Organized team activities started Monday Tuesday for the 49ers, but wide receiver A.J. Jenkins already has been hard at work this offseason, determined to rebound from a “humbling” rookie season. Jenkins dismissed feeling any pressure as he enters his second season, noting simply: “Pressure for what? It’s football.” Last season’s first-round draft pick, Jenkins has focused this offseason on adding muscle and knowledge. “I’m learning anything I can,” Jenkins said. He’s bulked up to 196 pounds, four pounds more than last season’s listed weight. “If I get to 200 (pounds), I’ll be good to go,” Jenkins said while looking at his larger biceps and wearing a sleeveless shirt. Jenkins lived with quarterback Colin Kaepernick and fellow receiver Ricardo Lockette for two months in downtown Atlanta while they honed their skills at a nearby training facility. Upon reporting to the 49ers’ offseason program, Jenkins and Lockette have become mentored by veteran receiver Anquan Boldin, who’s been schooling them on route running after practice. “He’s a real good vet, a good route runner and has real confidence in his ability,” Jenkins said. “He’s got the knowledge down.”