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 non - polar) 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 diffusion concentration to a facilitated diffusion concentration.
3. when molecules spread out, it is called active, and when they spread out using a channel protein, it is called energy (atp)
4. when substances move against their gradient, it is called channel protein (ion pore) transport, and it requires a carrier protein and does not change shape for transport.
5. what is the difference between channel proteins and carrier proteins?
6. how do carbohydrates function in the cell membrane?
7. 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 lipid - bilayer membrane by simple diffusion. Large, polar molecules and ions cannot pass through easily without the help of transport proteins.
2. a. Non - polar and small molecules can cross the membrane more easily as the lipid - bilayer is non - polar. b. Polar and large molecules cannot cross easily. c. Charged ions cannot cross the membrane without transport proteins due to the non - polar nature of the lipid - bilayer.
3. Membranes need protein channels to allow the passage of polar molecules, ions, and large molecules that cannot cross the lipid - bilayer by simple diffusion.
4. Particles naturally move from a high concentration to a low concentration by diffusion. Facilitated diffusion also moves from high to low concentration but uses transport proteins.
5. When molecules spread out randomly, it is called diffusion. When they spread out using a channel protein, it is called facilitated diffusion.
6. When substances move against their concentration gradient, it is called active transport, which requires a carrier protein and energy (ATP).
7. Channel proteins form a pore through which specific molecules or ions can pass. Carrier proteins bind to a molecule, change shape, and transport it across the membrane.
8. Carbohydrates in the cell membrane function in cell - cell recognition, adhesion, and as receptors.
9. The immune system uses carbohydrates on cell membranes (glycoproteins and glycolipids) to identify self - cells and prevent the immune system from attacking them.

Answer:

1. Could pass: Small non - polar molecules (e.g., O₂, CO₂). Could not pass: Large polar molecules, ions.
2. a. nonpolar, small; b. polar, large; c. cannot
3. To allow polar, ionic and large molecules passage.
4. high, low
5. diffusion, facilitated diffusion
6. active, energy (ATP)
7. Channel proteins form pores; carrier proteins bind and change shape.
8. Cell - cell recognition, adhesion, receptors.
9. Immune system.