A regulated body variable rises above its usual range. A control pathway activates effectors that lower the variable, and as the variable returns toward its normal range the corrective signal decreases. Why is this negative feedback?

Which statement best distinguishes natural selection from speciation at the level used in this course?

A skin cell is found to contain a DNA mutation, but it still responds normally to cell-cycle controls and is not dividing excessively. Which conclusion is most appropriate?

Which membrane-transport process moves a substance from lower concentration to higher concentration and requires cellular energy?

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?