ACT Reading Practice Test: Central Ideas and Supporting Details

Passage A: Social Science

This passage is adapted from an original article on city planning.

[1] Walk across almost any college campus and you will find them: narrow strips of bare dirt cutting diagonally across a lawn, usually connecting two doors that the official sidewalks join only by a long right angle. Landscape architects call these trails desire lines or desire paths. No one designs them. They appear because hundreds of people, each acting alone, decide that the shortest route is worth a little mud on their shoes.

[2] For decades, many grounds crews treated desire paths as damage. They put up low fences, planted hedges across the worn strips, or posted signs asking people to stay on the pavement. The results were often disappointing. Pedestrians stepped over the fences, the hedges developed gaps, and the signs faded while the paths grew wider.

[3] Some planners have since taken the opposite approach. Instead of fighting the trails, they study them. A few campuses have opened new buildings with no sidewalks at all, waited a season to see where the grass wore away, and then paved the routes that people had already chosen. The finished walkways looked less tidy on a site plan than a neat grid would have, but they matched the way people actually moved, and fewer new shortcuts appeared afterward.

[4] Desire paths also carry information that is hard to collect any other way. A survey can ask people how they travel, but people do not always remember or report their habits accurately. A worn line in the grass is a record of thousands of real choices. When a path leads to a gap in a fence or ends at a busy road with no crosswalk, it can point to a missing connection that the original design overlooked.

[5] None of this means every trail should be paved. Some cross fragile ground, and others are used only for a few weeks a year. The planners who value desire paths treat them as evidence, not as orders: each one raises a question about what people need, and the planner still has to answer it.

Passage B: Natural Science

This passage is adapted from an original article on insect behavior.

[1] In the rain forests of Central and South America, a line of leafcutter ants can stretch for more than a hundred yards, each worker carrying a piece of leaf larger than its own body. For a long time, observers assumed the ants were eating the leaves. They are not. The leaves are fertilizer.

[2] Inside the nest, smaller workers lick the leaf pieces clean, chew them into a pulp, and press the pulp into a spongy garden. On this garden grows a fungus that the colony tends the way a farmer tends a crop. The fungus breaks down the tough plant material, which the ants cannot digest on their own, and in return it produces swollen tips rich in nutrients. These tips are the main food of the colony's larvae.

[3] The work is divided by body size. The largest workers guard the trails and the nest entrances. Medium-sized workers cut and carry leaves. The smallest workers stay in the gardens, where they remove foreign fungi and spread fresh pulp. Some tiny workers even ride on the leaf pieces carried by their larger sisters, apparently to defend them from parasitic flies.

[4] A farm this crowded invites disease. The ants' gardens are threatened by a parasitic fungus that can ruin a crop quickly. Researchers have found that many leafcutter ants carry a coating of bacteria on their bodies, and that these bacteria produce compounds that slow the growth of the parasite. In effect, the ants grow their food with one partner and protect it with another.

[5] Leafcutter colonies can number in the millions, and they remove a large share of the leaves around their nests. Yet the same activity carries plant material deep into the soil, where its nutrients can reach the roots of trees. To a farmer whose orange trees have been stripped overnight, the ants are pests. To the forest, they are also part of the way nutrients are recycled.