20. The primary molecule of the cell (plasma) membrane is known as a .

21. Because the interior of the lipid bilayer contains the nonpolar , only small nonpolar substances are able to diffuse directly across the cell membrane.

Proteins within the cell membrane serve different functions. List four examples of membrane proteins found within the cell below:

Chinese privet is a plant that is native to china. over 150 years ago, chinese privet was introduced to the united states as a fast-growing shrub that serves as an excellent privacy hedge. with no natural herbivore, chinese privet quickly established itself and spread in natural areas throughout the southeast and eastern seaboard of the united states. its dominance in these areas has jeopardized the survival of native plant species. chinese privet provides evidence that introducing non-native organisms can cause environmental damage integrated pest management strategies will not decrease chinese privet populations american gardeners can easily control the spread of chinese privet non-native plant species have type i survivorship curves

Which of the organisms listed below performs nitrogen fixation? a. legumes b. plants c. bacteria d. fungi

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins