1. family and parenting
2. motherhood
3. pregnancy

Year 7
Summary Sheets
7A
Summary Sheets
Tissues and transplants
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A
All living things are made from cells. There are two basic types of cell:
Cell wall. This is like a box with many large
holes in it. It supports the cell and is very strong.
It is made out of a substance called cellulose.
Cell surface membrane. This
is like a very thin bag. It keeps
the cell together and controls
what goes into and out of the cell.
Nucleus. This is the ‘control
centre’ of the cell. It tells the
cell what to do.
Chloroplasts. These are green discs that allow
the plant to make food (by photosynthesis).
They contain a chemical called chlorophyll.
Cytoplasm. This is a watery
jelly-like substance. Many of the
cell’s activities take place here.
Vacuole. This is a storage space filled with a
liquid called cell sap.
A plant cell.
An animal cell.
Cells are very small. A microscope is used to see them. A microscope magnifies things. 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 with a microscope is 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 the cell.
To use a microscope you:
A
place the smallest objective lens over
the hole in the stage;
B
turn the focusing wheel to move the
objective lens close to the stage;
C
place the slide on the stage;
D
adjust the light source or mirror;
E
look into the eyepiece lens;
F
turn the focusing wheel until what you
see is in focus.
eyepiece lens
objective lens
focusing wheel
light source
or mirror
stage
slide
Some animal cells are adapted to do certain functions.
Ciliated 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 (neurons) are long so that
signals can be carried around the body
quickly.
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A
Summary Sheets (continued)
Some plant cells are adapted to do certain functions
Root hair cells in plant roots take water Palisade cells in plant leaves are packed
out of the ground quickly. The root hair with chloroplasts to help the plant
gives the water more surface to get into make food.
the cell.
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 is an organ. For example,
the heart is an organ and is made of muscle tissue and nerve tissue.
Organs have important functions:
Brain
controls the body.
Skin
for protection
and feeling.
Stem
carries substances
(such as water)
around the plant
and holds the
leaves in place.
Heart
pumps blood.
Lungs
for breathing.
Leaf
makes food by
the process of
photosynthesis.
Stomach
breaks up food.
Liver
makes and
destroys
substances.
Kidneys
clean the blood
and make urine.
Large instestine
removes
water from
unwanted food.
Root
takes water out
of the soil and
holds the plant
in the ground.
Small intestine
breaks up and
absorbs food.
Organs often work together in organ systems.
Organ system
Organs
Job
breathing system
windpipe (trachea), lungs
takes air into the body and gets rid of
waste gases
circulatory system
heart, blood vessels
carries oxygen and food around the
body
digestive system
mouth, gullet, stomach, intestines
breaks down our food
nervous system
brain, spinal cord, nerves
carries signals around the body
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Summary Sheets
bladder
oviduct
ovary
uterus
Reproduction
Reproduction produces new living things (offspring). Two
parents (one male and one female) are needed for sexual
reproduction. The offspring have features from each parent.
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cervix
vagina
glands
penis
sperm duct
urethra
testis
foreskin
scrotum
Female – ovaries are where the female
sex cells (egg cells) are produced.
The human reproductive systems
Humans have reproductive organs so that they can reproduce.
The ovaries and testes produce sex cells.
oviduct
ovary
uterus
cervix
vagina
Puberty and adolescence
Male
sex ce
bladder
glands
penis
sperm duct
urethra
testis
foreskin
scrotum
Female – ovaries are where the female
sex cells (egg cells) are produced.
Male – testes are where the male
sex cells (sperm cells) are produced.
Sex hormones cause big physical changes to occur during puberty.
Changes in boys
Changes in girls
• hair grows under arms, on face and on chest
• hair grows under arms
• pubic hair grows
• pubic hair grows
• shoulders get wider
• hips get wider
• body smell increases
• body smell increases
• testes start to make sperm cells
• ovaries start to release egg cells
• testes and penis get bigger
• breasts develop
• voice deepens (‘breaks’)
Adolescence is the time when puberty is occurring and emotional changes happen.
It starts between the ages of 10 and 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.
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.
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Summary Sheets (continued)
Sperm cells and egg cells
are adapted to their functions.
A sperm cell is much smaller
than an egg cell.
The tip of the head contains
chemicals which attack
the coat of the egg, helping
the sperm to burrow inside.
The nucleus contains half the
instructions needed to make
a new human.
Very little cytoplasm so that
the cell can have a thin,
streamlined shape.
The tail helps it to swim well.
A sperm cell.
Pregnancy
The cytoplasm contains a
store of food to provide
energy for the fertilised
egg cell.
