Which of the following is true of valves in veins?

A) They are associated with venous sinuses

B) They are most abundant in limbs

C) They contract to propel blood forward

D) They prevent blood pressure in veins from dipping below that of arteries

The salmon provide the important nutrient of nitrogen to the trees. The nitrogen is a (n) factor. * A. abiotic B. biotic

Which statement best describes the green house effect

Water is called the universal solvent because A) It is a nonpolar substance. B) Its molecule has no charge. Eliminate C) It is used around the world. D) It dissolves a variety of substances.

Explain a scenario in which secondary succession would occur.

Tricyclic antidepressants appear to work by blocking the reuptake of

In what two places on plants do seed grow?

Which statement describes gravity? Check all that apply There is no defined unit of measurement for gravity Gravity is the force that pulls objects toward Earth's center Objects that have a small mass will have no gravitational pull Gravitational

Which statement about crustaceans is true? * (A) all have the same number of appendages (B) all have an internal skeleton (C) all have an exoskeleton (D) only some have jointed appendages

5. The measurement of the amount of friction a surface will generate is called the of friction'.

How much of earth's air is made of Nitrogen?