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Biology for AP® Courses

Critical Thinking Questions

Biology for AP® CoursesCritical Thinking Questions
18 .
Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane such as the lipid-bilayer sphere, single-layer lipid sphere, and lipid-bilayer sheet? The image on the left shows a spherical lipid bilayer, shown as a half sphere whose surface is covered in the spherical polar heads, and thin, strandlike extend inward. In the core of the sphere is another half sphere, with the same anatomy. The image on the right shows a smaller sphere that has a single lipid layer only, made up of the spherical heads. The image at the bottom shows a lipid bilayer sheet; whose polar heads form the upper and lower surfaces, with tails extending toward each other in the middle.
  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.
19 .
The fluid mosaic model described the plasma membrane, seen here, as a mosaic of components. Why is it advantageous for the plasma membrane to be fluid in nature? The plasma membrane is composed of a phospholipid bilayer. In the bilayer, the two long hydrophobic tails of phospholipids face toward the center, and the hydrophilic head group faces the exterior. Integral membrane proteins and protein channels span the entire bilayer. Protein channels have a pore in the middle. Peripheral membrane proteins sit on the surface of the phospholipids, and are associated with the phospholipid head groups. On the exterior side of the membrane, carbohydrates are attached to certain proteins and lipids. Filaments of the cytoskeleton line the interior of the membrane.
  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 intracellular fluid, and helps in maintaining the physiological pH of the cell.
  4. Fluidity helps in providing mechanical strength to the plasma membrane.
20 .
List four components of a plasma membrane and explain their function.
  1. Phospholipids: form the bilayer; Carbohydrates: help in adhesion; Cholesterol: provide flexibility; Integral proteins: form transporters; Peripheral proteins: part of the cell’s recognition sites.
  2. Phospholipids: form the bilayer; Carbohydrates: help in adhesion; Cholesterol: form transporters; Integral proteins: provide flexibility; Peripheral proteins: part of the cell’s recognition sites.
  3. Phospholipids: form the bilayer; Carbohydrates: part of the cell’s recognition sites; Cholesterol: provide flexibility to the membrane; Integral proteins: form transporters; Intermediate filaments: help in adhesion.
  4. Phospholipids: form the bilayer; Carbohydrates: function as adhesion; Cholesterol: provide flexibility to the membrane, Integral proteins: form transporters; Intermediate filaments: part of the cell’s recognition sites.
21 .
Which explanation identifies how 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.
22 .
Both of the regular intravenous solutions administered in medicine, normal saline and lactated Ringer’s solution, are isotonic, such as seen in the middle image here. Why is this important? The left part of this illustration shows shriveled red blood cells bathed in a hypertonic solution. The middle part shows healthy red blood cells bathed in an isotonic solution, and the right part shows bloated red blood cells bathed in a hypotonic solution.
  1. Isotonic solutions maintain equilibrium and avoid the exchange of materials to or from the blood.
  2. Isotonic solutions disrupt equilibrium and allow better exchange of materials in the blood.
  3. Isotonic solutions increase the pH of blood and allow better absorption of saline in blood.
  4. Isotonic solutions decrease the pH of the blood and avoid the exchange of materials to or from the blood.
23 .
If a doctor injected a patient with what was labeled as an isotonic saline solution, but then the patient died, and an autopsy revealed that several of the patient's red blood cells had burst, such as in the image on the right, would it be true that the injected solution was really isotonic? Why or why not? The left part of this illustration shows shriveled red blood cells bathed in a hypertonic solution. The middle part shows healthy red blood cells bathed in an isotonic solution, and the right part shows bloated red blood cells bathed in a hypotonic solution.
  1. False, the solution was hypertonic.
  2. False, the solution was osmotic.
  3. False, the solution was hypotonic.
  4. True, the solution was isotonic.
24 .
How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?
  1. by expelling more cations than are taken in
  2. The sodium-potassium pump expels three ions 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 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 negative charge inside the cell by making the membrane impermeable to positively charged ions.
25 .
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 cell would not be able to get rid of extra sodium.
  4. The cell would not be able to bring sodium into the cell.
26 .
Which statement that describes processes of receptor-mediated endocytosis, 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 a 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. In exocytosis, waste material is enveloped in a membrane that fuses with the exterior of the plasma membrane via attachment proteins.
27 .
Describe the process of potocytosis. How does it differ 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 fluid.
  4. Potocytosis is a form of receptor-mediated endocytosis used for the absorption of water.
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