Questões de prática de leitura para o 8º ano, com respostas

Em inglêsThe Power Grid
Think of the electric grid as the circulatory system of a country. Power plants are the heart, pumping out electricity day and night. High-voltage transmission lines are the arteries, carrying that energy across long distances. Near towns and cities, devices called transformers lower the voltage, much as smaller blood vessels branch off to reach every part of the body. Voltage is the measure of the force that pushes electric current through a wire. If it were not reduced, the current entering a home would be strong enough to destroy appliances and start fires.

Like a body, the grid must stay in balance. Operators match the amount of electricity produced to the amount used every second. A heat wave that sends millions of air conditioners humming at once is a kind of cardiac stress test, and the system must respond within moments to avoid a blackout.

Em inglêsThe Goldilocks Zone
When astronomers search for planets that might support life, they look for the Goldilocks zone, the band of space around a star where it is neither too hot nor too cold. Closer in, a planet's water would boil away into space. Farther out, it would freeze into permanent ice. Only in the middle can liquid water, the solvent that carries chemicals through living cells, remain on the surface. Earth sits comfortably in the zone around the Sun. Venus, scorched by a thick blanket of carbon dioxide, lies near the inner edge, and Mars, frozen and thin-aired, lies near the outer edge.

Finding a planet in the zone does not guarantee life. Scientists describe the zone as a promising neighborhood, not a confirmed address. A planet also needs the right atmosphere, the right size and a steady star. Still, the phrase has caught on because the idea is so easy to picture: not too much, not too little, but just right.

Em inglêsReefs in Trouble
Coral reefs have been called the rainforests of the sea, and the name fits. Although reefs cover less than one percent of the ocean floor, they shelter about a quarter of all marine species. When ocean water grows too warm, corals expel the tiny algae that live inside their tissues and give them color and food. The result is called bleaching. A bleached reef is a ghostly white, and unless the water cools quickly, the corals starve.

Some scientists describe the damage as a slow-motion catastrophe. Others, more cautious, call it a serious decline that can still be slowed. Both groups agree on the measurements: in many regions, large stretches of reef have lost most of their living coral in a few decades. Protecting reefs, they say, means cutting pollution, limiting fishing near them and, above all, slowing the warming of the oceans.

Em inglêsAntibiotics and a Hidden Weakness
For decades, antibiotics seemed like miracle drugs. Infections that once killed thousands became curable in a week. But bacteria reproduce quickly, and each generation brings small random changes. Occasionally a change lets a bacterium survive a drug. When antibiotics are used too often, or when patients stop taking them early, the survivors multiply and pass on their resistance. Doctors now face strains that no common antibiotic can kill.

Researchers call this problem the Achilles' heel of modern medicine. A hospital can have the finest equipment in the world, but surgery, chemotherapy and organ transplants all depend on drugs that fight infection. If those drugs fail, the whole structure becomes vulnerable. Some experts also warn that careless overuse is like opening Pandora's box: once resistant strains appear and spread, they cannot be called back. Yet there is reason for hope. New drugs are in development, and hospitals that track their antibiotic use have cut resistant infections.

Em inglêsTwo Ways to Say It
Words can describe the same fact and leave very different impressions. Imagine two reports about a town council that cut the library's budget by ten percent. One says the council made a frugal decision to control spending. Another says the council slashed funding in a stingy attempt to save pennies. Both sentences report the same cut, yet the first suggests a sensible choice, while the second suggests a mean one.

Linguists call this difference connotation, the feelings and associations that cling to a word beyond its dictionary meaning. A word's denotation is the literal definition. Careful readers pay attention to both. When a writer chooses a loaded word such as slashed, hoarding or scheme, the writer may be trying to move the reader's emotions rather than just inform. That does not always make the choice wrong, since a writer may truly believe the situation is serious. It does mean readers should notice the word and ask whether the facts alone would produce the same reaction.

Em inglêsMore Than Dirt
To a gardener, soil is not just dirt. It is a living mixture of broken rock, water, air and humus, the dark material formed when dead plants and animals decay. Humus holds moisture like a sponge and releases nutrients slowly, which is why gardeners prize it. A soil rich in humus is said to be fertile, meaning it can support strong plant growth.

Soil scientists also describe soil by its texture, the sizes of the particles in it. Sand particles are the largest and let water drain quickly. Clay particles are the smallest and pack tightly, so water moves through them slowly. Loam, a balanced blend of sand, clay and silt, is often considered ideal. Healthy soil also needs aeration, the movement of air through tiny spaces between particles. Earthworms help by tunneling, which is why a gardener who sees plenty of them usually smiles.