Final answer:
At 6 weeks of pregnancy, the embryo has a functioning heart and organs start to form and function.
Step-by-step explanation:
During week six of pregnancy, the embryo measures about 8 mm (0.31 in.) in length. At this stage, the embryo has a functioning heart, which starts to beat, and basic structures begin to develop into areas that will become the head, chest, and abdomen. Organs also start forming and beginning to function, and the neural tube forms, which will develop into the spinal cord and brain.