跟美国学生同步学科学(彩色英文版 Grade 7)(txt+pdf+epub+mobi电子书下载)

作者：(加) 韦恩·艾弗里特

出版社：天津人民出版社

格式: AZW3, DOCX, EPUB, MOBI, PDF, TXT

跟美国学生同步学科学(彩色英文版 Grade 7)试读：

The human heart is one of the most amazing organs in the human body. It pumps life-giving blood throughout the body. It also works together with blood and blood vessels to make sure the cells get everything they need.

The heart, blood, and blood vessels are all part of the circulatory system. Blood carries oxygen and food to the cells of the body. The blood then returns to the heart.

The heart is located slightly to the left in the middle of the chest. It has two hollow spaces or chambers. The blood goes into the atria, and is then pumped into the ventricles —two lower chambers. From here blood goes to the lungs and to every cell in the body. A valve in each ventricle stops blood from flowing backwards.

An artery is a blood vessel that carries blood away from the heart. Arteries are sometimes as thick as a thumb.

Blood is composed of red cells, white cells, and platelets floating in a fluid called plasma. This is a liquid, which can easily pass through small blood cells into cells. It makes up over half of the blood. Plasma carries nutrients (food) from the stomach to be used as fuel for energy. Plasma also helps keep the body warm.

The blood returns to the heart through blood vessels called veins. The walls of a vein are much thinner than the walls of an artery. Two large veins bring the blood back to the heart. One comes from the brain and chest, while the other comes from the lower body.Word List

organ: part of an organism that has a special, vital function

chamber: a cavity in a plant or in the body of an animal

artery: a muscle-walled tube forming part of the blood circulation systemYou Practice

I. Answer the following questions.

1) Where is the heart located?

2) What is the circulatory system?

3) What is blood made from?

4) How are veins different from arteries?

5) Why is plasma important?

II. Word power—Use these words from the reading in sentences of your own.

1) organ________________________________________________

2) hollow_______________________________________________

3) chamber______________________________________________

4) artery________________________________________________

5) plasma_______________________________________________

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) Blood always travels at the same speed.

____2) Blood is mostly made of platelets.

____3) The heart is in the centre of the chest.

____4) Valves in the heart prevent blood from flowing upwards.

____5) Blood returns to the heart through arteries.02Clouds

There are several types of clouds that appear in the sky at various times of year. These different kinds of clouds can result in weather that brings rain or snow, or may simply stop the Sun from shining brightly. Clouds are made from tiny water droplets or ice crystals.

There are three basic forms of clouds. Stratus clouds form in a blanket-like layer. Cumulus clouds are puffy clouds that appear to rise up from a flat bottom. Finally, cirrus clouds form at very high altitudes out of ice crystals, and have a wispy, feather-like shape. The term “nimbus” is added to the name of the cloud if it brings rain or snow to an area.

The height of a cloud allows it to be grouped into a family. The families are: low clouds, middle clouds, high clouds, clouds that develop upwards, and clouds that develop vertically. Thunderstorms come from cumulonimbus clouds that develop upward.

Another type of cloud is fog. This kind of cloud develops at ground level. Any form of water particles that fall from the atmosphere and reach the ground is called precipitation. This happens when the water droplets or ice crystals in the cloud join together and become heavy enough to fall. This is how precipitation happens. It depends on the temperature in the cloud and in the air whether the precipitation will fall as rain or snow.

Heavy precipitation often comes from large cumulus clouds. On the other hand, long lasting precipitation comes from stratus clouds. Vertically-developed clouds hold the most precipitation. They are very turbulent, and often cause heavy downpours or even large amounts of snow. This is called a “cloudburst”.Word List

puffy: soft and pillowy

vertically: up and down

precipitation: droplets that fall to Earth in the form of rain, snow, hail, etc.

turbulent: changing very quickly

downpour: very heavy rainYou Practice

I. Answer the following questions.

1) What are the three basic types of clouds?

2) What are the various cloud families?

3) How is fog different from other kinds of cloud?

4) Why does snow sometimes happen instead of rain?

