Nutrients and Nutrition

Parasites are organisms that live inside or on another living organism (the host) and obtain nutrients at the host's expense. Examples include tapeworms, malaria parasites, and fungi like athlete's foot. Saprophytes (option A) feed on dead organic matter, autotrophs (option C) make their own food, and omnivores (option D) eat both plants and animals but don't live inside hosts.

Ingestion is the process of taking food into the body through the mouth - it's the first step of nutrition. Egestion (option A) is eliminating undigested waste, absorption (option B) is nutrients passing into bloodstream, and digestion (option D) is breaking down food. The sequence is: ingestion → digestion → absorption → egestion.

Humans are omnivores because they can digest and obtain nutrition from both plant sources (vegetables, grains, fruits) and animal sources (meat, dairy, eggs). Our digestive system includes enzymes for both plant cellulose breakdown and meat protein digestion. Autotrophs (option A) make their own food, herbivores (option B) eat only plants, and carnivores (option D) eat only meat.

Glucose is the primary form of sugar absorbed into human blood from the digestive tract. During digestion, complex carbohydrates (starch, sucrose, maltose) are broken down into glucose by enzymes. Glucose then enters bloodstream through intestinal walls via active transport and diffusion. Sucrose (option A), maltose (option C), and starch (option D) are too large to be absorbed directly - they must first be converted to glucose.

Photosynthesis produces glucose (a simple carbohydrate) as its primary product, using sunlight, water, and CO2. The glucose can be used immediately for energy, stored as starch, or converted to other carbohydrates like cellulose. While plants can synthesize fats, proteins, and absorb minerals, these are NOT direct products of photosynthesis. The overall reaction is: 6CO2 + 6H2O + light → C6H12O6 (glucose) + 6O2.

Glucose is a monosaccharide, meaning it consists of a single sugar unit and cannot be broken down into simpler carbohydrates. Lactose and sucrose are disaccharides (two sugar units bonded together), while maltose is also a disaccharide formed from two glucose molecules.

Autotrophs are organisms capable of synthesizing their own food using simple inorganic substances, typically through photosynthesis (like green plants) or chemosynthesis. Heterotrophs depend on other organisms for food, herbivores specifically eat plants, and saprophytes feed on dead and decaying organic matter.

Lactose is naturally present in mammalian milk and is commonly referred to as milk sugar. It is a disaccharide composed of glucose and galactose. Maltose is found in germinating grains, sucrose is common table sugar from plants, and glucose is a simple monosaccharide.

Monosaccharides are the simplest carbohydrates because they consist of a single sugar unit that cannot be hydrolyzed into smaller carbohydrates. Examples include glucose, fructose, and galactose. Disaccharides contain two monosaccharide units, while polysaccharides are long chains of many sugar units.

Adipose tissue is specialized connective tissue designed primarily for fat storage. It stores excess energy in the form of triglycerides (fats). Roughage refers to dietary fiber, vitamins are micronutrients needed in small amounts, and minerals are inorganic nutrients - none of which are stored in adipose tissue.

Vegetable oils like olive, sunflower, and canola oil are rich in unsaturated fatty acids, which are liquid at room temperature and considered heart-healthy. Milk and cheese contain mostly saturated fats, while coconut oil is unusually high in saturated fats despite being plant-based.

Fats act as thermal insulators by forming a layer beneath the skin that helps maintain body temperature and prevents heat loss. This is why marine mammals and animals in cold climates have thick fat layers (blubber). Carbohydrates and proteins primarily provide energy and building materials, while vitamins regulate various metabolic processes.

Oranges and other citrus fruits are excellent sources of vitamin C (ascorbic acid), containing approximately 50-60mg per 100g serving. While potatoes, spinach, and carrots contain some vitamin C, their concentrations are significantly lower. Citrus fruits are renowned for their high vitamin C content.

Vitamin D is uniquely synthesized in human skin when 7-dehydrocholesterol reacts with UVB radiation from sunlight, forming previtamin D3 which then converts to active vitamin D. No other vitamin is produced in this manner - vitamins A, B12, and C must be obtained from dietary sources.

Scavengers are organisms that feed on dead animals that they did not kill themselves. Examples include vultures, hyenas, and some insects. Herbivores eat plants, carnivores hunt and kill live prey, and omnivores eat both plants and animals - none of these specifically characterize consumers of dead animals.

Fats serve multiple crucial functions: they provide concentrated energy (9 kcal/g), support brain development (especially in infants), and are essential for hormone production (including steroid hormones). Blood clotting is primarily mediated by platelets and clotting factors (dependent on vitamin K), not fats - making this the correct exception.

Iodine is an essential component of thyroid hormones T3 (triiodothyronine) and T4 (thyroxine), which regulate metabolism, growth, and development. Iodine deficiency causes goiter (thyroid enlargement). Phosphorus is important for bones and ATP, sodium for nerve impulses, and calcium for bones and muscle function - but none are specifically required for thyroid hormone synthesis.

Iron is the central component of haemoglobin, the pigment that gives red blood cells their red colour and enables oxygen transport. Each haemoglobin molecule contains four iron atoms that bind to oxygen molecules. Phosphorus, potassium and magnesium are essential minerals but they do not form part of haemoglobin structure.

Vitamin K is essential for the synthesis of clotting factors in the liver, including prothrombin and factors II, VII, IX and X. Without adequate vitamin K, blood cannot clot properly, leading to excessive bleeding. Reproduction is controlled by hormones, while carbohydrate and amino acid metabolism involve different vitamin complexes.