Integration of Body Systems · Paper 2 — Free Biology HL Practice Questions

A student investigates the effect of exercise on heart rate. She measures her resting heart rate, then runs on a treadmill for 5 minutes at a constant speed, recording her heart rate every minute. Time — Heart rate / bpm Rest (0 min) — 72 1 min — 98 2 min — 115 3 min — 128 4 min — 135 5 min — 138

A clinical study investigates the role of the hypothalamus–pituitary–adrenal (HPA) axis integrating nervous and endocrine responses to acute psychological stress. Twenty healthy volunteers perform a 10-minute public speaking task. Blood samples are taken before the task (baseline), immediately after (0 min), and at 30 and 60 minutes after the task. Time point — Plasma cortisol ($\mu\text{g/dL}$) — Plasma ACTH (pg/mL) — Heart rate (bpm) Baseline — 10 — 20 — 70 0 min — 25 — 60 — 110 30 min — 35 — 45 — 80 60 min — 15 — 22 — 72 Additional information: - HPA axis pathway: stress $\rightarrow$ hypothalamus releases CRH $\rightarrow$ anterior pituitary releases ACTH $\rightarrow$ adrenal cortex releases cortisol; cortisol exerts negative feedback on the hypothalamus and anterior pituitary. - The sympathetic nervous system is activated during stress, releasing noradrenaline from nerve terminals and adrenaline from the adrenal medulla.