What was the major advance made in microscopy in the 20th century?

The first signs of cellular differentiation occur in the blastocyst. why is cellular differentiation important for the development of a fully formed human infant?

Each pair of clay balls represents two planetesimals. if each planetesimal is composed of the same material and is separated he the same distance, which pair experiences the frayed gravitational attraction?

The phylogenetic tree illustrates the relationship between humans and our closest living relatives. the tree was based on biochemical comparisons, including dna and amino acid sequences. according to the biomolecular data, we could infer that a) the four organisms do not have a common ancestor. b) humans are more closely related to chimps than any other apes. c) chimps are more closely related to gorillas than they are to humans. eliminate d) there is no evidence if any relationship between the four branches on the tree.