🧬 Nucleic Acids, Enzymes, Vitamins, and Lipids

Why These Biomolecules Matter in Agriculture

When a plant pathologist uses PCR to detect a virus in a potato sample, the technique relies on the biochemistry of nucleic acids. When a seed scientist tests lipase activity to assess seed viability, they are measuring enzyme function. When a nutritionist promotes biofortified crops rich in Vitamin A (golden rice, orange-fleshed sweet potato), they are applying knowledge of vitamins. And when an oilseed breeder improves the fatty acid profile of mustard, they are working with lipids. These four biomolecule classes underpin much of agricultural science.

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Enzymes

Enzymes are special classes of proteins that act as biological catalysts — they speed up chemical reactions without being consumed.

Feature	Detail
First enzyme discovered	Payen (diastase / amylase-related activity, 1833)
First enzymatic activity discovered by	Buchner (Zymase from yeast — the first enzyme found)
Term "enzyme" coined by	W. Kuhne (1878)
Lock and key model	Proposed by Fisher; introduced by Koshland

• A classic milestone in enzyme chemistry is the work of J.B. Sumner (1926), who purified and crystallized urease. This helped establish that enzymes are fundamentally proteinaceous in nature, apart from later-recognized catalytic RNAs such as ribozymes.
• In standard history recall, the discovery of catalytic RNA is linked with Altman and Cech, which is why a ribozyme is remembered as the exceptional catalytic molecule that is not a protein.

Characteristics of Enzymes

• Specific, proteinaceous, colloidal in nature.
• Sensitive to temperature and pH (each enzyme has an optimum).
• Often described as thermolabile and amphoteric because their protein nature makes them heat-sensitive and capable of acid-base behavior.
• Do not change the equilibrium of a reaction — only speed it up.
• Work by lowering the activation energy.
• Required only in very small quantities and generally regain their original state after the reaction cycle.
• In enzyme classification language, a hydrolase catalyzes bond cleavage by the addition of water, so enzymes such as amylase, lipase, and trypsin are all examples of hydrolytic enzymes acting on starch, fats, and proteins respectively.
• In ATP-linked biosynthetic reactions, enzymes named synthetases or ligases are classically described as joining two molecules together with energy input from ATP hydrolysis. A standard agricultural biochemistry example is glutamine synthetase, a key enzyme in the assimilation of ammonia into organic form.

Agricultural example: Amylase enzymes in germinating barley break down starch into maltose — the basis of the malting industry. Cellulase enzymes are used in biofuel production from crop residues. Lipase activity in stored oilseeds indicates rancidity (important for seed quality testing).

• The idea of an optimum pH becomes very intuitive when digestion enzymes are compared: pepsin works best in the strongly acidic environment of the stomach, whereas trypsin functions best under alkaline conditions in the intestine.
• In basic enzyme kinetics, the rate first rises as substrate concentration increases, but then approaches a limit when the available enzyme molecules become saturated. This classical relationship is described as a rectangular-hyperbola type curve in introductory biochemistry.

Factors Affecting Enzyme Activity

• Substrate concentration: reaction rate rises first and then levels off once all active sites become occupied.
• Enzyme concentration: increasing enzyme amount raises the rate only while substrate remains available in excess.
• Temperature: the classical recall is Q10 ≈ 2, meaning the rate often roughly doubles for each 10°C rise within the workable range; many introductory notes place the optimum range around 30-40°C, while many enzymes are strongly inactivated above about 55-60°C.
• pH: many enzymes work best near a moderate range around pH 7-8, but important exceptions include pepsin at low pH and trypsin under alkaline conditions.
• Water: low moisture suppresses enzyme action in dry seeds, whereas hydration during germination activates enzyme systems.
• Inhibitors and activators: chemical environment can either suppress or enhance catalysis.
• A standard agricultural example is glyphosate, which inhibits EPSP synthase in the shikimate pathway, disrupting aromatic-amino-acid synthesis and thereby killing susceptible weeds.

Apoenzyme, Cofactor, Coenzyme, and Holoenzyme

• Many enzymes work as a combined system rather than as protein alone.
• The protein part of an enzyme is called the apoenzyme.
• The required non-protein helper is called a cofactor.
• When the cofactor is an organic molecule that associates loosely with the enzyme, it is called a coenzyme. Common examples include NAD, NADP, and ATP.
• When the non-protein component remains tightly bound to the enzyme, it is commonly described as a prosthetic group.
• In many enzyme systems, the required helper may also be a metal activator such as Fe, Mg, Mn, or Zn, which is why cofactors are not limited to organic coenzymes alone.
• When the apoenzyme is combined with its required cofactor, the complete active unit is called a holoenzyme.

