The current study examined the relations among key variables that underlie reading comprehension of expository science texts in a diverse population of adult native English readers. Using Mechanical Turk to sample a range of adult readers, the study also examined the effect of text presentation on readers' comprehension and knowledge structure established after reading. In Study 1, ratings of situational interest, select reading background variables, and select measures of readers' knowledge structure accounted for significant variance in comprehension. In Study 2, the knowledge structure metrics of primacy, recency, and node degree as well as several text ratings were found to be comparable across text presentation formats. Participants who read the text sentence-by-sentence obtained higher scores on measures of comprehension and provided higher ratings of situational interest than those who received the whole paragraph text at once. Knowledge structure measures for the sentence-by-sentence and paragraph formats were similar (68% overlap). We discuss implications for future research examining factors that underlie the successful comprehension of science texts.