Nutrition in Animals-III

Starch is a polysaccharide that requires breakdown into simpler sugars before absorption. It must first be digested by salivary and pancreatic amylase into maltose, then further broken down by maltase into glucose. Lactose (a disaccharide) only requires lactase, while glucose and fructose are monosaccharides that can be absorbed directly without digestion.

Vitamins are essential organic compounds that the body requires in small amounts for normal metabolic functioning, enzyme activity, and tissue maintenance. Unlike macronutrients (carbohydrates, proteins, fats), vitamins don't provide energy directly but are crucial cofactors in metabolic reactions. They are not primarily energy sources or fiber providers.

Vitamin D is synthesized in the skin when 7-dehydrocholesterol is exposed to UV-B radiation from sunlight, earning it the name 'sunshine vitamin.' This process converts the cholesterol derivative into previtamin D3, which then becomes active vitamin D. Vitamins A, B, and C must be obtained from dietary sources as the human body cannot synthesize them.

Deficiency of vitamin C results in softening of gums. 

Fish is an excellent source of high-quality complete protein, containing all essential amino acids in optimal proportions. Fish typically provides 20-25g of protein per 100g serving. Potatoes are primarily carbohydrates, butter is mainly fat with minimal protein, and bananas are carbohydrate-rich with only about 1g protein per 100g.

The chemical name of vitamin C is ascorbic acid, a water-soluble antioxidant essential for collagen synthesis, wound healing, and immune function. Thiamine is vitamin B1, riboflavin is vitamin B2, and glutamic acid is an amino acid involved in neurotransmission, not a vitamin.

The rectum is the final section of the large intestine (about 12-15 cm long) that serves as a temporary storage chamber for fecal matter before elimination. While the large intestine as a whole absorbs water and electrolytes, the rectum specifically functions as a reservoir. The anus is the opening, and the appendix is a vestigial structure with no storage function.

Amoeba exhibits holozoic nutrition, where it ingests solid food particles through phagocytosis, forming food vacuoles where intracellular digestion occurs. Saprotrophic nutrition involves feeding on dead organic matter externally, parasitic nutrition involves living on a host organism, and ingestion is merely the process of taking in food, not a mode of nutrition.

Vitamin A is fat-soluble, meaning it dissolves in lipids and can be stored in body fat and the liver. Water-soluble vitamins (C and B-complex including riboflavin) dissolve in water, are not stored significantly, and excess is excreted in urine. This distinction is important for both absorption and toxicity considerations.

Stratified squamous epithelium is a multi-layered tissue that protects underlying structures from abrasion, mechanical stress, and pathogens. In the mouth cavity, it faces constant friction from chewing, food movement, and microbial exposure. The stratified arrangement allows surface cells to be worn away while deeper cells replace them, maintaining protection. This is why areas subjected to mechanical stress like the mouth, esophagus, and skin are lined with stratified epithelium rather than simple epithelium.

The small intestine consists of three sections: duodenum (shortest, 25 cm), jejunum (2.5 meters), and ileum (longest, ~3-4 meters). The ileum makes up approximately 60% of the small intestine's total length and connects to the large intestine at the ileocecal valve. The colon is part of the large intestine, not the small intestine.

Food follows a specific anatomical pathway through the digestive system. It begins in the mouth where mechanical and chemical digestion starts, then travels down the esophagus via peristalsis, enters the stomach for further breakdown, and finally passes to the small intestine for most nutrient absorption and the large intestine for water absorption. This sequence reflects the actual path food takes through the alimentary canal.

The inactive prorennin is converted to active rennin by HCl.

   A man cannot digest cellulose whereas cows can do so because their gut contains certain bacteria capable of digesting cellulose.

Chlorella is a genus of single-celled green algae that has been extensively researched by NASA and other space agencies as a potential food source for long-duration space missions. It grows rapidly, requires minimal space and resources, can produce oxygen through photosynthesis, and is rich in protein, vitamins, and minerals. While not yet standard operational space food, it remains the most studied and promising space food candidate among the options listed.

The minerals required in large quantities (macrominerals) by humans include calcium, phosphorus, sodium, magnesium, potassium, and sometimes sulfur and chloride depending on classification system. Option C (phosphorus, calcium, sodium, magnesium) contains four well-established macrominerals. The other options mix major and trace minerals - zinc, molybdenum, manganese, cobalt, and copper are all trace minerals needed in much smaller amounts, while nitrogen is an element obtained from organic compounds rather than as a mineral nutrient.

Glucose is a monosaccharide that requires no digestion - it can be absorbed directly through the intestinal wall into the bloodstream via specific transporters. Sucrose is a disaccharide that must first be broken down by the enzyme sucrase into glucose and fructose before absorption. Starch is a polysaccharide requiring extensive enzymatic breakdown by amylase into maltose and eventually glucose. Cellulose cannot be digested by humans at all due to lack of cellulase enzyme. Therefore glucose is the most easily and rapidly absorbed.

Night blindness is caused by the deficiency of vitamin A.