Which is the best definition of a cellular membrane

What do isotopes of uranium have the same number of? what do they have a different number of? a) same number of protons; different number of electrons b) same number of protons; different number of neutrons c) same number of electrons; different number of protons d) same number of neutrons; different number of protons

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above

Explain the significance of meiosis in sexual reproduction