<span>Physical Digestion - Physically breaking down (eg chewing)
Chemical digestion - chemically breaking down (eg chemicals in the stomach)</span>
A cell membrane is semi-permeable. This means that it is size-specific. It allows only a particular maximum size of particles to pass through it. Large molecules such as plasma proteins and lipid molecules cannot therefore penetrate while small moecules such as glucose will easily diffuse across it.
Secondly, a cell membrane is charged. The charge is as a result of a difference in ionization between the intracellular fluid and the extracellular fluid. Substances that have the same charge as the fluid into which they are diffusing will be hard to asorb due to repulsion effect. On the other hand, substances that have opposite charge as the fluid into which they are diffusing will be absorbed easily and faster.
Finally, the cell membrane is made of two layers. Lipid layer and phospholipid layer. Inside these layers, there are embedded particles and substances such as enzymes, receptors, hormones and ion channels. During diffusion of substances across cell membrane, some substances are speeded up by these substances. For instance, Translocase enzyme in the membrane of mitochondria speeds up the transfer of Carnitine transferase into the mitochondrial matrix.
The answer is letter D. Substrate; Active Site The enzyme
itself remains unchanged. It advise the
active place of an enzyme is frequently reshaped by interactions with the
substrate until the substrate is completely bound and the chemical reaction
occurs, the lock and key model.