The nucleus contains half
the instructions to make a
new human
A jelly coat makes sure that
only one sperm can enter.
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B
An egg cell.
If the egg cell meets a sperm cell in an oviduct, fertilisation can occur (the nuclei from
the two cells fuse). 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 foetus. 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. Frogs use external development. Humans use internal
development and produce fewer offspring than animals using external development
because the growing embryos are protected inside the mother.
While inside the uterus, the foetus is
supplied with oxygen and food by the
placenta. The placenta also gets rid of
waste (especially carbon dioxide) from
the foetus. The cord (or umbilical cord)
connects the foetus to the placenta.
placenta
amnion
waste materials
(e.g. carbon dioxide)
amniotic fluid to
protect the foetus
foetus
If a mother smokes, drinks too much
alcohol or takes drugs while pregnant,
she might damage the baby. The baby
might be premature.
food and
oxygen
umbilical cord
mother's blood
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
mother’s breasts contain mammary glands that produce milk to feed the baby. Breast milk
contains antibodies that help destroy microbes that might cause a disease in the baby.
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Summary Sheets
Habitats and adaptations
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.
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The rabbit’s environment
Physical
environmental factors:
it is light; it is cold
The area under the
log is a microhabitat.
A WOODLAND HABITAT
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.
Large ears to allow
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 underwater.
They have gills to take oxygen out of the water, fins to swim
with and streamlined bodies to help them move easily through
Does not drink
the water. This jack rabbit is another example.
Physical environmental factors change from day to day (daily
changes). Animals alter their behaviour in response to those
changes. For example, some animals only come out at night;
they are called nocturnal animals (e.g. owls).
heat to escape and
for good hearing.
Large hind legs
to run quickly
from animals
that might eat it.
and gets all its
water from its
food
Jack rabbits are adapted to
living in a desert habitat.
Physical environmental factors change over the year (seasonal changes). Organisms respond to
these changes by changing their behaviour or parts of their bodies. 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 below to discover some of these.
There is not much light for photosynthesis
in winter so many trees drop their leaves
(they are deciduous).
Trees that keep
their leaves are
evergreen.
Squirrels collect nuts in
autumn to eat in winter.
Hedgehogs hibernate
under piles of leaves.
Rabbits grow thicker fur
to keep them warm.
Organisms are in competition with each other. Animals compete for food and space. Plants
compete for light, water and nutrients (mineral salts).
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Summary Sheets (continued)
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 the
organisms in a food chain.
Food chains are joined to
form food webs. Food webs
can also show omnivores
(animals that eat both plants
and other animals).
grass
caterpillar
producer
robin
sparrowhawk
consumers
herbivore
carnivore
prey for the robin
prey for the
sparrowhawk
carnivore
predator of the
caterpillar
predator of the
robin
top predator
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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 is transfered 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!
Many predators have …
Many prey have …
forward-facing eyes to pinpoint the position of their
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:
Large
powerful beak
for crushing
seeds.
Sharp cutting
teeth to slice
through food.
Wide, ridged
teeth for
grinding up
grass.
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.
We can use this evidence to draw food chains and food webs for habitats.
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Summary Sheets
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.
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Lengths of middle
fingers (cm)
Lengths of middle fingers
and arms in Class 7B
Length of arms (cm)
Relationship: people with longer arms have
longer middle fingers.
Variation can have environmental or inherited causes.
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 such as the amount of
light, water, warmth or mineral salts in the soil.
Animals are also affected by environmental factors. Humans who get sunburnt or have scars are
examples.
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Summary Sheets (continued)
The cress seedlings on the left have not had
enough light.
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The plant on the left has not had enough water.
It has wilted.
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 put into are called kingdoms. The two largest are the
plant kingdom and the animal kingdom. One big difference between these two kingdoms is that
plants can make their own food and animals cannot.
The animal and plant kingdoms are divided into other groups. In the animal kingdom, 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 in the diagram.
