Why are nucleotides added in segments on the lagging strand?

Nucleotides are added in segments on the lagging strand during DNA replication because the DNA polymerase can only synthesize DNA in the 5' to 3' direction. As the replication fork opens, the lagging strand is oriented in the opposite direction, leading to the formation of short segments called Okazaki fragments. These fragments are synthesized individually and later joined together by the enzyme DNA ligase to create a continuous strand. This discontinuous synthesis is necessary to accommodate the antiparallel nature of the DNA double helix.