A person voluntarily lifts a cup with skeletal muscles while smooth muscle in the digestive tract continues contracting without conscious control. Which statement correctly identifies the broad nervous-system divisions involved?

A mutation changes the DNA sequence within a gene. Which pathway best explains how that change could eventually alter a trait?

A person has one typical allele and one recessive allele associated with an enzyme-deficiency disorder. The person does not show the disorder. Which statement is correct?

A structural protein in connective tissue is assembled by linking many smaller building units together. Which building units are used to make proteins?

Researchers ask 900 adults how many hours per week they spend outdoors and measure each person’s self-reported mood score. Adults who spend more time outdoors report higher mood scores. The researchers do not assign outdoor time. Which conclusion is justified by this study alone?

A mutation disables a protein that normally stops the cell cycle when severe DNA damage is detected. A damaged cell continues through replication and division. Why can this increase cancer risk?

After six months of endurance training, a person’s resting heart rate is lower than it was before training. Their inherited alleles have not changed. Which description is most accurate?

Several small studies support one explanation for a biological observation, but a later set of larger, better-controlled studies supports a different explanation. Which response best reflects how science works?

Phospholipids form much of the basic structure of the plasma membrane. Phospholipids belong to which biomolecule class?

Scientific reasoning Researchers survey 1,200 adults about how often they cook meals at home and measure each person’s blood pressure at one clinic visit. Adults who report cooking at home more often have lower average blood pressure. A headline summarizes the study as: “Cooking at home lowers blood pressure.” In 2–3 sentences, evaluate whether this study supports the causal claim and identify one plausible alternative explanation or confounding variable.