Union Pacific Corp.’s fourth-quarter profit jumped 24 percent as the nation’s largest freight railroad operator increased prices and hauled more cargo. CEO Jim Young said he expects the economy and the railroad’s revenue will continue growing in 2012. “Looking ahead, we expect continued slow but steady economic growth in 2012,’’ Young said Thursday. “The diversity of our unique railroad franchise will continue to provide growth opportunities in various markets.’’ Union Pacific shares rose $2.62, or 2.4 percent, to $112.44 in afternoon trading. The Omaha-based railroad company said that its net income rose to $964 million, or $1.99 per share, during the last three months of 2011.