Each phospholipid consists of a polar phosphate head and two non-polar lipid tails. The phospholipid bilayer consists of polar heads facing the inside and outside of the cell, which interact with polar, aqueous environments. The non-polar hydrocarbon tails are packed on the inside of the bilayer, as far away from the polar environments as possible.

Both prokaryotic and eukaryotic cells have plasma membranes that separates the cell's contents from the external environment. Prokaryotic cells frequently have more external layers (cell wall and cell capsule), since they are generally more exposed and require additional protection from the environment, but these layers will always lie one top of the fundamental cell membrane.

Prokaryotes have 70S ribosomes, while eukaryotes have 80S ribosomes. Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotes lack such organelles. Prokaryotic organisms are always unicellular, while eukaryotic organisms can be either unicellular (protists) or multicellular.

Cell containment, as the name suggests, is the process by which the contents of a cell (organelles, cytoskeleton, etc.) are contained within a region of space inside the cell. This means that there must be a barrier that prevents the contents from leaking out of the cell. This barrier is the phospholipid bilayer, or cell membrane. Phospholipid bilayers can be found in plasma membranes or in the membranes that cover the organelles. Recall that most organelles in an eukaryotic cell contain a phospholipid bilayer that separates the contents of the organelle from the cytosol.

Proper cell containment depends heavily on the properties of the phospholipid bilayer. The cell membrane is semipermeable; this means that the cell membrane only permits certain molecules to pass through. If the cell membrane were permeable to everything, then the contents inside the cell can easily traverse the cell membrane and exit the cell. The semipermeability of the cell membrane is very important to maintain cell containment and regulate the homeostatic environment of the cell interior.

The acidity of lysosomes and presence of mitochondrial DNA are irrelevant to cell containment. The acidity of lysosomes is important for eliminating biological waste products inside the cell, and the mitochondrial DNA is important to produce unique mitochondrial proteins; however, they do not play a role in maintaining the contents of the cell or an organelle.

As described in the question, the shell is protecting against osmotic stress. We would expect osmotic stress to be present when we put the oocysts in pure water, which is hypotonic relative to the oocyst itself. The tendency of non-protected cells to burst in such a condition is the result of osmotic stress caused by the influx of water diffusing across the membrane.

Because there is a smaller concentration of solute inside the cell than in the solution, it is said to be in a hypertonic solution. This will cause water from inside the cell to move outside the plasma membrane to account for this difference; therefore, the cell will crenate (shrink).

The trick to understanding this question is to remember that the sodium chloride actually consists of equal parts sodium ions and chlorine ions; therefore, the internal concentration of solute inside the red blood cell is actually twice the concentration of solute outside the cell. Since the cell contains a higher solute concentration compared to the extracellular environment, the solution is considered hypotonic. Water will flow toward the more concentrated region via osmosis, entering the cell and causing it to swell. Eventually, the swelling can cause the cell to lyse.

The major purpose of cholestrol in the plasma membrane is to maintain membrane fluidity. Carbohydrates and glycoproteins function in cell-to-cell recognition, and proteins function in the transport of particles through the membrane. Charged particles can't freely pass through the membrane unless it is through a carrier protein.

Pinocytosis, or "cell drinking", refers to the process by which extracellular fluids are engulfed by invaginations of the cellular membrane to create vesicles of the fluid. Phagocytosis is a similar mechanism that acquires extracellular solids into the cell. Receptor-mediated endocytosis occurs when hormones and nutrients bind to a ligand-specific receptor on the cellular membrane and clathrin-mediated endocytosis involves entrance to the cell via clathrin-coated pits.

The best answer would be pinocytosis, or "cell-drinking". Pinocytosis is a specific type of endocytosis; while pinocytosis refers to the uptake of fluids, endocytosis refers to any process involving cellular uptake via vesicles.

Phagocytosis is cellular uptake of large molecules or pathogens, and receptor-mediated endocytosis requires a particular ligand to initiate endocytosis.