7A Summary Sheets. Cells and their functions. All living things are made from cells. There are two basic types of cell:

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7A Summary Sheets

Cells and their functions

All living things are made from cells. There are two basic types of cell:

Animal cell Plant cell

Cells are very small. A microscope is used to see them. To use a microscope you:

i Place the smallest objective lens over the hole in the stage.

ii Turn the focusing wheel to move the objective lens close to the stage. iii Place the slide on the stage.

iv Adjust the light source or mirror. v Look into the eyepiece lens

vi Turn the focusing wheel until what you see is clear (in focus).

A microscope makes things appear bigger. It magnifies things. There are two lenses in a microscope. To work out the total magnification you multiply the magnification of the objective lens by the magnification of the eyepiece lens.

The object you want to look at using a microscope is called the specimen. It has to be thin to let light get through it. It is placed, with a drop of water, onto a slide. A coverslip is put on top. The coverslip stops the specimen from drying out, holds it flat and stops it moving. A stain might be used to help you see parts of

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Some cells have special shapes. They are adapted to do certain jobs.

Cilated epithelial cells are found

in tubes leading to the lungs. The strands at the top (cilia) wave about to move dirt out of the lungs.

Muscle cells are able to change

length. This helps us to move.

Nerve cells (neurones) are long

so that messages can be carried around the body quickly.

Root hair cells in plant roots take

water out of the ground quickly. The root hair gives the water more surface to get into the cell.

Palisade cells in plant leaves are

packed with chloroplasts to help the plant make food.

A group of cells that are the same, all doing the same job, is called a tissue (e.g. muscle tissue). A group of different tissues working together to do an important job makes an organ. For example the heart is an organ and is made of muscle tissue and nerve tissue.

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Organ system Organs Job

Breathing system Windpipe (trachea), lungs Takes air into the body

Circulatory system Heart, blood vessels Carries oxygen and food around the body Digestive system Mouth, gullet, stomach, intestines Breaks down our food

Flower Stamen, carpel Used for sexual reproduction in plants Nervous system Brain, spinal cord, nerves Carries messages around the body

Sex cells are produced by the reproductive organs. In plants, these are contained inside flowers. Sex cells are used for sexual reproduction which needs two parents. The offspring from sexual reproduction are different from the parents; they are new varieties.

The pollen grains need to be carried to the stigma of another flower. They can be carried by insects or the wind. The carrying of pollen from an anther to a stigma is called pollination.

Once on the stigma, a pollen grain grows a pollen tube which enters the ovule containing an egg cell. The nucleus from the pollen grain then joins with the nucleus inside the egg cell. This is called fertilisation.

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7B Summary Sheets

Reproduction

Reproduction produces new living things (offspring). In sexual reproduction the nucleus in a male sex cell joins (fuses) with the nucleus in a female sex cell. This is called fertilisation and produces a fertilised egg cell. When fertilisation happens outside an animal’s body it is called external fertilisation. Animals that use this method produce a lot of eggs since some will be eaten by other animals. Humans use internal fertilisation.

The fertilised egg cell grows into an embryo and the embryo eventually becomes a new living thing. Sexual reproduction needs two parents. The offspring from sexual reproduction are different from the parents; they are new varieties.

The human reproductive systems

Humans have reproductive organs so that they can reproduce. The ovaries and testes produce sex cells.

Puberty and adolescence

The reproductive organs get bigger and start to make sex cells at puberty. This is a time when major physical changes occur in our bodies. These changes are caused by sex hormones.

Changes in boys Changes in girls

• voice deepens (‘breaks’) • underarm hair grows

• shoulders get wider • breasts develop

• hair grows under arms, on face and on chest • ovaries start to release egg cells

• pubic hair grows • hips get wider

• testes and penis get bigger • pubic hair grows • testes start to make sperm cells • body smell increases • body smell increases

Adolescence is the time when puberty is occurring and emotional changes happen. It starts between the ages of 10–15 and ends at about 18. The changes start sooner

in girls. After puberty, men produce sperm cells for the rest of their lives. Women stop releasing egg cells at the age of 45–55. This is called the menopause.

