def build_concentartion(species_id, number):
    """
    Builds the concentration component for each species
    Parameters
    ----------
    species_id      : int
                     species id from the species_indices dictionary
    number          : float
                    stoichiometric co-eff of the species
                    for specific reactions
    Returns
    ----------
    concentration   : string
                    the concentration component of that particular
                    species
    """

    if abs(float(number)) == 1:
        concentration = '* y[%s] ' % species_id
    else:
        concentration = '* y[%s] ** %s ' % (species_id, abs(float(number)))

    return concentration