On the lake, the wind pushed the water into waves. The air acted on the water.

A lake on a windy day, its water pushed into waves.

A plant's roots hold it in the ground, and they take in water from the soil.

On the hill, the tree roots grew through the loose soil and held it together.

So the rain could not wash the soil away. The living things acted on the land.

Tree roots spread over the soil of a hillside.

In the field, the rain watered the grass, and the grass grew tall. The water acted on the living things.

A field of tall grass after rain.

The four examples as arrows: from the air to the water, from the water to the land, from the living things to the land, and from the water to the living things.

The four interactions the class saw on the walk.