Final answer:
In most animals and plants, the organism has 18 chromosomes in its body cells and non-chromosomes in its sex cells because it is diploid in body cells and haploid in sex cells.
Step-by-step explanation:
In most animals and plants, the organism has 18 chromosomes in its body cells and non-chromosomes in its sex cells because it is diploid in body cells and haploid in sex cells.