Term	Meaning
Apoenzyme	Protein part alone; inactive by itself in many enzyme systems
Cofactor	Non-protein component needed for enzyme activity
Coenzyme	Organic cofactor, often vitamin-derived and loosely bound
Prosthetic group	Non-protein component that is tightly bound to the enzyme
Holoenzyme	Complete active enzyme = apoenzyme + cofactor

Specificity of Enzymes

Type of specificity	Meaning	Classical example
Absolute specificity	Acts on a single substrate only	Urease acting on urea
Group specificity	Acts on a group of related substrates with similar bonds	Amylase acting on starch-like alpha-linked glucans
Optical specificity	Distinguishes between stereochemical forms	Maltase acting on the alpha but not the beta glycosidic form

Simple vs Conjugated Enzymes

• Simple enzymes are composed only of protein. Common recall examples include trypsin, pepsin, amylase, and urease.
• Conjugated enzymes require a protein part plus a non-protein component, which connects directly with the apoenzyme-cofactor-holoenzyme framework above.

Inducible vs Constitutive Enzymes

• Inducible enzymes appear mainly in the presence of their relevant substrate or signal. A standard plant example is nitrate reductase.
• Non-inducible / constitutive enzymes are produced more continuously as part of the cell's basic metabolic machinery.

Six Major Enzyme Classes

The International Union of Biochemistry (IUB) grouped enzymes into six major classes.

Class	Main role	Classical examples
Oxidoreductases	Catalyze oxidation-reduction reactions	Alcohol dehydrogenase, peroxidase, cytochrome oxidase, nitrate reductase
Transferases	Transfer functional groups between molecules	Hexokinase
Hydrolases	Break bonds with the addition of water	Invertase / sucrase, amylase, lipase, phosphatase, pepsin, trypsin
Lyases	Remove groups without hydrolysis, often forming double bonds	Carboxylase, aldolase, fumarase
Isomerases	Interconvert optical, positional, or geometrical isomers	Retinene isomerase
Ligases	Join molecules using energy from high-energy bonds	Glutamine synthetase, DNA ligase

Mechanism of Enzyme Action

• The active site is the region of an enzyme where the substrate binds and catalysis occurs.
• The transient intermediate stage between substrate and product is called the transition state.
• Activation energy is the minimum energy needed for substrate molecules to reach that transition state.
• Reaction rate increases as activation energy falls, which is why enzymes accelerate reactions by providing a lower-energy pathway.
• The classical lock-and-key model is linked with Emil Fischer (1894), while the induced-fit hypothesis was proposed by Koshland (1959).
• Isoenzymes / isozymes are multiple molecular forms of an enzyme that catalyze the same reaction within a species or even within a single cell type; lactate dehydrogenase is the standard example.

Vitamins as Cofactors and Coenzymes

• Many vitamins function as parts of coenzymes, which help enzymes transfer electrons, carbon groups, or other chemical fragments.
• Biotin is especially important in carboxylation reactions and is a classic example of a vitamin acting through coenzyme function.
• In direct vitamin-biochemistry recall, pantothenic acid is linked with coenzyme A (CoA), while niacin is linked with the electron-transfer coenzymes NAD and NADP.
• The language of metabolites, pathways, and coenzymes is central to biochemistry because enzymes do not act in isolation; they act inside linked metabolic networks.

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Vitamins

• The term vitamin was introduced by Casimir Funk (1912).
• Vitamins mainly act as cofactors for enzymatic activity.
• Vitamins are required only in small quantities for proper growth and development, and unlike carbohydrates, fats, or proteins, they do not themselves provide energy.
• In standard agricultural biochemistry classification, the sulphur-containing vitamins are commonly identified as thiamine and biotin.
• Niacin is classically linked with tryptophan because it can be synthesized from tryptophan in the body.
• Among the B-complex vitamins, vitamin B12 is the one classically noted for containing cobalt.
• Vitamin A is classically associated with the early discovery work of McCollum and Davis (1913).
• Introductory nutrition recall commonly treats the total number of well-defined vitamins as 13.
• Vitamins C and E are the standard antioxidant-vitamin recall pair.
• Vitamin D is often described as functioning in a hormone-like manner, and its active physiological form is remembered as calcitriol.

