2 - Life on Our Planet

2.1 Life on our Planet

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.

Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:

■ the advantages of classifying the range of species that exist on the planet and the methods used

■ the similarities and differences between species to gain an understanding of evolutionary and ecological relationships

■ the reasons for the distribution of animals or plants in a particular habitat

■ how organisms have adapted to the conditions in which they live

■ the factors for which organisms are competing in a given environment.

2.2 Biomass and energy flow through the biosphere

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.

Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:

■ interpreting and constructing pyramids of biomass

■ the efficiency of energy transfer at different stages of a food chain

■ the recycling of organic waste products from the garden or kitchen.

2.3 The importance of carbon

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.

Candidates need to:

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 removed 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. Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:

■ human interference in the natural carbon cycle, eg the destruction of rainforests and other forms of vegetation without replanting.

Suggestions for practical work that could be used to support Theme 2

It is the responsibility of the centre to be aware of the health and safety implications of any practical work, and to

ensure that risk assessments for practicals are carried out.

■ Investigate the effect of light on the growth of seedlings.

■ Investigate the effect of gravity on growth in germinating seedlings.

■ Investigate the effect of water on the growth of seedlings.

■ Use of a movement sensor to measure the growth of plants and seedlings.

■ Investigate the effect of rooting compounds and weed killers on the growth of plants.

■ Investigate size and rate of diffusion – acid penetration of indicator jelly blocks – good for planning practice.

■ Carry out a European banded snail survey.

■ Use of choice chambers, eg with woodlice.

■ Investigate plant growth, varying the conditions, eg degrees of shade, density of sowing, supply of nutrients.

■ Investigate the effect of phosphate on oxygen levels in water using jars with algae, water and varying numbers of drops of phosphate, then monitoring oxygen using meter.

■ Role play – A4 sheets labelled with different stages of the carbon cycle. Candidates arrange themselves in the correct order to pass along a ball labelled as carbon.

■ Look at variation in leaf length or width, pod length and height. Compare plants growing in different conditions – sun/shade.

■ Test crushed shells (eg cockle, oyster) with dilute hydrochloric acid to show that they contain carbonates.

■ Use samples of organisms, identify their features and classify them.

■ Measure size and surface area (using different-sized flasks and monitoring how quickly they cool).