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Science years 8–10: free practice, theory and problems

All living organisms are built of cells. In the body, billions of cells work together in tissues, organs and organ systems.

7 parts49 problemsPractice examFree

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Cells and the body
Chemistry: atoms and reactions
Forces, speed and energy
Electricity
Ecology and climate
Genetics and evolution
The universe

1. Cells and the body

What is it about?

All living organisms are built of cells. In the body, billions of cells work together in tissues, organs and organ systems.

Key points

Animal cells have a cell membrane, a nucleus (with DNA) and mitochondria (where energy is released by cellular respiration).
Plant cells also have a cell wall, chloroplasts (photosynthesis) and a large vacuole.
The nervous system sends fast electrical signals. The hormone system sends slower signals through the blood (for example insulin and adrenaline).
The immune system fights bacteria and viruses. Vaccines train the immune system to recognise a pathogen.
Antibiotics work against bacteria, but not against viruses.

Example

When you get a fright, the adrenal glands release adrenaline. The heart beats faster and the muscles get more blood – the body gets ready to act.

Cellular respiration: sugar + oxygen → carbon dioxide + water + energy.

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2. Chemistry: atoms and reactions

What is it about?

All matter is built of atoms. In a chemical reaction the atoms swap partners and new substances form.

Key points

The atom has a nucleus with protons (+) and neutrons, and electrons (−) around it.
The atomic number is the number of protons and decides which element it is.
The periodic table orders the elements. Elements in the same group are alike.
In a chemical reaction no atoms disappear – they are just put together in new ways.
Combustion: fuel + oxygen → carbon dioxide + water + heat.
pH: below 7 is acidic, 7 is neutral, above 7 is basic. Acid + base can neutralise each other.

Example

When a candle burns, the wax reacts with oxygen and becomes CO₂ and water vapour. The atoms still exist – in the air.

Signs of a chemical reaction: gas, colour change, light, heat or a new solid.

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3. Forces, speed and energy

What is it about?

Forces make things start, stop and turn. Energy cannot be created or destroyed – only change into other forms.

Key points

Speed: $v = \frac{s}{t}$ (distance divided by time). 1 m/s = 3.6 km/h.
Force is measured in newtons (N). The gravitational force on you is $G = m \cdot g$ , where $g \approx 9.8$ N/kg.
Friction acts against the motion and turns kinetic energy into heat.
Work: $W = F \cdot s$ (force times distance), measured in joules (J).
Forms of energy: kinetic, potential, heat, chemical, electrical.
Power is energy per second: $P = \frac{E}{t}$ , measured in watts (W).
Density: $\rho = \frac{m}{V}$ . Substances less dense than water float.

Example

You cycle 6 km in 20 minutes (1200 s). $v = \frac{6000}{1200} = 5$ m/s, that is 18 km/h.

Energy is conserved: when a ball falls, potential energy becomes kinetic energy.

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4. Electricity

What is it about?

Electric current is charges (electrons) moving. It powers everything from your phone to an electric car.

Key points

Voltage $U$ (volts, V) is the "pressure" that drives the current.
Current $I$ (amperes, A) is how much charge passes per second.
Resistance $R$ (ohms, Ω) is how hard it is for the current to get through.
Ohm's law: $U = R \cdot I$ .
Series circuit: one path for the current. If one bulb blows, all go out. Parallel circuit: several paths – like in your house.
Electrical power: $P = U \cdot I$ .
Electricity is made in generators driven by water, wind, steam or sunlight (solar cells).

Example

A kettle on 230 V draws 8 A. Power: $P = 230 \cdot 8 = 1840$ W.

More resistance gives less current at the same voltage.

Practise electricity in the app →

5. Ecology and climate

What is it about?

All living things are connected in ecosystems. Human emissions affect both nature and the climate.

Key points

A food web shows many food chains that are linked. Only about 10 % of the energy passes on to the next level.
The carbon cycle: plants take up CO₂ in photosynthesis, and CO₂ is released again by respiration, decay and combustion.
The greenhouse effect is natural and keeps the Earth habitable. More CO₂ and methane strengthen it and cause global warming.
Consequences: more extreme weather, rising sea levels, melting ice and species losing their habitats.
Sustainable development: meeting our needs without ruining things for future generations.

Example

If wolves disappear from an area, the deer population can grow so much that it eats the young trees – the whole ecosystem changes.

Fossil fuels (coal, oil, gas) release carbon that has been stored for millions of years.

Practise ecology and climate in the app →

6. Genetics and evolution

What is it about?

Why do you look like your parents? And how has life on Earth changed over millions of years?

Key points

DNA is the recipe for how an organism is built. A gene is a piece of DNA that codes for a protein.
Humans have 23 pairs of chromosomes – one set from the mother and one from the father.
A gene can have different versions (alleles). A dominant allele shows even if you have only one. A recessive allele shows only if you have two.
Mutations are changes in DNA. They create new variation.
Natural selection (Darwin): individuals that are best adapted survive and have the most offspring, so their traits become more common.

Example

Both parents have brown eyes but carry a recessive allele for blue. The child can get blue eyes if it inherits the blue allele from both.

Evolution happens in populations over many generations, not in one individual.

Practise genetics and evolution in the app →

7. The universe

What is it about?

The Earth is one planet around one star in one galaxy among billions. The distances are so large that we measure them in light years.

Key points

A light year is how far light travels in one year: about 9.5 trillion km.
The Sun is a star in which hydrogen fuses into helium (fusion) and gives off light and heat.
The Milky Way is our galaxy, with more than 100 billion stars.
The Big Bang: the universe began about 13.8 billion years ago and is still expanding.
Light from the Sun takes about 8 minutes to reach the Earth. When we look out into space, we look back in time.
Gravity keeps the planets in orbit around the Sun and the Moon around the Earth.

Example

The star Proxima Centauri is 4.2 light years away. The light we see tonight was sent out more than four years ago.

Stars are suns – many of them have their own planets.

Practise the universe in the app →

Example problems with solutions

Here are some of the problems in science years 8–10. In the app, calculation problems get new numbers every time, so you can practise until it sticks – and take a graded practice exam before the real one.

Cells and the body: Where is DNA found in an animal cell?

Answer: In the nucleus

DNA is in the nucleus (and a little in the mitochondria).

Chemistry: atoms and reactions: What decides which element an atom is?

Answer: The number of protons

Atomic number = number of protons.

Forces, speed and energy: What is force measured in?

Answer: Newtons

Force is measured in newtons (N).

Electricity: What is current measured in?

Answer: Amperes

Current $I$ is measured in amperes (A).

Practise all the problems →

Science years 8–10: free practice, theory and problems

Contents

1. Cells and the body

What is it about?

Key points

Example

2. Chemistry: atoms and reactions

What is it about?

Key points

Example

3. Forces, speed and energy

What is it about?

Key points

Example

4. Electricity

What is it about?

Key points

Example

5. Ecology and climate

What is it about?

Key points

Example

6. Genetics and evolution

What is it about?

Key points

Example

7. The universe

What is it about?

Key points

Example

Example problems with solutions