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The menstrual cycle

The menstrual cycle starts with menstruation (the loss of the uterus lining and some blood through the vagina). It takes 28–32 days for each cycle. About 14 days after menstruation starts, an egg cell is released from an ovary. This is called ovulation. If the egg cell is not fertilised, the uterus lining starts to break down and the cycle starts again.

Sex

The sperm cells enter the vagina during sexual intercourse. Semen (sperm cells mixed with special liquids from the glands) is forced out of the penis and into the top of the vagina. This is called ejaculation. The semen is moved into the top of the uterus and the sperm cells can swim down the oviducts.

Egg cells and sperm cells are adapted to their functions.

Pregnancy

If the egg cell meets a sperm cell in an oviduct fertilisation can occur. The fertilised egg cell divides to form a ball of cells (an embryo). The embryo travels to the uterus where it sinks into the soft lining

(implantation). The woman is now pregnant. Once it has developed all its organs (after about 10 weeks) it is called a fetus. It takes about 40 weeks (9 months) for a fertilised egg cell to grow into a baby ready to be born. This time is called the gestation period.

The fertilised egg cells of many animals grow and develop outside their parents. This is called external development. Humans use internal development and produce less offspring than animals using external development since the growing embryos are protected inside the mother.

While inside the uterus, the fetus is supplied with oxygen and food by the placenta. The placenta also gets rid of waste (especially carbon dioxide) from the fetus. The cord (or umbilical cord) connects the fetus to

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If a mother smokes, drinks too much alcohol or takes drugs while pregnant she might damage the baby. The baby might be premature.

Birth

When the baby is ready to be born, the uterus starts contractions and the woman goes into labour. The muscles of the cervix relax. The baby is pushed out head first through the cervix and the vagina. After birth, the baby starts to breathe and the cord is cut. The scar left behind is the navel. After this the placenta is pushed out of the uterus. This is the afterbirth. The baby is fed on milk, often from the mother’s breasts which contain mammary glands that produce milk. The milk contains antibodies which help destroy microbes that might cause a disease in the baby.

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7C Summary Sheets

Habitats

A habitat is the area where an organism lives. The surroundings of an organism are called its environment. The conditions in an environment are caused by physical environmental factors. Examples include how light it is and what the temperature is. Smaller areas in a habitat are called microhabitats.

Where you can find a certain organism in a habitat is known as the organism’s distribution. A community is all the plants and animals in a habitat.

Jack rabbits are adapted to living in a desert habitat.

Animals and plants are adapted to where they live. This means that they have certain features that allow them to survive in a habitat. For example, fish are adapted to living under water. They have gills to take oxygen out of the water, fins to swim with and streamlined bodies to help them move easily through the water. Here is another example:

Physical environmental factors change from day to day (daily changes). Animals that only come out at night are called nocturnal animals (e.g. an owl).

Physical environmental factors change over the year (seasonal changes). Organisms adapt to these changes. When it starts to get colder, some birds migrate to warmer countries where there is more food. There are other ways plants and animals cope. Look at the picture to discover some of these.

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Organisms are in competition with each other. Animals compete for food and space. Plants compete for light, water and nutrients (mineral salts).

Feeding relationships

An animal that hunts other animals is a predator. What it hunts is its prey. We can show what eats what on a food chain. Different words are used to describe what the organisms do in a food chain.

producer consumers

herbivore carnivore carnivore prey for the robin prey for the

sparrowhawk predator of the caterpillar predator of the robin top predator

grass ⎯⎯⎯→ caterpillar ⎯⎯→ robin⎯⎯⎯⎯→ sparrowhawk

Food chains are joined to form food webs. Food webs can also show omnivores (animals that eat both plants and other animals).

Plants are producers because they can produce their own food. Energy from the Sun is used to help them do this. This light energy is turned into chemical energy in the producer. When a consumer eats a producer, the consumer gets the chemical energy.

Food chains and food webs show how energy flows through a community.

Animals that are predators have adaptations that allow them to catch their prey. Animals that are prey have adaptations for avoiding being eaten!

