An illuminating theme -- light -- ignites the bakers' creativity in the kitchen. Guest judge: actor Irene Choi ("Insatiable").

Married bakers who live and work together say "I do" to delicious sweets. Guest judges: husband-and-wife TV hosts Nick and Vanessa Lachey.

The bakers bring their A-game in a trio of inventive, science-inspired rounds. Guest judge: actor Paris Berelc ("Alexa & Katie").

An ocean theme sends bakers into the deep to make seascapes, aquatic creatures and salty-sweet flavors.

A family theme stirs fond memories for tight-knit bakers who are brothers and sisters, mothers and sons and more. Guest judge: chef Carla Hall.

Geeky science-themed challenges get the creative juices flowing -- along with oozy zombie 'blood.'

The contestants serve up sweets with summery flavors that evoke the great outdoors.

The baking teams pour buzz-worthy ingredients like coffee, honey and alcohol into amazing edible creations.

The teams wax nostalgic with extra-sweet treats inspired by popular candies.

Sweet and salty snacks yield yummy flavors over a trio of junk food-inspired rounds. Guest judge: comedian Fortune Feimster.

The bakers rush to make winning desserts inspired by the judges' favorite holidays.

Fashion-forward challenges force the frazzled contestants to think outside the box.

Magical cupcakes, edible illusions and levitating cakes? What sorcery is this?! Guest judge: magician Justin Willman ("Magic for Humans").

Teams take a tropical vacation with bold agendas and breezy flavors. Guest judge: actor Garcelle Beauvais (“The Real Housewives of Beverly Hills”).

From lofty nests to baking with insects, these avian-themed challenges are for the birds. Guest judge: actor and singer Naya Rivera ("Glee").

The teams work to wow the judges with confections that bring the element of surprise.

A darkly delicious blackout theme puts the bakers to the test — and the results are decadent. Guest judge: actor and musician Tyler Posey ("Teen Wolf").

Breakfast-, lunch- and dinner-themed challenges determine which team is the hungriest for victory. Guest judge: celebrity cake designer Ron Ben-Israel.

Bakers who first met online attempt to re-create popular dessert trends and serve up the next big thing. Guest judge: "Candy Queen" Jackie Sorkin.

As time ticks down on three chocolate-themed rounds, the bakers try not to lose their tempers. Guest judge: chocolatier Jacques Torres ("Nailed It!").