Classification of Vitamins

Type	Vitamins	Key Feature
Water soluble	Vitamin B complex & Vitamin C	Excreted easily; not stored in body
Fat soluble	Vitamin A, D, E, K	Stored in body fat and liver

Agricultural connection: Biofortification breeding programmes target vitamin content in crops:

• Vitamin A → Golden Rice (beta-carotene enriched), orange-fleshed sweet potato
• Vitamin C → Amla (Indian gooseberry), guava
• Vitamin E → Sunflower and wheat germ oil

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Nucleic Acids

Nucleic acids are polymers of nucleotides joined by phosphodiester bonds.

Functions:

1. Transmission of hereditary characters from parents to offspring.
2. Synthesis of proteins.

Types: DNA (Deoxyribose Nucleic Acid) and RNA (Ribose Nucleic Acid).

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Components of Nucleic Acids

Component	Examples
Sugar	Ribose (RNA) or Deoxyribose (DNA)
Phosphate group	Phosphoric acid
Nitrogenous bases	Purines (A, G) and Pyrimidines (T, C, U)

Term	Definition
Nucleoside	Sugar + Nitrogenous base
Nucleotide	Nucleoside + Phosphate group

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Nitrogenous Bases

Type	Bases	Ring Structure
Purines	Adenine (A), Guanine (G)	Double ring
Pyrimidines	Thymine (T), Cytosine (C), Uracil (U)	Single ring

Base Pairing Rules (Chargaff's Rules):

• Adenine (A) pairs with Thymine (T) — 2 hydrogen bonds
• Guanine (G) pairs with Cytosine (C) — 3 hydrogen bonds
• In RNA, Thymine is replaced by Uracil (A pairs with U)

Mnemonic: Pure As Gold = Purines are Adenine and Guanine.

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DNA (Deoxyribonucleic Acid)

Feature	Detail
Sugar	Deoxyribose (pentose)
Location	Nucleus, Chloroplast, Mitochondria
Function	Protein synthesis; hereditary material
Status	Hereditary material in almost all organisms

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RNA (Ribonucleic Acid)

Feature	Detail
Sugar	Ribose
Location	All living cells (mostly in cytoplasm)
Function	Coding, decoding, gene expression; protein synthesis via translation

Types of RNA

Type	Full Name	Function
tRNA	Transfer RNA	Carries amino acids to ribosome
mRNA	Messenger RNA	Carries genetic code from DNA to ribosome
rRNA	Ribosomal RNA	Structural component of ribosomes (most abundant)

Agricultural relevance: RNA viruses cause many major crop diseases — rice tungro, tomato spotted wilt, potato virus Y. Detection of these viruses using RT-PCR (Reverse Transcriptase PCR) is based on understanding RNA structure.

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Lipids

Lipids are organic compounds containing hydrogen, carbon, and oxygen atoms that form the structural framework of cell membranes and serve as energy reserves.

• Lipids are defined as esters of glycerol and fatty acids (triglycerides).
• In practical chemical definition, lipids are insoluble or only sparingly soluble in water but dissolve readily in non-polar solvents such as chloroform or benzene.
• Include: fats, waxes, sterols, fat-soluble vitamins, monoglycerides, and phospholipids.
• Because lipids are highly reduced energy-storage molecules, they supply far more energy per unit weight than carbohydrates or proteins.
• In practical nutrition recall, the gross calorific value sequence is commonly stated as fat (about 9.45 kcal/g) > protein (about 5.65 kcal/g) > carbohydrate (about 4.1 kcal/g).
• The more physiologically used energy values are usually remembered as fat 9 kcal/g, carbohydrate 4.1 kcal/g, and protein 4 kcal/g.
• This is why fats are commonly described as supplying a little more than twice as much energy per unit weight as carbohydrates or proteins.
• Fats and oils also have a lower specific gravity than water, which is why they typically float on water.
• Lipids are also important for the absorption of fat-soluble vitamins, especially A, D, E, and K, and for the formation of steroid hormones.

Types of Lipids

In classical biochemistry classification, lipids are often grouped as simple lipids, compound lipids, and derived lipids. This older framework is still useful because it separates reserve fats from membrane lipids and from lipid-derived components.

