A little time.
A closer look.

Your goal: Connect the heart, lungs, and blood vessels into one explanation of oxygen delivery.

1. Follow one red blood cell

   Watch the four-minute lesson. Pause once to trace the route through the heart, lungs, and body.

2. Zoom in on the alveoli

   Watch the four-minute lesson. Read the companion explanation of what crosses the respiratory membrane.

3. Check the organ jobs

   Complete the six-question organ challenge in 3–5 minutes and read the feedback.

Your goal: Use observations of skin layers to explain how structure relates to protection and repair.

1. Begin with a first look at the skin model

   Before the explanations, explore independently for five minutes using the on-page controls in their cut, lift, and peel order. Record three things you notice, two things you find interesting, and one question in your journal. Use your own words; scientific vocabulary can come later.

2. Watch how a cut heals

   Watch the five-minute lesson, then read its skin-repair notes. Compare one idea with something you noticed in the model.

3. Practice with tissue evidence

   Complete the tissue challenge. Use its structure-and-function clues and read the explanations after each response.

Your goal: Distinguish element identity from charge, then connect molecules with ATP and cellular work.

1. Start with atoms, elements, and ions

   Watch the four-minute lesson. Write one sentence about what proton number tells you and another about what changes when electrons are gained or lost.

2. Follow matter and energy through metabolism

   Watch the eight-minute lesson. Pause at its questions and attempt an answer before continuing.

3. Test the element-identity rule

   Watch the short and answer one companion question in your own words before revealing its reasoning.