* Starch: Starch is a large, complex carbohydrate. It will not cross a thin polyethylene membrane. Polyethylene is a very dense polymer with small pores, and starch molecules are simply too big to fit through.
* Iodine: Iodine is a small, nonpolar molecule. It can cross a thin polyethylene membrane. While polyethylene is generally impermeable to water-soluble substances, smaller nonpolar molecules can pass through the membrane to a degree.
* Water: Water molecules are small but polar. They will partially cross a thin polyethylene membrane. Polyethylene is not completely impermeable to water, but it will restrict the passage of water molecules significantly.
In summary:
* Starch: No
* Iodine: Yes
* Water: Partially
Important Note: The permeability of polyethylene to these substances can be influenced by factors like:
* Thickness of the polyethylene membrane: Thinner membranes will generally allow for more permeability.
* Temperature: Higher temperatures can increase the rate of diffusion.
* Concentration gradients: Larger differences in concentration on either side of the membrane will lead to faster diffusion.