Type	Composition	Key Role
Triglycerides	Glycerol + 3 fatty acids	Energy storage (oils in seeds)
Phospholipids	2 fatty acids + Glycerol + Phosphate group	Cell membrane structure (polar lipids)
Glycolipids	Glycerol + Fatty acids + Carbohydrates	Cell recognition

• Simple lipids are chiefly neutral fats and waxes, built mainly from fatty acids esterified with alcohols.
• In older classification language, these reserve fats and waxes are often grouped under simple / neutral lipids and treated as the main saponifiable storage lipids.
• Compound lipids include phospholipids and glycolipids, where the basic lipid unit is combined with phosphate or carbohydrate groups.
• In the same older wording, compound / complex lipids are also treated as saponifiable lipids because they still contain hydrolysable fatty-acid linkages.
• Derived lipids refers to lipid-derived substances such as fatty acids, sterols, and related hydrolysis products that arise from or function alongside the major lipid classes.

Agricultural connection: The oil content and fatty acid composition of oilseed crops (groundnut, mustard, sunflower, soybean) are primary breeding targets. High oleic acid varieties are preferred for better shelf life and heart health.

Waxes and Lipid Storage Examples

• Waxes differ from ordinary triglyceride fats because they are formed from long-chain fatty acids combined with long-chain monohydric alcohols, rather than with glycerol.
• This is why waxes usually serve more protective or surface-related roles, while triglycerides are the dominant reserve lipids in seeds and many storage tissues.
• A classic natural example is beeswax, which contains myricyl palmitate.
• In agriculture-linked examples, jojoba oil is often discussed as a liquid wax rather than a typical edible oil.
• In many oil-bearing plants, reserve lipids are concentrated in the seed endosperm, while oil palm is a useful contrast because oil occurs both in the mesocarp (palm oil) and in the kernel/endosperm (palm kernel oil).
• In compact edible-oil recall, coconut oil is classically associated with a high proportion of lauric acid.
• In compact edible-oil recall, palm oil is classically associated with a relatively high proportion of palmitic acid.
• Among animal sterols, cholesterol is the standard major example, and it is commonly recalled as a precursor for vitamin D, estrogen, and testosterone.
• Hydrolysis of fats is catalyzed by lipase, the standard enzyme recall paired with lipid breakdown.

Fatty Acids: Saturated vs Unsaturated

Type	Key feature	Agriculture relevance
Saturated fatty acids	No double bonds	Usually more stable and less reactive
Unsaturated fatty acids	One or more double bonds	Important for edible oil quality, nutrition, and oxidative stability

• As a broad physical trend, fats richer in saturated fatty acids tend to be more solid at room temperature, whereas oils richer in unsaturated fatty acids tend to remain more liquid at room temperature.
• In the same simple contrast, fats are usually described as solid at room temperature, whereas oils are liquid because of their higher unsaturation.
• In direct fatty-acid recall, the classic saturated fatty acid examples are lauric, myristic, palmitic, and stearic acid. These are commonly used as reference examples when contrasting solid fats with more unsaturated edible oils.
• In direct unsaturated-fatty-acid examples, oleic, erucic, linoleic, linolenic, and arachidonic acid are the standard names students are expected to recognize quickly.
• Monounsaturated fatty acids (MUFA) carry a single double bond; the standard recall examples are oleic acid and erucic acid.
• When two or more double bonds are present, the fatty acid is described as polyunsaturated (PUFA). In this exam-oriented context, linoleic acid and alpha-linolenic acid are the most familiar plant-linked examples.
• In compact PUFA examples, linoleic, linolenic, and arachidonic acid are the usual trio.
• In direct fatty-acid nomenclature recall, alpha-linolenic acid is classically treated as an omega-3 fatty acid, while linoleic acid is treated as an omega-6 fatty acid.
• Among the unsaturated fatty acids encountered in introductory notes, oleic acid and linoleic acid are often highlighted as especially abundant in nature.
• Arachidonic acid is also remembered as the major biochemical precursor for prostaglandins.
• In food-processing terms, hydrogenation adds hydrogen across the double bonds of unsaturated fatty acids, converting a more liquid oil into a more solid fat; this is the classical logic behind products such as vanaspati.
• In practical nutrition and food-processing discussions, partial hydrogenation is also linked with the formation of trans fats, which are generally considered undesirable because they worsen the health profile of the final fat.
• In practical industrial-agriculture recall, linseed oil is the classic drying oil used in paints and varnishes.

Oil Quality Constants and Rancidity

• Stored fats and oils are also judged by a few standard chemical constants that reflect chain length, unsaturation, and deterioration.

