Question

1. what molecules can cross the membrane? what molecules cannot?

could pass could not pass

1. circle each correct term in parentheses.

a. in order to cross the membrane, molecules need to be (polar or nonpolar) and (large or small.)
b. molecules that cannot cross the membrane are (polar or nonpolar) and (large or small)
c. if molecules are charged, like ions, they (can or cannot) cross the membrane

1. why do membranes need protein channels?
2. particles naturally want to move from a ____________ concentration to a ____________ concentration.
3. when molecules spread out, it is called ____________________________, and when they spread out using a channel protein, it is called ____________________________
4. when substances move against their gradient, it is called ____________________________ transport, and it requires a carrier protein and ____________________________
5. what is the difference between channel proteins and carrier proteins?

how do carbohydrates function in the cell membrane?

1. what system in your body uses carbohydrates to id cells as belonging to you in order to decide whether or not to attack them?

Explanation:

1. Small non - polar molecules like oxygen and carbon dioxide can pass through the membrane. Large polar molecules like glucose and charged ions cannot pass through easily without assistance.

8a. Non - polar and small molecules can cross the membrane.
8b. Polar and large molecules cannot cross the membrane easily.
8c. Charged molecules (ions) cannot cross the membrane easily without help.

1. Membranes need protein channels because many polar and charged molecules that are essential for cell function cannot cross the non - polar lipid bilayer on their own. Protein channels provide a hydrophilic pathway for these molecules.
2. Particles naturally move from a high concentration to a low concentration.
3. When molecules spread out, it is called diffusion. When they spread out using a channel protein, it is called facilitated diffusion.
4. When substances move against their gradient, it is called active transport, and it requires a carrier protein and energy (usually in the form of ATP).
5. Channel proteins form a pore through the membrane for specific molecules to pass through by facilitated diffusion. Carrier proteins bind to specific molecules, change shape, and transport the molecule across the membrane, which can be involved in both facilitated diffusion and active transport.
6. Carbohydrates in the cell membrane are often attached to proteins (glycoproteins) or lipids (glycolipids) and function in cell - cell recognition, cell adhesion, and as receptors for certain molecules.
7. The immune system uses carbohydrates on cell membranes to identify cells as self or non - self.

Answer:

1. Could pass: Small non - polar molecules (e.g., oxygen, carbon dioxide). Could not pass: Large polar molecules (e.g., glucose), charged ions.

8a. Non - polar, small
8b. Polar, large
8c. Cannot

1. To allow polar and charged molecules to cross.
2. High, low
3. Diffusion, facilitated diffusion
4. Active, energy (ATP)
5. Channel proteins form pores, carrier proteins bind and change shape for transport.
6. In cell - cell recognition, adhesion and as receptors.
7. Immune system