Gas exchange occurs when organisms absorb one gas and release another through various methods like gills, lungs, or diffusion. Ventilation refers to pumping fresh air or water across gas exchange surfaces to maintain concentration gradients and maximize diffusion. The alveoli in human lungs facilitate efficient gas exchange through properties like a large surface area, thin epithelial cells, moisture film, and dense capillary network.

1. 6.4 Gas exchange

12. 6.5 Nerves, hormones and homeostasis

23. Click4Biology shows an alternate diagram to show how feedback mechanisms react to increases or decreases from the set point. Use the image that works best for you. Use specific examples of hormonal feedback.

29. 6.6 Reproduction