Constant	What it measures	Practical meaning
Saponification value	Milligrams of KOH required per gram of fat or oil	Higher values are associated with fats containing relatively shorter-chain fatty acids
Iodine value	Grams of iodine absorbed by 100 g of fat or oil	Indicates the degree of unsaturation; higher value means more double bonds
Reichert-Meisel (R.M.) value	Millilitres of 0.1 N alkali needed to neutralize the water-soluble steam-volatile fatty acids from a standard fat sample	Useful in dairy-fat analysis; a fall in R.M. value can indicate adulteration of butter or ghee with non-milk fat
Polenske value	Millilitres of 0.1 N alkali needed to neutralize the water-insoluble steam-volatile fatty acids from a standard fat sample	Complements the R.M. value when characterizing fats containing volatile fatty-acid fractions
Acid value	Milligrams of KOH required to neutralize the free fatty acids in 1 g of fat or oil	Reflects the amount of free fatty acids formed during decomposition or storage

• An increase in free fatty acids usually means the oil is undergoing hydrolytic deterioration.
• For this reason, a rising acid value is used as a practical indicator of rancidity in stored fats and oils.

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Vitamins — Deficiency Diseases and Agricultural Sources

Vitamin	Chemical Name	Deficiency Disease	Rich Agricultural Source
Vitamin A	Retinol	Night blindness, Xerophthalmia	Carrot, Papaya, Mango
Vitamin B₁	Thiamine	Beriberi	Whole grains, Legumes
Vitamin B₂	Riboflavin	—	Almonds, mushrooms, leafy vegetables
Vitamin B₃	Niacin	Pellagra	Groundnut, Meat
Vitamin B₆	Pyridoxine	—	Avocado, poultry, fish
Vitamin B₇	Biotin	—	Walnut, peanut, egg yolk
Vitamin B₉	Folic acid	Megaloblastic anaemia	Green leafy vegetables, Pulses
Vitamin B₁₂	Cyanocobalamin	Pernicious anaemia	Fish, eggs, poultry, meat, dairy products
Vitamin C	Ascorbic acid	Scurvy	Amla, Citrus, Guava
Vitamin D	Calciferol	Rickets, Osteomalacia	Sunlight, Fish liver oil
Vitamin E	Tocopherol	Reproductive failure	Vegetable oils, Wheat germ
Vitamin K	Phylloquinone	Haemorrhage	Green leafy vegetables, Soybean

• Vitamin D can be synthesized in the skin when it is exposed to UV-B sunlight, which is why sunlight itself is treated as a physiologically important source.
• Severe deficiency states are often summarized as impaired red-blood-cell or haemoglobin status in the anaemia-linked vitamins, especially folate and B₁₂.
• Raw egg white can contribute to biotin deficiency because the protein avidin binds biotin strongly and reduces its availability.
• In enzyme-measurement recall, the SI unit of enzyme activity is the katal (kat).
• In amino-acid analysis, the classical color reaction used for quantitative estimation is the ninhydrin test.

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Primary and Secondary Plant Metabolites

• Primary metabolites are compounds directly required for normal growth, development, and core metabolism. Carbohydrates, proteins, lipids, and nucleic-acid related intermediates fall into this basic metabolic category.
• Secondary metabolites are organic compounds that are not directly part of the plant's primary growth processes, but they are still biologically important in defence, signalling, stress response, and ecological interaction.
• Secondary metabolites are often synthesized when plants respond to pathogens, herbivores, environmental stress, or interactions with other organisms.
• In plant-defence language, such responses are often initiated by elicitor signals, which stimulate the plant to activate defence pathways and increase the production of protective secondary metabolites.

Group	Common examples	Main ecological or practical role
Alkaloids	Nicotine, caffeine, quinine, atropine, morphine, codeine, cocaine	Defence, medicinal use, physiological activity
Phenolics	Anthocyanins, tannins, lignin, coumarins	Pigmentation, defence, structural support, aroma
Terpenoids	Essential oils, resins, carotenoid-related compounds	Defence, attraction, fragrance, plant protection

• In plants, many phenolic compounds arise through the shikimate pathway or through the acetate-malonate pathway.
• Lignin is built from aromatic alcohol units such as p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, and contributes to rigidity and mechanical support in plant tissues.
• The classic medicinal example of an alkaloid is quinine, obtained from the bark of the Cinchona tree.
• Tannins are astringent phenolic compounds and are classically associated with the tanning of animal hides into leather.
• Coumarin is a phenolic compound associated with the characteristic aroma of freshly cut grasses.
• Additional source-use recalls often paired with alkaloids include atropine from belladonna, reserpine from Rauvolfia serpentina, and the anticancer compounds vinblastine / vincristine from Catharanthus roseus (periwinkle).
• A classic economic example of a plant isoprenoid product is natural rubber from the latex of Hevea brasiliensis.

