Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stimulus indicating lowered oxygen tension. Hypoxia, defined as a decline in O2 levels below normoxic levels of 20.8 - 20.95%, results in metabolic adaptation at both the cellular and organismal level.

The chemical reactions and pathways resulting in the formation of nicotinamide adenine dinucleotide, a coenzyme present in most living cells and derived from the B vitamin nicotinic acid; biosynthesis may be of either the oxidized form, NAD, or the reduced form, NADH.

Any process that generates nicotinamide adenine dinucleotide (NAD) from derivatives of it, without de novo synthesis; salvage is usually from the degradation products nicotinic acid (Na) and nicotinamide (Nam).

Any process that results in a change in state or activity of the symbiont or its cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of detecting molecules of its host organism. The host is defined as the larger of the organisms involved in a symbiotic interaction.

The membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins.