| Glucose | Monosaccharide | C6H12O6 | Primary energy source; carbon backbone | Photosynthesis, polysaccharide hydrolysis | Glycolysis, glycogen/starch synthesis |
| Fructose | Monosaccharide | C6H12O6 | Energy source; sugar transport form in plants | Sucrose hydrolysis, photosynthesis | Glycolysis, fructans |
| Sucrose | Disaccharide | C12H22O11 | Transport sugar in plants/algae | Photosynthesis in source tissues | Energy in sink tissues |
| Maltose | Disaccharide | C12H22O11 | Intermediate in starch breakdown | Amylase activity | Glucose |
| Starch | Polysaccharide | (C6H10O5)n | Plant/algal energy storage polymer | Photosynthesis, glucose polymerization | Glucose via amylases |
| Glycogen | Polysaccharide | (C6H10O5)n | Fungal/animal energy storage polymer | Glucose polymerization | Glucose via glycogenolysis |
| Cellulose | Structural polysaccharide | (C6H10O5)n | Plant/algal/fungal cell walls | UDP-glucose | Microfibrils, glucose |
| Lignin | Aromatic polymer | C9H10O2 units | Plant structural polymer; recalcitrant C | Monolignol biosynthesis | Phenolics, humus |
| Chitin | Structural polysaccharide | (C8H13O5N)n | Fungal/insect cell walls | UDP-N-acetylglucosamine | N-acetylglucosamine monomers |
| Fatty acids (saturated) | Lipid | Variable | Membrane components, energy storage | Acetyl-CoA | Triacylglycerols, phospholipids |
| Fatty acids (unsaturated) | Lipid | Variable | Membrane fluidity, signaling | Acetyl-CoA + desaturation | Membrane lipids, oxylipins |
| Triacylglycerol (TAG) | Lipid | Glycerol + 3 fatty acids | Energy storage lipid | Fatty acid synthesis, glycerol | Fatty acids via lipases |
| Phospholipids | Lipid | Glycerol + 2 fatty acids + phosphate | Membrane bilayer structure | Fatty acid + glycerol + phosphate | Membranes, signaling lipids |
| Sterols (ergosterol, cholesterol) | Lipid | C28–C27 sterol skeleton | Membrane fluidity, precursors to hormones | Isoprenoid biosynthesis | Hormones, vitamin D |
| Carotenoids (β-carotene, lutein) | Isoprenoid pigment | C40Hx | Photoprotection, antioxidants | Isoprenoid pathway | Vitamin A, photoprotective pigments |
| Alkaloids (caffeine, nicotine) | Nitrogenous secondary metabolite | Variable | Defense, signaling | Amino acid-derived pathways | Plant defense, allelopathy |
| Phenolic acids (ferulic, gallic) | Aromatic acids | Variable | Antioxidants, antimicrobial | Phenylpropanoid pathway | Lignin, tannins |
| Tannins | Polyphenolic polymer | Variable | Antimicrobial, protein binding | Phenolic acid polymerization | Humus, complexed proteins |
| Flavonoids | Polyphenolic secondary metabolite | Variable | Antioxidant, UV protection | Phenylpropanoid + acetate pathway | Pigments, antioxidants |
| Terpenes (monoterpenes, sesquiterpenes) | Isoprenoid secondary metabolite | C10–C15 hydrocarbons | Volatile signals, defense | Isoprenoid pathway | Aroma, allelopathic compounds |
| Organic acids (citric, malic, oxalic) | Carboxylic acids | Variable | pH buffering, chelation, metabolic intermediates | Respiration, fermentation | CO2, chelated minerals |
| Amino acids | Organic nitrogen compounds | Variable | Protein building blocks, metabolism | Nitrogen assimilation | Proteins, secondary metabolites |
| Peptides | Organic nitrogen compounds | Variable | Signaling, antimicrobial activity | Ribosomal/non-ribosomal synthesis | Functional proteins, degradation products |
| Proteins | Polymers of amino acids | Variable | Enzymes, structural, signaling | Translation | Functional cellular components |
| Nucleotides (ATP, GTP, CTP, UTP) | Nucleic acid monomers | Variable | Energy, nucleic acid synthesis | Nucleotide biosynthesis | RNA, DNA, signaling nucleotides |
| Nucleic acids (DNA, RNA) | Polynucleotide | Variable | Genetic information storage & expression | Nucleotide polymerization | Transcription, translation products |
| Lipopolysaccharides (LPS) | Glycolipid | Lipid A + core + O-antigen | Structural outer membrane in Gram-negative bacteria | Fatty acids, sugars | Outer membrane structure |
