There are several main functions that the cell has to carry out: molecule transport, reproduction, and energy conversion.
To survive, organisms need to get energy. Energy is captured in many ways, glycolysis, TCA cycle being one of them. The whole set of chemical reactions that cells use to receive energy is called metabolism.
Organisms also need to reproduce (the production of offspring by one or more parents). Sexual reproduction is accomplished in human being by fusion of male sex cell called sperm and female sex cell called ovum.
Mutation is also an important characteristic of living organisms. Mutations are random changes in the structure or composition of DNA, which can be caused by mistakes in reproduction or external events, such as UV damage.
Molecular transport in the cell exist in 2 ways namely active transport and passive transport
Active Transport: requires energy and a carrier protein to transfer small molecules against their concentration gradient such as electrolytes, hydrogen ions, glucose amino acids etc. Macromolecules, which include proteins, polynucleotide, and polysaccharides, also use active transport mechanism for their movements across the cell membranes. There are two basic means of active transport - by exocytosis and by endocytosis. Exocytosis involves sending macromolecules out of the cell, while the opposite applies to endocytosis.
Passive transport: For small molecules such as oxygen, water, ethanol and carbon dioxide, the molecules could easily cross the membrane via passive transport, in the form of simple diffusion along a concentration gradient
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