The period in which life began on Earth is known as the _____ era.

a. Cenozoic
b. Mesozoic
c. Precambrian
d. Cretaceous
e. Paleozoic


Ans: c. Precambrian

Biology & Microbiology

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This cytoskeletal structure is composed of actin and regulates cell shape, cell movement, and muscle contraction.

A. microfilaments B. intermediate filaments C. microtubules D. both microfilaments and intermediate filaments E. both microfilaments and microtubules

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Stem cells are _____

a. unspecialized b. specialized c. unable to divide d. always pluripotent e. only found in embryos

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Unique features of skates and rays are their

a. gill slits. b. adipose tissues. c. flat bodies. d. spiracles. e. countershaded bodies.

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Arsenic poisoning affects ATP production by ____

a. using excess oxygen b. interfering with Krebs cycle and electron transport chain reactions c. increasing carbon dioxide levels d. blocking glucose entry into cells

e. blocking the enzymes of glycolysis

Biology & Microbiology