Cambridge IGCSE0610

Food supply

Biology 0610 Chapter Notes

What this chapter covers

Food supplyHabitat destructionPollutionConservation
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In this chapter

  1. 1Population Growth and Food Demand
  2. 2Intensive Farming and Monocultures
  3. 3Agriculture's Impact on Ecosystems
  4. 4Water Pollution from Fertilisers
  5. 5Causes and Consequences of Famine
  6. 6Sustainable Food and Fishing

1. Population Growth and Food Demand

The global human population is growing at an exponential rate, meaning it is increasing faster and faster over time. Currently over 8 billion, it places enormous pressure on Earth's resources. Every additional person requires food, water, and space to live. This directly increases the demand for food, forcing agricultural systems to produce more yield from the available land. This rising demand is the primary driver behind many modern farming practices and their associated environmental problems.

Key term

Exponential Growth: A pattern of growth that increases at a rate proportional to the current size, resulting in a J-shaped curve on a graph.

Examiner insight

Marks are often awarded for clearly linking the concept of population growth to specific increased demands, such as for more land for farming or more protein sources.

Fun fact

It took all of human history until 1804 for the world's population to reach 1 billion. The eighth billion was added in just 11 years (2011-2022).

Worked example 13 marks

The global population was approximately 6.1 billion in the year 2000 and 7.8 billion in 2020. Calculate the percentage increase in population over this 20-year period. [2 marks] Explain one reason why this trend is a concern for global food security. [1 mark]

  1. 1

    Step 1: Calculate the absolute increase in population. 7.8 billion - 6.1 billion = 1.7 billion.

  2. 2

    Step 2: Calculate the percentage increase. (Increase / Original Population) x 100 = (1.7 / 6.1) x 100 = 27.9%. [2 marks]

  3. 3

    Step 3: Explain the implication. A larger population requires more food to be produced, putting greater strain on agricultural land, water resources, and increasing the risk of food shortages and famine in vulnerable regions. [1 mark]

Recap

  • The human population is increasing exponentially.
  • Population growth increases the demand for food, water, and land.
  • This demand drives the need for more intensive agriculture.
  • Meeting the food demand for a growing population is a major global challenge.

Quick check

  1. Describe the general trend of human population growth over the past 200 years.1 mark

2. Intensive Farming and Monocultures

To meet the high demand for food, modern agriculture often uses intensive farming methods. These aim to maximise the yield (amount of crop produced) from a piece of land. Key features include:

  1. Monoculture: Growing vast fields of a single crop species. This is very efficient for planting and harvesting with large machinery.
  2. Machinery: Large machines like tractors and combine harvesters allow a small number of people to farm a very large area.
  3. Fertilisers: Chemicals containing mineral ions like nitrates and phosphates are added to the soil to replace those absorbed by crops, ensuring rapid growth and high yields.
  4. Pesticides: Chemicals used to kill pests that would otherwise eat the crops (insecticides) or compete with them (herbicides).

Key term

Monoculture: The agricultural practice of growing a single crop species in a field at a time.

Examiner insight

Be prepared to discuss both the advantages (e.g., high efficiency, high yield) and disadvantages (e.g., loss of biodiversity, pollution) of these methods.

Fun fact

The 'Green Revolution' in the mid-20th century saw the widespread introduction of high-yield crop varieties, fertilisers, and pesticides, which is estimated to have saved over a billion people from starvation.

Worked example 14 marks

A farmer wants to increase the amount of wheat they produce. Describe two intensive farming methods they could use and explain how each method increases the yield.

  1. 1

    Method 1: Use of fertilisers. Fertilisers add essential mineral ions, such as nitrates for protein synthesis and magnesium for chlorophyll, back into the soil. This ensures that a lack of minerals does not become a limiting factor for plant growth, allowing the wheat to grow faster and larger, thus increasing yield. [2 marks]

  2. 2

    Method 2: Use of pesticides (herbicides). Herbicides are chemicals that kill weeds. By spraying the field, the farmer removes competing plants that would otherwise use up water, light, and mineral ions from the soil. This leaves more resources available for the wheat crop, increasing its growth and final yield. [2 marks]

Recap

  • Intensive farming aims to maximise crop yield per unit area.
  • Monoculture is the efficient practice of growing a single crop.
  • Fertilisers supply essential mineral ions to the soil.
  • Pesticides kill pests (insects) and herbicides kill weeds (competing plants).
  • Large machinery increases the efficiency of farming.

