Biological:
* Cell membranes: These are the most common examples. They allow small molecules like water, oxygen, and carbon dioxide to pass through freely, but restrict the passage of larger molecules like proteins and carbohydrates.
* Blood vessel walls: These allow small molecules like oxygen, carbon dioxide, and nutrients to pass through, but prevent blood cells and large proteins from escaping.
* Kidney tubules: These selectively filter waste products from the blood while allowing essential nutrients and water to be reabsorbed.
Non-biological:
* Dialysis membrane: Used in hemodialysis to filter waste products from the blood of patients with kidney failure.
* Reverse osmosis membrane: Used in water purification to separate water molecules from dissolved impurities.
* Cellophane: A thin, transparent material often used in experiments demonstrating osmosis.
* Certain types of plastics: Some plastics are designed to be permeable to specific gases, like oxygen or carbon dioxide, while blocking others. This is used in packaging, for example, to allow food to breathe while remaining sealed.
* Synthetic membranes in fuel cells: These allow hydrogen ions to pass through, facilitating the chemical reaction that produces electricity.
Key takeaway:
Semipermeable objects are characterized by their ability to allow some substances to pass through while blocking others, based on size, charge, or other properties. This selective permeability is essential for many biological processes and technological applications.