Cell biologists hypothesize that millions of years ago the nucleus of eukaryotic

Question

Cell biologists hypothesize that millions of years ago the nucleus of eukaryotic cells appeared when a prokaryotic cell engulfed another prokaryotic cell, without destroying the engulfed cell.

True

False

: If you examine the cell-cell junctions in a beetle (an invertebrate) at Florida National University, you will find that it has __________________ junctions as opposed to the tight junctions that you would find in a student (vertebrate).

symport

striated

scaffolded

septate

Your heart muscle cells, which form fibers, beat all at the same time thanks to a rapid exchange of ions through their:

claudin junctions

apical junctions

integrin junctions

gap junctions

Fibronectins may have been the first extracellular matrix proteins to evolve in animal cells.

True

False

symport

striated

scaffolded

septate

Explanation / Answer

1.True

This could be explained to some extent by the Endosymbiosis Theory (proposed by Margulis). Symbiosis is a type of interaction between two organisms in which both are mutually benefited. Endosymbiont refers to an organism which lives inside another. Endosymbiosis came about when large cells engulfed small cells.

According to the theory, the interaction begins when a large anaerobic cell engulfs a smaller aerobic cell. The aerobic cell, now living inside the anaerobic cell, efficiently metabolizes food molecules using oxygen and shares the excess ATP with its host, the large anerobe. In due course of time, most of DNA from the smaller aerobic cell made its way into the nucleus of host cell and the two separate organisms became one - the ancestor of all the eukaryotic cells we see today.

2. Septate.

Invertebrate epithelial cells have septate junctions as opposed to the tight junctions seen in vertebrates. Septate junctions were first identified in Drosophila salivary glands. They appear ladder-like under electron microscopy.

3. Gap junctions.

Gap junctions are specialized intracellular connections between cells. They directly connect the cytoplasm of two cells allowing the passage of various molecules, ions and electrical impulses between them.

In cardiac muscle, there are numerous gap junctions between adjacent cells. These allow action potentials to spread immediately from one cardiac muscle fiber to another, allowing them to contract together as a unit.

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