The stack of thylakoids inside a chloroplast is called:

1. A chloroplast holds flattened membrane sacs called thylakoids. 2. These sacs are arranged in stacks. 3. Each stack of thylakoids is called a granum. 4. The stroma is the fluid around the grana, not the stack itself. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 4 'Cell Structure', sections 4.1-4.6_