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💪 Muscle Pairs and Diffusion

See how antagonistic muscle pairs bend and straighten your joints, then discover how diffusion moves substances in and out of your cells.

lessons

~20 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

Muscles Work in PairsExplain how antagonistic muscle pairs like the biceps and triceps move a joint in two directions.Muscles create movement by contracting and pulling, never pushing, so they work in antagonistic pairs. To bend the elbow the biceps contracts and the triceps relaxes; to straighten it they swap, and pairs like this move joints all over the body.
Diffusion Moves SubstancesDefine diffusion and explain how it moves substances into and out of cells across exchange surfaces.Diffusion is the passive spread of particles from high to low concentration, driven by their random movement. It moves oxygen into the blood and carbon dioxide out, and it works fastest across thin, moist surfaces with a large area, like the lungs.

Questions this course answers

Muscles create movement by doing what?

Muscles move bones by contracting and pulling; they cannot push.

When you bend your arm, what do the biceps and triceps do?

To bend the arm the biceps pulls while the triceps relaxes.

Why must muscles work in antagonistic pairs?

One muscle pulls the bone one way; its partner pulls it back.

What is diffusion?

Diffusion spreads particles from crowded to less crowded areas.

In the lungs, why does oxygen diffuse from the air into the blood?

Oxygen moves down its concentration gradient, air to blood.

Which feature makes a surface good at diffusion?

Thin, large, moist surfaces speed up diffusion.

Grounded in trusted sources

BBC Bitesize
Britannica
KidsHealth (Nemours)
NHS

Every Wunder lesson is built from real, reputable sources — never invented.

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