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Many predators have... Many prey have...

forward facing eyes to look out for prey. eyes on the sides of their heads so that they can keep a lookout behind them.

large, sharp claws. some form of protection (e.g. horns, spines or armour).

Often, animals have adaptations for eating, either in or on their mouths:

You can find evidence of what has been eating something by: • seeing it happen

• finding animal droppings or footprints near a damaged plant or dead animal • finding teeth marks in a damaged plant or dead animal.

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7D Summary Sheets

Variation and classification

Variation

A species is a group of organisms that can reproduce with one another to produce offspring that will also be able to reproduce. The differences between organisms are known as variation. There is variation between different species and between members of the same species.

There is variation between different species. Lions and tigers are different species. Tigers have stripes, lions do not.

There is variation between members of the same species. All tigers have different patterns of stripes.

Sometimes there is a relationship or correlation between two features. A relationship is normally best shown on a line graph. The line will go steadily up or steadily down.

Variation can have environmental or inherited causes.

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Environmental variation

An organism’s surroundings are known as its environment. The conditions in an environment are called environmental factors. Plants are affected by environmental factors like the amount of light, the amount of water, the amount of warmth and the amount of mineral salts in the soil.

The cress seedlings on the left have not had enough light. The plant on the left has not had enough water. It has wilted.

Animals are also affected by environmental factors. Humans who get sunburnt or have scars are examples.

Inherited variation

This is caused by features being passed from parents to their offspring.

In humans, natural eye colour and natural hair colour are both examples of inherited variation.

Classification

There are so many species that we need to put them into groups. This is called classification.

The first set of groups that organisms are divided into are called kingdoms. The two largest kingdoms are the plant kingdom and the animal kingdom. The main difference between these two kingdoms is that plants can make their own food and animals cannot.

The animal kingdom is divided into other groups. The vertebrates are animals that have a backbone. There are five sorts of vertebrate. There are another eight groups which are all invertebrates. The most important groups to know about are in bold type.

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7E Summary Sheet

Acids and alkalis

Indicators are coloured dyes which often come from plants such as red cabbage and beetroot. Acids make indicators change colour. Litmus is an indicator which turns red in acids. Common acids include vinegar and lemon juice. Fizzy drinks, pickles and spicy sauces also contain acids. Stronger acids such as sulphuric and nitric acids can be more dangerous. Often they are corrosive.

Alkalis have a different effect on indicators to acids. Litmus turns blue in alkalis. Alkalis can also be corrosive. Weak alkalis include soap and toothpaste.

Bottles in the laboratory and tankers carrying chemicals on the road all have to carry hazard warning labels to show when there is a chemical hazard. Some of the common warning signs are:

toxic (poisonous) harmful (irritant) corrosive flammable

The strengths of acids and alkalis can be measured on the pH scale, which runs from 1 to 14. pH numbers 1 to 6 are acids, 7 is neutral, and 8 to 14 are alkalis. You can find out the pH number using a universal indicator, or by using a pH meter.

Alkalis can cancel out acids, making them neutral. Neutralising reactions can be important:

• in gardening and agriculture, to make sure the soil is the correct pH • when dealing with insect stings and bites

• to control indigestion caused by excess acid in the stomach • to keep foods such as jam at the correct pH.

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Simple chemical reactions

Chemical reactions

In a chemical reaction a new substance is always formed. Most chemical changes are not easily reversed; they are irreversible. In a physical change no new substance is formed. Melting and evaporation are examples of physical changes. Physical changes are usually reversible.

You can tell that a reaction has occurred if there is a colour change or when a gas is given off. Most chemical reactions also involve an energy change. This is usually in the form of heat, but can also involve light being given off (for example, when something burns).

Reactions of acids

Some metals react with acids, and hydrogen gas is produced. When acids react with chemicals called carbonates, carbon dioxide gas is given off. Carbonates are found in rocks such as limestone or marble, and in some cooking ingredients and indigestion tablets.

You can test the gas made in a reaction to find out what it is:

Hydrogen burns with a squeaky pop if a lighted splint is held near the test tube. Carbon dioxide will put out a lighted splint, and it makes limewater turn milky. Oxygen makes flames burn more brightly, and will relight a glowing splint.

