A cell biologist tells you about a structure called a chloroplast and explains to you that this cell part is found only in plant cells. She tells you that the chloroplast helps the plant produce energy and that it contains its own genetic material and may make copies of itself. After studying this new information, you are asked which theory of cell evolution the example of the chloroplast supports.
Which statement would be correct based on the evidence presented?
Inside Out or Outside In
Whenever research is to be done, scientists will design experiments to test their new ideas, then use the results to
prove, or perhaps modify their ideas. When a long-held idea is challenged, such as the prevailing theory as to how
complex cells evolved, it can lead to exciting new discoveries and open up new areas of research, such as a brand new
idea called the “inside-out” theory.
The idea of how complex cells evolved is one that has perplexed researchers for many centuries. Scientists have long
thought about the question of how very simple cells, known as prokaryotes, evolved into the modern, complex cells of
today, which are known as eukaryotes. Prokaryotic cells are little more than a tiny pouch, with everything the organism
needs stuffed inside. Eukaryotic cells, on the other hand, are much larger and more complex, containing a number of
compartments, each specialized to carry out a different function. Two scientists are discussing two ways of thinking
about how complex cells have evolved. A summary of their statements are written below:
I still believe the prevailing theory, known as the endosymbiotic or “outside-in” theory. It states that eukaryotic cells
began to form when an ancient bacteria engulfed or swallowed a smaller prokaryotic cell. The smaller cell evolved while
inside to become a structure such as the mitochondria. Scientists point to the fact that this organelle has its own DNA
and was equipped to be living independently, as evidence for this theory.
I am challenging this long-held belief by proposing an “inside-out” theory for complex cell evolution. I believe that
simple bacteria reached out parts of their cell membranes, called “blebs,” to trap other smaller bacteria and use their
energy to get bigger and grow bigger blebs. Eventually the bacteria had acquired enough size and energy to out-
compete the smaller cells and build structures to help them survive better. Scientists have even found some simple
bacteria that do indeed produce blebs to back up their idea.