Essential Natural Science 1

Contents

About this book . . . 3

Learning to learn Getting closer to the stars! . . . 6

1

2

Learning to learn All creatures great and small . . . 28

3

4

5

6

7

Learning to learn Rock stars and instruments . . . 84

8

9

10

11

Learning to learn It’s elementary! . . . 128

12

13

14

Vocabulary . . . 160

Key language . . . 164

PAGE

Learning to learn

ABOUT THIS BOOK

• Look at these illustrations. Match them to the units on the opposite page. Then look at the book, and check your answers.

B Unit... A Unit... E Unit... D Unit... H Unit... G Unit... K Unit... J Unit... C Unit... F Unit... I Unit... Unit... N M Unit... L Unit... 877306 _ 0001-0005.qxd 15/2/08 18:25 Página 3

YOU ALREADY KNOW A LOT!

Work with a partner. Try to answer these questions.

THE UNIVERSE

How many planets in our galaxy can you name?

THE EARTH

How long does it take the Earth to rotate on its axis? And how long does it take to orbit the Sun?

INVERTEBRATES

Can you name six invertebrates?

PLANTS

Plants are autotrophic: they make their own food.

What is the name of the process by which plants do this?

THE EARTH’S ATMOSPHERE

Can you name three meteorological instruments? What does each one measure?

THE HYDROSPHERE

Water is present on Earth in gaseous, liquid and solid form. Name four different places where you can find water in nature.

The Universe

8

1

Content objectives In this unit, you will … • Learn about the characteristics of the

Universe

• Calculate astronomical sizes and distances • Analyse the components of the Universe • Compare sizes: the Sun and the planets • Create a constellation poster What do you remember?

• What are the points of light in this photo? • What is the difference between …

– a star and a planet? – a moon and a comet?

Key language

Describing

Planets are spherical bodies which orbit the Sun. Asteroids are rocky objects which are irregular in shape.

Comparing

Dwarf planets are smaller than planets. The Earth is larger than Mercury

Giving instructions

Study the constellations. Research more about them on the Internet.

STUDY A UNIT

Look at page 8, the first page of Unit 1

• What is the title of the unit?

• How many different sections are there on the page? What are they about?

• What do you think you will learn about in Unit 1?

Now look at the rest of Unit 1

• How many sections are there in this unit? • What are most of the illustrations about? • Some words are in bold. Why is this? • How many activities are there in this unit? • What will you do in the Hands on section, page 15?

• What can you find on page 17? How is this useful?

Symbols

• The text is recorded on the CD. • The information you need is

available on the CD.

MINERALS

Quartz is a mineral. Can you name any other minerals? Can you say what each is used for?

MATTER AND ITS PROPERTIES

Oil floats on water.

Which has the greatest density, oil or water?

THE STATES OF MATTER

Look at these three drawings.

They represent a solid, a liquid and a gas. Can you match each drawing to its state?

7

Getting closer to the stars!

closer view of distant things. Astronomers use large telescopes to study the planets, stars, and other objects in space. Without telescopes, we wouldn’t know much about celestial bodies!

eyepiece: lens

to view the image

focus adjustment:

move this to make the image clearer Look through

this end. The things you observe seem closer!

Some telescopes are small enough to be carried in one hand. Others can be huge, bowl-shaped radio telescopes, more than 300 metres in diameter. This is longer than three football pitches!

Lenses or mirrors?

Telescopes with lenses are called refracting telescopes. Lenses bend the light.

The largest telescopes use mirrors instead of lenses Telescopes with mirrors are called reflecting telescopes. Mirrors reflect light.

Optical telescopes consist of a long tube, with one end narrower than

the other. They can “perceive” light, just like eyes.

objective lens: the

lens closest to the object being viewed

tube

tripod: three-legged

stand to support the telescope

OOPS! Wrong end!

How does a telescope work?

Objects reflect light. This light enters our eyes, and we see the object. Optical telescopes have an objective lens: a curved piece of glass at the wide end. This lens bends the light from the object so that it forms an image – a picture of the object – inside the telescope. The light from this image then goes through the eyepiece, at the narrow end of the telescope. The eyepiece bends the light back again, so the object looks big.

The Gran Telescopio Canarias (GTC), also called GranTeCan, is a 10.4 m

reflecting telescope, located on a volcanic peak (2,400 metres) on the island of La Palma, Spain.

It took seven years to construct!

Activities

1. Galileo Galilei invented the telescope. Why was this such an important discovery? What did astronomers know about the stars before then? 2. Research. Have you heard of the Hubble telescope? When was it built?

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The Universe

1

U N I T

Content objectives

• Learn about the characteristics of the Universe

• Calculate astronomical sizes and distances • Analyse the components of the Universe • Compare sizes: the Sun and the planets • Create a constellation poster

What do you remember?

• What are the points of light in this photo? • What is the difference between …

– a star and a planet? – a moon and a comet?

Key language

Describing

Planets are spherical bodies which orbit the Sun. Asteroids are rocky objects which are irregular in shape.

Comparing

Dwarf planets are smaller than planets. The Earth is larger than Mercury.

Giving instructions

Study the constellations.

Research more about them on the Internet.

Activities

1. Find ten words in the word search.

2. Imagine an alien friend from

another galaxy wants to write to you. Write your galactic address.

What makes up the Universe?

The Universe is all the matter, energy and space that exists.

The Universe is made up of galaxies which contain stars. Stars can have planetary systems made up of planets and satellites. Galaxies are separated by vast spaces.

1.

What is the Universe like?

M P L A N E T S I G R L A A S A L U A T S R P T K N E L T T A E Y S E N A H C L W O H B R X E L A T M S U N Y I Y M O O N L G T K E S W C P A E

Scientists developed two different theories to explain what the Universe was like.

In 1610, Galileo Galilei invented the telescope, and proved the Heliocentric theory: the planets and stars revolve around the Sun. • Geocentric theory

2nd_{century BC: Ptolomy}

proposed that the Earth was the centre of the Universe. That is, the Sun, Moon and planets orbited the Earth.

• Heliocentric theory In 1542, Nicolas Copernicus proposed that the Sun was at the centre of the Universe.

Galaxies are a vast collection of stars, dust and gases, held together by the

gravitational attraction between the components. They appear in groups called

galaxy clusters. Scientists think the vast spaces between the galaxies are empty.

Our galaxy, the Milky Way, belongs to the Local Group galaxy cluster.

Stars form when clouds of gases are pulled together by gravitational forces. They

are so hot inside that they emit heat and light. A galaxy can have up to five hundred thousand million stars. An enormous cloud of gas and dust, a nebula, surrounds the stars.

