After 20 years, the Science Museum of Minnesota is shutting down one of its most popular exhibits at the end of the summer as part of a broader plan to revamp its spaces.

The Cell Lab, a hands-on biology lab, has been a staple of the St. Paul museum since it opened its 370,000-square-foot building along the Mississippi River in 1999. Donning white lab coats and goggles, kids perform experiments with microscopes and other microbiology equipment.

But the materials are dated and the museum, which drew 815,000 visitors last year, is working on a plan to update and rework its spaces.

“We value what it has been and what it has provided over the last 20 years. But we need to stay relevant,” said Mimi Daly Larson, vice president of mission advancement at the museum. “We know that our constituents’ expectations are changing. What’s expected in 1999 is different from today.”

The Cell Lab will close Sept. 6 and the space will be used to test out new exhibits, she said, adding that the museum hasn’t ruled out another version of life science experiments. It’s part of a broader multiyear transformation of the museum unlike anything it’s done since opening its building in 1999, Larson said.

Other big attractions — from Target Field to the Mall of America — constantly revamp its amenities, and the Science Museum needs to do the same, Larson said. Last year, the museum closed its “perception theater,” which had also been open since 1999, and launched “Infestation,” which Larson said is part escape room, part scavenger hunt.

Inside the Cell Lab, the news was met with disappointment from some visitors and some of the 800 volunteers who help the museum, many of whom are grad students, nurses, retired scientists or teachers. The lab, which is part of the museum’s human body gallery, features stations with screens that give kids — and adults — directions via an original 1999 program that the Science Museum created. It instructs them in how to extract DNA from wheat germ, determine the blood type from sheep’s blood or dissect fruit flies’ larvae to isolate chromosomes, among other things.

It has become a destination spot in the museum, especially since it’s the only laboratory setting, said Roger Benepe, the programs gallery coordinator.

“When I heard it was going away, I thought, ‘What a loss,’ ” he said. “It really puts the learning in their hands. It’s just such a unique experience. I’m sad. All of this is still relevant.”

The Cell Lab was created by the Science Museum, which has a little-known department that designs exhibits for other museums and nonprofits across the country. The museum even helped other museums create similar labs.

“I love to see the sparkle in kids’ eyes when they do experiments. Who knows who will walk out and become a doctor or scientist?” said Dan Berend, 73, of Edina, a retired Wells Fargo employee and self-described “science nut” who has volunteered at the museum for five years. “It’s a unique part of the museum. It’s dumber than dumb they’re closing it.”

While the current Cell Lab was “beloved,” Larson added that visitors’ feedback showed that “we need to change.”

The museum, a nonprofit with an annual budget of about $40 million, hit a low point for attendance with 537,500 visitors in 2014. Founded in 1907 as a natural-history museum, the Science Museum is shifting to focus more on creating its own exhibits rather than featuring traveling blockbusters. It is also reinvesting in its own scientific research done by nearly two dozen in-house scientists. Leaders hope the new approach will attract repeat visitors and stabilize the museum’s finances; it’s had to tap its endowment some years to cover expenses.

After spending three hours at the museum with her family on Tuesday, Ellie Samek, 11, requested they return again Wednesday. The Missouri family said they’ve never visited such an elaborate science museum back home or in other major cities they’ve visited, and Samek was excited to spend more time in the Cell Lab.

She studied blood types in school, but the lab brings the concepts off the page of a book to real life, the sixth-grader said: “It’s fun to do more hands on.”