In animals:
* Capillaries: The smallest blood vessels, where gas exchange occurs.
* Alveoli: Tiny air sacs in the lungs, where oxygen diffuses into the blood.
* Proximal convoluted tubule: Part of the nephron in the kidneys, where waste products are filtered.
* Endothelium: The inner lining of blood vessels, lymphatic vessels, and other body cavities.
* Epithelium: The outermost layer of skin and other surfaces, providing protection and barrier function.
In plants:
* Xylem: The tissue that transports water and minerals throughout the plant.
* Phloem: The tissue that transports sugars and other organic compounds throughout the plant.
* Root hairs: Extensions of root cells that increase surface area for water absorption.
* Guard cells: Specialized cells that control the opening and closing of stomata, pores on leaves for gas exchange.
Why are single-celled walls beneficial?
* Increased surface area: Thin walls maximize the surface area for diffusion and exchange of substances, like gases and nutrients.
* Reduced diffusion distance: This allows for faster and more efficient exchange.
* Flexibility: One-cell-thick walls allow for more flexibility and adaptability in some structures.
* Efficiency: Minimizing the number of cells involved in these processes reduces the overall energy expenditure.
Important Note: While many structures have walls that are primarily one cell thick, they often have additional layers or structures that provide support and stability.