5) Why is it a good idea to bring an umbrella outside if there are vertically-formed clouds in the sky?

II. Fill in the blanks—Complete the following sentences with words from the reading.

1) Clouds are made from very small water d_______.

2) Cumulonimbus clouds develop u_____.

3) The lowest kind of cloud is f__.

4) Very heavy rain is called a d_______.

5) Cumulus clouds look p____.

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) Precipitation happens when water droplets join together and become heavy enough to fall.

____2) Cirrus clouds develop close to the ground.

____3) Nimbus is added to a name if there is thunder.

____4) Downpours usually happen when there are wispy clouds.

____5) Stratus clouds are formed out of ice crystals.03Lizards

Lizards are part of the reptile family, which also includes snakes, turtles, crocodiles, and alligators. Like other reptiles, lizards are cold-blooded. This means that they cannot control their own body temperature — it is controlled by their surroundings. Their skin is also made of scales.

Lizards often need to shed their skin because it does not grow with them. However, similar to humans, they use lungs to breathe. These interesting creatures have a special organ on the roof of their mouths, which they use for smelling. This is called the Jacobsen' s organ. Their eyes and ears are on the sides of their heads.

The body shape of lizards is very simple. They have a head, a pair of legs, a long body, another pair of legs, and a tail. Their tails are prehensile,and can help them balance, swim, or grab tree branches. Lizards have a huge range of sizes. They range from about 4 centimetres to 2.5 metres. The komodo dragon is the largest kind of lizard. They live in Indonesia. The smallest lizards live in the British Virgin Islands.

Lizards are found on every continent except Antarctica and are most commonly found in tropical rain forests. Many of them are nocturnal, as they prefer being active in the cooler evening. Lizards that live in cold climates hibernate in the winter as their bodies cannot handle cold temperatures.

Some lizards are carnivores, while others are herbivores. The komodo dragon, for example, eats anything it can find, but prefers bigger prey such as deer and cattle. Herbivores, on the other hand, eat leaves, fruit, flowers, and other plants.

Lizards often fall prey to birds, snakes, bears, raccoons, and coyotes. They try to avoid predators by hiding underground or behind rocks during the day. At night they stay in a nice, warm burrow under the ground.Word List

surroundings: environment, area

nocturnal: most active at nightYou Practice

I. Answer the following questions.

1) What are two interesting things about lizards?

2) Where are the largest and smallest lizards found?

3) Why do lizards often need to shed their skin?

4) What is the basic body shape of a lizard?

5) How do lizards often stay away from predators?

II. Word power—Use these words from the reading in sentences of your own.

1) lungs________________________________________________

2) prehensile_____________________________________________

3) control_______________________________________________

4) creatures______________________________________________

5) herbivore_____________________________________________

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) The komodo dragon hibernates in the winter.

____2) The largest lizards live in the British Virgin Islands.

____3) Lizards are commonly found in Antarctica.

____4) Lizards often drink water.

____5) Lizards like really hot weather.04Population

A population refers to all the individuals of a species that live together in one place at one time. This definition allows scientists to refer to all different kinds of populations — bacteria, human, or animal, for example. Populations tend to grow because pairs of individuals have many offspring over the period of their lifetime. Predicting how a population will grow is the job of demographers. These scientists study three main features of population in order to predict growth: size, density, and dispersion.

Population size is very important. The number of individuals in a population can affect the population' s ability to survive. Smaller populations are more at risk of becoming extinct due to floods, fires, or other natural disasters.

Population density is the number of people that live in a certain area such as a square kilometre. 1f the individuals in an area are few and far between, it is more difficult for them to get together and reproduce. Because of this, the reproduction rate is lowered.

The final important feature is dispersion, which is the way individuals are arranged in a particular space. The three main patterns of dispersion are: randomly spaced, evenly spaced, and clumped. If they are randomly spaced, there is no pattern. If they are regularly spaced, they are at regular intervals. And if they are clumped, they are located in clusters.Word List

offspring: babies

intervals: amounts of space

clumped: a mix of many individuals in a small space and other spaces where there are not many individualsYou Practice

I. Answer the following questions.

1) What is a population?

