GCSE Science B Unit 1 (My World)

Earth is the only planet in the solar system known to support life. In this unit candidates will learn about the science that explains many different aspects of the world around us and about how scientists have developed explanations for these phenomena.

This unit is assessed by a 1-hour written paper, which is worth 25% of the overall marks for the specification. Application of knowledge and understanding gained in discussing, evaluating and suggesting implications of data and evidence is also assessed in the written paper. Areas that could be covered are highlighted at the end of each context.

Candidates need to understand that:

For many centuries, our ancestors thought the Earth was the centre of the universe. Science has since taught us that this is incorrect. We know that the Earth lies within the Milky Way galaxy (a group of stars), which is located somewhere within the universe. Scientists have discovered that the Sun is one star in the Milky Way. Even smaller in scale than a galaxy is a solar system. Our solar system comprises one star (the Sun) and planets orbiting it.

Scientists use many different techniques to observe and search for patterns in the universe in an attempt to understand and gather evidence concerning how it began, what it is like and how it is changing. They have gathered much evidence from the use of telescopes, both on Earth and in space, and from the study of light reaching us from stars in distant galaxies.

Candidates need to:

1. Know that observations of the solar system and the galaxies in the universe can be carried out on the Earth or from space.
2. Know that observations are made with telescopes that may detect visible light or other electromagnetic radiations such as radio waves or X-rays from space, and that these observations provide evidence for changes taking place in the universe.
3. Understand that if a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency (Doppler effect).
4. Explain why there is a red-shift in light observed from most distant stars and galaxies. The further away stars or galaxies are, the more their light is red-shifted. This indicates that distant galaxies are moving away from us, and that the further away a galaxy is the faster it is moving away.
5. Explain how the observed red-shift provides evidence that the universe is expanding and supports the 'Big Bang' theory (that the universe began from a very small initial point).

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• 3.3.1.1 Our changing universe

Candidates need to understand that:

The Earth is a planet that has changed since its formation and is still changing. The surface of the Earth has cooled after a period of intense volcanic activity and has become able to sustain plant and animal life. The surface of the Earth continues to change due to the activity of volcanoes and earthquakes, mainly along the edges of tectonic plate boundaries.

Alongside these changes the atmosphere has altered to enable life to evolve, from being rich in carbon dioxide to containing enough oxygen to support life. Environmental scientists are beginning to understand the processes that cause the natural greenhouse effect and maintain the heat balance and global climate that enable life on Earth.

Candidates need to:

1. Know that the surface of the Earth has changed over time as a result of cooling.
2. Know that the Earth consists of a mantle, core and crust, surrounded by the atmosphere.
3. Know that the Earth's crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates).
4. Explain how convection currents within the mantle cause the movement of tectonic plates.
5. Describe how movement of tectonic plates can cause disastrous consequences such as earthquakes and volcanoes.
6. Know that during the first billion years of the Earth's existence there was intense volcanic activity.
7. Know that volcanic activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans.
8. Understand that some theories suggest that, during this period, the Earth's atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas. HT only: there may also have been water vapour and small proportions of methane, hydrogen and ammonia.
9. Describe how plants and algae produced the oxygen that is now in the atmosphere by photosynthesis.
10. Describe how the atmosphere surrounding the Earth allows light energy radiated from the sun to pass through.
11. Explain how greenhouse gases in the atmosphere keep temperatures on Earth stable and warm enough to support life, by allowing short-wave radiation to pass through the atmosphere to the Earth's surface but absorbing the outgoing long-wave radiation from the Earth.

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• 3.3.1.2 Our changing planet

Candidates need to understand that:

The Earth's crust, sea and atmosphere, and the organisms living on Earth, are the ultimate sources from which all useful substances are obtained. Metals, metal ores, limestone and fossil fuels are examples of materials obtained from the Earth. Scientists are sometimes able to use these materials directly, but many have to be processed or reacted with other substances to make useful products.

Understanding the chemical structure of these raw materials and their chemical reactions enables scientists to make the best use of them.

Candidates need to:

1. Be able to classify materials as elements, compounds or mixtures.
2. Describe the structure of the atom in terms of numbers of protons, neutrons and electrons and their arrangement. Atoms contain the same number of protons (positive charge) and electrons (negative charge). The protons and the neutrons (no charge) are at the centre, in the nucleus, and the electrons are positioned around the outside of the atom.
3. Explain the difference between atoms, molecules and ions.
4. Define the terms atomic number and mass number.
5. Know that useful materials can be removed from the ground by mining or quarrying.
6. Give examples of substances used straight from the ground (gold, sulfur, limestone and marble).
7. Describe how salt is separated from rock salt before use.
8. Describe how fuels (hydrocarbons) are separated from crude oil (fractional distillation).
9. Describe how metals are separated from their ores:
   (a) metals more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive
   (b) metals less reactive than carbon are extracted from their ores using carbon and carbon monoxide as reducing agents
   (c) lead and iron may be made from their oxides by reduction:
   
   • extraction of lead: carbon and carbon monoxide can act as reducing agents (2PbO + C → 2Pb + CO₂ and PbO + CO → Pb + CO₂ ).
   • extraction of iron: iron oxide (Fe₂O₃) and coke (carbon) are heated to produce iron. The coke burns to produce carbon dioxide (C + O₂ → CO₂). The carbon dioxide reacts with the coke to produce carbon monoxide (C + CO₂ → 2CO). When heated, the iron oxide reacts with the carbon monoxide to produce iron. Iron oxide is reduced and carbon monoxide is oxidised (Fe₂O₃ → 2Fe + 3CO₂).
10. HT only: describe air (the atmosphere) as a mixture of gases with different boiling points that can be fractionally distilled to provide new materials for industrial processes (helium for balloons, argon for filament lamps and electrical discharge tubes, nitrogen for ammonia – which is used for making fertilisers) and either used directly or used to make another product.