Planets are bodies which orbit some stars. They do not emit light; they receive light

from the star. They make up planetary systems. Our planetary system is the Solar

System. It is made up of eight planets and one star, the Sun, as well as moons,

comets and asteroids. The Solar System is located on a spiral arm of the Milky Way.

Natural satellites orbit some planets. The Earth’s natural satellite is the Moon.

2.

How big is the Universe?

The radius of the Sun is 109 times greater than the radius of the Earth.

Activities

3. Express the distance of Mercury, Mars and Pluto from the Sun in kilometres.

4. Research the term light-year. Why is it used in astronomy?

Source of light Time to reach

the Earth

the Sun 8 mins. 20 sec

Centauri, the

nearest star 4 light-years

Betelgeuse 500 light-years

The Earth seems huge, but, in reality, it is small compared to the Sun. The Sun is only one of the millions of stars in the Milky Way. To imagine the size of the Universe,

use these comparisons with everyday objects. • Imagine the Sun is the size of a pea.

• The closest star is another pea, five hundred and forty kilometres away from the first pea. • The Earth is like a particle of dust situated

two metres away from the first pea.

• The Milky Way contains one hundred thousand million peas which form a circle with a radius of seven million kilometres.

What units of measurement do astronomers use?

• Astronomical unit (AU). This is the distance from the Earth to the Sun. Approximately

150 million kilometres. Compare the distance

of these planets from the Sun: – Mercury: 0.4 AU

– Mars: 1.5 AU – Pluto: 39.4 AU

• Light-year. This is the distance light travels in one year. Light travels 300,000 km

in one second or

9.5 trillion km in one year.

Did you know that...?

Mars Mercury Pluto

rotational axis of the Moon rotational axis

terrestrial orbit

ecliptic plane

The Solar System was formed approximately five thousand million years ago from the gas and dust of a nebula.

Our Solar System is made up of the Sun, eight

planets with their satellites, dwarf planets and small solar system bodies. The Sun is the central

body.

• The Sun consists mainly of two gases:

hydrogen and helium. It is the closest star

to Earth.

• Planets are spherical bodies which revolve around the Sun. They all move in elliptical orbits, held by the gravitational force of the Sun. Planets are much larger than other celestial bodies which orbit the Sun.

Mercury, Venus, Earth and Mars are made up

mainly of rock. Jupiter, Saturn, Uranus and

Neptune are made up mainly of gases.

• Dwarf planets are spherical bodies which orbit the Sun. They are smaller than planets.

• Small solar system bodies are other celestial bodies which orbit the Sun. They include

asteroids, comets and satellites. Satellites

orbit planets and consist of rock.

3.

What makes up the Solar System?

Activities

5. Which planet …

• takes the longest to orbit the Sun? • is the fastest to orbit the sun? • has the longest days? • has the shortest days?

6. Why is a “day” on Venus longer than its “year”? 7. What is an orbit?

8. What do you call the imaginary plane of the Earth’s orbit?

Planet Distance from

Sun (AU)

Period of rotation

Period of revolution

Mercury 0.39 58.65 days 88 days

Venus 0.72 243 days 224.6 days

Earth 1.00 23 h 56 mins 365.25 days

Mars 1.52 24 h 37 mins 1.88 years

Jupiter 5.20 9 h 55 mins 11.86 years

Saturn 9.54 10 h 40 mins 29.46 years

Uranus 19.19 17 h 14 mins 84.07 years

Neptune 30.06 16 h 7 mins 164.82 years

How do the planets move?

Celestial bodies like the Earth, have two types of movement:

The planets in the Solar System

Orbit. A curved path which

a celestial body follows in its revolution around another celestial body. The orbit of the Earth around the Sun is an ellipse.

Rotation. Celestial bodies spin or rotate

on an invisible axis. This invisible line is called the rotational axis.

Revolution. Celestial

bodies revolve around other celestial bodies.

4.

Which are the inner planets?

INNER PLANETS

Terrestrial or rocky planets: the crust and mantle are made of rock. The core is metallic

Mercury Venus Earth Mars

Diameter (Earth = 1) 0.382 0.949 1 0.532 Diameter (km) 4,880 12,104 12,740 6,794 Average surface temperature (ºC) ⫺180 to 430 ºC 465 ºC ⫺89 to 58 ºC ⫺82 to 0 ºC Atmosphere none CO2 N2+O2 CO2 Satellites 0 0 1 2 Rings no no no no Interesting characteristics the smallest and closest to the Sun rotates in opposite direction the only planet with life very thin atmosphere

CO2⫽ carbon dioxide N2 ⫹ O2= nitrogen⫹ oxygen

In 2004, the robots Spirit and Opportunity landed on Mars. They investigated the possible existence of water. The Earth is the only planet that has life on it. The other

planets are too hot or too cold. Mercury Diameter: 4,880 km Venus Diameter: 12,104 km Earth Diameter: 12,740 km Mars Diameter: 6,794 km

The inner planets are the four planets closest to the Sun: Mercury, Venus, the Earth and Mars.

Did you know that...?

Pluto, Ceres and Eris are dwarf planets. Pluto used to be considered a planet. In 2006, the International Union of Astronomers reclassified it as a dwarf planet.

Ceres

Jupiter, Saturn, Uranus and Neptune are the four outer planets. They are called gas giants because they consist mainly of gases.

5.

Which are the outer planets?

Activities

9. Which planet …

• has the most satellites? • is closest to the Sun? • supports life? • is the largest in the

Solar System?

• spins on its axis in the opposite direction? 10. If you live on Venus, will

the Sun rise in the East and set in the West?

OUTER PLANETS

Gas giants: they consist mainly of gases

Jupiter Saturn Uranus Neptune

11.209 9.44 4.007 3.883

142,984 120,536 51,118 49,492

⫺150 ºC ⫺170 ºC ⫺200 ºC ⫺210 ºC

H2⫹He H2⫹He H2⫹He H2⫹He

63 59 27 13

yes yes yes yes

largest planet,

most satellites system of rings

rotational axis is almost horizontal

greatest distance from the Sun

H2⫽ hydrogen He ⫽ helium Jupiter Diameter: 142,984 km Saturn Diameter: 120,536 km Uranus Diameter: 51,118 km Neptune Diameter: 49,492 km

Saturn’s rings are made up of small particles, mostly ice.

6.

What are small Solar System bodies?

• Asteroids are rocky objects which are irregular in shape. They can be several hundred kilometres in diameter, but most are only a few metres wide. Asteroids orbit around the Sun. Most of them are between the orbits of Mars and Jupiter. This area is called the asteroid belt.

• Comets are small bodies that travel around the Sun in highly elliptical orbits. They are irregular in shape. The nucleus is made up of a mass of ice, dust and gas. When comets travel close to the Sun, some of the ice evaporates, creating the long, bright tails of the comets.

