Expository Essay Examples: 15+ Free Samples for Students

"Why Do Leaves Change Color in Fall?"

Every autumn, trees transform into spectacular displays of red, orange, and yellow. This annual color show isn't just beautiful—it's science in action. Leaves change color in fall due to chemical processes triggered by changes in temperature and sunlight.

During spring and summer, leaves are green because of chlorophyll. This chemical helps plants make food from sunlight through photosynthesis. Chlorophyll is so strong that it covers up other colors in the leaf. As long as trees are making food, the leaves stay green.

When fall arrives, days become shorter and temperatures drop. Trees sense these changes and stop making chlorophyll. As the green chlorophyll fades away, other colors that were hidden all summer finally show through. Yellow and orange colors come from carotenoids, the same pigments that make carrots orange. These pigments were always in the leaves but couldn't be seen under all the green.

Red and purple colors are different. These come from anthocyanins, which trees actually create in the fall. Scientists think trees make these pigments to protect their leaves while they prepare for winter. Bright sunny days and cool nights trigger the most anthocyanin production, which is why fall colors are brightest in certain weather conditions.

Different trees have different amounts of these pigments. That's why oak trees turn brown, maple trees turn bright red, and birch trees turn golden yellow. The exact colors depend on the type of tree and the weather conditions that fall.

Understanding why leaves change color helps us appreciate the science behind autumn's beauty. Next time you see colorful fall leaves, you'll know you're watching chemistry at work.

"The Impact of Sleep on Academic Performance"

Teenagers today face mounting academic pressure, extracurricular commitments, and social obligations, often sacrificing sleep to manage their busy schedules. However, this trade-off comes at a significant cost. Insufficient sleep negatively impacts student academic performance through reduced concentration, impaired memory consolidation, and decreased cognitive function.

The most immediate effect of sleep deprivation is reduced concentration during school hours. When students don't get adequate sleep, their ability to focus on lectures, participate in discussions, and complete assignments diminishes significantly. A 2023 study published in the Journal of Adolescent Health found that students who slept fewer than seven hours per night showed a 35% decrease in sustained attention compared to well-rested peers. This reduced focus manifests in classrooms as difficulty following complex explanations, increased distraction, and lower engagement with learning material. Teachers report that sleep-deprived students often stare blankly, struggle to take notes, and ask for repeated explanations of concepts.

Beyond attention problems, insufficient sleep impairs the brain's ability to consolidate memories, a process essential for learning. During deep sleep stages, the brain transfers information from short-term to long-term memory storage. According to the National Sleep Foundation, students who consistently sleep seven to nine hours retain approximately 20% more information than those sleeping fewer than six hours. This difference becomes particularly evident during exam periods. Research from the University of California, Los Angeles shows that students who pulled "all-nighters" before exams scored an average of 12% lower than students who studied less but slept adequately. The brain simply cannot effectively store new information without proper rest.

The most concerning impact of sleep deprivation is decreased overall cognitive function, particularly in the prefrontal cortex responsible for critical thinking and problem-solving. Adolescent brains are still developing, making them especially vulnerable to sleep loss. Studies using brain imaging technology reveal that sleep-deprived teenagers show reduced activity in regions governing judgment, impulse control, and complex reasoning. This impairment affects performance on standardized tests, where students must analyze passages, solve multi-step problems, and synthesize information. The College Board reports that students averaging eight hours of sleep score 100-150 points higher on the SAT compared to those sleeping six hours or less.

The relationship between sleep and academic success is clear and well-documented. Students who prioritize adequate sleep demonstrate better concentration in class, retain more information, and perform better on assessments. While it may be tempting to sacrifice sleep for additional study time, research consistently shows this strategy backfires. Schools, parents, and students themselves must recognize that sleep is not a luxury but a biological necessity for optimal academic performance.