Analysis of test questions: autotrophic microorganisms can use carbon dioxide and water to generate organic matter without using ready-made carbon-containing organic matter; Heterotrophic microorganisms can only use ready-made carbon-containing organic matter, so their main difference is different carbon sources. So choose one

Test center: This question examines the composition of the culture medium.

Comments: This question is intended to examine the comprehension ability of candidates, and it is a moderately difficult question.