Activities

11. Compare the main characteristics of the inner and outer planets. 12. Describe an inner or outer planet. Your partner will identify it.

This inner planet This outer planet

is smaller / larger than is the largest / smallest. has (no)

the Earth. … satellites.

The atmosphere is made up of

carbon dioxide. helium. …

The Solar System. Observe the elliptic paths of the planets’ orbits around the Sun. Notice that the orbit of Pluto, a dwarf planet, is more inclined.

Halley’s comet has a bright tail. It was named after the English scientist Edmund Halley. He was the first scientist to calculate the orbit of this comet. Halley’s comet will next be visible from Earth in 2061.

Uranus Saturn comet Earth Mercury Venus Pluto Neptune Jupiter Mars Asteroid belt 877306 _ 0008-0017.qxd 25/11/09 09:29 Página 14

Hands on

Prepare a constellation poster

1

2

a. Find more information in encyclopedias or on the Internet.

b. Draw the constellation, or cut out a drawing or a photo of it.

c. Write some sentences about the constellation. Constellations are imaginary patterns of bright stars.

All societies have invented constellations. The Ancient Greeks invented the constellations we call the twelve signs of the zodiac.

There are 88 official constellations. However, most of them do not really look like the mythical figures they represent.

The night sky looks different in the Northern and Southern Hemispheres. The position of the constellations changes with the seasons because of the movement of the Earth.

Activities

13. Look up the constellation for your sign of the zodiac.

a. Find out where and when it is most clearly visible in the sky. Is it in the Northern or the Southern Hemisphere?

b. Write the dates associated with this sign.

14. Choose another constellation.

Research more about it on the Internet.

Ursa major Gemini

Cassiopeia Orion

Orion represents the hunter.

The three stars in the middle are his belt. His sword hangs from his belt.

You can see his sword and his bow.

The constellation Orion

Activities

15. Label each diagram with the name of … a. a theory of the universe

b. the person who proposed the theory.

16. Make a drawing of the Solar System and label it: the Sun, the inner planets, the outer planets, Pluto and the asteroid belt.

17. Make a timetable of your daily activities on these planets. Give an approximate duration for each. • Earth. Rotation: 24 hours

• Mercury. Rotation: 58.65 Earth days • Jupiter. Rotation: 9.841 Earth hours

18. What two types of movement do all planets have? Describe them.

19. Describe the composition, temperature and movement of the Sun.

20. Make an illustrated list of the planets. Write them in order: start with the closest one to the Sun.

21. Talk about astronomical distances with a partner.

How far away is … from …? It is … km / … light-years away.

22. Research the latest astronomic discoveries. Report your findings to the class.

23. This drawing shows the positions of a comet in orbit.

When a comet gets close to the Sun, why does it develop a tail? Why does an asteroid not?

Duration on …

Activities Earth Mercury Jupiter

Astronomic distances from the Earth

Object Distance space station 300 km weather satellite 36,000 km the Moon 384,000 km the Sun 150,000,000 km Pluto 6,000,000,000 km

Alpha Centauri 4 light-years

24. Draw a diagram of the Solar System seen from above. Include the rotation and revolution movements of each planet.

25. Copy and complete to situate the Moon in the Universe:

The Moon is a satellite of … which belongs to the planetary system called … . The star of this planetary systems is … . It belongs to a galaxy called … . This galaxy is part of the galaxy cluster called … .

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Early concepts

• Geocentric theory: the Earth is the centre of the Universe. The Sun, Moon, stars and planets revolve around the Earth.

• Heliocentric theory: the Sun is the centre of the Universe. The Earth, planets and stars revolve around the Sun.

Components

• Galaxies are grouped together in galaxy clusters. • Galaxies contain thousands of millions of stars. • Stars are massive spherical bodies of gases. Some

stars have planetary systems with planets, satellites, asteroids and comets.

THE UNIVERSE

What should you know?

Units of measurement

• Astronomical unit (AU): the distance between the Earth and the Sun, about 150 million kilometres.

• Light-year. The distance that light travels in one year: about 9.5 trillion kilometres.

The Solar System

Projects

INVESTIGATE:Could Mars support life?

First, list the factors that make life possible on Earth.

Then, investigate this website: http//solarsystem.nasa.gov/planets/profile.cfm?Object=Mars

WEB TASK: Do you want to visit Mercury, Jupiter or Mars?

The Solar System is the planetary system of our Sun. It consists of:

• The Sun: a medium-sized star in the Milky Way galaxy. • Planets:

Inner: Mercury, Venus, Earth and Mars. All are rocky.

Outer: Jupiter, Saturn, Uranus, and Neptune. All are gaseous. • Dwarf planets: Pluto, Ceres, Eris

• Natural satellites: celestial bodies which revolve around planets and dwarf planets. • Small Solar System bodies

Asteroids: small rocky bodies which orbit the Sun. Some form belts. The asteroid belt: a band of asteroids between the orbits of Mars and Jupiter. Comets: masses of ice and rock found beyond the orbit of Pluto.

1

Planet Earth

2

U N I T

Content objectives

• Learn about the Earth’s characteristics • Identify lunar phases

• Describe the geosphere

• Learn about the Earth’s “spheres” • Reproduce conditions of solar and lunar

eclipses

What do you remember?

• In this photo, what does each colour correspond to? • Is the Earth an outer or an inner planet?

• What is the interior of the Earth like?

• Where does life exist on Earth: in the geosphere or the biosphere?

Key language

Describing

Water exists in three states. It takes 28 days to orbit the Earth.

Expressing cause and result

This causes the sequence of day and night. This makes the seasons occur.

Comparing

The days get shorter.

Ocean trenches are the deepest areas.

The Earth is special for many reasons. The Earth is the only planet with:

• an atmosphere containing oxygen • an average temperature of 15ºC • a water cycle

• life as we know it

All these characteristics make the Earth a unique planet in the Solar System.

• The atmosphere consists of a mixture of gases.

Nitrogen and oxygen are the most abundant.

Oxygen is essential for plant and animal respiration. There is also carbon dioxide, essential for photosynthesis.

• The average temperature is 15°C on the Earth’s surface. This is possible because of the distance from the Sun and the composition of the atmosphere.

• Water exists in three states (ice, liquid, water vapour) due to temperature variations. These variations make the water cycle possible.

1.

What is the Earth like?

Activities

1. Draw a diagram of the Earth, as seen from space. Draw two people: one at the North Pole and one at the South Pole.

2. Find out the mixture of gases and the average temperatures of Venus and Mars. Why do you think life is only possible on Earth?

Photo of the Earth and the Moon taken by satellite. Volcanoes are proof of intense geological activity.