Quick check

  1. What is the purpose of using fertilisers in agriculture?1 mark
  2. Define the term 'monoculture'.1 mark

3. Agriculture's Impact on Ecosystems

While intensive farming increases food production, it has severe negative impacts on the environment and biodiversity. Large-scale deforestation is carried out to clear land for crops or for grazing cattle, destroying habitats for countless species. To make fields larger and more efficient for machinery, hedgerows are often removed. Hedgerows are vital habitats and 'wildlife corridors' for birds, insects, and small mammals. The practice of monoculture itself creates an environment with very low biodiversity, as only one plant species is present and it supports a very limited range of other organisms compared to a natural forest or grassland.

Key term

Biodiversity: The variety of different species of organisms in an ecosystem.

Examiner insight

Questions often ask for specific examples of how agriculture reduces biodiversity. Mentioning habitat destruction through deforestation and the removal of hedgerows are excellent, specific examples to use.

Worked example 14 marks

A farmer removes a 500-metre hedgerow to join two small fields into one large one. Describe two negative effects this could have on the local environment.

  1. 1

    Effect 1: Habitat Loss. The hedgerow provides a home and food source for many organisms like birds, insects, and small mammals. Removing it destroys their habitat, which can lead to a decrease in their population size or cause them to leave the area. [2 marks]

  2. 2

    Effect 2: Reduced Biodiversity / Fragmentation. The hedgerow acts as a 'corridor' allowing animals to move safely between different areas, like woodlands. Removing it isolates populations, reducing gene flow and the overall biodiversity of the farmland ecosystem. It also directly reduces the number of plant and animal species in the immediate area. [2 marks]

Recap

  • Deforestation for agriculture is a major cause of habitat destruction.
  • Removing hedgerows to create larger fields reduces biodiversity.
  • Hedgerows provide habitats and act as wildlife corridors.
  • Monocultures have very low biodiversity compared to natural ecosystems.

Quick check

  1. State one reason why a field of wheat has low biodiversity.1 mark

4. Water Pollution from Fertilisers

Runoff from agricultural land is a major source of water pollution. When heavy rain follows fertiliser application, the excess nitrates and phosphates are washed from the soil into nearby rivers and lakes. This leads to a destructive process called eutrophication.

  1. Nutrient Loading: Nitrates and phosphates from fertiliser enter the water.
  2. Algal Bloom: These nutrients cause a rapid, massive growth of algae and surface plants.
  3. Light Blocked: The thick layer of algae blocks sunlight from reaching plants deeper in the water, which then die.
  4. Decomposition: Bacteria and fungi decompose the dead algae and plants. This process requires a lot of oxygen (aerobic respiration).
  5. Oxygen Depletion (Anoxia): The decomposers use up so much dissolved oxygen that the water becomes anoxic.
  6. Death of Ecosystem: Fish, insects and other aquatic organisms die due to the lack of oxygen.

Key term

Eutrophication: The process where a body of water becomes overly enriched with minerals and nutrients, which induces excessive growth of algae and leads to oxygen depletion.

Examiner insight

Examiners look for a clear, logical sequence of events when you describe eutrophication. Don't just say 'fertilisers kill fish'; explain the full chain reaction involving the algal bloom and decomposers.

Worked example 16 marks

Describe the sequence of events that can lead to the death of fish in a lake following the overuse of nitrate fertilisers on nearby fields.

