What anatomical feature of the veins maintains a unidirectional flow of blood back toward the heart?

A vaccine a. can be harmful because it contains pathogens such as viruses. b. contains a changed pathogen, so the pathogen is no longer harmful. c. provokes a response from the viral immune system. d. all of the above

The growth patterns of ivy wisteria and other vines that wrap around objects is an example of

Why is sickle cell disease classified as a recessive disorder?

All living and nonliving parts of a environment

Which organism would more closely resemble it's parent, one produced by asexual reproduction, or one produced by sexual reproduction? why?

What accounts for genetic biodiversity existing in modern multicellular organisms?

Torri and Tamara are both performing scientific investigations on the learning capabilities of mice. In Torri's experiment, she sets up two knobs in a cage with a mouse. When the mouse touches the knob on the left, it receives a small shock.

What did Chargaff discover while studying bases in the DNA of organisms?

Russia's system of government and identify its basic structure.

Which statement about the light microscope is correct?