Nutrition Study Guide

📖 Core Concepts Nutrition – biochemical/physiological process using food + water to supply energy & building blocks; imbalance → malnutrition. Nutrients – substances (elements or macromolecules) that provide energy & structural components for survival, growth, reproduction. Macronutrients vs. Micronutrients – required in large amounts (carbs, protein, fat) vs. trace amounts (vitamins = organic, minerals = inorganic). Essential vs. Nonessential – essential cannot be synthesized by the body; must be obtained from diet. Nonessential can be made from other compounds. Autotrophs / Heterotrophs / Mixotrophs – carbon source: CO₂ (autotroph), other organisms (heterotroph), both (mixotroph). Energy vs. Nutrient Flow – energy flows one‑way, non‑cyclic; mineral nutrients cycle through biogeochemical loops. Optimal Foraging Theory – organisms maximize nutrient gain per unit time/energy spent (cost‑benefit analysis). 📌 Must Remember 30 elements in organic matter; N, C, P are most critical. Caloric values: carbohydrate = 4 kcal g⁻¹, protein = 4 kcal g⁻¹, fat = 9 kcal g⁻¹. 1 Calorie (kcal) raises 1 kg of water by 1 °C. Overnutrition of macronutrients → obesity, type 2 diabetes, cardiovascular disease, certain cancers. Deficiency signs: blindness (vit A), anemia (iron), scurvy (vit C), preterm birth/cretinism (multiple micronutrients). Daily Reference Values (DRVs) – recommended intake ranges for average healthy people; used on food labels. Liebig’s law of the minimum – growth limited by the scarcest nutrient. 🔄 Key Processes Nutrient Acquisition Animals → ingestion of other organisms. Plants → absorb inorganic ions from soil & CO₂ from atmosphere. Fungi → extracellular enzyme breakdown → uptake via mycelium. Metabolic Utilization Absorption → precursor metabolites → biosynthetic reactions → polymerization → assembly of cellular structures. Photosynthesis (Plants) Light energy → chloroplasts → convert CO₂ + H₂O → glucose + O₂. Optimal Foraging Decision Calculate energy gain / (search time + handling time) → choose prey/resource with highest ratio. 🔍 Key Comparisons Autotroph vs. Heterotroph – CO₂ fixation vs. consumption of organic carbon. Phototroph vs. Chemotroph – energy from light vs. chemical compounds. Organotroph vs. Lithotroph – electrons from organic matter vs. inorganic substances (e.g., H₂S, Fe²⁺). Prototroph vs. Auxotroph – can synthesize all essentials vs. must obtain one or more from the environment. Specialist vs. Generalist Forager – single food source specialization vs. broad diet flexibility. ⚠️ Common Misunderstandings “All vitamins are micronutrients” – true, but not all micronutrients are vitamins (minerals are also micronutrients). “More calories always mean better nutrition” – excess calories cause overnutrition; quality of macronutrient sources matters. “Plants get nitrogen directly from air” – most rely on soil nitrogen (ammonium/nitrate) supplied by bacterial fixation. “Energy flow is cyclic” – it is unidirectional; only nutrients cycle. 🧠 Mental Models / Intuition “Supply‑and‑Demand” – think of nutrients like currency: essential nutrients are mandatory payments; nonessential are optional purchases. “Cost‑Benefit Balance Sheet” for foraging: each food item = profit (nutrients) – cost (search + handling). “Building Blocks” – nutrients → precursors → polymers → functional structures, analogous to LEGO bricks building a model. 🚩 Exceptions & Edge Cases Mixotrophs – can switch between autotrophic and heterotrophic modes (e.g., carnivorous plants). Auxotrophic microbes – may acquire essential nutrients from host or environment, influencing symbiotic relationships. Overnutrition of specific micronutrients (e.g., iron overload) can be toxic despite being essential. 📍 When to Use Which Identify nutrient source: if organism obtains carbon from CO₂ → label autotroph; if from food → heterotroph. Choose energy acquisition label: presence of chloroplasts or light‑absorbing pigments → phototroph; otherwise chemotroph. Classify trophic strategy: if electron donor is organic → organotroph; if inorganic (H₂S, Fe²⁺) → lithotroph. Apply foraging model: use optimal foraging calculations when asked to compare two food patches or predict diet breadth. 👀 Patterns to Recognize Triad of nutrient needs in any organism: carbon source, energy source, electron source. Cyclic vs. Linear – nutrient cycles always involve a return to the environment; energy diagrams end with heat loss. Deficiency → Specific Clinical Signs – match vitamin/mineral lacking to hallmark symptom (e.g., scurvy ↔ vitamin C). Caloric density pattern – fats ≈ double the calories of carbs/proteins → watch for high‑fat foods in obesity questions. 🗂️ Exam Traps “All organisms need sunlight” – only phototrophs; many bacteria/fungi are chemotrophs. “Micronutrients are only vitamins” – ignores minerals; both are micronutrients. Confusing “overnutrition” with “overfeeding” – overnutrition specifically refers to excess of macronutrients leading to metabolic disease, not just caloric surplus. Mistaking “mixotroph” for “heterotroph” – mixotrophs can also photosynthesize; answer choices that omit this dual capability are wrong. Assuming nitrogen fixation is universal in plants – most rely on soil nitrogen; only legume–rhizobia symbioses fix atmospheric N₂. --- If any section lacked sufficient detail from the source outline, a placeholder has been inserted, but the outline provided ample information for all headings.