Question

A biologist has found an organism she cannot identify while doing a census in a swamp. Which of the following would be the best characteristic to look for in order to decide whether this organism should be classified as a protist or as a plant?
Answer

If it can photosynthesize, it is a plant.

If it is unicellular, it is a protist.

If it must live in water, it is a protist.

If it produces spores, it is a plant.

Answer 1

None of these really work:

Many protists (such as dinoflagellates) are capable of photosynthesis.

Entire clades of green algaes (kingdom plantae) are unicellular.

Seaweeds must live in water to survive, and they are not protists.

As for the spores thing, only more primitive plants such as ferns are capable of producing those.

Answer 2

@Navanax - Great answer. I do want to bring up though - for choice two, isn't that slightly dependent on how the term "plant" is defined? If, perhaps, this question were found in an older textbook - it seems to me that choice two would be best because older definitions of "plant" were restricted to the traditional definition - i.e, excluding the green algae. I know even some newer textbooks, like Campbell's (9th ed.) still continue to use the traditional definition, and group the algae separately. That being said - has the newer "Viridiplantae" definition of plant become universally accepted amongst biologists now?

Answer 3

im not sure but thank-you!

Answer 4

@kma230 Yes and no; as far as I understand it, Viridiplantae is a subkingdom comprising green algae and land plants, but hasn't become the definition of the kingdom plantae, under which red algae are also classified.

Answer 5

I see - Plantae in this sense being the same as Archaeplastida ( http://en.wikipedia.org/wiki/Archaeplastida)? Thanks for clarifying.

Answer 6

Bad link, sorry - http://en.wikipedia.org/wiki/Archaeplastida