• The Earth has a relatively large natural

satellite, the Moon. The gravitational attraction

of the Moon causes ocean tides.

• The Earth’s magnetic field protects living beings from dangerous solar radiations.

• Conditions exist for life. Thousands of millions of years of evolution have produced the variety of species there are today. This includes

humans.

• There is considerable geological activity on the Earth: earthquakes, volcanoes, mountain

building, erosion, etc.

2.

How does the Earth move?

• Rotation: The Earth rotates on a slightly tilted axis, always in the same direction. This

rotation causes the sequence of day and night. • Revolution: The Earth’s revolution around the

Sun is an ellipse. It takes 365 1⁄4days to

complete the revolution. This is one year.

The rotation of the Earth. It is day on the half of the Earth facing the Sun. It is night on the half facing away from the Sun.

direction of rotation North Pole South Pole Northern Hemisphere plane of the Earth’s orbit Southern Hemisphere rotational axis Sun’s rays Equator D a_y Night

The seasons in the Northern Hemisphere

Spring. The days get longer and the nights get shorter until 21st_June -the longest day.

Spring equinox 21st_March

Winter. The days get longer and the nights get shorter. On 21st_March, day and night are the same length.

Winter solstice

21st_December

Summer. The days get shorter and the nights get longer. On 22nd_September day and night are the same length. Summer

solstice 21st_June

Autumn. The days get shorter and the nights get longer until 22nd December- the shortest day. Autumn

equinox 22nd_September Solar rays strike the Earth at a

steeper angle and produce less heat.

What causes the seasons on Earth?

Two factors combine to cause the seasons: • the revolution of the Earth around the Sun • the Earth’s axis is tilted at an angle of about 23.5º The tilt of the axis causes differences in temperature and in the duration of day and night.

The Sun’s rays strike the Earth in different ways depending on the seasons.

The tilt of the axis makes the seasons occur at different times of the year in the Northern and Southern Hemispheres.

Summer

Winter

Solar rays strike perpendicular to the Earth’s surface and produce more heat.

23.5°

The Moon moves in two different ways: • Rotation. The Moon takes 29.5 days to

rotate once on its axis: a “lunar day”.

• Revolution. The Moon takes about twenty-eight days (twenty-seven days and eight hours) to orbit the Earth once. A “lunar month” is the period of time

between two new moons. It is about 29.5 days. A “lunar day” is as long as a “lunar month”. As a result, the same side of the Moon always faces the Earth.

3.

How does the Moon move?

The same side of the Moon always faces the Earth. The red dot indicates the dark or hidden side. It is never visible from Earth.

New Moon

The Moon is between the Sun and the Earth, so the Moon is not visible. The dark side (not illuminated) faces the Earth. The Moon rises and sets with the Sun, but you cannot see it from Earth. The phases of the Moon

First Quarter

Half the side is lit by the Sun. The illuminated part slowly increases. It rises at noon

and sets at midnight.

Last Quarter

Half the side is lit by the Sun. The illuminated part slowly shrinks. It rises at midnight and sets at noon.

Full Moon

When the Earth is between the Moon and the Sun, the entire Moon is visible. The illuminated side faces the Earth. It rises and sets with the Sun.

Activities

3. Draw a diagram to show the phase of the Moon in the Northern Hemisphere today. 4. When is there a New Moon?

5. Draw a diagram of the phases of the Moon in the Southern Hemisphere.

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Hands on

If the Moon passes between the Sun and the Earth, and blocks off the sunlight, a solar eclipse occurs.

If the Moon passes behind the Earth, so the Earth prevents sunlight from reaching the Moon, a lunar eclipse occurs.

Reproducing eclipses

1

2

3

the Moon the Sun

the Earth

Activities

6. Find out when the next solar and lunar eclipses will take place.

Visit this site:

http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html 7. How must you protect your eyes when observing a

solar eclipse? Materials

Solar eclipse Lunar eclipse

umbra penumbra Moon Earth umbra penumbra Earth Sun Sun Moon 877306 _ 0018-0027.qxd 15/2/08 18:24 Página 22

• The geosphere. The solid part which includes the crust, mantle and core. The upper 100 km of the geosphere is called the lithosphere: it is the most rigid part.

• The atmosphere. The air: a layer of gases which envelops the Earth.

• The hydrosphere. All the water on the Earth. • The biosphere. All the living things which

inhabit the Earth.

4.

How many “spheres” make up the Earth?

Activity

8. Show the three layers of the geosphere in a diagram. Label each layer: main components,

temperature and state: solid or liquid. Label the two types of crust.

continental crust

(thickness varies from 7 to 70 km)

oceanic crust (thickness varies from 7 to 10 km) The geosphere

The geosphere consists of three concentric layers: the crust, mantle and core. The crust and the upper mantle make up the lithosphere.

The crust is the outer layer of

rock. The most abundant minerals are silicates. • The continental crust

makes up the continents. Granite is the most common rock. • The oceanic crust makes up

the ocean floor. It was created by intense volcanic activity at mid-oceanic

ridges. Basalt, a

volcanic rock, is the most common rock.

The Earth is the only known planet which contains water and living things. It is made up of four interrelated parts or “spheres”. These are:

The mantle is the middle layer,

below the crust. It lies 2,900 km below the

surface. It is made up of mostly solid rock

material. The temperature is

higher here, from 1,000ºC to

4,000ºC, so some areas are melted rock.

The core is the

centre of the Earth, below the mantle. It is made up mainly of iron. The temperature is over 4,000°C. The outer

core is liquid. The inner core is solid. mantle outer core (liquid) inner core (solid) 877306 _ 0018-0027.qxd 24/11/09 13:10 Página 23

5.

What is the surface of the Earth like?

the vast expanses of water on its surface. The distribution of materials that make up the Earth’s crust form the different types of land relief.

Continental relief features

• The average altitude is 600 m. • The three main relief features are:

– Mountain ranges. Chains of high mountains. Examples: the Himalayas in Asia or the Andes in South America.

– Great plains. Large extensions of flat land. Examples: the Amazon plain in South America or the Sahara desert in Africa. – Continental shelves. The areas near the

coastline, under the sea, that are made of continental crust, not oceanic crust. These areas slope down from the coastline to a few kilometres out to sea, to a depth of about 200 metres.

Ocean floor relief features

• The average depth is 4,500 m. • The main relief features are:

– Oceanic (mid-oceanic) ridges. Chains of submarine mountains with intense volcanic activity. Example: the Mid-Atlantic ridge.

– Oceanic trenches. The deepest areas of the ocean. Example: Mariana Trench: 11,034 m deep.

– Abyssal plains. The largest plains on the planet: 4,000 or 4,500 m deep.

