What structure in an animal cell acts as a barrier between cell and the external environment?

What is thought to have caused the ice ages? A. Earths magnetic field B. Earths precession C. Earths rotation D. Earths tilt

The last part of the metamorphosis of a tadpole to an adult frog results in the disappearance of the tail.

Which discovery did not contribute to cell theory

Which base is found only in DNA? adenine

Income level is the most accurate factor in determining support levels for police. a. True b. False

The species name for the red maple is?

What pumps oxygen-rich blood to the body? A. Right Atrium B. Right Ventricle C. Left Atrium D. Left Ventricle

To be useful in science a hypothesis must be

How did Alexander Fleming's research solve a societal problem? He developed ways to treat inherited diseases. He advocated for regular hand washing to kill germs. He discovered a new type of medicine that could treat infections.

Which best describes the process of peer review? A. Scientists examine each other's work to make sure it is not biased or unreliable. O B. Scientists prevent other scientists from seeing their experimental data C.