Biodiversity, Cycles and Human Impact
Biodiversity is the variety of species living in an ecosystem or on Earth, and a high level of biodiversity keeps ecosystems stable by reducing how dependent any one species is on a single other species for food, shelter or maintaining the physical environment. Human activities such as land use, deforestation, pollution and global warming reduce biodiversity, while carbon is cycled between the atmosphere, living organisms and the environment through photosynthesis, feeding, respiration, combustion and decomposition.
Before you start
Make sure you're comfortable with these topics first:
Method
- Define biodiversity and explain why a high level of it matters: greater biodiversity means an ecosystem is less dependent on any single species, making it more stable and better able to cope with change, and it also maintains the resources, such as food and medicines, that humans rely on.
- Learn the main pressures that reduce biodiversity: land use for building, farming, quarrying and waste disposal leaves less land for other organisms; pollution of water (for example from sewage or fertiliser), air (from smoke and acidic gases) and land (from landfill waste and toxic chemicals) harms organisms directly or damages their habitat.
- For deforestation questions, give a named cause, for example clearing tropical rainforest for cattle farming, rice fields or biofuel crops, or draining peat bogs, and two linked consequences: loss of habitat reduces biodiversity, and removing trees both releases stored carbon and reduces the amount of carbon dioxide removed from the atmosphere by photosynthesis.
- Learn how global warming affects biodiversity: rising average temperatures can change the distribution of species, since some organisms migrate towards the poles or to higher altitudes, and can disrupt the timing of natural events such as bird migration, which can reduce biodiversity where species cannot adapt quickly enough.
- For questions on maintaining biodiversity, name a specific method, such as breeding programmes for endangered species, protecting and regenerating rare habitats, reintroducing hedgerows and field margins around farmland, or reducing deforestation and the use of peat, and link it to the specific problem it addresses.
- For the carbon cycle, describe the processes in a logical sequence: photosynthesis removes carbon dioxide from the atmosphere and converts it into carbon compounds in plants; feeding transfers these carbon compounds along food chains; respiration by plants, animals and microorganisms releases carbon dioxide back into the atmosphere; combustion of wood and fossil fuels releases carbon dioxide; and decomposition of dead organisms and waste by microorganisms also releases carbon dioxide, through the decomposers' own respiration.
Worked example
A region of tropical rainforest covers an area of 4500 km2. Over twenty years of deforestation for cattle farming, the forested area is reduced to 3150 km2. Calculate the percentage decrease in the forested area.
- Calculate the decrease in area: 4500 - 3150 = 1350 km2.
- Write the percentage change formula: percentage decrease = (decrease in area / original area) x 100.
- Substitute the values: percentage decrease = (1350 / 4500) x 100.
- Calculate: 1350 / 4500 = 0.3, and 0.3 x 100 = 30.
- Final answer: the forested area has decreased by 30%.
Practice questions
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Q1State what is meant by the term biodiversity.Show answer
Answer: The variety of different species of organisms living in an ecosystem, or on Earth as a whole.
Q2State one way in which high biodiversity benefits an ecosystem.Show answer
Answer: It makes the ecosystem more stable, because species are less dependent on any single other species for food, shelter or maintaining the physical environment (accept: it maintains resources, such as food or medicines, that humans depend on).
Q3State one human activity that reduces the amount of land available for other organisms.Show answer
Answer: Any one of: building, farming, quarrying, or dumping waste.
Q4A peat bog covered an area of 850 hectares in 2015. By 2025, drainage for farmland had reduced the peat bog to 680 hectares. Calculate the percentage decrease in the area of the peat bog.Show answer
Answer: 20% (decrease = 850 - 680 = 170 hectares; percentage decrease = 170 / 850 x 100 = 20%).
Q5Explain why large-scale deforestation increases the concentration of carbon dioxide in the atmosphere.Show answer
Answer: Burning or decomposing the removed trees releases the carbon stored in them as carbon dioxide, and with fewer trees left there is less photosynthesis taking place to remove carbon dioxide from the atmosphere, so the concentration increases.
Q6State one method used to try to maintain biodiversity.Show answer
Answer: Any one of: breeding programmes for endangered species, protecting and regenerating rare or threatened habitats, reintroducing hedgerows and field margins around fields, or reducing deforestation and the destruction of peat bogs.
Q7Name the biological process that removes carbon dioxide from the atmosphere and converts it into carbon compounds in a plant.Show answer
Answer: Photosynthesis.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
State two ways in which a rising human population can lead to a reduction in biodiversity.
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Describe how carbon dioxide in the atmosphere is converted into carbon compounds in a plant, and how carbon is later returned to the atmosphere as carbon dioxide. Refer to photosynthesis, feeding, respiration and decomposition in your answer.
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Large areas of tropical rainforest are being cleared to provide land for cattle farming and for growing crops. Evaluate the impact of this deforestation on biodiversity and on the concentration of carbon dioxide in the atmosphere.
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the biodiversity, cycles and human impact worksheet pack - 20 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 24 of GCSE Biology Workbook, the whole course as one free printable PDF.
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