In multicellular organism, transportation among cell occurs through plasma membrane. There are some advantages of substance transportation to the cell, some of them are as follows.
1. Maintaining the stability of pH.
2. Maintaining the concentration of substances in cell for enzyme activities.
3. Obtaining the supply of food, energy material, and other raw material.
4. Secreting poisonous metabolism waste.
5. Providing important ion for nerve and muscle activities.
The substances that can pass through the plasma membrane are usually soluble substances. Beside the molecule size, substance characteristics influenching membrane transportation include electric change, amount of water molecule that bonds, and power to pass through in lipid.
Plasma membrane has selective characteristic which is an ability to choose which molecule can pass through it. It is related to membrane permeability characteristic. Some membrane permeability characteristics are as follows.
1. Permeable, Which can be passed through by all substances.
2. Impermeable, which cannot be passed through by all substances.
3. Differential permeable (selective permeable) , which can oly be passed through by certain substances. For example, semipermeable membrane in nucleus, food vacuole (contractile), and plasma membrane.
Substance movement through membrane is distinguished into two types, passive movement, which does not consume energy, and active movement, that consumes energy. Passive movement includes diffusion and osmosis, while active movement includes active transport, endocytosis, and ectocytosis.