A challenge to traditional (pre-1860) ideas about species came from embryology, when it was discovered that embryos of dissimilar organisms, such as sharks and humans, resemble each other. Embryology involves the study of the formation and the development of an embryo and the fetus. It is one type of evidence of evolution such that the embryos of many different kinds of animals, mammals, reptiles, birds, fish among others, are similar showing a common ancestry.
In protista kingdom the organisms are represented in cartoon classified
Answer: The DNA double helix is held together by two types of bonds,
covalent and hydrogen.
Explanation: Covalent bonds occur within each linear strand and strongly
bonds the bases, sugar and phosphate groups.