Burning

When a metal burns, the metal combines with oxygen from the air to form a chemical called an oxide. We can show this using a word equation. The chemicals that you start with are called the reactants. The chemicals at the end are called the products.

magnesium + oxygen

reactants → magnesium oxideproducts

Fossil fuels contain a lot of carbon and hydrogen. When they burn they use up oxygen from the air and produce water and carbon dioxide. We can show the reaction using a word equation. Energy is in brackets in this equation because it is not a chemical substance.

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Fire

A fire needs three things to keep burning: fuel, oxygen and heat. We show these three things on the Fire Triangle.

If any one of these three things runs out, the fire will go out.

Fire extinguishers are used for putting out fires. There are different types of fire extinguisher, and it is important always to use the correct sort for a particular fire. Sand or fire blankets can also be used to put out fires.

Water is often used to put out fires, because it takes away the heat. However, water should never be used on oil or petrol fires, because it makes the burning fuel spread out.

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7G Summary Sheets

Solids, liquids and gases

SOLID

• Solids are made up of particles that are very close together and are held tightly together by strong bonds.

• Solids cannot be squashed, do not flow, have a fixed shape and volume, and have a high density.

LIQUID

• Liquids are made up of particles that are fairly close together; the bonds between the particles are weaker than the bonds in solids.

• Liquids cannot be squashed, flow quite easily, and have a fixed volume but no fixed shape.

• Although they are dense, liquids usually have a lower density than solids.

GAS

• Gases are made up of particles that are well spread out, with no bonds between them.

• Gases are quite easy to squash, flow easily, have no fixed volume and no fixed shape.

• Gases have a lower density than liquids.

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LIQUID

GAS

Diffusion

The natural mixing of substances is called diffusion. Diffusion occurs because particles in a substance are always moving around. Diffusion is fastest in gases, and slower in liquids. Diffusion in solids is extremely slow.

Pressure in gases

Pressure is caused by particles hitting the walls of the container they are in. If the pressure becomes too great for a fixed container to hold, it will burst.

The pressure may increase because:

• the container has been squashed, making the volume smaller; this means that the particles will be hitting the walls more often.

• the number of particles has been increased, which means there are more particles moving around to hit the walls.

• the temperature of the particles has increased, so they will move around faster and hit the walls harder and more often.

If the particles are in a container which is flexible, like a balloon or a syringe, an increase in pressure will make the volume increase.

The idea of particles is a theory that scientists use to explain observations. Scientists use theories to make predictions, and test the predictions to find out if they are correct. If the predictions are not correct, then the theory may have to be changed to help to explain the new evidence.

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7H Summary Sheets

Solutions

Some solids dissolve in water to make a solution. These solids are soluble. A solution is made from a solute (solid) and a solvent (liquid). When a solution is formed, the liquid is always clear (transparent).

Solids that do not dissolve are insoluble. When an insoluble solid is mixed with water, the water goes cloudy. Sometimes the solid will sink to the bottom of the water.

The total mass of a solution equals the mass of solvent added to the mass of solute.

Water is the most common solvent. It is easily available, cheap, and dissolves a lot of different solutes. Other liquids (e.g. white spirit, ethanol) can also be used as solvents. Solutes which are insoluble in water may dissolve in other solvents.

If you keep adding solutes to a solvent, you will get to a point where no more will dissolve. A saturated solution cannot dissolve any more solute. More solid will dissolve if you add more solvent (e.g. water) or increase the temperature.

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Mixtures can be separated using different methods:

Method Used to separate Apparatus used Examples

Filtering (Filtration) Solid particles which do not dissolve from the liquid they are in

• Tea leaves from a cup of tea • Sand from a

mixture of sand and water

Evaporation Dissolved substances

from a solution • Salt from salt solution

Distillation (Evaporation followed by condensation)

The liquid from the dissolved solid in a solution or one liquid from a mixture of liquids

• Water from salt solution • Alcohol from a

mixture of alcohol and water

Chromatography The colours can be separated from a mixture of colours • The colours found in ink • The food colourings found in fruit juice

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7I Summary Sheets

Energy resources

Energy is needed to make things happen. There are different kinds of energy, such as light energy and heat energy that we get from the Sun, and electrical energy.