2) What is the difference between population size and population density?

3) Why are smaller populations more at risk of becoming extinct?

4) What are the three main features of dispersion?

5) In the area where you live, is the population randomly spaced, evenly spaced, or clumped?

II. Word power—Use these words from the reading in sentences of your own.

1) offspring_____________________________________________

2) extinct_______________________________________________

3) density_______________________________________________

4) pattern_______________________________________________

5) cluster_______________________________________________

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) Population can only refer to people.

____2) Demographers are scientists who predict population.

____3) If a population is clumped together, it is difficult for it to survive.

____4) If the reproduction rate is high, it is easier for a population to survive.

____5) Demographers can predict exactly how much a population will increase by in the next 20 years.05Trees

The main part of a tree is called a trunk. There are two main kinds of trees: conifers and broad-leaved.

Conifers grow in a triangular shape, while broad-leaved trees are usually rounded. In order to be called a tree, a plant must be over 6 metres tall and have only one trunk. If it is less than 6 metres tall, it is called a shrub. Redwoods are the tallest trees in the world. They can grow to be well over 100 metres tall!

The various parts of a tree all work together in order to grow. Leaves make food by using sunlight and gases in the air. The roots take water and minerals from the soil. The leaves need water, and the roots need food. The trunk carries sap up and down the tree. Sap is the name of the tree' s food.

The leaves of broad-leaved trees are thin, flat, and usually wide. These trees are usually deciduous. This means that they lose their leaves in fall. The veins in a leaf carry food and water around the leaf. Young leaves are especially tasty to deer and other animals.

Conifers are trees that produce cones. Many of them have hard, spiky needles, which animals cannot eat. Some trees have beautiful blossoms, which attract bees and other insects. On conifers, the cones are blossoms. Male cones produce pollen and this is blown to the female ones and seeds begin to grow.

Some trees use their fruit to spread seeds. Animals eat the fruit and leave the seeds in their droppings. These seeds may grow into new trees.Word List

broad: wide

spiky: sharp

droppings: waste from the bodyYou Practice

I. Answer the following questions.

1) What are the main differences between broad-leaved trees and conifers?

2) What happens if a tree is less than 6 metres tall?

3) Which trees are the tallest?

4) How do new conifers begin growing?

5) If you were a tree, would you rather be a broad-leaved tree or a conifer? Why?

II. Fill in the blanks—Complete these sentences with words from the reading.

1) If a plant is not tall enough, it is called a s____.

2) Deciduous trees l___their leaves in fall.

3) Some trees spread seeds by using f____.

4) Animals like to eat young l_____.

5) Leaves need s_______in order to grow.

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) All trees produce fruit.

____2) The shape of all leaves is basically the same.

____3) A redwood tree is a kind of shrub.

____4) Wind helps new trees grow.

____5) Animals like to eat spiky needles.06Ocean Life

The world' s oceans are filled with thousands of living things. Scientists believe that thousands of species have yet to be discovered.

Many ocean plants either float on the surface or grow in shallow water. And just like plants on the land, plants in the ocean need sunlight to grow. The deepest parts of the ocean do not contain plant life because sunlight cannot reach deep into the ocean.

A common type of plant in the ocean is phytoplankton. These plants are very tiny, but they give off more oxygen than any other plants on Earth. Seaweed is a type of plant that floats on the water. 1t can be used for food as well as material for housing, ropes, and baskets.

Kelp is an ocean plant that can reach up to 80 metres in length! This mainly brown plant is the largest in the world. It can grow 60 centimetres a day, but needs a lot of sunlight to survive.

There is animal life throughout the ocean. Coral is a common ocean animal, although many people think it is a plant. It is very colourful and has tentacles for catching small fish.

There are many types of fish living in the oceans including tuna, sharks, eels, and stingrays. And in addition to fish, there are many mammals in the ocean including dolphins, whales, seals, and manatees.

