Zona occludens are formed at __________ junctions and desmosomes are formed at __________ junctions. 

Which of the following is true regarding desmosomes and hemidesmosomes? 

Which of the following criteria does not help differentiate between prokaryotes and eukaryotes?

In which of the following pH environments would an enzyme from the small intestine most likely be active?

Which of the following is NOT a function of peroxisomes?

Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.

In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.

The failure of phagocytosis in the initial stages of endosymbiosis could have been due to the failure of host cells to produce digestive enzymes. Most cells generate digestive enzymes into the vesicle that houses newly-phagocytosed material, or phagosome. Failure to form which of the following would be expected in a cell that was unable to digest compounds in its phagosome?

One component of the immune system is the neutrophil, a professional phagocyte that consumes invading cells. The neutrophil is ferried to the site of infection via the blood as pre-neutrophils, or monocytes, ready to differentiate as needed to defend their host.

In order to leave the blood and migrate to the tissues, where infection is active, the monocyte undergoes a process called diapedesis. Diapedesis is a process of extravasation, where the monocyte leaves the circulation by moving in between endothelial cells, enters the tissue, and matures into a neutrophil.

Diapedesis is mediated by a class of proteins called selectins, present on the monocyte membrane and the endothelium. These selectins interact, attract the monocyte to the endothelium, and allow the monocytes to roll along the endothelium until they are able to complete diapedesis by leaving the vasculature and entering the tissues.

The image below shows monocytes moving in the blood vessel, "rolling" along the vessel wall, and eventually leaving the vessel to migrate to the site of infection.

A scientist is investigating the digestive enzymes present in a neutrophil as it digests foreign material. Where are these enzymes most likely to be stored immediately before they are used to break down phagocytosed material?

Which of the following scenarios could directly cause cell death?

Which of the following may be the pH inside a lysosome?

There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.

Cisternal Maturation Hypothesis

In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.

In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.

Vesicular Transport Hypothesis

In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.

In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.

Microtubules are closely associated not only with vesicular transport, but also with cilia and flagella physiology. Which statement is true regarding cilia and flagella?

I. Most ciliated cells have many cilia structures

II. Most flagellated cells have only one flagellum

III. Only flagella have a 9+2 microtubule arrangement

IV. Both cilia and flagella move via the action of dynein