Producers rely on light because that is what they use to "produce" food. Consumers, however, also rely on light, because first of all they need to see, and second of all, the light fuels growth of producers, which in turn, when consumers eat the producers, promote growth of other consumers.
Two chromosomes that are similar but not identical are called homologous chromosomes. When the chromosomes are duplicated, two identical chromosomes are called sister chromatids.