– Submarine volcanoes may create volcanic

archipelagos. Examples: the Canary Islands,

the islands of Hawaii.

Oceanic relief forms can rise up to 2 km from the ocean floor. In some places they appear above the water to form islands. Example: Iceland.

Cross-section of the Earth’s surface

mountain range continental great plain

submarine volcano mid-oceanic ridge oceanic trench abyssal plain abyss continental shelf 877306 _ 0018-0027.qxd 24/11/09 13:10 Página 24

6.

What are the other three Earth “spheres”?

or systems are the atmosphere, the hydrosphere and the biosphere.

The atmosphere

The atmosphere is the layer of air which surrounds the Earth. Air is a mixture of gases. The main components are: nitrogen (78 %) and oxygen (21 %). Oxygen is one of the necessary conditions for life. There are also small quantities of carbon

dioxide (CO2) and other gases.

The hydrosphere

The hydrosphere is all the water on, under and above the Earth.

The hydrosphere is made up almost exclusively of liquid water, but also snow and ice. Other materials in the

hydrosphere are the mineral salts in water. Sea water is very rich in mineral salts, but fresh water has few salts.

The biosphere

The biosphere includes all the living things which inhabit the Earth. Living things influence the physical and chemical changes in the Earth. For example:

• In the Earth’s crust: Animals live in the ground and plants take mineral salts from the soil. Plant roots can break up rocks.

• In the atmosphere: Microorganisms which live in the soil produce nitrogen. Oxygen is produced during

photosynthesis by plants, algae and some bacteria. Many living things cause evaporation.

• In the hydrosphere: Living things contain water. Plants take water from the ground. Many organisms live in aquatic environments.

Activities

9. Say a relief feature. Your partner says if it is continental or ocean floor.

10. Which continental feature is under the sea?

11. Describe the four different spheres that make up the Earth. List

examples of features in each sphere.

Coral produces exoskeletons which accumulate to form a rocky shelf. This atolon in Tahiti is

made up of living things.

Did you know that...?

The water cycle refers to how water evaporates, rises, condenses, falls to the Earth as rain or snow and moves around.

This cycle was described 2,500 years ago by Thales.

Activities

12. Draw the Earth. Include an arrow pointing in the direction in which it revolves. When does the Sun rise where you live?

13. Draw the Earth and its orbit. Show four positions. a. Indicate the solstices and the equinoxes. Divide

the orbit into four parts: one for each season in the Northern Hemisphere.

b. Colour each season a different colour. Tip: summer begins with the summer solstice and ends with the spring equinox.

14. Why is the Sun higher over the horizon at noon in summer than in winter? Does this occur at the same time of year in both hemispheres? 15. Think about the seasons. Use this information:

Solstices. summer / winter

Equinox. spring / autumn. The Sun is above the Equator. Day and night are the same length. a. When it is summer in the Southern Hemisphere,

what season is it in the Northern Hemisphere? And when is it spring there?

b. What causes this difference in the seasons? 16. Match each picture of the Moon with a number

in the diagram below.

17. The ecliptic is an imaginary plane. It passes through the centre of the Earth and the centre of the Sun. a. Does it go through the centre of the Moon? b. Does it pass through only sometimes?

How often? When?

18. The Moon has a dark side because each time it completes a turn around the Earth, it rotates on its own axis. This takes 28 days.

With a partner, demonstrate the movement of the Moon around the Earth.

19. What are the main differences between the continental crust and the oceanic crust? 20. Match each phrase to: geosphere, hydrosphere,

atmosphere or biosphere. • water in a river

• waves in the sea • sand on a beach

• fish, birds, plants or other living things • the air you breathe

• clouds

21. Two friends are collecting rocks. Who is right? Why? Girl: These rocks belong to the geosphere.

Boy: No, they belong to the lithosphere. 22. Think about the Earth’s rotation and answer.

a. Why are days longer in the summer? b. Why do days and nights last for six months

at the poles?

c. How are day and night produced? Make a drawing to show this.

23. Identify: summer solstice, winter solstice. Explain your answer. 1 2 3 4 5 6 7 8 A B C D E F G H 877306 _ 0018-0027.qxd 24/11/09 13:10 Página 26

• It has an intense magnetic field.

• The atmosphere contains mainly nitrogen, oxygen and carbon dioxide. • The average temperature is 15ºC.

• Water exists on Earth in solid, liquid and gaseous states. There is a water cycle.

• The Earth has one large natural satellite, the Moon. • Life exists on Earth.

• Rotation. The Earth rotates on its axis. The axis is tilted 23.5º. This rotation creates day and night.

• Revolution. The Earth revolves around the Sun. Its orbit is elliptical. These two movements and the Earth’s tilt cause the seasons. Other consequences are the differences in the length of day and night.

THE EARTH

What should you know?

The Moon takes almost 28 days to orbit the Earth. It takes the same length of time to rotate once on its axis.

Lunar phases: New Moon, First Quarter, Full Moon and Last Quarter. • Solar eclipse: the Moon blocks the light from the Sun.

• Lunar eclipse: the Earth blocks the light from the Sun so it does not reach the Moon.

The gravitational attraction or “pull” of the Moon on the oceans causes the tides.

Geosphere: the solid part of the Earth. It consist of the: • Lithosphere: the crust and the upper mantle.

– Continental crust: makes up the continents.

– Oceanic crust: makes up the ocean floor. The Earth’s surface is made up of continental features and ocean floor features.

• Mantle: the middle layer of the Earth, made of rock.

• Core: the centre of the Earth, made up of metals. Outer core: liquid. Inner core: solid.

Atmosphere: the layer of air which surrounds the Earth. It consists of a mixture of gases.

Hydrosphere: all the waters on the Earth.

Biosphere: the part of the Earth where living things exist. Living things can be aquatic or terrestrial.

Special characteristics

of Earth

Movements

The Moon, the Earth’s

satellite

The four Earth “spheres”

Projects

EXPERIMENT:Think about the geosphere.

• Shake together a mixture of gravel, cork and water. Allow this to settle. Observe the separation in layers by density. • Compare with the diagram of the geosphere on page 23. Identify the crust, mantle and core represented

in your experiment.

WEB TASK:Find out about artificial satellites.

