On a visit to the Energy Department on Thursday, first lady Michelle Obama quizzed middle-school students about red blood cells and nanotechnology during a practice science quiz competition.

Mrs. Obama also praised department employees during her 13th stop on a tour of the federal bureaucracy.

"You don't often get the thanks that you deserve," she said. "Sometimes you get a lot of the blame and none of the credit for the progress that has gone on in this country."

The first lady said the agency's work has been critical for bolstering the economy, promoting national security and preserving the environment.

"What you're doing here couldn't be more urgent," she said. "And it's not easy. Everyone knows it's not easy."

Mrs. Obama commended the agency's educational initiatives. "We all know that we can't transform our energy future unless we transform our education system," she said. "So that's why were so pleased by what folks here at the Department of Energy are doing to get young people excited about science."

After her speech, Mrs. Obama and Energy Secretary Steven Chu took turns asking questions of 7th and 8th graders from Kenmoor Middle School in Landover, Md., and Takoma Park Middle School in Takoma Park, Md., during an unofficial practice Science Bowl competition.

The Energy Department coordinates Science Bowl competitions around the country. Winning teams from each regional competition will compete at the National Science Bowl this spring.

"I'll be reporting the results back to the president," Mrs. Obama joked before asking the first question. "So no pressure, young people."