Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan and line it with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat the butter and sugar with an electric mixer until light and fluffy, about 2-3 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the orange juice and zest.
Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined.
Fold in the poppy seeds.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 40-45 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.