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.

Recall that endocytosis is the process by which solid particles and fluid and transported from the outside to the inside of the cell by the use of vesicles.

When a cell engulfs a foreign pathogen, it creates a vesicle known as a phagosome. The phagosome carries the pathogen within the cell and fuses with a lysosome, which allows hydrolytic enzymes to digest the pathogen. The process of engulfing the pathogen in a vesicle is known as phagocytosis.

A cell can also form a vesicle around fluids in the extracellular space, via the process of pinocytosis. This vesicle can also fuse with lysosomes, allowing the breakdown of small particulates in the vesicle, which can then be used for energy.

Both phagocytosis and pinocytosis are forms of endocytosis.

ATP synthase is an important enzyme that is required for oxidative phosphorylation, a process that produces majority of the ATP in a cell. Both exocytosis and endocytosis are active processes. This means that they require energy (ATP) input; therefore, ATP synthase is essential for both endocytosis and exocytosis.

All proteins are synthesized by ribosomes, but the location of the ribosome can vary depending on the function and destination of the protein.

Ribosomes can be found as either as free-floating organelles in the cytosol or as part of the rough endoplasmic reticulum. The proteins synthesized on the rough endoplasmic reticulum will undergo modification and vesicular packaging, and are often destined for regions outside of the cell. These proteins can be expelled from the cell via exocytosis.

On the other hand, free-floating ribosomes in the cytosol produce proteins that are destined to remain in the cytosol. These proteins, once synthesized, are transported within the cytosol and never make contact with the cell exterior. The proteins from free-floating ribosomes do not undergo exocytosis.

Exocytosis is the process by which materials and fluid are transported from the inside of the cell to the outside of the cell by the use of vesicles. Endocytosis is the process by which materials and fluid are transported from the outside to the inside of the cell by the use of vesicles. The question suggests that the proteins are synthesized inside the cell and then packaged into vesicles.

This process is common for a few different types of proteins. Membrane proteins will be integrated into these vesicles and introduced to the cell membrane by fusion of the vesicle. Some proteins destined for the lumens of cell organelles will also be packaged into vesicles, which will fuse with organelle membranes to deposit their contents. Most commonly, however, vesicles will fuse with the cell membrane and release protein contents into the extracellular space via exocytosis.

Golgi apparatus vesicles will never be involved in endocytosis. Of the two options involving exocytosis, only one offers the correct explanation (deposition of proteins into the extracellular space).