What is the name of the main embryonic cell layer from which the nervous system is derived in most metazoans?
a. endoderm
b. mesoglea
c. mesoderm
d. ectoderm
Ans: d. ectoderm
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Scientists speculate that extinctions did not occur in Africa as they did on other continents because animals coevolved with _______ in Africa.
A. plants B. diseases C. parasites D. humans
In a frog in which the diploid number of chromosomes per cell is 24, what is the total number of
chromatids present during Prophase I?
a. 0 b. 6 c. 12 d. 24 e. 48
During normal DNA replication, part of the DNA at the ends of linear chromosomes is not copied into
the new DNA strands because
a. DNA ligase cannot join pieces at the end of a chromosome. b. RNA primers at the beginning of a new strand cannot be replaced with DNA. c. those ends are Okazaki fragments that are lost. d. cells do not need the DNA at the ends of chromosomes. e. the ends of chromosomes are made of protein, not DNA.
A cell moves sodium ions against its concentration gradient. This is an example of ____
a. active transport b. osmosis c. diffusion d. facilitated diffusionc e. diffusion through a channel