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• 3.3.1.3 Materials our planet provides

Candidates need to understand that:

Commercial organisations make products for consumers to buy. Chemical companies have to make profits and need to maximise the amount of product produced from the starting materials. For this reason, chemists often have to work quantitatively (ie accurately to measure the amounts of reactants and products).

When buying a product the consumer is often encouraged to think about the energy used, and waste produced, in making the product in addition to its cost and effectiveness.

Candidates need to:

1. Explain why mass is conserved in chemical reactions and that during a reaction products with different properties are formed as a result of atoms rearranging.
2. Know that, when producing new products, chemical reactions can be represented by using balanced chemical equations.
3. Explain why, in order to produce a product economically and safely, it is important that the correct amount of material is used.

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• 3.3.1.4 Using materials from our planet to make products

Candidates need to understand that:

There is a wide variety of life on Earth that has evolved over time and is still changing today. Scientists have been able to classify this wide variety of life into different groups. Scientists realise that living organisms continually evolve to become better adapted for the environment they live in. This means that many species on Earth are still evolving by a process called natural selection.

Candidates need to:

1. Understand that there is a huge variety of life, which is categorised into kingdoms.
2. Understand that animals and plants can be classified according to their physical characteristics.
3. Explain why classification is important as an international method of grouping living organisms with similar characteristics to aid naming and identification.
4. Know that, to survive, organisms require a supply of materials from their surroundings and from other living organisms:
   (a) plants need sunlight, water and nutrients to survive
   (b) animals need food, mates, shelter and a suitable territory.
5. Explain how animals, plants and microbes may be adapted for survival in the conditions where they normally live:
   (a) plants adapt to conditions through changes in surface area, water storage tissues and extensive root systems
   (b) in the case of animals factors should include surface area, insulation, body fat and water storage
   (c) microbes (extremophiles) have been found living in the Arctic, volcanic vents, very dry environments and severe chemical environments.
6. Explain how evolution occurs via natural selection.
7. Explain how individuals with characteristics most suited to the environment are more likely to survive and breed successfully.
8. Know that the genes that have enabled these individuals to survive are then passed on to the next generation.
9. Explain the effect of the external features light (phototropism), temperature, day length and gravity (gravitropism) on plant growth.
10. Explain the role of auxins in controlling plant growth.

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• 3.3.2.1 Life on our planet

Candidates need to understand that:

The total living organic matter produced in a given area is called the biomass. Biomass refers to all living things. Ecologists can find out what happens to energy and biomass as it passes along the food chain by observing the numbers and sizes of the organisms in food chains.

Candidates need to:

1. Know that energy enters the biosphere as sunlight.
2. Know that sunlight is converted to chemical energy and stored in organic compounds (biomass) by producers.
3. Know that biomass is broken down to release energy through respiration by consumers.
4. Know that energy leaves the biosphere as heat.
5. Understand that food chains show the flow of matter and energy between all the producers and consumers in a given ecosystem.
6. Know that the mass of living material (biomass) and amount of energy at each stage in a food chain is less than it was at the previous stage.
7. Be able to calculate the percentage of energy transfer at each stage of a food chain.
8. Explain the reasons for the inefficiency of the energy transfer:
   (a) some plant material passes out of the body of a herbivore as faeces without being digested
   (b) energy is transferred to the environment in respiration
   (c) some energy passes to decomposers in dead remains.
9. Know that microorganisms function better in warm, moist conditions and in a plentiful supply of oxygen.
10. Know that when living things die their bodies are broken down by decomposers, so releasing the elements they contain.
11. Know that these minerals can be used by plants to grow so that the cycle repeats over again.
12. Use data to construct pyramids of biomass to scale.

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• 3.3.2.2 Biomass and energy flow through the biosphere

Candidates need to understand that:

Carbon is the basis of all organic molecules and is the major element within our bodies.

The carbon cycle is the process through which carbon is cycled through the air, ground, plants, animals, and fossil fuels. Large amounts of carbon exist in the atmosphere as carbon dioxide (CO₂). Carbon dioxide is cycled by green plants and algae during photosynthesis to make organic molecules. Decomposers break down dead organic matter, and release carbon dioxide into the air. Carbon is also 'locked away' in fossil fuels such as coal, petroleum and natural gas. Carbon may be used in the formation of calcium carbonate.

1. Know that carbon dioxide is removed from the environment by green plants and algae for photosynthesis.
2. Know that the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins, which make up the bodies of plants and algae.
3. Know that when green plants and algae are eaten by animals some of the carbon becomes part of the fats and proteins that make up their bodies.
4. Understand that when green plants, algae and animals respire some of this carbon becomes carbon dioxide and is released into the atmosphere.
5. Understand that when plants, algae and animals die, some animals and microorganisms feed on their remains and release carbon dioxide into the atmosphere when they respire.
6. Know that carbon is stored in fossil fuels and is released as carbon dioxide when they are burnt.
7. Explain how limestone (calcium carbonate) is formed from carbon dioxide dissolved in water:
   a) over long time scales, carbon is removed from seawater when the shells and bones of marine animals and plankton collect on the sea floor. These shells and bones are made of limestone, which contains carbon. When they are deposited on the sea floor, carbon is stored from the rest of the carbon cycle for some amount of time
   b) the amount of limestone deposited in the ocean depends on the amount of warm, tropical, shallow oceans on the planet because this is where limestone-producing organisms such as corals live.

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• 3.3.2.3 The importance of carbon