In cells, some molecules can move down their concentration gradients by crossing the lipid portion of the membrane directly, while others must pass through membrane proteins in a process called facilitated diffusion.

Facilitated diffusion therefore allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.

Figure 4. Simple Diffusion across the Cell (Plasma) Membrane. The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. In contrast to facilitated diffusion, which does not require energy and carries molecules or ions down a concentration gradient, active transport pumps molecules and ions against a concentration gradient.

Explanation:

richard allen was a minister for a african methodist episcopal church. he was also a educator and a writer one of america most active and influential black leaders. in 1794, he founded a african methodist episcopal church in philadelphia, pennsylvania. the church that he founded was the first independent african american denomination in the united states. he was a influential leader that makes many people feel comfortable under his preachings. they trusted him and supported him even though it could get them in trouble because slavery was happening. he risked his life to bring slaves and others closer to god and writing books. as a boy he and his family were slaves but some how he managed to teach himself how to read, write and preach. he has written four books about his life, slavery and hymns/preaching.

president thomas jefferson hoped that the embargo act of 1807 would the united states by demonstrating to britain and france their dependence on american goods, convincing them to respect american neutrality and stop impressing american seamen. instead, the act had a devastating effect on american trade.