Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?

1. Phospholipids are amphipathic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.
2. Phospholipids are lipophilic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.
3. Phospholipids are amphipathic molecules. The nonpolar head faces towards other fatty acid tails and the polar fatty acid tails face towards water.
4. Phospholipids are hydrophilic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.

Why is it advantageous for the plasma membrane to be fluid in nature?

1. Fluidity allows greater flexibility to the cell and motion of membrane components required for transport.
2. Fluidity helps only in transport of some materials, and does not contribute to the flexibility.
3. Fluidity helps in maintaining the pH of the intracellular fluid, and helps in maintaining the physiological pH of the cell.
4. Fluidity helps in providing mechanical strength to the plasma membrane.

What are four components of a plasma membrane? Explain each component’s function.

1. Phospholipids form the bilayer; carbohydrates help in adhesion; cholesterol provides flexibility; integral proteins form transporters; peripheral proteins are part of the cell’s recognition sites.
2. Phospholipids form the bilayer; carbohydrates help in adhesion; cholesterol forms transporters; integral proteins provide flexibility; peripheral proteins are part of the cell’s recognition sites.
3. Phospholipids form the bilayer; carbohydrates are part of the cell’s recognition sites; cholesterol provides flexibility to the membrane; integral proteins form transporters; intermediate filaments help in adhesion.
4. Phospholipids form the bilayer; carbohydrates function as adhesion; cholesterol provides flexibility to the membrane; integral proteins form transporters; intermediate filaments are part of the cell’s recognition sites.

Discuss why the following affect the rate of diffusion: molecular size, temperature, solution density, and the distance that must be traveled.

1. Larger molecules move faster than lighter molecules. Temperature affects the molecular movement. Density is directly proportional to the molecular movement. Greater distance slows the diffusion.
2. Larger molecules move slower than lighter molecules. Increasing or decreasing temperature increases or decreases the energy in the medium, affecting molecular movement. Density is inversely proportional to molecular movement. Greater distance slows the diffusion.
3. Larger molecules move slower than lighter molecules. Temperature does not affect the rate of diffusion. Density is inversely proportional to molecular movement. Greater distance speeds up the diffusion.
4. Larger molecules move slower than lighter molecules. Increasing or decreasing temperature increases or decreases the energy in the medium, affecting molecular movement. Density is inversely proportional to the molecular movement. Greater distance speeds up the diffusion.

Both of the regular intravenous solutions administered in medicine, normal saline and lactated Ringer’s solution, are isotonic. Why is this important?

1. Isotonic solutions maintain equilibrium and avoid the exchange of materials to or from the blood.
2. Isotonic solutions disrupt equilibrium and allow for better exchange of materials in the blood cells.
3. Isotonic solutions increase the pH of the blood and allow for better absorption of saline in the blood cells.
4. Isotonic solutions decrease the pH of the blood and avoid the exchange of materials to or from the blood cells.

A doctor injects a patient with what the doctor thinks is an isotonic saline solution. The patient dies, and an autopsy reveals that many red blood cells had burst. Was the solution the doctor injected really isotonic?

1. No, the solution was hypertonic.
2. No, the solution was either hypotonic or hypertonic.
3. No, the solution was hypotonic.
4. Yes, the solution was isotonic.

How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?

1. The sodium-potassium pump forces out three (positive) Na⁺ ions for every two (positive) K⁺ ions it pumps in; thus, the cell loses a net positive charge of one at every cycle of the pump.
2. The sodium-potassium pump expels three K⁺ for every two Na⁺ inside the cells, creating a net positive charge outside the cell and a net negative charge inside the cell.
3. The sodium-potassium pump helps the development of a negative charge inside the cell by making the membrane more permeable to negatively charged proteins.
4. The sodium-potassium pump helps in the development of a negative charge inside the cell by making the membrane impermeable to positively charged ions.

Potassium is a necessary nutrient in order to maintain the function of our cells. What would occur to a person that is deficient in potassium?

1. The excess sodium disrupts the membrane components.
2. The excess sodium increases action potential generation.
3. The cells would not be able to get rid of extra sodium.
4. The cells would not be able to bring in sodium.

Which statement describes processes of receptor-mediated endocytosis and exocytosis, and the changes in the membrane organization involved with each?

1. Receptor-mediated endocytosis involves the binding of a ligand to its receptor, resulting in the formation of a clathrin-coated vesicle that enters the cell. In exocytosis, waste material is enveloped in a vesicle that fuses with the interior of the plasma membrane via attachment proteins.
2. In receptor-mediated endocytosis, waste material is enveloped in a membrane that fuses with the interior of the plasma membrane via attachment proteins. Exocytosis involves the opsonization of the receptor and its ligand in clathrin-coated vesicles.
3. In receptor-mediated endocytosis, waste material is enveloped in a membrane that fuses with the interior of the plasma membrane via attachment proteins. Exocytosis involves the opsonization of the receptor and its ligand in caveolae-coated vesicles.
4. Receptor-mediated endocytosis involves the opsonization of the receptor and its ligand in clathrin-coated vesicles that enter the cell. In exocytosis, waste material is enveloped in a membrane that fuses with the exterior of the plasma membrane via attachment proteins.

Describe the process of potocytosis and explain how it differs from pinocytosis.

1. Potocytosis is a form of receptor-mediated endocytosis where molecules are transported via caveolae-coated vesicles. Pinocytosis is a form of exocytosis used for excreting excess water.
2. Potocytosis is a form of exocytosis where molecules are transported via clathrin-coated vesicles. Pinocytosis is a form of receptor-mediated endocytosis used for excreting excess water.
3. Potocytosis is a form of receptor-mediated endocytosis where molecules are transported via caveolae-coated vesicles. Pinocytosis is a mode of endocytosis used for the absorption of extracellular water.
4. Potocytosis is a form of receptor-mediated endocytosis used for the absorption of water. Pinocytosis is a mode of endocytosis used for the excretion of extracellular water.