We need fuels to provide energy in our homes, factories and for transport. A fuel is something which can release heat energy.

Fossil fuels

Fossil fuels:

• are made from plants and animals which were trapped in mud and rocks millions of years ago • include coal, oil and natural gas

are non-renewable (they take millions of years to form, and so our supplies will run out) • produce gases which cause pollution when they are burnt

• are relatively cheap to obtain

contain chemical energy which changes to heat energy when they are burnt

• originally got their energy from the Sun. The plants that became coal got their energy from the Sun, and the animals that became oil got their energy from plants which got their energy from the Sun. Electricity is not a fuel. It has to be generated using other energy resources.

How coal is formed.

How oil and natural gas are formed.

Making fossil fuels last longer

We can make fossil fuels last longer by using less energy. We could walk or cycle whenever we can, or use a bus instead of using a car. Walking and cycling would make us fitter and healthier, and there would be less

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Renewable energy resources

Renewable energy resources:

• include solar, wind, tidal, wave, biomass, geothermal and hydroelectricity • do not produce harmful gases

• can be expensive • will not run out.

Energy in food

Humans and other animals need energy to live. We get our energy from chemical energy stored in food. We need to choose our food so that we get the right amount of energy. If we eat too much we could get fat and become unhealthy. If we do not eat enough we will get thinner and may become ill.

The unit for measuring energy is the joule (J). There is a lot of energy stored in food, so we usually measure the energy in food using kilojoules (kJ). 1kJ = 1000J.

Energy from the Sun

Most of the energy resources we use originally came from the Sun. Only geothermal energy, nuclear power and tidal power do not depend on energy from the Sun.

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7J Summary Sheets

Electrical circuits

Electricity is a flow of electrons. Electricity can flow through conductors but not through insulators. Metals are good conductors of electricity.

Circuits

A complete circuit is needed for electricity to flow. We use symbols when we draw circuits:

Component Symbol Component Symbol

cell variable resistor

battery of cells motor

bulb ammeter

switch fuse

resistor

The current is the amount of electricity flowing in the circuit. The units for current are amps (A). Current is measured using an ammeter.

The resistance of a circuit is a way of saying how easy or difficult it is for electricity to flow. • high resistance = hard for electricity to flow = small current

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Circuits can be series or parallel circuits.

Series circuit Parallel circuit

• If one bulb breaks, all the others go off. • The current is the same everywhere.

• If you put more bulbs in they will be dimmer, because it is harder for the electricity to get through. The resistance of the circuit is higher.

• The voltage from the cell or power pack is divided between the components.

• If one bulb breaks, the bulbs in the other branches stay on.

• The current splits up when it comes to a branch. The current in all the branches adds up to the current in the main part of a circuit.

• If you add more bulbs they stay bright. It is easier for the current to flow with more branches, because there are more ways for the electrons to go.

• The voltage is the same across all the branches of the circuit.

Electricity and heat

• When electricity flows through a wire, the wire can get hot. • Hot wires are used in electric fires, irons and cookers.

A fuse is a thin piece of wire that melts if too much electricity flows through it. It is used for safety.

Electricity and your body

Electrical signals in your body travel along nerves. If an electrical current passes through your body you may get an electric shock. This could burn you, or stop your heart or lungs working.

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7K Summary Sheets

Forces and their effects

Forces are pushes or pulls. Forces can:

• change the shape or size of an object

• change the speed things are moving (make them move faster or slower) • change the direction of a moving object.

The units for measuring force are newtons (N).

Friction is a force caused by two things rubbing together. Air resistance and water resistance are kinds of friction. They are sometimes called drag.

Upthrust pushes things up. Solid things, like your chair, give you upthrust. Things float in water because of upthrust.

Contact forces need to touch the thing that they are affecting. Examples of contact forces are: • friction

• air resistance • water resistance • upthrust.

Some forces do not need to touch the thing that they are affecting. They are called non-contact forces. There are three non-contact forces:

magnetism

gravity

static electricity.

