Answer: A semipermeable membrane is a layer that only certain molecules can pass through. Semipermeable membranes can be both biological and artificial. Artificial semipermeable membranes include a variety of material designed for the purposes of filtration, such as those used in reverse osmosis, which only allow water to pass. The biological membranes of cells are created by two sheets of phospholipid, which contain a lipid tail attached to a polar head. The tail regions of each sheet cluster together, while the heads of the molecules point outward. The polar heads point both outward toward the environment of the cell and inward toward the cytosol. In this way, a hydrophobic region of lipid tails separates the two bodies of solution. This can be seen in the image below.
Explanation: sorry if its too much wording i tried to shorten it as much as possible
because it is hard to breakdown fat in a very short time while ATP can be broken down in a very short time.Fats have a very strong bond of molecular chains and this makes it hard to breakdown quickly
