In science, a hypothesis is a testable explanation for an observed pattern that can be investigated with experiments or further observations. Here, the scientist notices that ornamental grass is taller in a creek bed and proposes that water availability is responsible. That proposed explanation is a hypothesis because it makes a specific, testable claim about cause and effect that researchers can evaluate by manipulating water levels and controlling other factors to see if growth changes. If more water consistently leads to taller grass under controlled conditions, the hypothesis gains support; if not, it would be revised or rejected. This idea differs from a fact, which is an observed statement that is verified, and from a theory, which is a broad, well-supported framework that explains many related phenomena after extensive testing.

Information flows from DNA to RNA to protein. In transcription, a gene in DNA is used as a template to synthesize messenger RNA. The mRNA then travels to a ribosome, where translation reads its codons and assembles the corresponding amino acids to form a protein. This sequence—DNA to RNA to protein—explains how genetic information is expressed, which is why this option is the best description of the central dogma. The other statements mix up the order or skip the RNA step; for example, translating RNA into DNA or using proteins to produce DNA runs counter to the standard flow. There are special cases like reverse transcription in some viruses, but they are exceptions rather than the rule and don’t redefine the general flow. Replication of DNA is about copying genetic material for cell division and isn’t part of the gene-expression pathway.

A point mutation is a single nucleotide change in the DNA sequence. Because genes are read in codons, changing one base can shift the meaning of that codon, potentially swapping one amino acid for another (a missense change), creating a stop codon that truncates the protein (a nonsense change), or altering the start codon and changing where translation begins. These changes can affect the protein’s size, structure, and function. Sometimes the new codon still codes for the same amino acid (a silent mutation), so function may stay the same, though it can also subtly influence how much protein is made or how it folds. Larger-scale changes like chromosomal rearrangements aren’t point mutations, and mutations don’t always have no effect—many point mutations can alter function, though some are neutral.

Photosynthesis has two linked stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, energy from light drives the splitting of water, releasing oxygen, and generates ATP and NADPH as energy carriers. In the Calvin cycle, ATP and NADPH power the fixation of carbon dioxide into triose phosphates, which are later used to synthesize sugars such as glucose. So the statement that correctly describes both stages is that the light-dependent reactions produce ATP, NADPH, and O2, while the Calvin cycle uses those energy carriers to fix CO2 into sugars. The other descriptions mix up which stage does CO2 fixation, which stage produces ATP, and what each stage releases, leading to incorrect roles and outputs.