Body-Part Clues at the Desert Research Blind

A Class Investigates Desert Structures

At a desert research blind, a class watches wildlife without approaching it. The students study prickly pear cacti nearby and night recordings of kangaroo rats. A structure is a body part. Some structures are on the outside of a living thing. Others are inside.

The cactus has broad, green stems called pads. A waxy skin covers each pad, and spines stick out from its surface. A ranger's photograph of a cut pad shows moist tissue inside. After several rainless days, living pads still feel firm. The cactus also has spreading roots near the soil surface. After a brief rain, these roots take up water from the damp ground. Older photographs show flowers, then fruits containing seeds. Some planted seeds later produce small cacti.

In the night recordings, a kangaroo rat pushes against the ground with its long hind feet and leaps toward its burrow when an owl approaches. The burrow is a hole in the ground, not a body part. The rat gathers seeds and eats them. A body diagram shows a stomach inside the rat. The stomach breaks up food; other digestive parts take nutrients from it. Nutrients provide materials and energy for growth. Inside the chest, lungs take in air, and the heart pumps blood around the body.

The class investigates a question: Could an outside covering slow water loss from moist material inside? They use sponges as models of moist pad tissue and wax paper as a model of the waxy skin. The model does not include living cells, roots, flowers, or spines.

Step 1: Students put equal-sized dry sponges into two matching trays. They add 40 grams of water to each sponge. Step 2: They cover the top and sides of one sponge with wax paper, leaving the other uncovered. Step 3: They place both trays beside each other on a shaded shelf for four hours. Sponge size, starting water, place, and time stay the same. The covering is what changes. Step 4: The teacher removes the cover and weighs the sponges. The class calculates the water lost. Their first results appear in the graph. Two fresh pairs are tested the same way. In Trial 2, the covered sponge loses 8 grams and the uncovered sponge loses 26 grams. In Trial 3, they lose 6 grams and 24 grams.