Balanced forces

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Density and floating

You can decide if something will float by working out its density. Density is the mass of a certain volume of something, and it can be calculated using this formula:

density =

The units for density are g/cm3.

The density of water is 1g/cm3. If an object has a density less than 1g/cm3 it will float. If its density is

greater it will sink.

Measuring forces

Elastic materials will stretch with a force and then return to their original shape when the force is taken away.

Materials like Plasticine will stretch with a force but they will not return to their original shape afterwards. Plasticine is not elastic.

Springs are used to measure the size of a force because they are elastic. A big force stretches a spring further than a small force. Force meters have springs inside them.

This force meter is measuring a force of 1 N.

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Weight and mass

Your mass is the amount of substance in your body. Your mass is measured in kilograms (kg).

Your weight is a force caused by gravity pulling on your body. The newton (N) is the scientific unit used to measure forces, and so it is also used as the unit for weight.

Wherever you take an object, its mass will not change but its weight depends on the force of gravity. An object on the Moon would have a smaller weight than on Earth, because the Moon’s gravity is not as strong as Earth’s.

On Earth, gravity pulls on every kilogram of mass with a force of 10 N.

Friction

Friction is a contact force. Friction can: • slow things down

• wear things away • produce heat • make a noise.

Friction is sometimes helpful, for instance: Friction is not always helpful: • your shoes grip the floor because of friction

• tyres and brakes use friction • pencils write because of friction.

• parts of engines wear away because of friction

• friction makes bicycles harder to pedal.

Friction can be increased by using rough surfaces, or by using materials like rubber that have a lot of friction.

Friction can be reduced by using smooth surfaces, or by lubrication. Things like oil or grease are lubricants, and help things to move past each other easily.

Speed

To measure how fast something is travelling you need to measure the distance it travels and the time taken. Units of speed are km/h or m/s or mph. The units for speed depend on the units you have used to measure the distance and the time.

Stopping distances

A moving car takes some time to stop. The distance it travels while the driver is deciding whether to stop is called the thinking distance, and the distance it travels while it is slowing down is called the braking distance. If you add the two distances together you get the stopping distance.

Stopping distances are longer if the road is wet or icy, if the car has worn tyres, or if the driver is tired or has been drinking alcohol.

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Distance/time graphs

A journey can be shown on a distance/time graph. This graph shows a person running, then stopping for a rest, then walking slowly. The steeper the line on the graph, the faster they are moving.

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7L Summary Sheets

The Solar System and beyond

We live on a planet called the Earth. The Earth gets heat and light from the Sun. The Earth spins on its axis once every 24 hours. The side of the Earth facing the Sun has daylight, and it is night on the side facing away from the Sun.

The Earth orbits around the Sun. It takes one year to go around once. A year is actually 365.25 days long, so every four years we have a leap year, when an extra day is added.

The Moon is a satellite of the Earth. It orbits the Earth once every 28 days. This is called a lunar month. We can see the Moon because it reflects light from the Sun. The Moon seems to change shape during the month. The different shapes are called phases of the Moon. The phases happen because we cannot always see all of the part that is lit by the Sun.

Sometimes the Moon blocks the light from the Sun. When this happens we get a solar eclipse. If the Moon goes into the shadow of the Earth we get a lunar eclipse.

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There are nine planets orbiting the Sun, and lots of asteroids. Most of the planets have moons orbiting around them. The Sun, the planets and their moons, and the asteroids make up the Solar System. The nine planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. You can remember the order of the planets using this sentence ‘My Very Easy Method Just Sums Up Nine Planets’.

Planets do not make their own light. We can sometimes see the planets because they reflect light from the Sun.

The Sun is a star. It is a ball of gas that gives out large amounts of heat and light energy. The Sun is like the stars you can see in the sky at night. The stars do not look very bright because they are a lot further away than the Sun. People often group stars into patterns called constellations.

The Sun is one of millions of stars in our galaxy, which is called the Milky Way. There are millions of galaxies in the Universe.

The stars are a very long way from Earth. Scientists measure distances to the stars using light years. A light year is the distance that light can travel in one year.

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