Both anime shows how human body works with the means of portraying various components as anthropomorphised beings. The shows mostly focus on fights between virus/bacteria and human defense mechanisms. Both are enjoyable way to learn biology facts about human biology.
Both are shows about human body, with anthropomorphized cells as characters.
While Hataraku Saibou usually focuses on how the body fights against threats in more action-oriented manner and with very anime presentation, Micro Patrol explains how human body works more thoroughly, is more cartoony, educational and aimed at children.
They take place in a human body, where cells work together to fight viruses, repair the body and transport oxygen. They both teach you some useful stuff about the cells and what's going on in the human body. Hataraku Saibou just does it in a more anime-feeling way, while Seimei is meant more for kids. They are really similar, but if you enjoyed Hataraku Saibou, you shouldn't really go watch Seimei, I'm just putting it out there.
We have anthropomorphic cells that run through your body and the both shows explains in a fun interactive way a bit how your body works. If you liked Hataraku Saibou (Cells at Work!) you could enjoy Seimei no Kagaku: Micro Patrol, no doubt.
I've seen Seimei no Kagaku: Micro Patrol (aka. "Once Upon a Time... Life") dubbed in my mothers tounge back in the day when I was a kid not only once, but twice.
Both are "edutainment" anime that use humor to educate its audience on real concepts. Hetalia focuses on history while Hataraku Saibou discusses biology. Though Hetalia has an overarching WWII storyline and repeating gags, like Hataraku Saibou, Hetalia can be picked up at any episode due to its episodic formula.
These two shows use anthropomorphism to illustrate an entity's "way of life". Hataraku Saibou illustrates the daily function of cells through human jobs and personalities. Hetalia illustrates the intermingled history of countries through its affinity or lack of affinity between characters as well as portraying their culture through habits and personality traits of their characters.
Both shows humanize inanimate objects, in not only for humorous purposes but also to shed light on the real-life actions behind them (the human body in Cells at Work and the country relations during WWII in Hetalia)
Similarly, both shows consist of a large cast, yet focuses mostly on select few members
So you wanna watch anime and learn biology at the same time? Welcome. While in Hataraku Saibou we have actual cells living and working inside the human body, in Moyashimon we have a protagonist who can see bacteria. Although the settings aren't the same, both feature biology and microorganisms as important/main characters in the series. And, yes, you will feel attached to them.
Both are set in a world that feels very alien to the viewer, lives by strict rules and is under constant attack of alien entities (lunarians in Houseki no Kuni and bacteria in Hataraku Saibou). Both have a large cast of human-like, but not actually human characters, with different episodes focusing on different ones, and protagonists (Phos in Houseki no Kuni and Red Blood Cell in Hataraku Saibou) who are pretty incompetent and strive to become better at their job.
Land of the Lustrous and Cells at Work! are both adaptations of manga from a monthly magazine published by Kodansha. The characters in both series are humanoid versions of non-human things, cells in Cells at Work! and gems in Land of the Lustrous. Everyone in each society has a specific role that they are best at and must do. The society in each anime must fight of an invading species, Lunarians in Land of the Lustrous and Bacteria in Cells at Work!. The main character in both series aren't good at their job at first, but slowly improve over the show.
Both series star ambitious but inexperienced people in 'messenger' positions that take them through all areas of an operation - the human body, and anime production.
Both series have similar 'female' leads, but the real fun in these series is meeting the other eccentric specialists in the operation and joining the main character during her education and development. Both series have a similar tone of voice and teach the viewer about the process, but Shiro Bako is aimed at a slightly more mature audience and also adds a level of character development and depth to the experience.
There is an arc in Gintama (episodes 167-170) that is vastly similar to Cells At Work!. The Yorozuya travel into Tama-san's body and inside of it can be found white blood cells and viruses visualized as humans. Both settings inside the bodies are also seem more adventurous and welcoming than you might expect.
One Punch Man and Hataraku Saibou are story about certain groups that doing their job to save "the world".
Immune Cells = Heroes
Viruses, Bacterias, etc. = Monsters
Both have serious action scenes as well as comedy scenes. In One Punch Man, the story is mostly focused on Saitama, the overpowered hero. While in Hataraku Saibou, it's more like "Hero of the Day". However, the plot is different. Hataraku Saibou is an educational story about how cells work, while One Punch Man is a story about Heroes.