Explain a complex idea in an essay
Grade 9 Reading Worksheet - Challenge Me
Circle the best answer.
Read this first
How a Cloud Forms (informative draft)
[1] On a warm summer afternoon, a clear sky can fill with tall white clouds within a few hours, even though nobody sees the water that builds them arrive. [2] That water was in the air all along, as an invisible gas called water vapor, which enters the air whenever water evaporates from oceans, lakes, damp soil and the leaves of plants. [3] A cloud forms when that vapor turns back into tiny drops of liquid water, and the change needs two things: cooler air and something for the water to collect on.
[4] Rising air cools as it climbs, and that cooling is what allows the invisible vapor to condense, or turn back into liquid droplets. [5] Air can rise for different reasons. [6] Then it gets colder up there.
[7] Cooling alone, however, is not enough to make a cloud. [8] The vapor condenses on condensation nuclei, and without them very few droplets would form even in cold, damp air. [9] Each droplet is far smaller than a raindrop and so light that gently rising air can keep it floating for a considerable time. [10] When billions of these droplets crowd together, they scatter sunlight in every direction, and the cloud looks white from below and from the side.
[11] The same two steps explain fog, which is a cloud that forms at ground level, and the misty breath that people see on a cold morning. [12] Forecasters watch for rising air and for air that already holds nearly as much water vapor as it can, because those two signs warn that clouds may soon build. [13] That is how clouds form, and now you know the steps.
Sentence [4] makes a two-part point: rising air cools, and cooling lets vapor turn to liquid. Which pair should replace [5] and [6] for Ari?
- As air rises, the pressure around it drops, so the air expands and its temperature falls. Cooler air cannot hold as much water vapor, so the extra vapor condenses into droplets.
- Clouds are grouped by shape and height, such as puffy cumulus clouds and thin, high cirrus. Thick gray clouds look dark because they block much of the sunlight.
- As air rises, the pressure around it drops, so the air expands and its temperature falls. In other words, air that moves upward becomes cooler as it climbs.
- As air rises, the pressure around it drops, so the air expands and its temperature falls. Air at the top of a tall mountain is usually much colder than the air in the valley far below.
The essay is for readers who are new to weather. Which sentence should Bo put before [8], so that its hard term makes sense?
- When billions of the finished droplets crowd together, they scatter the sunlight, and a white cloud appears in the sky.
- Condensation nuclei vary in size and in what they are made of, and those differences decide how easily each one gathers water vapor from the air.
- Water vapor makes up a small share of the air, and the amount changes from place to place and from day to day.
- The air is full of specks too small to see, such as dust, sea salt and smoke, and water vapor needs these specks as surfaces to collect on.
Esme wants to replace the weak ending in [13]. Which conclusion gathers the essay and says why the idea matters?
- A cloud forms when rising air cools and its water vapor condenses on tiny specks of dust, salt or smoke that float in the air.
- Knowing that a cloud needs cooling air and specks to collect on means that a careful reader can predict tomorrow's weather exactly, hour by hour, for any town.
- Knowing that a cloud needs both cooling air and specks to collect on explains much of the weather, because rain and snow begin as these tiny droplets.
- The tallest storm clouds can tower more than ten kilometers into the sky, where many of their droplets freeze into ice.
How Muscles Move a Bone (informative draft)
[1] Every movement of the body, from a blink to a long jump, depends on muscles, but a muscle can do one thing only: it can pull, and it cannot push. [2] A muscle is a bundle of long cells called fibers, and when a signal from a nerve reaches those fibers, they shorten, so the whole muscle becomes shorter and thicker. [3] Because a muscle can only pull, the body needs a clever arrangement to move a bone back and forth.
[4] The answer is that the muscles attached to bones work in pairs, with each muscle pulling a bone the opposite way from its partner. [5] Muscles are in pairs. [6] They do stuff together.
[7] The pull reaches the bone through a tendon, and the bone moves because it turns at a joint. [8] In the arm, the elbow works much like the hinge of a door, so the forearm swings up and down as the muscles take turns pulling. [9] Bones cannot move by themselves, since they are stiff levers that turn at a joint only when a muscle pulls on them. [10] The same partnership moves the leg, since muscles on the front of the thigh straighten the knee and muscles on the back of the thigh bend it.
[11] Pairs of muscles also hold the body still, because both partners can tighten a little at the same time to keep a joint steady. [12] Even standing upright takes steady work from pairs of muscles in the legs, the hips and the back, which is why a person who stands for hours becomes tired. [13] So muscles are really cool, and that is the end of my essay.
Jun sees that sentence [4] makes a two-part point: one muscle pulls a bone one way, its partner pulls it back. Which pair should replace [5] and [6]?
- When the biceps on the front of the upper arm shortens, it pulls the forearm up and bends the elbow. In other words, the elbow bends because the muscle on the front of the upper arm gets shorter.
- The heart is also a muscle, but it beats on its own without a person deciding to move it. Muscles also make heat, which is why a person shivers in the cold.
- When the biceps on the front of the upper arm shortens, it pulls the forearm up and bends the elbow. To straighten the arm, the triceps on the back shortens while the biceps relaxes.
- When the biceps on the front of the upper arm shortens, it pulls the forearm up and bends the elbow. A person lifting a heavy bag uses the biceps to raise it toward the chest.
The essay is for readers who are new to how the body works. Which sentence should Kira put before [7], so that its term makes sense?
- With the arm bending and straightening by turns, a person can lift, throw and reach in many directions during a day.
- The human body has more than six hundred muscles, and some of the largest of them are found in the legs and the back.
- A muscle is not attached to a bone directly; it is joined to the bone by a tough cord of tissue called a tendon.
- Tendons are made mostly of collagen, which gives them great strength and lets them stretch very little under a load.
How a Compost Pile Turns Scraps into Soil (informative draft)
[1] A heap of fallen leaves, grass clippings and vegetable peels left in a corner of a yard will slowly shrink and darken, until after some months it looks like rich, crumbly soil. [2] That change is not caused by the weather alone; it is the work of living things, mostly bacteria and fungi too small to see, along with worms and insects. [3] These decomposers feed on the old plant matter and break it down into simpler substances, and a gardener who understands what they need can make the process much faster.
[4] Decomposers need a balance of two kinds of material, which gardeners often call greens and browns. [5] Greens are one kind. [6] Browns are another kind.
[7] The decomposers also need air and water, so a pile is kept about as damp as a wrung-out sponge and turned now and then with a garden fork. [8] As aerobic bacteria multiply, the center of the pile can grow surprisingly hot. [9] The heat comes from the energy the bacteria release as they work, and the middle of a large pile can reach about 60 degrees Celsius, which is hot enough to destroy many weed seeds.
[10] As the food supply runs low, the pile cools, worms and fungi finish the job, and what is left is dark, crumbly compost. [11] Compost mixed into a garden helps the soil hold water and returns nutrients that growing plants can use. [12] In conclusion, compost is when stuff rots in a pile.
Sentence [4] says decomposers need two kinds of material, greens and browns. Which pair should replace [5] and [6] so that both kinds are explained for Milo?
- Greens, such as grass clippings and vegetable scraps, are rich in nitrogen, which decomposers use to grow. Too many greens can make a pile wet, heavy, airless and smelly within a week or two.
- Greens, such as grass clippings and vegetable scraps, are rich in nitrogen, which decomposers use to grow. Browns, such as dry leaves and straw, are rich in carbon, which gives them energy.
- Many towns collect yard waste each fall and turn it into compost in long rows. Finished compost is often spread on gardens in spring before planting.
- Greens, such as grass clippings and vegetable scraps, are rich in nitrogen, which decomposers use to grow. That is, fresh green material supplies the nitrogen they need.
The essay is for readers who have never made compost. Which sentence should Noah put before [8], so that its hard term makes sense?
- Aerobic bacteria break down plant matter faster than anaerobic bacteria do, which is why turning the pile matters so much.
- When the pile finally cools and smells like damp earth, the compost is ready to be spread on a garden.
- A single spoonful of healthy garden soil can hold many millions of bacteria of a great many different kinds.
- Most of the bacteria at work in a healthy pile need oxygen to live, and bacteria of this kind are called aerobic bacteria.
Pia wants to replace the weak ending in [12]. Which conclusion gathers the essay and says why the idea matters?
- A compost pile shows that decay returns nutrients to the soil, so a garden with compost will need no water or care again.
- Some gardeners also keep red worms in an indoor bin, where the worms turn kitchen scraps into compost through the winter.
- Decomposers break down greens and browns in a damp, airy pile, which heats up, cools again and leaves behind dark compost.
- A compost pile shows that decay is not waste but work done by living things, work that returns nutrients from old plants to new ones.
How a Hot-Air Balloon Rises (informative draft)
[1] A hot-air balloon has no engine and no wings, yet it can lift a basket of passengers hundreds of meters into the sky using little more than air and a flame. [2] The trick depends on a simple fact about air, which is that a given space filled with warm air weighs less than the same space filled with cool air.
[3] Heating air makes it less dense, and less dense air is pushed upward by the denser air around it. [4] Heat does something to the air. [5] And then it goes up.
[6] A pilot controls the height of the balloon by changing the buoyant force on it, mostly with the burner that roars above the passengers' heads. [7] Opening the burner heats the air inside the envelope, the large fabric bag, and the balloon rises, while letting that air cool makes the balloon sink. [8] A balloon has no way to steer, so the pilot moves sideways by rising or sinking into layers of wind that blow in different directions. [9] Because cold air is denser than warm air, a balloon gets more lift on a cold morning than on a hot afternoon.
[10] Weather balloons are filled with helium, a gas lighter than air, rather than heated air, and many of them climb more than thirty kilometers before they burst. [11] Their instruments send back readings of temperature, pressure and wind on the way up, and a small parachute carries the instruments back to the ground after the balloon bursts. [12] That's basically how balloons work, which is pretty cool.
Ren sees that sentence [3] makes a two-part point: heating makes air less dense, and denser air pushes it up. Which pair should replace [4] and [5]?
- Heated air molecules move faster and spread apart, so a balloonful of warm air weighs less than the same space of cool air. Put another way, hot air is lighter than an equal space of cold air.
- Heated air molecules move faster and spread apart, so a balloonful of warm air weighs less than the same space of cool air. The heavier cool air sinks beneath it and pushes it up, as water pushes up a cork.
- Heated air molecules move faster and spread apart, so a balloonful of warm air weighs less than the same space of cool air. That is why the air near a ceiling is often a little warmer than the air near the floor.
- The first passengers of a hot-air balloon, in France in 1783, were a sheep, a duck and a rooster. Modern balloons are made of strong nylon sewn in long panels.
The essay is for readers who are new to physics. Which sentence should Tala put before [6], so that its hard term makes sense?
- The buoyant force on a balloon equals the weight of the air it displaces, a rule known as Archimedes' principle.
- Balloon flights usually take place soon after sunrise or shortly before sunset, when the winds tend to be calm.
- When the flight is over, the pilot lets the air inside cool, and the balloon sinks slowly back to the ground.
- The upward push that a fluid such as air or water gives to an object inside it is called the buoyant force.