Describe the human alimentary canal and explain how the ileum is adapted for absorption.

You're on a roll — 6. a) I cannot draw diagrams. However, a labeled diagram of the alimentary canal of humans would typically show: • Mouth (oral cavity): Where food enters and mechanical digestion begins. • Pharynx: Connects the mouth to the esophagus. • Esophagus: Muscular tube that transports food from the pharynx to the stomach via peristalsis. • Stomach: J-shaped organ where chemical and mechanical digestion continue, producing chyme. • Small intestine: Divided into duodenum, jejunum, and ileum; primary site of nutrient absorption. • Large intestine: Divided into cecum, colon, rectum, and anal canal; absorbs water and electrolytes, forms feces. • Anus: External opening for defecation. • Accessory organs: Liver (produces bile), Gallbladder (stores bile), Pancreas (produces digestive enzymes and hormones). b) The ileum is adapted to its function of absorption in several ways: • Long length: Provides a large surface area for absorption. • Folded inner surface: The inner lining has numerous folds called plicae circulares (or folds of Kerckring), which further increase the surface area. • Villi: The folds are covered with millions of tiny, finger-like projections called villi, dramatically increasing the surface area for absorption. • Microvilli: Each epithelial cell on the surface of the villi has microscopic projections called microvilli, forming a "brush border" that further expands the absorptive surface. • Rich blood supply: Each villus contains a dense network of capillaries to efficiently transport absorbed nutrients away from the intestine. • Lacteal: Each villus also contains a central lymphatic vessel called a lacteal, which absorbs digested fats. • Thin walls: The walls of the villi are very thin (one cell thick), allowing for rapid diffusion and active transport of nutrients into the bloodstream or lacteal. c) Importance of the following vitamins in humans: i) Vitamin A: Essential for vision, particularly in low light (component of rhodopsin). It is also crucial for immune function, cell growth and differentiation, and maintaining healthy skin and mucous membranes. ii) Vitamin D: Primarily important for calcium and phosphate absorption from the gut, which is vital for the formation and maintenance of strong bones and teeth. It also plays a role in immune system function and muscle function. 7. a) How the following organisms are adapted to life in their habitat: i) Insects: • Exoskeleton: A hard, protective outer covering that provides support, prevents water loss, and offers protection against predators. • Wings: Many insects possess wings for flight, allowing them to escape predators, find food, and disperse to new habitats. • Tracheal system: A network of tubes for efficient gaseous exchange, delivering oxygen directly to tissues. • Small size: Allows them to exploit diverse microhabitats and requires fewer resources. • High reproductive rate: Ensures survival of the species despite predation. ii) Freshwater Amoeba: • Contractile vacuole: Actively pumps out excess water that enters the cell by osmosis, preventing the cell from bursting in a hypotonic freshwater environment. • Pseudopods: Extensions of the cytoplasm used for locomotion (amoeboid movement) and engulfing food particles (phagocytosis). • Flexible cell membrane: Allows for changes in shape, movement, and engulfment of food. • Simple diffusion: Gaseous exchange and waste excretion occur directly across the cell surface due to its small size and large surface area to volume ratio. b) Explanation of the following biological facts: i) Fish would suffocate on land with much oxygen supply: Fish breathe using gills, which are adapted to extract dissolved oxygen from water. On land, the delicate gill filaments collapse and stick together due to the lack of water support. This significantly reduces the surface area available for gaseous exchange, preventing efficient oxygen uptake, even if atmospheric oxygen is abundant. The gills also dry out, further impairing their function. ii) Amoeba lacks a circulatory system: Amoeba is a single-celled organism with a very small size and a large surface area to volume ratio. Nutrients, oxygen, and waste products can easily diffuse directly across its cell membrane to all parts of the cell. Therefore, it does not require a complex circulatory system to transport substances, unlike larger, multicellular organisms. 8. a) Processes by which nitrogen is removed from the atmosphere and soil: • Denitrification: This is the primary process by which nitrogen is removed from the soil and returned to the atmosphere. Denitrifying bacteria (e.g., Pseudomonas, Bacillus) convert nitrates (NO_3^-) in the soil back into gaseous nitrogen (N_2) or nitrous oxide (N_2O), which then escape into the atmosphere. This process occurs under anaerobic (low oxygen) conditions. • Leaching: Nitrates (NO_3^-) are highly soluble in water and can be washed out of the soil by rain or irrigation, moving into groundwater or surface water bodies. This removes nitrogen from the soil available to plants. • Harvesting of crops: When crops are harvested, the nitrogen absorbed by the plants from the soil is removed from the ecosystem. If the plant material is not returned to the soil, this represents a net loss of nitrogen. • Erosion: Soil erosion by wind or water can physically remove topsoil, which contains organic matter and nitrogen compounds, from an area. b) How nitrogen fixation is important in nature: Nitrogen fixation is the process by which atmospheric nitrogen gas (N_2), which is unusable by most organisms, is converted into ammonia (NH_3) or other nitrogen compounds that can be assimilated by living things. Its importance includes: • Making nitrogen available to plants: Nitrogen is a crucial component of proteins, nucleic acids (DNA and RNA), and chlorophyll. Nitrogen fixation makes this essential nutrient available to plants, which form the base of most food webs. • Maintaining ecosystem productivity: By providing a usable form of nitrogen, nitrogen fixation supports plant growth and, consequently, the entire ecosystem's productivity and biomass. • Nutrient cycling: It is a vital step in the nitrogen cycle, ensuring the continuous circulation of nitrogen through the atmosphere, soil, and living organisms. • Fertility of soil: Nitrogen-fixing bacteria (e.g., Rhizobium in legumes, free-living Azotobacter) enrich the soil with nitrogen compounds, naturally improving soil fertility without the need for synthetic fertilizers. Send me the next one 📸