Other animals commonly found in the ocean are octopus, lobster, crabs, jellyfish, squid, and many more. Still other animals live in the ocean as well as on the land. These animals include sea turtles, saltwater crocodiles, and polar bears. There are also many sea birds that rely on the ocean for food. These birds include penguins, pelicans, puffins, gulls, and many others.Word List

tentacles: limbs similar to arms or legs

species: various types of plants and animalsYou Practice

I. Answer the following questions.

1) What are some examples of plants that live in the ocean?

2) What are some examples of animals that live in the ocean?

3) What is an ocean plant that looks like an animal?

4) Why is there no plant life very deep in the ocean?

5) What are some examples of sea birds?

II. Word power—Use these words from the reading in sentences of your own.

1) tentacles______________________________________________

2) kelp_________________________________________________

3) sunlight______________________________________________

4) coral_________________________________________________

5) species_______________________________________________

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) Most ocean plants are found in deep water.

____2) Small fish often eat coral.

____3) Kelp grows very quickly.

____4) Crocodiles live only on land.

____5) Phytoplankton is very large.07Coral Reefs

Coral reefs are very beautiful, natural structures. The various types of coral are very colourful because of natural pigments. They can be white, red, pink, purple, and many other colours. These amazing creatures are animals that act like plants. Similar to plants, they stay in one place and receive their energy from the Sun. A kind of microscopic algae lives inside of coral, providing it with food and allowing it to grow faster.

Most coral reefs are found in clear, tropical oceans in water less than 50 metres deep. This is due to the fact that they need light in order to survive. The three main types of coral reef are: fringing reefs, barrier reefs, and atolls.

Fringing reefs grow along the coastal shorelines of continents and islands. There are many of them in Hawaii and the Caribbean. Barrier reefs, on the other hand, are found offshore in the Caribbean and the Indo-Pacific. They are a series of shallow coral islands that surround a lagoon. Australia is home to the largest coral reef in the world. The Great Barrier Reef extends over 2000 kilometres.

The water in coral reef ecosystems is between 20 and 28 degrees Celsius and usually along the eastern coasts of land. Waves are very important to the health of coral reefs. They bring in food and nutrients to coral reefs. They also stop sediment from settling on the reef.

The plants that flourish in coral reefs grow because of the process of photosynthesis. And the same as on dry land, the animals of the coral reefs get their energy by eating the plants.

Amazingly, coral reefs make up only 1% of the ocean floor, but they are home to 25% of the life in the ocean!

Coral reefs are helpful to the planet. They remove and recycle carbon dioxide from the air, which can contribute to global warming. They also protect the land from large waves when the weather is very stormy. Unfortunately, pollution, overfishing, and sewage are responsible for the destruction of many coral reefs.Word List

pigment: the natural colouring of animal or plant tissue

lagoon: a body of water surrounded by water on three sides

flourish: to do very well

sewage: human waste matter that comes from sewersYou Practice

I. Answer the following questions.

1) What are three interesting things about coral reefs?

2) What are the three main types of coral reefs?

3) Why are coral reefs found in shallow waters?

4) What is a similarity between fringing reefs and barrier reefs?

5) In what way are coral reefs good for the Earth?

II. Word power—Use these words from the reading in sentences of your own.

1) pigment______________________________________________

2) microscopic___________________________________________

3) offshore______________________________________________

4) lagoon_______________________________________________

5) pollution______________________________________________

III. True / False / Not Given—Write T if the sentence is true, F if it is not true, or NG if there is no information about this sentence.

____1) Coral reefs are home to an amazing amount of life.

____2) Coral reefs grow in cold water.

____3) Some coral reefs are threatened because of human activities.

____4) The Caribbean is home to more than one kind of coral reef.

____5) Fringing reefs are found far from land.08Birds

There are nearly 10,000 kinds of birds, and they come in all sizes—from the tiny hummingbird to the giant ostrich. All birds have two wings, two legs, a beak or bill, and feathers.

Birds can be found nearly everywhere in the world. There are,for example, land birds, water birds, arctic birds, and tropical birds. Some birds eat insects, while others eat fruit and seeds. There are also birds that eat meat and fish.

All birds have several characteristics in common no matter where they live or what they look like. All birds have feathers, which help them in various ways. They help them to fly, to carry water to their young, or they may be used for warmth.

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