Unit 9
Body systems.
How the body takes things in, shares them out and moves: the gut, the lungs, the heart's two loops, and muscles as levers.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 32 practice questions · about 2 hours
Digestion
What happens to a meal: a stomach that empties slowly, the small intestine where food is absorbed, why fat stays longer, what bile does, and what reaches the large intestine.
Breathing and gas exchange
How air gets into the lungs, how much of it really reaches the air sacs, why a deep breath beats a fast one, and why in thin air the blood carries less oxygen.
The heart and circulation
Two loops and one heart: where each side of the heart sends the blood, arteries and veins, cardiac output as rate times stroke volume, and what changes as the heart speeds up.
The systems work together
One chain from the air to the muscle: how blood is redirected in exercise, why the brain always gets the same, what changes after a meal, and which systems work harder in a run.
Muscles and levers
Muscles only pull, so they work in pairs; the biceps pulls eight times the weight because its tendon sits close to the elbow; and inside the muscle, actin and myosin filaments slide past each other and pull hardest in the middle.