The scientific method is a systematic approach to answering scientific questions, which involves making observations, formulating hypotheses, testing those hypotheses through experiments or other empirical methods, analyzing the results, and drawing conclusions based on the evidence gathered.

A hypothesis is a tentative explanation for a phenomenon or set of observations, whereas a theory is a well-supported and widely accepted explanation that has been repeatedly tested and confirmed through empirical research.

A molecule is a group of two or more atoms that are chemically bonded together, while a compound is a substance made up of two or more different elements that are chemically bonded together in a fixed ratio.

Natural selection is the process by which certain traits become more or less common in a population over time, based on their fitness or ability to survive and reproduce in a given environment. Individuals with advantageous traits are more likely to survive and pass on those traits to their offspring, while individuals with less advantageous traits are less likely to survive and reproduce.

DNA (deoxyribonucleic acid) is a double-stranded molecule that contains the genetic information of an organism, while RNA (ribonucleic acid) is a single-stranded molecule that plays a key role in protein synthesis and other cellular processes. RNA is made up of nucleotides that are similar to those in DNA, but with a different sugar molecule (ribose) and a slightly different chemical structure.

The greenhouse effect is a natural process by which certain gases (such as carbon dioxide, methane, and water vapor) trap heat in the Earth's atmosphere, causing the planet's temperature to rise. These gases absorb and re-emit infrared radiation from the sun, which would otherwise escape into space. However, human activities such as burning fossil fuels and deforestation have increased the concentration of greenhouse gases in the atmosphere, leading to global warming and other climate changes.

Prokaryotic cells are simple, single-celled organisms that lack a nucleus or other membrane-bound organelles, while eukaryotic cells are more complex, multi-cellular organisms that have a nucleus and other membrane-bound organelles. Eukaryotic cells are typically larger and more structurally diverse than prokaryotic cells.

An element is a pure substance made up of only one type of atom, while a compound is a substance made up of two or more different elements that are chemically bonded together in a fixed ratio. Elements cannot be broken down into simpler substances by chemical means, while compounds can be broken down into their component elements.

Vaccines work by exposing the immune system to a harmless or weakened form of a virus or bacterium, which triggers an immune response and stimulates the production of antibodies that can recognize and neutralize the pathogen if it is encountered again in the future. This process creates immunity to the disease without causing illness.

Mitosis is the process by which a single cell divides into two identical daughter cells, each with the same number of chromosomes as the original cell. Meiosis is a specialized type of cell division that occurs in the reproductive cells (sperm and eggs) and results in four genetically diverse daughter cells, each with half the number of chromosomes as the original cell. Meiosis