How organisms are organised
Like any well-run operation, a body is made of specialised parts
ALL LIFE is made of cells. But to build a complex, multicelled organism from those cells almost always requires them to come in more than one type. This means that as cells multiply in a growing organism they need to differentiate, which they do by expressing different subsets of genes from within the genome they all share. Different patterns of gene expression produce different types of cell.
These complex patterns of gene expression appear to be the preserve of eukaryotes—creatures built of cells that have their primary genomes wrapped up in a complex compartment called a nucleus. Sponges, descended from some of the earliest multicellular creatures, have a handful of cell types. Plants have dozens. Complex animals have hundreds.
This article appeared in the Schools brief section of the print edition under the headline “Leaves, limbs and lights”
From the August 14th 2021 edition
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