Nicotinamide Adenine Dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD) are coenzymes associated with reversible oxidation and decrease reactions. Then, these lessened coenzymes can give these electrons to some other biochemical response ordinarily engaged with a procedure that is anabolic (like the union of ATP).

Biomolecules are basically all the carbon compounds obtained from the living tissue. All the major components that make up a living being that is the carbohydrate, proteins, lipids contain carbon in one form or the other.

The cellulose micromolecules are small in size and have low molecular weights which is less than 1000 daltons. They have simple molecular structure and often high solubility in the intracellular fluid. These include inorganic compounds such as water, mineral salts, and gases as well as organic compounds such as sugars, lipids, amino acids and nucleotides. The small molecules are the substrates and products of metabolism in the cell. The micromolecules act as building blocks for the macromolecules. 

• Body needs phosphorus to build and repair bones and teeth.
• It also helps nerves to function.
• Calcium is important on blood clotting, muscle contraction, and strengthening bones. 

Magnesium is an important macronutrient required by plants in large quantity. Magnesium is a constituent of chlorophyll pigment and is required as an essential cofactor for all the reactions catalysed by kinase enzymes like hexokinase. Magnesium is also important for structural integrity of ribosomes. Ribosomes are the cell organelles involved in protein synthesis.

The blood glucose level in body is tightly regulated by a number of mechanism. The normal blood glucose level in humans should not exceed 140 mg per decilitre after meals and is maintained between 70 to 100 mg per decilitre under fasting conditions without food. Glucose is a precious metabolite and, hence, is actively reabsorbed by the kidney tubules. Any excess quantity of glucose is converted into glycogen which is stored in liver and muscles. Any further excess is converted to fats and stored for long term deposit. In humans and most other mammals, acetyl CoA formed in the liver during oxidation of fatty acids may enter the citric acid cycle or may be converted to ketone bodies, i.e., acetoacetate, $\beta$-hydroxy-butyrate and acetone for export to other tissues. Overproduction of ketone bodies can occur in conditions of severe starvation and in uncontrolled diabetes.

The nerves responsible for sensing a stimulus and sending information about the stimulus to your central nervous system are called afferent neurons. The nerves that carry signals away from the central nervous system in order to initiate an action are called efferent neurons.

Sporopollenin is found in outer layer or exine of pollen grains. It is extremely resistant and can withstand extremes of temperature presumably as an adaptation to protect the male gametophyte. The exine is weak at few points where sporopollenin is missing. These are germ pores from where pollen germinates that is, pollen tube protrudes out during  germination.

Proteins are very versatile biomolecules performing different structural and functional roles. Proteins are also information molecules having amino acids joined together in a unique sequence which is decided by the sequence of nucleotides in nucleic acids DNA and RNA. Because different animals will have different sequence of nucleotides in DNA, the proteins synthesized in their body will also have different sequence of amino acids.

Tracer elements are radioisotopes which are used to trace the path of molecules in metabolic pathways. Thus elucidating the metabolic pathway. For example an important experiment proving that DNA carries genetic information, was based on tracer techniques. In 1952 Alfred D. Hershey and Martha Chase used radioactive phosphorus (32P) and radioactive sulfur (35S) tracers to show that when the bacterial virus (bacteriophage)T2 infects its host cell, Escherichia coli, it is the phosphorus-containing DNA of the viral particle, not the sulfur-containing protein of the viral coat, that enters the host cell and furnishes the genetic information for viral replication.

A water molecule has two hydrogen and one oxygen atom and is smallest among the given options. An enzyme can be as small as a chain of 60 amino acid residues, while a bacterium ranges in 1 micrometre in diameter. The chromosome contains linear DNA molecule which is 2 m long. Nucleus diameter is  6 micrometers. The correct ascending order of size is water molecule, enzyme, bacterium, chromosome and nucleus. 

DNA is chemically less reactive as compared to RNA.
RNA mutate at a faster rate because from DNA, RNA is formed duirng transcription and there are more chances of mutation during this phase.
Saccharin is an artificial sweetener with effectively no food energy which is about 300-400 times as sweet as sucrose.
hnRNA is heterogenous nuclear RNA. Its processing includes addition of a cap. The cap is 5'methyl guanosine that is added immediately after the start of the transcription. This reaction is catalysed by guanylyl transferase.

Carbohydrates are the primary cellular fuel used to derive energy. Fats and proteins are used under starvation when carbohydrates are not available. Vitamins are not a major source of energy but are required as coenzymes for many enzymatic reactions in body metabolism.

Polymerisation is the process by which the simpler units known as monomers attach with the help of chemical bond to form a long chain or branched structure. It helps to produce new chemicals like glycogen, cellulose, fatty acids etc. The complex molecules (e.g. glycogen) are large in size and are unable to cross the semipermeable membrane by the process of osmosis. So they are osmotically inactive. These large size molecules which are used mainly for storage is broken down into simple molecules for metabolic need.  So, the correct answer is option D.

