Which statement best sums up the passage?

A lichen is a partnership of more than one kind of life; it grows very slowly, it makes soil, and it fails where the air is dirty. (The four paragraphs cover the partnership, the correction to it, the slow growth and rock work, and the weakness. Only one choice holds those together, and the others contradict the text.)

What did researchers find when they examined lichen cells more closely?

that a yeast was also present in many lichens (Paragraph two states it: a third member, a yeast, had been there all along and was missed.)

A wall in a city centre is bare, while a wall of the same age in the countryside is covered in lichen. What does the passage most support?

The city air carries more pollution. (The last paragraph says a lichen absorbs whatever the air carries and disappears where the air is dirty, so its absence is evidence about the air. Stone type, rain and cleaning are never discussed.)

In "Lichens grow at a pace that is hard to imagine", the word "pace" means

the speed at which something happens (The next sentence gives millimetres per year, which is a rate. So "pace" means how fast or slow the growth is.)

Two Lives in One: Level 3 Reading Comprehension Questions

The grey-green crust on an old stone wall is not one organism. A lichen is a fungus living together with a partner that can feed it: an alga, a bacterium that works like one, or both. The fungus builds the body and holds the water. The partner turns sunlight into sugar. Apart, neither would last long on bare rock; together they cover mountains.

For a century, textbooks called this a partnership of two. Then researchers looked at the cells more closely and found a third member in many lichens, a yeast that had been present all along and missed by everyone. The old picture was not wrong so much as too small.

Lichens grow at a pace that is hard to imagine. Some spread less than a millimetre a year, so a patch the size of a coin may be older than the wall it sits on. They also work on the stone, releasing weak acids that loosen its grains and begin the slow business of making soil.

They have one weakness. A lichen takes in whatever the air carries and cannot spit any of it out again. Where the air is dirty, the crust disappears, which is why a wall covered in lichen is also a report on the air around it.

Comprehension questions