ANIMAL KINGDOM
VERTEBRATES
AMPHIBIANS
INVERTEBRATES
BIRDS
• moist skin
• lay eggs in water
• eggs coated
in jelly
FISH
• feathers
• eggs have a
hard shell
MAMMALS
• hair
• give birth to live young
• produce milk
• have wet scales
• have fins to move
• breathe using gills
REPTILES
• dry scales
• eggs have a leathery shell
CNIDARIANS
MOLLUSCS
• fleshy pad
for movement
ARTHROPODS
• jointed legs
• bodies in sections
• thick, hard exoskeleton
CRUSTACEANS
• 5-7 pairs of legs
• chalky shell
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INSECTS
ECHINODERMS
• bodies in five parts
• spiny outer covering
ARACHNIDS
ROUNDWORMS
FLATWORMS
SPONGES
CENTIPEDES and MILLEPEDES
• 3 pairs of legs
• 4 pairs of legs
• many pairs of legs
• body in 3 sections • body in 2 sections • many body sections
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ANNELIDS
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7E
7
E
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. Two common hazard warnings are:
irritant or harmful
corrosive
Acids and alkalis can be either irritant or corrosive. The hazard will depend on the type of acid and
whether it is concentrated or dilute. In factories and in the laboratory at school we need to carry out risk
assessments. This allows us to consider the level of risk and take action to reduce the chance of harm.
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, which means they will attack your skin and seriously harm you. Alkalis can also be
corrosive (e.g. oven cleaner). Common weak alkalis include soap and toothpaste.
Sulphuric acid is one of the most important chemicals that is manufactured. It has a wide range of
uses, including making paints, dyes and fertilisers.
Indicators are coloured dyes that change colour when mixed with acids or alkalis. They often
come from plants such as red cabbage and beetroot. Litmus is an indicator that turns red in acids
and blue in alkalis.
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.
strong acid
1
2
stomach
acid
weak acid
3
4
vinegar
lemon
juice
5
neutral
6
skin
fizzy
drinks
7
pure
water
milk
blood
weak alkali
8
9
indigestion
powder
strong alkali
10
11
washing
powder
12
13
14
oven
cleaner
toothpaste
Alkalis can cancel out acids, making them neutral. When this happens it is called neutralisation.
Neutralisation 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.
Manufacturing chemicals can be of benefit to society in a number of ways, but there can also be
concerns, for example about pollution. The building of chemical factories often causes a lot of debate
in local communities, with strong arguments being made both for and against new projects.
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Summary Sheets
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 or sound being given off (for example, when something burns).
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Some chemical reactions involve decomposition (chemicals being split up). This needs a source of
energy (usually heat or electricity).
Reactions of acids
Some metals react with acids, and hydrogen gas is produced. When acids react with limestone,
carbon dioxide gas is given off.
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 in air, 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. Here is an example:
magnesium + oxygen
reactants
magnesium oxide
product
Burning is also known as combustion. In a combustion reaction, some energy has to be supplied
at the beginning to start the reaction. Once the reaction has started, it will produce its own heat.
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Summary Sheets (continued)
A fire needs three things to keep burning: fuel, oxygen and heat. We show these three things on
the fire triangle.
HE
YG
EN
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F
OX
AT
FUEL
If any one of these three things is taken away, 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. Fire blankets and foam,
powder or carbon dioxide (CO2) extinguishers work by stopping oxygen getting to the flames.
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 not in this equation because it is not a chemical substance.
fuel + oxygen
carbon dioxide + water
Pollution can occur if there is not enough oxygen for complete combustion. Carbon monoxide is
a poisonous gas, and soot (carbon) can also be formed if the oxygen supply is restricted further.
Smoke is made up of soot and any other solid particles, such as metal oxides.
Explosions
Explosions are very fast reactions that give out a lot of heat and produce lots of gases. Fuels such
as natural gas can produce an explosive mixture with oxygen. This is a combustion explosion.
Explosives are chemicals that often contain all the oxygen they need to react inside the chemical.
They can react by decomposition as they do not need any oxygen from the air.
Some explosives, such as nitroglycerine, are very unstable and will react with only a tiny amount
of added energy. A safer explosive, such as dynamite, will not react until a detonator is used.
Explosives are used for weapons, quarrying rock, building roads and demolishing old buildings.
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Summary Sheets
The three states of matter
A theory is used to explain observations (data). Scientists also 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 explain the new evidence.
The different properties of solids, liquids and gases can be explained by the particle theory (or
particle model). Solids, liquids and gases (the three states of matter) need to be handled and
stored differently because of these different properties. For instance, solid materials can be taken to
a landfill site.
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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 are dense (are
heavy for their size). (Volume is the amount of
space something takes up. It is measured in units
such as cubic centimetres (cm3).)
LIQUID
• Liquids are made up of particles that are fairly
close together; the bonds between the particles
are weaker than the bonds in solids. This allows
the particles to move past each other.
• Liquids cannot be squashed, flow quite easily and
have a fixed volume but no fixed shape.
• Although they are dense, liquids are usually less
dense 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 are not dense.
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Summary Sheets (continued)
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.
Dilution
When you add water to orange squash you dilute it. The colour becomes paler because the
orange coloured squash particles are spread out more by the water particles.
