Final answer:
The correct description of what happens when a multicellular organism's single cell divides is that chromosomes are duplicated before cell division, ensuring each new daughter cell has a complete set. This is essential for proper cell function and is a fundamental aspect of mitosis.
Step-by-step explanation:
The process you're asking about is where a single cell, the fertilized egg known as a zygote, divides to eventually form a multicellular organism. The correct statement that describes what happens during this process is that before cell division, chromosomes are duplicated so that each new daughter cell has a complete set of chromosomes. This ensures that all cells have the same genetic information and can function properly. This process is known as mitosis in somatic cells, which is essential for growth, tissue repair, and maintenance in multicellular organisms.
In contrast to asexual single-celled organisms that reproduce by simply dividing their DNA and splitting into two new cells, multicellular organisms like humans undergo a complex process where each cell inherits an exact copy of the DNA from the parent cell. This is crucial because any failure in this process can lead to serious consequences, including diseases like cancer.