Biochemistry is the study of chemical processes within and relating to living organisms It focuses on understanding how biological molecules give rise to the processes that occur within living cells and between cells which in turn relates greatly to the study and understanding of tissues, organs, and organism structure and function. Biochemical processes give rise to the complexity of life. Hence, the study of the physicochemical nature of bio-molecules is biochemistry.

Galactose is a monosaccharide which is also known as brain sugar. It is an important constituent of glycoprotein and glycolipids.

Carbohydrate, on the basis of the number of molecules present, is divided into monosaccharides, disaccharide and polysaccharides. Fructose is also known as the fruit sugar and is a monosaccharide. It is a 6 carbon molecule. Glycine is the simplest amino acid as it contains hydrogen in the side chain. Lactose is a disaccharide which means it has two molecules of same or different monosaccharide units. Lactose is also known as the milk sugar. 

Macromolecules are the molecules made by the attachment of micro molecule. These are complex molecules. Cellulose, DNA, and glycogen are macromolecules as they are formed by linkage of simple monomers.

Polymerization is the process by which the simpler unit known as monomers attaches with the help of chemical bond to form a long chain or branched structure. It helps to produce new chemicals. It is a process of joining repeating units to form a macromolecule is known as polymerization. For example, proteins are building blocks of the body. The proteins are made up of amino acids. The amino acids are linked together by peptide bonds to form a protein. 

Amino acids are amphoteric compounds having a carboxylic group, amino group, hydrogen and a substituent group bonded to same carbon atom called the $\alpha$-carbon atom. The substituent group may be having one or more carboxylic groups or amino groups. In case the substituent group is having an extra amino group, the amino acid will be having more than one amino groups and will be positively charged at neutral pH and will be a basic amino acid like lysine and arginine.

Enzymes, vitamins and hormones are critical to the central role of these elements in the metabolism. Some enzymes in addition to the proteinaceous part require an additional organic molecule coenzyme. Most of the coenzymes are derived from vitamins. Hormones are chemically a diverse group. They may be amines or steroids or peptides. The hormones regulate body metabolism over a longer duration and slowly effect the developmental changes during the development of an organism. The main difference between the enzyme (coenzyme) and hormones is the time scale of their operation. Both are similar in their role in regulating body metabolism.

Antibodies are the structures that help in maintaining the immunity of the body towards the antigens that are infectious agent whether be it bacteria or viruses.

Isomers are molecules that have the same molecular formula but have a different arrangement of the atoms in space. That excludes any different arrangements which are simply due to the molecule rotating as a whole or rotating about particular bonds. For example, in respiration, 3PGA and 2PGA, PGAL and DHAP, Glucose and Fructose. 

Lecithin is a phosphorylated glyceride. It is a phospholipid with glycerol, fatty acids ,a phosphate group and choline. It is found in the cell membrane. Palmitic acid is a saturated fatty acid with 16 carbon atoms. Adenylic acid is also called as Adenosine monophosphate (AMP). It is an adenosine with a phosphate group and the ribose sugar. It is an ester of phosphoric acid and the adenosine. Alanine is a neutral amino acid. It contains one amino group and one carboxylic group.

The composition of the different organic compounds in the animal body in terms of dry weight is as protein-71%, lipid-12%, nucleic acid-7%,  carbohydrate-5% and inorganic and other materials-5%. These four classes of organic material are important and form the basis of organic constituents in the cell. All these macromolecules except lipids are formed by the process of polymerisation. Due to their large size and complex 3-dimensional shape, these organic biomolecules function as structural components, enzymes, energy sources,molecular messengers, nutrient stores and sources of genetic information. Carbohydrates are polyhyroxyaldehydes or polyhyroxyketones or substances that gives this on hydrolysis. They are classified as monosaccharides, oligosaccharides and polysaccharides. Pentoses and hexoses are the most important sugars. Complex polysaccharides are important components of inter-cellular ground substances. Lipids are major and essential components of biological membranes. They are important dietery components and forms major forms of energy, because of their high calorific value. Protein is a polymer of different amino acids linked together by peptide bonds. Proteins can be fibrous or globular. Structural proteins serve as building materials for cells and tissues. Functional proteins regulate metabolism. Nucleotides, the monomer units of nucleic acids serve many important functions in cells. They store the genetic information in them. They are also primary carriers of chemical energy in cells, structural components of many enzyme cofactors and cellular second messengers. Thus, the four macromolecules play a significant role in performing various cellular functions.

A number of purine bases containing methyl substituents occur in plants and plant products and many of them have pharmacological properties. For example Theophylline is chemically 1,3-dimethylxanthine. It is found in tea. Theobromine occurs in cocoa. It is chemically 3,7-dimethylxanthine. Caffeine is present in coffee. It is chemically 1,3,7-trimethylxanthine.