2

All creatures great and small

1. How many living creatures can you find?

2. Check your answer in the word snake.

3. Now put them into three different groups. Explain why you chose them.

f rog e l ep h a n t f l o w e r a n t b u t t e_{r f l ym on}key t r ee m o s sf e r n f u n g_i 877306 _ 0028-0029.qxd 15/2/08 18:21 Página 28

4. Match each task, a-f, to its corresponding part of the microscope.

5. Look at the pond water through the microscope. What a surprise!

Use the code to write the vowels and discover the names of the microorganisms. Code: A__ E__ I__ O__ U__

Look at these drops of water from the pond. Can you see anything in them? Some living things are so small they cannot be seen with the naked eye. They can only be seen through a microscope.

iris diaphram

eyepiece

tube

light source base

Optical microscope stage coarse focusing knob fine focusing knob cover slip objective lenses nosepiece arm

a. This magnifies the specimen b. This increases the amount of

light

c. This is where you put the specimen

d. This is where you look through e. This is where you change the

magnification

f. This is used for fine focusing

____GL__N__ PR__T__Z____ B__CT__R____

Living things

3

U N I T

Content objectives

• Define the characteristics of living things • Describe cell structure and cell functions

• Classify unicellular and multicellular living things • Classify living things into five kingdoms

• Make slides to study cells

What do you remember?

• Can you name any of these living things?

• Classify them into groups: plants, animals, vertebrates, invertebrates. • What do all living things do?

• What is the animal kingdom?

• What kingdom do human beings belong to?

Key language

Expressing facts

Living things feed, reproduce and interact.

Making impersonal statements

Cells are organised into levels.

Expressing purpose

Photosynthesis enables plants to obtain energy. Water is used to transport substances.

Activities

1. True or false? Biodiversity refers to all living things. 2. Why does biodiversity vary throughout the world? 3. Match each photo with a factor that reduces

biodiversity. a. pollution

b. destruction of habitats c. uncontrolled hunting

d. introduction of exotic species Biodiversity is the variety of life on Earth in all its

forms. Biodiversity is the result of a slow process called evolution. Evolution began with the first life forms and still continues today. Species change, and adapt to the environment.

Scientists believe there may be more than thirty million species. Approximately two million species have been classified.

Biodiversity varies tremendously throughout the world. It is influenced by climate zones and habitats. For example, more than half the world’s species live in tropical rain forests and coral reefs. Some countries have many different climate zones and habitats. As a result, they have more biological diversity. For example, Spain has more biological diversity than other European countries.

1.

What is biodiversity?

hunting and fishing endangers many species: for example the Iberian lynx (Lynx pardinus) is in danger of extinction.

Pollution of water, soil and the atmosphere, caused by agricultural, industrial and urban development.

Did you know that...?

Rain forests have the greatest biodiversity.

What factors can reduce biodiversity?

Whole species of living things become extinct every day for these four factors:

1

3

4 2

2.

What do all living things have in common?

composition.

All living things also carry out three functions: nutrition, interaction with the environment and reproduction.

Nutrition refers to all the processes which enable

living things to obtain the energy and matter they need to live.

Living things can be classified into two groups depending on how they feed.

• Autotrophs produce the organic substances which they need from inorganic substances. They take substances like water, mineral salts and carbon dioxide from the soil and the atmosphere. To obtain these substances, autotrophs need energy. They get energy from sunlight through a process called

photosynthesis. Chlorophyl enables them to do

this. Plants, algae and some bacteria are autotrophs.

• Heterotrophs feed on organic matter which is already elaborated: for example, living things or their remains. Animals, fungi, some bacteria and all protozoa are heterotrophs.

Interaction with the environment: all the

processes which enable living things to react to changes in their environment. For example: plants grow towards the light; animals flee from

predators.

Reproduction: refers to all the processes which

enable living things to create new living things. There are two basic types:

• Asexual reproduction involves one living thing. For example: a sponge can produce buds which give rise to new sponges.

• Sexual reproduction involves living things of different sexes. Each one provides a sex cell or

gamete. The two sex cells join to form the first

cell of a new living thing, the zygote.

What function is this cheetah carrying out?

Why are all the flowers following the Sun? What function are they carrying out?

Activities

4. Complete:

5. Test your partner. Ask questions:

Which processes enable living things to ... ... create new living things?

... adapt to their environment? ... obtain the energy they need?

Heterotrophs feed on ... . Autotrophs obtain ... .

Sexual reproduction involves ... . Asexual reproduction involves ... .

3.

What are living things made up of?

Activities

6. Compare organic and inorganic substances:

7. Ask questions about organic and inorganic substances. For example:

8. Use the pie charts to calculate, in grams, the approximate value of each group of biomolecules: a. Weigh yourself, then

calculate the biomolecules in your body. For example, 100 kgs = 60 kg water b. a sunflower: 2.250 grams. All living things are made up of chemical substances. Carbon (C), oxygen (O),

hydrogen (H), and nitrogen (N) make up about 95 % of all living matter. Combinations of these elements form molecules of living matter called

biomolecules.

Living things are made up of two kinds of substances: inorganic and organic.

Inorganic substances

Inorganic substances do not contain carbon. They are present in living things and non-living things. The principle inorganic substances are:

• Mineral salts have various functions: they make up different structures, like shells, bones and teeth. They are present in internal fluids, like tears, sweat and blood.

• Water is the most abundant substance in living things. Living things obtain water directly by drinking it, or indirectly from substances that contain water. Plants obtain water from the environment. Water is necessary for chemical reactions and to transport all other substances.

Organic substances

Organic substances are unique to living things. Carbon is their principal element. Organic substances present in living things are:

Organic and inorganic substances are present in different amounts in plants and animals.

Plants Animals water 74 % lipids 0.8 % glucides 19 % proteins 3.2 % mineral salts 3.2 % lipids 20 % water 60 % glucides 0.6 % proteins 16 % mineral salts 3.4 %

Biomolecules Example Use/Function

Glucides glucose cellulose

to provide energy to make structures Lipids fatty acids

cholesterol to provide energy to make structures Proteins haemoglobin antibodies keratin to transport oxygen

to fight microorganisms that cause disease to make structures: hair, nails

Nucleic acid

DNA RNA

to control cell function and heredity

… substances are …; … substances have …

How are (lipids) used by living things?

They are used to … 877306 _ 0030-0041.qxd 25/11/09 09:43 Página 33

4.

What are cells?

Cells are the smallest unit of life. They are the structural and functional units for all living things.

• All living things are made up of one or more cells. • Cells carry out the functions of nutrition, interaction

with their environment and reproduction. • Most cells are very small. For example, skin cells

are approximately one hundredth of a millimetre in size.

• All cells come from other cells.

• Prokaryotic cells have no nucleus. They have no nuclear membrane. Genetic material is dispersed throughout the cytoplasm. They are simpler and smaller than eukaryotic cells. Bacteria are made up of prokaryotic cells.

How is a cell organised?

• The cell membrane covers the whole cell.

• Cytoplasm is the inside of the cell. It is a jelly-like substance. Many of the chemical reactions of the cell take place here. Organelles are small structures in the cytoplasm. They are responsible for respiration, making and storing nutrients, etc.

