Organisms exchange substances with their environments

• The oxygen dissociation curve of hemoglobin describes the relationship between the partial pressure of oxygen in the blood and the percentage of hemoglobin saturated with oxygen

  
• The curve is sigmoid, with a steep slope at low oxygen pressures due to positive cooperativity, and a shallow slope at high oxygen pressures due to negative cooperativity
• The transport of water and nutrients in plants involves the xylem and phloem, with xylem transporting water from roots to leaves and phloem transporting nutrients from leaves to the rest of the plant

  
• Source cells in plants produce nutrients, while sink cells use these nutrients
• In fish, bony fish have gills with gill filaments and lamellae for gas exchange, maintaining a steep diffusion gradient by flowing blood and water in opposite directions
• Insects use spiracles and tracheal tubes for gas exchange, with gases moving through diffusion, muscle contraction, and volume changes in tracheoles
• In the mammalian gaseous exchange system, the lungs have a large surface area for gas exchange, surrounded by the rib cage and separated from the abdomen by the diaphragm
• Ventilation in mammals involves inspiration (raising ribs and flattening diaphragm) and expiration (lowering ribs and raising diaphragm), facilitated by intercostal muscles and diaphragm
• A spirometer measures lung volume, with vital capacity being the maximum air volume inhaled or exhaled in a breath, and tidal volume being the volume of air breathed in and out at rest
• Digestion involves hydrolyzing large molecules into smaller ones for absorption, with carbohydrates digested by amylases, lipids by lipases, and proteins by peptidases
• Absorption in mammals occurs in the ileum, with amino acids absorbed by co-transport with Na+ ions, and monoglycerides and fatty acids diffusing into epithelial cells and reforming into triglycerides
• Haemoglobin is a globular protein carrying oxygen in the blood, with each molecule capable of carrying four oxygen molecules
• At high oxygen pressures, hemoglobin is not saturated with oxygen in the lungs, binding oxygen to transport it to the tissues
• Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin to absorb oxygen efficiently at low partial pressures in the placenta
• The Bohr effect states that in the presence of carbon dioxide, the affinity of hemoglobin for oxygen decreases, causing oxygen to be released for tissues
• The cardiac cycle has 3 stages: cardiac diastole, atrial systole, and ventricular systole
• Arteries are thick-walled to withstand high blood pressure, contain elastic tissue for stretching, and smooth muscle to vary blood flow
• Capillaries are the site of metabolic exchange, being only one cell thick for fast exchange of substances
• Veins carry blood back to the heart, have a wide lumen to maximize blood volume, and contain valves to prevent backflow
• Tissue fluid is a liquid containing dissolved oxygen and nutrients, exchanged for waste products like carbon dioxide in the tissues
• The lymphatic system carries excess tissue fluid back to the blood, filtering out bacteria and foreign material
• Xylem transports water and minerals in plants through transpiration, while phloem transports sugars through translocation
• The diagram of the transport of water and nutrients in plants shows the xylem and phloem as the main transport tissues, with xylem transporting water from roots to leaves and phloem transporting nutrients from leaves to the rest of the plant

  
• Xylem vessels in plants are long cylinders made of dead tissue with open ends, containing pits for water movement, thickened with lignin for flexibility, and involved in transpiration to supply water and minerals, supporting processes like photosynthesis and growth
• Transpiration in plants involves water absorption through roots, movement up the stem via xylem, and release as water vapor through stomata, enabling processes like photosynthesis, growth, and temperature control
• Xerophytes are plants adapted to dry conditions with features like smaller leaves, densely packed mesophyll, thick waxy cuticle, closed stomata, hairs, and rolled leaves to minimize water loss and survive in arid environments
• Water enters root hair cells and moves into the xylem tissue through symplast or apoplast pathways, aided by root pressure, cohesion-tension theory, and capillary action, supporting the movement of water up the stem in plants
• Translocation in plants involves phloem vessels transporting nutrients like sucrose between sources (e.g., leaves) and sinks (e.g., roots), requiring energy and facilitated by companion cells, plasmodesmata, and hydrostatic pressure gradients
• Tracer experiments using radioactivity labeled carbon dioxide can trace the movement of sugars through plants, showing that sugars are transported in the phloem, supporting the role of phloem in translocation