Dietary Fibre

• Defined as the sum of lignin and polysaccharides that are not digested by human digestive enzymes.
• Important for digestive health.

Agricultural note: High-fibre crops include whole grains (oats, barley), pulses, and millets. Breeding for appropriate fibre content is important for both human nutrition and animal fodder quality.

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Summary Cheat Sheet

Concept / Topic	Key Details
Enzyme definition	Biological catalysts; special class of proteins
First enzymatic activity	Discovered by Buchner (Zymase from yeast)
Term "enzyme" coined by	W. Kuhne (1878)
Lock and key model	Proposed by Fisher; introduced by Koshland
Enzymes work by	Lowering activation energy; do NOT change equilibrium
Enzyme nature	Proteinaceous, colloidal, specific to substrate
Apoenzyme	Protein part of an enzyme
Cofactor	Non-protein component required for activity
Coenzyme	Organic cofactor such as NAD, NADP, ATP
Metal activator examples	Fe, Mg, Mn, Zn
Holoenzyme	Complete active enzyme = apoenzyme + cofactor
Term "vitamin" coined by	Funk
Vitamins act as	Cofactors for enzymatic activity
Biochemistry term introduced by	Carl Neuberg (1903)
Vitamin especially linked with coenzyme role in carboxylation	Biotin
Fat-soluble vitamins	A, D, E, K (mnemonic: ADEK)
Water-soluble vitamins	B complex & C; excreted easily, not stored
Sulphur-containing vitamins	Thiamine and Biotin
Nucleic acids	Polymers of nucleotides joined by phosphodiester bonds
Nucleoside	Sugar + Nitrogenous base
Nucleotide	Nucleoside + Phosphate group
Purines	Adenine (A) & Guanine (G) — double ring
Pyrimidines	Thymine (T), Cytosine (C), Uracil (U) — single ring
A–T base pairing	2 hydrogen bonds
G–C base pairing	3 hydrogen bonds
RNA vs DNA bases	Uracil replaces Thymine in RNA
DNA sugar & location	Deoxyribose; in nucleus, chloroplast, mitochondria
DNA function	Hereditary material; protein synthesis
tRNA	Carries amino acids to ribosome
mRNA	Carries genetic code from DNA to ribosome
rRNA	Structural component of ribosomes; most abundant RNA
Lipids definition	Esters of glycerol and fatty acids (triglycerides)
Gross calorific value order	Fat > Protein > Carbohydrate
Physiological fuel values	Fat 9 kcal/g; Carbohydrate 4.1 kcal/g; Protein 4 kcal/g
Phospholipids	2 fatty acids + glycerol + phosphate; form cell membranes
Saturated fatty acids	No double bonds
Unsaturated fatty acids	One or more double bonds
Waxes	Long-chain fatty acids + long-chain monohydric alcohols
Classic liquid wax example	Jojoba oil
Oil palm storage contrast	Oil in mesocarp and kernel/endosperm
Saponification value	mg of KOH needed per gram of fat/oil
Iodine value	Measure of the degree of unsaturation
Acid value	Measure of free fatty acids and storage deterioration
Fats and oils in water	Usually float because their specific gravity is lower than water
Dietary fibre	Lignin + non-digestible polysaccharides
Vitamin A deficiency	Night blindness, Xerophthalmia — source: Carrot, Papaya, Mango
Vitamin B₁ deficiency	Beriberi — source: Whole grains, Legumes
Vitamin B₃ deficiency	Pellagra — source: Groundnut, Meat
Vitamin C deficiency	Scurvy — richest source in India: Amla
Vitamin D deficiency	Rickets, Osteomalacia — source: Sunlight
Vitamin K deficiency	Haemorrhage — source: Green leafy vegetables, Soybean
Vitamin D synthesis	Skin can synthesize it on exposure to UV-B sunlight
Raw egg white and biotin	Avidin binds biotin and can reduce its availability
SI unit of enzyme activity	Katal (kat)
Quantitative amino-acid test	Ninhydrin test
Secondary metabolites	Compounds important in defence, signalling, and stress response
Major secondary-metabolite groups	Alkaloids, Phenolics, Terpenoids
Quinine source	Cinchona bark
Tannin	Astringent phenolic used in tanning leather
Coumarin	Phenolic compound linked with freshly cut grass aroma
Lignin	Structural phenolic polymer contributing rigidity to plant tissues