Joel S. Marcus, founder, chairman, and chief executive of Alexandria Real Estate Equities, has focused the real estate investment trust on developing properties for the life sciences industry. While it operates in other biotechnology and medical technology hubs from New York to San Francisco, the Pasadena, Calif., company’s largest cluster of properties is in Greater Boston, where it owns 3.5 million square feet of space in Cambridge’s Kendall Square, along Route 128, and in Boston’s Longwood Medical Area. On a visit to Cambridge, the 67-year-old Marcus spoke with Globe reporter Robert Weisman. Here’s what he found out: