Diagram labels and flow charts: how a solar still works
You can match a diagram or a flow chart to the part of a passage that describes it, and copy each answer exactly.
A solar still is a box with a glass lid. It turns salt water into drinking water, using nothing but sunlight.
You'll read how one is built and how it works. Then you label a diagram of it and complete a flow chart of the process.
In both tasks the answers are words from the passage, and the instructions say how many you may use. An answer over that limit is marked wrong.
Warm-up
Top, middle or bottom?
Diagram tasks are often about where things are. Read the two sentences and find the part at the very bottom.
Read thisThe seeds sit in a tray of soil. Under the tray is a heating mat, and a clear plastic lid covers the top.
Which part is at the bottom?
How it works
Label the diagram below. Choose ONE WORD ONLY from the passage for each answer.
| Where on the still | Label |
|---|---|
| Top | a sheet of 1 |
| Along the lower edge of the top | a narrow 2 |
| Leading out of the box to a storage container | a short 3 |
| Base | a basin, painted 4 on the inside |
| Under the basin | insulation, often made of 5 |
In the exam this is a drawing of the still seen from the side, with a line from each label to its part. Here each label sits next to the place it points to, from top to bottom.
Complete the flow-chart below. Choose NO MORE THAN TWO WORDS from the passage for each answer.
HOW A SOLAR STILL WORKS
Sunlight passes through the cover and is absorbed by the basin.
As the water warms, some of it turns into 6.
The salt and any 7 are left in the basin.
The warm, 8 air rises until it reaches the cover.
On the cool underside of the cover, the vapour 9.
Because the cover 10, the drops run down it and are collected.
The boxes follow the order of the process. The flow chart calls the glass the cover, which is the kind of rewording to expect.
Both tasks often come with a passage that describes how something is built or how a process works. The diagram shows the parts, and the flow chart shows the steps in order.
The method
- 1Read the instruction for the limit
ONE WORD ONLY means one word. NO MORE THAN TWO WORDS means one or two. The instruction also says whether the words come from the passage or from a list.
- 2Study the picture before the passage
Read the title and every label, including the ones already filled in. They tell you what is shown and which words to scan for.
- 3Find the section
The answers usually come from one section of the passage, though not always in the same order as the labels. Here, the parts are in one paragraph and the steps in another.
- 4Follow position and sequence words
For a diagram, look for words like under, along and at the top. For a flow chart, look for as, then, so and because.
- 5Copy the word exactly
Check that it fits the grammar of the label, and that it is spelled letter for letter as the passage spells it.
The passage
Fresh water from the sun
A On many small islands and dry coasts, people live beside more water than they could ever use, yet they have too little to drink. Seawater is far too salty to drink, and fresh water may have to be brought in by boat. Large desalination plants can remove the salt, but they are expensive to build and use a great deal of energy. For a single household, a much simpler device can do the same job with nothing but sunshine. It is called a solar still.
B A basic solar still is a shallow, watertight box. Its lower part is a basin that holds a few centimetres of salt water. The inside of the basin is painted black, because dark surfaces absorb more of the sun's energy than pale ones. The basin rests on a layer of insulation, often made of foam, which stops heat escaping through the bottom. The top of the box is a sheet of glass, set at an angle so that it slopes down towards one side. A narrow channel runs along the lower edge of the glass, and a short pipe leads from this channel to a storage container outside the box.
C The still copies the water cycle on a very small scale. Sunlight passes through the glass and is absorbed by the black basin, which warms the water. As the water warms, some of it evaporates, turning into water vapour. The salt cannot evaporate, so it remains in the basin, along with any dirt. The warm, damp air inside the box rises until it reaches the glass, which is kept cooler by the air outside. There, the vapour condenses into tiny droplets of fresh water on the underside of the glass. Because the glass slopes, the droplets run down it into the channel and do not fall back into the basin. From the channel, the water flows through the pipe into the container.
D The water in the basin never needs to boil. Water evaporates well below its boiling point, and the warmer it is, the faster it evaporates. On a sunny day the water in a still becomes hot, but it stays well below boiling.
E A still's output depends mainly on the weather. It produces the most water on bright, cloudless days and much less when the sky is overcast. Even in good conditions the process is slow. A basin of one square metre usually produces only a few litres a day, so a family may need several square metres of stills for its drinking water. A still also needs regular care. Salt gradually builds up in the basin and has to be flushed out, and the glass must be kept clean, because dust on its surface blocks some of the sunlight.
F For these reasons, solar stills suit places with strong sunshine and few other sources of clean water. In one fishing village, a small charity has helped families to build stills from wood, glass and black plastic sheeting. The stills cannot supply enough water for washing or for crops, but they give each household a small, steady supply of safe drinking water without any fuel or electricity.
Watch me do one
I'll take label 2: a narrow ______, along the lower edge of the top.
A narrow tells me the gap is a noun for something long and thin: a pipe, a channel, a strip.
The label mentions an edge, so I scan paragraph B for edge. I find A narrow channel runs along the lower edge of the glass.
Pipe comes a few words later, and a pipe is narrow too. But the pipe leads from this channel to a storage container, so it starts where the channel ends. That is label 3.
The part that runs along the edge is the channel. One word, spelled the way the passage spells it: channel.
Practice with Elita6 questions
The other nine answers, in five exercises, and one question on counting words. Each exercise shows the paragraph you need.
Labels 1 and 3
Use paragraph B. Write one word from the passage in each gap.
Read thisA basic solar still is a shallow, watertight box. Its lower part is a basin that holds a few centimetres of salt water. The inside of the basin is painted black, because dark surfaces absorb more of the sun's energy than pale ones. The basin rests on a layer of insulation, often made of foam, which stops heat escaping through the bottom. The top of the box is a sheet of glass, set at an angle so that it slopes down towards one side. A narrow channel runs along the lower edge of the glass, and a short pipe leads from this channel to a storage container outside the box.
Top: a sheet of . Leading out of the box to a storage container: a short .
Write no more than 1 word in each gap.
Labels 4 and 5
Both labels are at the bottom of the still. Use paragraph B again, one word in each gap.
Read thisA basic solar still is a shallow, watertight box. Its lower part is a basin that holds a few centimetres of salt water. The inside of the basin is painted black, because dark surfaces absorb more of the sun's energy than pale ones. The basin rests on a layer of insulation, often made of foam, which stops heat escaping through the bottom. The top of the box is a sheet of glass, set at an angle so that it slopes down towards one side. A narrow channel runs along the lower edge of the glass, and a short pipe leads from this channel to a storage container outside the box.
Base: a basin, painted on the inside. Under the basin: insulation, often made of .
Write no more than 1 word in each gap.
Flow chart: gaps 6 and 7
The flow chart follows paragraph C. Write no more than two words from the passage in each gap.
Read thisThe still copies the water cycle on a very small scale. Sunlight passes through the glass and is absorbed by the black basin, which warms the water. As the water warms, some of it evaporates, turning into water vapour. The salt cannot evaporate, so it remains in the basin, along with any dirt. The warm, damp air inside the box rises until it reaches the glass, which is kept cooler by the air outside. There, the vapour condenses into tiny droplets of fresh water on the underside of the glass. Because the glass slopes, the droplets run down it into the channel and do not fall back into the basin. From the channel, the water flows through the pipe into the container.
As the water warms, some of it turns into . The salt and any are left in the basin.
Write no more than 2 words in each gap.
Flow chart: gaps 8 and 9
Gap 8 describes the air. Gap 9 needs a verb, because the vapour has no verb yet.
Read thisThe still copies the water cycle on a very small scale. Sunlight passes through the glass and is absorbed by the black basin, which warms the water. As the water warms, some of it evaporates, turning into water vapour. The salt cannot evaporate, so it remains in the basin, along with any dirt. The warm, damp air inside the box rises until it reaches the glass, which is kept cooler by the air outside. There, the vapour condenses into tiny droplets of fresh water on the underside of the glass. Because the glass slopes, the droplets run down it into the channel and do not fall back into the basin. From the channel, the water flows through the pipe into the container.
The warm, air rises until it reaches the cover. On the cool underside of the cover, the vapour .
Write no more than 2 words in each gap.
Flow chart: gap 10
The last box gives a reason, so look for because in the passage.
Read thisThe still copies the water cycle on a very small scale. Sunlight passes through the glass and is absorbed by the black basin, which warms the water. As the water warms, some of it evaporates, turning into water vapour. The salt cannot evaporate, so it remains in the basin, along with any dirt. The warm, damp air inside the box rises until it reaches the glass, which is kept cooler by the air outside. There, the vapour condenses into tiny droplets of fresh water on the underside of the glass. Because the glass slopes, the droplets run down it into the channel and do not fall back into the basin. From the channel, the water flows through the pipe into the container.
Because the cover , the drops run down it and are collected.
Write no more than 2 words.
Counting words
Gap 6 allows no more than two words. Three students wrote these answers. Which answer is marked wrong?
Read thisAs the water warms, some of it evaporates, turning into water vapour.
As the water warms, some of it turns into ______.
Words to keep
Take in light, heat or liquid. A black surface absorbs more of the sun's energy.
Change from a liquid into a gas. Water evaporates faster when it is warm.
Change from a gas into a liquid, usually on a cool surface. Steam condenses on a cold bathroom mirror.
Water in the form of a gas, which you cannot see. The air in the still fills with water vapour.
Material that stops heat getting in or out. Foam insulation keeps the heat in the basin.
Covered with cloud. The still produces little water on overcast days.
Clean something by sending water through it. Salt that builds up in the basin has to be flushed out.
Before you go
Read the instruction first: how many words, and whether they come from the passage or a list.
Study the diagram or flow chart before the passage, and scan for the words printed on it.
Expect the answers to come from one section, though not always in order.
Copy each word exactly as the passage spells it, and check it fits the grammar of the gap.
Next: The next lesson is a lecture on how scientists track migrating animals. You complete a summary of it as you listen.