Final answer:
Oxygen and carbon dioxide, lipids, and steroid hormones can easily diffuse through the plasma membrane because they are either small, uncharged or hydrophobic. Charged ions like sodium require specialized transport proteins to pass through the membrane.
Step-by-step explanation:
Substances That Can Easily Diffuse Through the Plasma Membrane
The plasma membrane, composed of a lipid bilayer, allows the passage of certain substances through simple diffusion. Substances that can easily diffuse through this membrane include small, uncharged molecules like oxygen (O) and carbon dioxide (D), as well as hydrophobic molecules like lipids (F) and steroid hormones (E). These molecules can move through the membrane without the aid of transport proteins because they are either nonpolar or have a hydrophobic nature that allows them to penetrate the hydrophobic lipid core of the plasma membrane. Oxygen and carbon dioxide have no charge, which enables them to pass through the membrane with ease. However, charged ions such as sodium cannot simply diffuse due to their charge and require specialized transport mechanisms. Lipid-soluble substances are able to enter cells and be transported into body tissues and organs without obstacles.
Proteins (A) and sodium ions (B), being large and charged respectively, cannot easily diffuse through the plasma membrane without the help of transport proteins. Substances like amino acids and simple sugars also do not pass through the membrane easily and require assistance for transport.