• Genetic material controls and regulates how cells work. This DNA contains the hereditary information that is passed from one cell to the daughter cell. DNA makes up the chromosomes.

Prokaryotic cell organelles cytoplasm cell membrane genetic material Eukaryotic cell nucleus organelles cytoplasm cell membrane

Activity

9. Read the chart, then make sentences to describe the cells: Eukaryotic cells are

found in animals.

Eukaryotic cells

Prokaryotic cells

found in animals bacteria

size big small

nucleus yes no

complexity complex simple

What are the two basic types of cells?

Did you know that...?

Robert Hooke was the first person to use the term cells. In 1665, with this microscope, he observed cavities in a thin slice of cork, and called them cells.

• Eukaryotic cells have a nucleus, separated from the cytoplasm by the nuclear membrane. Algae, protozoa, fungi, animals and plants have eukaryotic cells.

Both animals and plants have eukaryotic cells, but there are some differences.

• Plant cells have a rigid cell wall which surrounds the plasmatic membrane. The cell wall gives the cell its shape and strengthens it. • Plant cells are usually polyhedral, but animal

cells are various shapes: round, square, star-like.

• Plant cells have unique organelles called

chloroplasts which are responsible for

photosynthesis.

• The nucleus of plant cells is usually found on one side. A vacuole takes up most of the space. Animal cells also have vacuoles, but they are smaller.

5.

How do animal and plant cells differ?

Cell membrane. Like a

skin around the cell. It

keeps the cell together and controls what passes in and out. Nucleus. Contains genetic material. Cytoplasm. Contains the organelles: mitochondria, vacuoles… Vacuoles.

Like bags, surrounded by membranes where substances, mainly water, accumulate. Mitochondria. Where energy is obtained from nutrients. Chloroplasts. These store a green pigment,

chlorophyll, which absorbs the Sun’s energy to elaborate organic matter during photosynthesis. Cell wall.

A thick, rigid wall made of cellulose.

Animal cell Plant cell

Activities

10. Make a Venn diagram: show the similarities and differences between animal and plant cells.

11. Draw and label an animal cell with all its parts.

Activities

12. Label each plant cell indicating its magnification.

13. Imagine that your hypothesis were incorrect. What result would make this obvious?

14. Imagine you have an unidentified sample. Hypothesis: If this is a living thing, it will be made up of cells. Is this hypothesis correct? Can you use it to differentiate between living and non-living things? What would you do to classify the sample as living or non-living?

Hands on

A hypothesis is a proposal. It is used as a basis for reasoning. Scientists use experiments and observation to test the validity of a hypothesis. Hypotheses show the relationship between two or more facts. For example: we know that cell walls in plant cells are made of cellulose.

Cellulose is a rigid substance that holds the cell parts together in a polyhedral shape.

Resulting hypothesis: If you observe cells through

a microscope that are polyhedral in shape and joined together by thick walls, you know they are plant cells.

1

2

3

the microscope and draw the specimen. Use different magnifications.

At higher magnifications you may be able to see and count the chloroplasts.

Making a specimen of plant cells

1

2

3

4

microscope and draw the specimen.

Making a specimen of animal cells

Notice that the plant cells have a polyhedral shape.

The animal cells are irregular, and they are not joined together.

Check your hypothesis

Making a hypothesis. Using a microscope to study cells

1 2 3 1 ₂ 3 4 phyllodes 877306 _ 0030-0041.qxd 18/2/08 09:38 Página 36

Living things can be classified into two different groups: unicellular and multicellular.

• Unicellular living things have only one cell. They sometimes form colonies. Unicellular living things feed, interact with the environment and reproduce. Example: paramecia.

• Multicellular living things have many different cells. Example: plants and animals.

6.

How do living things differ?

Multicellular organisation

Cells in multicellular living things are organised in levels. The cells work together to carry out the vital functions.

• Cells are specialised: they have specific functions. Each type has a unique shape and structure.

• Tissues are groups of cells with the same

function. Example: muscle cells form muscle

tissue.

• Organs are groups of various tissues which act together. Example: a muscle is an organ made up of muscle tissue, nerve tissue, connective tissue and blood tissue.

• Systems are made up of several organs. Example: the digestive system includes the stomach, the intestines, etc.

Form and function of cells

Specialised Cells

Sperm cells

have a tail (flagellum) so they can swim toward the ovum

Red blood cells

consist mainly of haemoglobin to transport oxygen

Neuron or Nerve cells

are like wires with a lot of extensions so they can conduct and capture messages

Root hair cells

are long and thin so they can absorb water and mineral salts from the soil

Cells Tissue Organ Muscular system muscle cell muscle tissue muscular system muscle

Activities

15. Describe one of the specialised cells. Your partner identifies it. For example: A: It has no nucleus. B: A red blood cell.

16. What is the difference between tissues, organs and systems?

Example: ... are made up of... 877306 _ 0030-0041.qxd 25/11/09 09:43 Página 37

7.

What are the five kingdoms?

Scientist classify all living things into five kingdoms by three main criteria: type of cells, how the cells are grouped, and nutrition.

Contains unicellular, prokaryotic organisms. They may be autotrophic or heterotrophic.

Bacteria and cyanobacteria.

Contains unicellular and multicellular living things. They are all eukaryotes. They have no tissues. They may be autotrophic or heterotrophic. Protozoa, algae.

Contains unicellular and multicellular living things. They are eukaryotes. They have no tissues. They are heterotrophic.

Yeasts, moulds, mushrooms.

Contains multicellular eukaryotes. They have tissues. They are autotrophic.

Mosses, ferns, flowering plants.

Contains multicellular eukaryotes. They have tissues. They are heterotrophic.

Animals: may be invertebrate or vertebrate.

Plant Kingdom

Monera Kingdom Protoctist Kingdom Fungi Kingdom

Animal Kingdom

Activity

17. Copy and complete the table to describe the five kingdoms.

Kingdom Type of cells Tissues Autotrophic / Heterotrophic

Moneran Prokaryotic

Protoctist No tissues

Fungi Eukaryotic Heterotrophic

Plant

Animal They have tissues

Living things can be differentiated by the way they feed, reproduce, interact with their enviroment, etc. They are classified into different groups. The main group is the kingdom. Each kingdom is then divided into subgroups.

This is how you are classified.

A species is the first level of classification for living things. A species is a set of living things which are physically similar. They reproduce and usually have fertile descendants.

Animals from the same species have similar appearances.

However, there can be differences in structure, size and colouring between the male and the female. This difference is called

dimorphism.

8.

How are living things classified?

9.

What is a species?

