Glucose 1 - phosphate}}$

$\underset{\text{(Change in position of one constituent or Carbon group )}}{\text{Xylulose 5 - phosphate} \xrightarrow{\text{Epimerase}} \text{Ribulose- 5 - phosphate}}$

(vi) Ligases are enzymes catalysing bonding of two chemicals with the help of energy obtained from ATP resulting formation of bonds such as C O, C S, C N and P O e.g., pyruvate carboxyl use

$$ \mathrm{Ab}+\mathrm{C} \rightarrow \mathrm{A}-\mathrm{C}+\mathrm{b} $$

Pyruvric acid $+ CO_{2}+\mathrm{ATP}+ H_{2} \mathrm{O} \stackrel{\text { pyruvate carboxylase }}{\rightleftharpoons}$ Oxaloacetic $+\mathrm{ADP}+\mathrm{Pi}-$

Answer

Nucleic acids are long chain macromolecules which are formed by end to end polymerisation of large number of repeated units called nucleotides. Nucleic acids show a wide range of secondary structures. A secondary structure is the set of interactions between bases and sugar phosphate backbone and is responsible for the shape that nucleic acid.

James Watson and Francis Crick proposed a secondary structure of DNA molecules based on the crystallographic studies.

(i) DNA or deoxyribonucleic acid is a helically twisted double-chain polydeoxyribonucleotide macromolecule.

(ii) The two strands of DNA run anti-parallely to each other called as DNA duplex.

(iii) The spiral twisting of DNA has two types of alternate grooves, i.e., major and minor.

(iv) One turn of $360^{\circ}$ of the spiral has about 10 nucleotides on each strand of DNA, occupying a distance of about $3.4 \mathrm{~nm}$.

(v) The nucleotides within each strand are held together by the phosphodiester bonds between the $5^{\prime}$ carbon of one nucleotide and the $3^{\prime}$ carbon of the adjacent nucleotide. These strong covalent bonds holds the sugar/phosphate backbone together. (vi) The two strands of DNA are held together by weak hydrogen bonds between the nitrogenous bases. These hydrogen bonds are base specific. That is adenine forms 2 hydrogen bonds with thymine $\mathrm{CA}=\mathrm{T}$ and cytosine forms 3 hydrogen bonds with guanine ( $\mathrm{C} \equiv \mathrm{G}$ ).

(vii) As specific and different nitrogen bases occur on two DNA chains, they are said to be complementary, i.e., purine lies opposite to pyrimidine. This purine-pyrimidine pairing also contributes to the thickness of strand, i.e., $2 \mathrm{~nm}$, and makes the two chains complementary.

Answer

Difference between a nucleotide and nucleoside is as follows

Nucleoside	Nucleotide
Nucleoside is a compound formed by the union of the nitrogenous base with a pentose sugar	Nucleotide is compound formed by union of nitrogen base, a pentose sugar and phosphate.
It is slightly basic in nature	A nucleotide is acidic in nature
It is a component of nucleotide and forms with both ribose and deoxyribose sugars.	Nucleotide is formed through phosphorylation of nucleoside
e.g., cytidine, uridine, adenosine, guanosine, thymidine and inosine.	e.g., AMP, GMP, CMP, UMP, dTMP (deoxythymidine monophosphate)

Answer

Lipids are the esters of higher fatty acid with alcohol, such as glycerol, etc.

These can be classified as

1 Simple Lipids are esters of fatty acids with alcohol. These may be

(i) Fats These are esters of higher fatty acids with glycerol (triglycerides).

(ii) Waxes These are esters of higher fatty acids with alcohol other than glycerol.

2 Compound or conjugated lipids, are those compounds which contain simple lipids and prosthetic (other additional) group. They include

(i) Glycerophospholipids, also known as phospholipids in which one of the fatty acid is replaced by phosphoric acid which is linked to nitrogenous groups like choline, ethanolamine, serine etc, e.g., Lecithin and cephalin, etc.

(ii) Sphingo lipids, are lipides having phosphoric acid with amine alcohol 4-sphinganine or sphingosine instead of glycerol in addition to fatty acid and choline.

(iii) Glycolipids, i.e., those which contain spinganine with a fatty acid and a monosaccharide sugar, e.g., cerebrosides and gangliosides.

3 Steroids are compounds with different chemical nature but similar physical properties. Their structure is based upon a 4 ring cyclopentenoperhydro phenanthrene, e.g., cholesterol.

4 Prostoglandins are derivatives of arachidonic acid and contain $20 \mathrm{C}$-atoms. These are biologically active lipids.