Science Reviewer Terms and Definitions

John Dalton proposed the modern atomic theory in the early 19th century, asserting that all matter is composed of indivisible atoms. He introduced key concepts such as the idea that atoms of the same element are identical and that chemical reactions involve the rearrangement of these atoms. Dalton's work laid the foundation for understanding chemical compounds and reactions, significantly advancing the field of chemistry and shaping our comprehension of matter at a fundamental level. His theories were instrumental in moving beyond philosophical ideas to a scientific framework for studying atoms.

J.J. Thomson discovered the electron in 1897 through his experiments with cathode rays, demonstrating that they were composed of negatively charged particles. He proposed the Plum Pudding Model in 1904, suggesting that atoms are made up of a positively charged "soup" with negatively charged electrons embedded throughout, similar to plums in a pudding. This model was significant in advancing atomic theory, although it was later replaced by more accurate models as further discoveries were made about atomic structure.

Sublimation is the process where a substance transitions from a solid state directly to a gas without passing through the liquid phase. This occurs under specific conditions of temperature and pressure, allowing molecules to gain enough energy to break free from their solid structure. Common examples include dry ice (solid carbon dioxide) and mothballs (naphthalene), which sublimate at room temperature. This phenomenon is significant in various natural and industrial processes, including freeze-drying and the behavior of certain materials under specific environmental conditions.

In an experiment, the dependent variable is the factor that researchers measure to assess the effects of changes made to the independent variable. It reflects the outcomes or responses that occur as a result of manipulating the independent variable. By observing the dependent variable, scientists can determine the relationship between the two variables and draw conclusions about the effects of the experimental conditions.

Mitochondria are not exclusive to animal cells; they are also present in plant cells, fungi, and many protists. These organelles are essential for cellular respiration, converting nutrients into energy in the form of ATP. Both animal and plant cells rely on mitochondria for energy production, although plant cells also contain chloroplasts for photosynthesis. Thus, the statement claiming that mitochondria are found only in animal cells is incorrect.

A hypothesis serves as a foundational element in scientific research, representing a testable statement based on prior knowledge or observations. It allows researchers to formulate predictions that can be validated or refuted through experimentation and analysis. By being testable, a hypothesis enables the scientific method to progress, fostering a systematic approach to understanding phenomena. Thus, characterizing a hypothesis as an educated guess underscores its role in guiding investigations while remaining open to evidence-based conclusions.

Plant cells have distinct features that set them apart from animal cells. The cell wall provides structural support and protection, while chloroplasts are essential for photosynthesis, allowing plants to convert sunlight into energy. Additionally, the large central vacuole serves multiple functions, including storage of nutrients and waste products, and maintaining turgor pressure to keep the plant rigid. In contrast, animal cells lack these structures, relying on different mechanisms for support and energy production.