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Pressure in gases
Pressure is caused by particles hitting the walls of the container they are in. 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 flexible container, like a balloon, an increase in pressure will make the
volume increase. If the pressure becomes too great the balloon will burst.
Air pressure is the pressure caused by air particles around us. Air pressure lets us suck things up
using a straw and also causes a container to collapse if the air is sucked out. If all the air is sucked
out of a container, you get a vacuum – nothingness.
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Summary Sheets
Rock textures
Rocks are made of grains. Each grain is made of a chemical
called a mineral. The texture of a rock is a description of the
size and shape of the grains.
Sandstone has rounded grains. It is permeable, because water
can get into gaps between the grains.
Granite has interlocking grains.
The interlocking grains are sometimes
called crystals. Rocks with interlocking
grains are not porous.
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Weathering
Rocks can be worn away. This is called weathering.
Chemical weathering happens when rain water reacts
with minerals in the rock. Rain water is slightly acidic,
because it contains dissolved gases.
Physical weathering can happen in different ways. The minerals in a rock expand if the rock gets
hot, and contract if it cools. These changes in size can produce strong forces. If the rock is heated
and cooled over and over again, the forces can make cracks in the rock. This is called onion-skin
weathering.
Physical weathering can also happen if water gets into a crack in the rock and freezes. Water
expands when it turns into ice, and makes the crack wider. This kind of physical weathering is
called freeze–thaw action.
Biological weathering is when rocks are broken up or worn away by plants and animals. For
example, plant roots can grow into cracks in rocks and make the cracks bigger.
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Summary Sheets (continued)
Erosion and transport
Weathered pieces of rock fall to the bottom of cliffs. This
movement of bits of rock is called erosion. The bits of rock
can be transported away by flowing water, wind and ice
(glaciers). Pieces of rock bump into each other while they are
being transported, and bits get knocked off them. This is called
abrasion. The bits of rock carried by a river are called sediment.
Forming sedimentary rocks
Fast-moving water can move larger pieces of rock than slow-moving water. Rivers slow down
when they flow into a lake or the sea. The slow-moving water cannot carry all of the sediment, so
some of it is deposited on the bottom. Sediments often form layers. Layers of sediment can also
form when sea water evaporates and leaves salts behind.
Sometimes dead plants or animals fall to the bottom of the sea. If their remains get covered by
other sediments they may form fossils. When a dead organism forms a fossil, its form can still be
seen because its hard parts have been turned into stone. Fossils can help geologists find out how
rocks were formed.
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H
If a lot of plant material is buried at once, it may turn into coal. When tiny sea plants and animals
get buried they sometimes turn into oil or natural gas. These are all fossil fuels.
The higher layers squash the lower layers, squeezing out the water from the gaps between the
grains of sediment (compaction). Dissolved minerals in the water can crystallise in the gaps as a
‘glue’ that sticks the grains together (cementation).
Evidence in the rocks
Geologists can explain how sedimentary rocks formed using evidence in the rocks.
Rounded grains in the rock show that the sediments must have been transported for a long time,
because abrasion has smoothed them. Sharp-edged grains show that the grains were probably not
transported for very long.
Small grains show that the grains
were deposited by wind (which
can only move very small particles),
or by slow-moving water. Rocks
with large grains, or with a mixture
of grain sizes (such as
conglomerate) must have been
deposited by fast-moving water.
layers of
sedimentary rock
Layers in the rock show that the
river that deposited them
changed speed from time to time.
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Energy and sustainable living
Most things that happen need a store of energy. Fuels store energy, and this energy is transferred
when the fuels burn. Burning fuels are used to heat things.
Fossil fuels:
• are made from plants and animals that 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 that cause pollution and global warming when burnt
• are relatively cheap to obtain
• contain a store of energy that is transferred to their surroundings when 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.
mud
Electricity is not a fuel. It has to be generated using other energy resources.
mud
coal
mud
How coal is formed.
cap rock
cap rock
mud
coal
Mud
oil and gas
coal
oil and gas
cap rock
How oil and natural gas are formed.
Caprock
Making fossil fuels last longer
oil and gas by using less of them.
We can make fossilcoal
fuels last longer and help to reduce global warming
We Coal
could walk or cycle whenever we can, or useOilaand
bus
instead of using a car. Walking and cycling
gas
would make us fitter and healthier, and there would be less pollution if there were not as many
cars on the roads. We could also save energy by keeping our houses cooler and putting on more
clothes if we are cap
cold
instead of turning up the heating.
rock
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Renewable energy resources:
• include solar, wind, tidal, wave, biomass, geothermal and hydroelectricity
• do not produce harmful gases or contribute to global warming
• can be expensive
• will not run out.
solar panels
solar cells
wind
turbine
biomass
Energy in food
Humans and other animals need energy to live. The energy resource for our bodies is the energy
stored in food. We need to choose our food so that we get the right amount of energy.
