Principles of Ecology. - ppt download

Types of organisms

Types / January 28, 2018

It is in the inference family of questions, but most strongly supported question stems are often less strict. In other words, the correct answer may be not be something that must be true, but is very close to it.

This is a stimulus without a conclusion, which is often the case for inference questions.

We are told that some organisms originate by one organism engulfing another organism. The one that was eaten becomes part of the one that ate it.

So in other words, this is an endosymbiotic situation according to the stimulus:

Organism A engulfs Organism B

We now have an organism called Godzilla.

It is no longer called Organism A, as it now has Organism B functioning with it, so it differs from its old self in a respect.

The first part of the stimulus is used to acquaint you with endosymbiosis.

We are next told about an unusual nucleomorph found in a plant, we will call it Plant C. We are told that a nucleomorph is a structure that contains DNA and resembles a nucleus.

We are told that there are 2 versions of a gene in the DNA in the nucleomorph of this plant.

We are told that if the nucleomorph were not the remains of an engulfed organism's nucleus, then one would expect to find 1 version of the gene.

So from our information given in the stimulus, we know that we have two versions, so we are looking at the real possibility of this nucleomorph being the remains of an engulfed organism's nucleus.

This would give us support to postulate that Plant C originated from endosymbiosis.

Answer choices:

A) Contain nucleomorph -> Organism originated through endosymbiosis

We have no justification for us to believe that endosymbiosis is necessary for containing a nucleomorph.

B) Attractive wrong answer here. We know that some genetic information of another organism is found in the nucelomorph of Plant C. However, we are not told that all of the genetic material of another organism is found there. Plus, we were told that during endosymbiosis one organism engulfs part of another organism. So it could be the case that not all of the organism was used.

C) We have no information as to how nucleomorphs originate. You could be born with one before endosymbiosis took place.

D) 2 organisms undergo endosymbiosis -> At least 1 of them contains a nucleomorph.

We do not have justification as to the makeup of organisms before endosymbiosis. It could be true that nucleomorphs are formed only after endosymbiosis.

E) This has the most support for it.

We have a situation of 2 versions of a gene being found in the nucleomorph of Plant C.

All you need is here