What does it mean to be selectively or semi-permeable

Selectively permeable or semipermeable means specific substances are allowed to pass through the plasma membrane.

Explanation:

The plasma membrane is selectively or semipermeable in nature because the plasma membrane allow only specific molecules such as nonpolar substances or hydrophobic substances such as steroidshormone to pass through it and prevent the passage of polar solute molecules such as water,glucose.

   To transport these polar solutes across the membrane an additional protein is needed in case of transport of water channel protein is needed whereas in case of glucose transport carrier protein is required.

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.

i thinking chemical change