Question

1. which of the following describes how phospholipid regions are positioned in the cell membrane?

(a) hydrophilic phosphate head regions are positioned toward aqueous environments
(b) hydrophobic fatty acid tail regions face each other within the exterior (outside) of the cell membrane
(c) hydrophilic phosphate head regions face each other within the interior (inside) of the cell membrane
(d) hydrophobic fatty acid tail regions are positioned toward aqueous environments

1. water crosses the plasma membrane of certain eye cells at a higher rate than it does in other cell types. which of the following best explains why the rate of water transport is higher in the eye cells?

(a) the eye cells move water against the concentration gradient, which is faster than moving water with the concentration gradient.
(b) the eye cells have more protein channels (aquaporins) that allow water to pass through in greater quantities than the phospholipid bilayer allows.
(c) the eye cells have more atp than other cells do, which allows them to use active transport to move water across the membrane more rapidly.
(d) the eye cells modify water molecules so that they are positively charged, allowing them to cross the phospholipid bilayer more easily than unmodified water molecules.

1. in rattlesnake venom there are molecules that can cause hemolysis, or breakage of the hydrophilic heads from the hydrophobic tails in red blood cells. in this venom, there are three enzymes:

• phospholipase, which degrades phospholipids
• neuraminidase, which removes cell surface carbohydrates
• protease, which degrades proteins

which of these enzymes are responsible for fatal red blood cell hemolysis?
(a) the neuraminidase would degrade the carbohydrate - rich membrane, leading to cell breakage
(b) the protease would degrade transmembrane proteins leading to cell lysis
(c) the phospholipase would degrade the phospholipids, or the component of a membrane creating a barrier
(d) the combination of all three enzymes degrading at the same time caused hemolysis

1. which of the following statements explains how the cell membrane’s structure contributes to its role in maintaining homeostasis?

(a) the cell membrane is composed only of rigid structures that prevent any substances from passing through, which ensures complete isolation from the external environment.
(b) the cell membrane’s phospholipid bilayer acts as a barrier, while embedded proteins selectively allow or block specific molecules from entering or leaving, thus helping to balance internal conditions.
(c) the cell membrane continuously produces energy by breaking down nutrients to power the movement of substances in and out of the cell.
(d) the cell membrane directly replicates dna to create instructions for maintaining balance in the cell.

Explanation:

Question 1 (Cell Membrane Phospholipid Positioning)

Phospholipids have hydrophilic heads (phosphate - based) and hydrophobic tails (fatty acid - based). In the cell membrane, the hydrophilic heads face the aqueous environments (inside and outside the cell), and the hydrophobic tails face each other in the interior of the membrane. Option A: Hydrophilic heads face aqueous environments (correct orientation). Option B: Hydrophobic tails face each other in the interior, not exterior. Option C: Hydrophilic heads face aqueous environments, not each other inside. Option D: Hydrophobic tails face each other, not aqueous environments. So the correct answer is A.

Water transport across cell membranes can be via simple diffusion (slow) or facilitated diffusion through aquaporins (protein channels, faster). Option A: Moving against concentration gradient is active transport, not faster than with gradient. Option B: More aquaporins allow more water to pass, explaining higher rate (correct). Option C: Water transport is usually passive, not active (ATP - driven). Option D: Water isn't modified to cross the bilayer. So the correct answer is B.

Hemolysis is the breakage of the hydrophilic heads from hydrophobic tails in red blood cells. Phospholipase degrades phospholipids (the main component of the cell membrane with hydrophilic heads and hydrophobic tails). Option A: Neuraminidase degrades carbohydrates, not related to phospholipid structure. Option B: Protease degrades proteins, not phospholipids. Option C: Phospholipase degrades phospholipids, disrupting the membrane structure and causing hemolysis (correct). Option D: Not all three enzymes are needed; phospholipase is the key for phospholipid degradation. So the correct answer is C.

Answer:

A. Hydrophilic phosphate head regions are positioned toward aqueous environments

Question 2 (Water Transport in Eye Cells)