The entry of substances(nutrients) that are found in the extracellular environment and are used to obtain matter and energy.
The transformation of substances (metabolism) which is the set of chemical processes that uses nutrients and which takes place inside the cells.
The excretion or expulsion of waste substances resulting from metabolism into the extracellular environment.
SUBSTANCE WITH SMALL MOLECULES
Substances with small molecules such as oxygen.The movement of substances molecules by means of diffusion occurs along the concentration gradient.
SUBSTANCE WITH MEDIUM-SIZE MOLECULES
Channels which are proteins that open up to form a channel that allows the substances to flow along the concentration gradient.
Pumps which are protein structures that pump the substances through the membranes against the concentration of gradient.They need energy to do this.
SUBSTANCES WITH LARGE MOLECULES
Substances with large molecules cannot pass through the membranes. In such cases they are transported as follows:
The membranes sinks and engulfs the particle in a vesicle that is incorporated into the cytoplasm.This process is called endocytosis.
The vesicle fuse with the lysosomes, which contain digestive substances that digest the c tents of the vesicle and form other smaller ones.
The residue produced during digestion is expelled in a process called exocytosis.