Which form of passive transport allows small molecules, such as oxygen, to cross the cell membrane?

In what for do plants utilize nitrogen? why do they need nitrogen?

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.