When a donkey and a mare mate, the result is a mule. Mules are sterile because donkeys (Equus asinus), and horses (Equus caballus) belong to different species.

donkey

female horse - mare

mule

The lion and lioness are examples of dimorphism.

A male peacock uses its colourful tail to attract the female.

Activities

18. Make a list of animals that show sexual dimorphism. 19. Describe the differences

between the male and female of some animals. CLASSIFICATION Kingdom Phylum Sub phylum Class Order Family Genus Species Animal Chordate Veterbrate Mammal Primate Hominid Homo Homo sapiens BECAUSE YOU...

Are a heterotroph, cells form tissues

Have a spinal chord

Are a chordate with a backbone

Have warm blood; babies drink mother’s milk

Your thumbs and fingers work together

Walk upright

Talk, have a long childhood

Are intelligent, have little body hair ... YOU

Activities

20. Study the illustrations. Which represent living things? Which characteristics support your decision?

21. Classify these living things as autotrophic or heterotrophic.

22. Copy and complete the chart.

23. Draw an animal cell with the most important organelles. What structures would transform it into a typical plant cell? Draw them.

Include: mitochondria, cytoplasm, cell membrane 24. Test your classmates. Ask questions about the five

kingdoms.

Biomolecule Function

Glucides Lipids Proteins

25. Study the cell diagrams. Match each with a name and description.

1. They are long and thin in order to absorb water and mineral salts from the soil.

2. They are shaped like wires with a lot of extensions. They conduct messages around the body.

3. They have a tale (flagellum) which enables them to swim towards the ovum.

4. They have no nucleus so they have room to transport oxygen in the haemoglobin. – Sperm cell – Neuron – Red blood cell – Root hair cell

26. Complete the table on sexual dimorphism. A D B E C F A _B C D E F H G

Animal Group Male Female

lion mammal long mane no mane

Which kingdoms are made up of have autotrophs / eukaryotes? no tissues?

unicellular and multicellar living things? A B C D 877306 _ 0030-0041.qxd 20/2/08 13:16 Página 40

What should you know?

• They are born and they die.

• They have a similar chemical composition. • They are made up of cells.

• They have three vital functions: nutrition, interaction with the environment, and reproduction.

Composition

They are made up of two kinds of substances:

• Inorganic substances. Not exclusive to living things: water and mineral salts.

• Organic substances. Exclusive to living things: glucides, lipids, proteins and nucleic acids.

Cells

Cells consist of:

• A plasmatic membrane which surrounds the cell. • Cytoplasm or internal matter. It contains the organelles

(mitochondria, chloroplasts, etc.).

• Genetic material. This controls cell functions. There are various kinds of cells:

• Prokaryotic. With no nucleus and no nuclear membrane. • Eukaryotic. With a nucleus and a nuclear membrane.

Animal and plant eukaryotic cells are different. Living things may be:

• Unicellular. Consisting of one cell.

• Multicellular. Consisting of many cells forming tissues, organs and systems.

Classification and biodiversity

Living things are classified into kingdom, phylum, subphylum, class, order, family, genus and species. There are five kingdoms:

• Monera Kingdom: unicellular, prokaryotic living things. They may be autotrophic or heterotrophic.

• Protoctist Kingdom: unicellular and multicellular living things. They are eukaryotes and have no tissues. They may be autotrophic or heterotrophic.

• Fungi Kingdom: unicellular and multicellular beings. They are eukaryotes and have no tissues. They are heterotrophic. • Plant Kingdom: multicellular eukaryotes. They have tissues

and they are autotrophic.

• Animal Kingdom: multicellular eukaryotes. They have tissues and they are heterotrophic.

LIVING THINGS

INVESTIGATE:an organisation trying to save the biodiversity of the planet. Give examples of actions taken.

Projects

WEB TASK:Learn how you can protect the biodiversity.

3

Invertebrates

4

U N I T

Content objectives

• Recognise the main characteristics of invertebrates

• Classify invertebrates into groups • Describe invertebrate life functions

• Make a model of an invertebrate that can float • Differentiate between bilateral and radial

symmetry

What do you remember?

• What characteristics make the giant squid an invertebrate? • Do you know any invertebrates with …

– a soft, porous body?

– an elongated body with rings? – a soft body covered by a shell? – an external skeleton?

Key language

Making generalisations

Most sponges live in the sea. Some molluscs have no shell.

Making impersonal statements

Their bodies are divided into segments. They are made up of one or two valves.

Expressing contrast

Some are carnivores, but others are herbivores.

Did you know that...?

The giant squid is the largest known invertebrate: 20 m long, 1,000 kg. Its tentacles are more than 15 m long. It lives deep in the ocean: 400 to 1,500 m below the surface.

Activities

1. What part of a sponge body does the name porifera refer to?

2. Copy the drawing of the sponge. Use arrows to label the flow of water. Show the entry points and the exit point. 3. Talk about cnidaria.

The animal kingdom is made up of multicellular, eukaryotic organisms. They are heterotrophic and sensitive to their environment.

How are animals classified?

Animals are classified in two groups:

• Invertebrates. Animals with no backbone. Some, like worms or jellyfish, have no skeleton. Others, like insects or spiders, have an external skeleton or

exoskeleton.

• Vertebrates. Animals with a backbone which is part of their internal skeleton or endoskeleton.

The simplest invertebrates

The simplest invertebrate animals are classified into two groups: porifera and cnidaria. Porifera and cnidaria have no organs.

Porifera

Sponges belong to this group. Most live in the sea. Their bodies are full of pores and channels, so water circulates in and out of them. They feed by filtration. Water enters though the central cavity, deposits nutrients, and leaves through a hole called the osculum. Sponges do not move around; they are attached to rocks or coral.

Cnidaria

There are three different groups of cnidaria: jellyfish, corals and sea anemones. Their main characteristics are:

• radial symmetry.

• a soft body, with only one opening, the mouth, which is surrounded by tentacles.

• a gastrovascular cavity, something like a stomach, connected to the mouth.

• Nutrition. Cnidaria are carnivorous: they use their tentacles to capture prey.

• Interaction. Most cnidaria live in the sea. Jellyfish can float; corals and sea anemones live fixed to the sea bed. • Reproduction. In their lifetime, cnidaria usually pass

through both the polyp and the medusa stages: Polyps reproduce asexually by budding.

Jellyfish (medusae) reproduce sexually: there are male and female specimens.

1.

What makes up the animal kingdom?

Cross-section of a porifera Cnidaria tentacles Which are have can tentacles? carnivorous? radial symmetry? an opening at the top? a body like a tube? float? osculum water exits water enters channels polyp pores jellyfish 877306 _ 0042-0051.qxd 15/2/08 18:30 Página 43