Bran: The multi-layered outer skin of the kernel that helps to protect the other two parts of the kernel from sunlight, pests, water, and disease. It contains important antioxidants, iron, zinc, copper, magnesium, B vitamins, fiber, and phytonutrients.
Germ: The embryo, which, if fertilized by pollen, will sprout into a new plant. It contains B vitamins, vitamin E, antioxidants, phytonutrients, and unsaturated fats.
Endosperm: The germ’s food supply, which, if the grain were allowed to grow would provide essential energy to the young plant. As the largest portion of the kernel, the endosperm contains starchy carbohydrates, proteins, and small amounts of vitamins and minerals.
Source for kernel diagram: http://wbc.agr.mt.gov/Consumers/diagram_kernel.html