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). 1 kJ = 1000 J.
Energy from the Sun
Most of the energy resources we use store energy that originally came from the Sun. Only
geothermal power, nuclear power and tidal power do not depend on energy from the Sun.
light
energy
chemical
energy
chemical
energy
in corn
in cornflakes
chemical
energy
chemical
energy
chemical
energy
in grass
in cow
in milk
from
the Sun
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Electrical circuits
Electricity is a flow of electrons. Electricity can flow through conductors but not through
insulators. Metals are good conductors of electricity. Plastics are good insulators.
Cells and power packs provide safe, low-voltage electricity. Most appliances use mains electricity.
This can be dangerous if it is not used properly.
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A complete circuit is needed for electricity to flow.
We use symbols when we draw circuits:
Component
Symbol
Component
cell
switch
battery of cells
fuse
bulb
ammeter
Symbol
The current is the amount of electricity flowing in the circuit. The unit for current is the amp (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
• low resistance = easy for electricity to flow = large current
Thin wires and resistors have high resistances. Thick wires have low resistances.
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Electricity and heat
When electricity flows through a wire, the wire can get hot. Hot wires are used in electric fires,
irons and cookers.
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J
A fuse is a thin piece of wire that melts if too much electricity flows through it. It is used for safety.
Models
We can use models to help us to think about electricity and circuits. One model for a circuit is a
central heating system. The boiler and pump represent the cell, the pipes represent the wires, and
the radiators represent bulbs.
Circuits can be series or parallel circuits.
SERIES 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.
PARALLEL CIRCUIT
• 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.
Electricity and your body
Electrical signals in your body travel along nerves. If an electric current passes through your body
you may get an electric shock. This could burn you, or stop your heart or lungs working.
Electricity can be used to help the body. A pacemaker is used to help people whose hearts do not
work properly. A defibrillator can be used to start someone’s heart if it has stopped beating.
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Forces
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 unit for measuring force is the newton (N).
Friction is a force caused by two things rubbing together. Air resistance and water resistance are
kinds of friction.
Solid things, like your chair, push up on you. Upwards forces from water or air are called 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
Some forces do not need to touch the thing
that they are affecting. They are called noncontact forces. There are three non-contact
forces:
• air resistance
• magnetism
• water resistance
• gravity
• upthrust.
• static electricity.
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K
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
•
produce heat
• wear things away
•
make a noise.
Friction can be increased by using rough surfaces, or by using materials such as 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.
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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 =
mass
volume
The units for density are g/cm3.
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K
The density of water is 1 g/cm3. If an object has a density less than 1 g/cm3, it will float. If its
density is greater, it will sink.
Balanced forces
Balanced forces are forces that cancel each other out. Balanced forces do not change the speed
that something is moving.
Upthrust
The forces on the balloon are
balanced. The balloon will not
move.
weight
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Measuring forces
N
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.
0
1
2
3
4
5
This force meter
is measuring a
force of 1 N
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.
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K
Speed
To measure how fast something is travelling, you need to measure
the distance it travels and the time taken. Units for speed are km/h or m/s or mph. The unit for
speed depends 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 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. Stopping distances are also longer if the car is travelling faster.
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.
Distance (km)
3
2
1
0
0
10
20
30
40
Time (minutes)
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Axis
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 29.5 days. This is called a lunar month.
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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.
there is a solar
eclipse here
Sun
Sun
Moon
Moon
Earth
Earth
not to scale
not to scale
A solar eclipse.
A lunar eclipse.
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The Earth’s axis is tilted. When the northern hemisphere is tilted towards the Sun it is summer
in the UK. Days are longer than nights, and the Sun is higher in the sky. The Sun’s rays are more
concentrated, so it feels hotter.
N
N
UK
Sun’s rays
Sun’s rays
The Sun’s rays
are concentrated
in the summer
S
UK
The Sun’s rays
are spread out
in the winter
S
There are eight planets orbiting the Sun and three dwarf planets. There are also lots of asteroids,
which are small lumps of rock, and comets. Most of the planets have moons orbiting around
them. The Sun, the planets and their moons, and the asteroids and comets make up the Solar
System.
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The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Asteroid belt
Uranus
Sun
Pluto
Saturn
Ceres
Eris
Mars
Venus
Earth
Mercury
Neptune
Jupiter
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. 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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