The largest mass extinction was in the

a.

Precambrian time.

c.

Paleozoic era.

b.

Cenozoic era.

d.

Mesozoic era.

How many electrons are there in a completed outer shell for period 1?

How do scientists produce new genetic variations not found in nature? By A) transforming RNA B) using gel electrophoresis. C) using lasers to cut and paste DNA. D) causing mutations with chemicals or radiation.

Sympatric speciation involves reproductive isolation of dispersed populations. is common in plants since many plant species can reproduce by self-fertilization. is often associated with polyploidy in animals.

The edges of most lithospheric plates are characterized by

When a Gila monster uses a rock for shade from the noonday sun, it is interacting with a. an abiotic factor b. another organism c. an ecosystem d. its community

Which curve was most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?

Based on the text, why might the California's Division of Safety of Dams have ordered in 2001 that the Calaveras Reservoir be kept at no more than 40% full?

What role does nitrogenous bases have in DNA and RNA

How do carnivores (which eat only meat) obtain nitrogen for building critical organic molecules? A) They eat consumers, which ate plants, which absorbed it from the soil. B) They absorb the nitrogen in the ground through their skin.

In purebred Labrador retrievers, the dominant fur-color allele, B, results in black fur, and the recessive allele, b, results in yellow fur. Suppose the Happy Labrador Ranch breeds yellow and black Labrador retrievers.