The only known source of human embryonic stem cells is:

a. placental tissue.
b. umbilical cords.
c. early human embryos.
d. brain tissue.
e. nerve tissue.


C

Biology & Microbiology

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Examine Figure 23.2 in your textbook. According to the figure, the closest relatives of turtles are:

A. lizards and snakes. B. sauropsids. C. tetrapods. D. crocodiles and alligators. E. hagfish.

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Escherichia coli infections:

What will be an ideal response?

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Based on the number of species, the most successful extant phylum of plants is the

A. Coniferophyta. B. Hepaticophyta. C. Charophyta. D. Pterophyta. E. Gnetophyta. F. Anthophyta.

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The substances in cell membranes that form a barrier to the movement of materials across the membrane are

A) carbohydrates. B) nucleic acids. C) lipids. D) external proteins. E) internal proteins.

Biology & Microbiology