  1. 1

    Step 1: Fertilisers are leached from the soil or washed by rain into the lake (runoff). [1 mark]

  2. 2

    Step 2: The high concentration of nitrates causes a rapid growth of algae, known as an algal bloom. [1 mark]

  3. 3

    Step 3: This algal bloom blocks sunlight from reaching the submerged plants, causing them to die. [1 mark]

  4. 4

    Step 4: Bacteria decompose the dead plants and algae. [1 mark]

  5. 5

    Step 5: During decomposition, these bacteria respire aerobically, using up large amounts of dissolved oxygen in the water. [1 mark]

  6. 6

    Step 6: The oxygen level in the water becomes too low for fish to survive, and they die from suffocation. [1 mark]

Recap

  • Excess fertiliser can wash from fields into rivers and lakes.
  • This process is called eutrophication.
  • Nutrients cause a rapid growth of algae called an algal bloom.
  • Decomposition of the dead algae by bacteria uses up dissolved oxygen.
  • Lack of oxygen causes fish and other aquatic animals to die.

Quick check

  1. In eutrophication, what causes the oxygen level in the water to drop?1 mark

5. Causes and Consequences of Famine

Famine is a widespread scarcity of food in a region, leading to severe malnutrition, starvation, disease, and a high death rate. While the world produces enough food to feed everyone, famine still occurs due to a complex mix of factors:

  • Unequal distribution: Food surpluses in developed countries often do not reach areas of need due to cost, politics, and logistics.
  • Drought: Prolonged periods of low rainfall cause crop failure and death of livestock.
  • Flooding: Severe floods can destroy crops and fertile topsoil, making land unusable.
  • Poverty: People may be unable to afford food even if it is available, or farmers cannot afford seeds and fertilisers to grow it.
  • Conflict: War and civil unrest disrupt farming, destroy infrastructure, and prevent aid from being delivered.

Key term

Famine: An extreme scarcity of food in a region, leading to widespread malnutrition and death by starvation.

Examiner insight

High-scoring answers often recognise that famine is a complex issue caused by a combination of environmental, social, and economic factors, not just a single cause like 'no rain'.

Worked example 14 marks

Explain how two different factors can contribute to famine in a country.

  1. 1

    Factor 1: Drought. A prolonged lack of rainfall means that crops fail to grow because water is a key requirement for photosynthesis and plant cell structure. Livestock may also die from thirst or lack of grazing. This leads to a severe shortage of locally produced food. [2 marks]

  2. 2

    Factor 2: Unequal distribution / Poverty. A country may suffer from famine even if food is available globally or in other parts of the country. If the population is too poor to buy the food, or if transport links are inadequate to move food from a port to an inland area, people will starve. This shows that access to food is as important as its production. [2 marks]

Recap

  • Famine is an extreme shortage of food.
  • The main problem with global food supply is unequal distribution, not a lack of production.
  • Natural causes of famine include drought and flooding.
  • Human causes of famine include poverty, conflict, and poor distribution networks.

Quick check

  1. Other than drought, state two possible causes of famine.2 marks

6. Sustainable Food and Fishing

Sustainable food production aims to produce food in a way that can be maintained for future generations without causing permanent damage to the environment. In farming, this can involve using crop rotation and natural fertilisers (manure) to maintain soil health, and using biological control (introducing a predator to kill a pest) instead of chemical pesticides. In fishing, global fish stocks are threatened by overfishing. Sustainable fishing methods are crucial for conservation:

  • Fishing quotas: Setting legal limits on the mass of a certain fish species that can be caught in a season. This prevents too many adult fish from being removed.
  • Net size regulation: Enforcing a minimum mesh size for fishing nets. This allows smaller, younger fish to swim through, escape, and grow to maturity to reproduce. This ensures the next generation of fish.

Key term

Sustainable: Meeting the needs of the present without compromising the ability of future generations to meet their own needs.

Examiner insight

When discussing sustainable fishing, providing specific methods like quotas and mesh size regulations demonstrates a deeper understanding than just saying 'don't fish too much'.

Worked example 14 marks

Describe two conservation measures used to make fishing more sustainable and explain how each one helps to protect fish stocks.

  1. 1

    Measure 1: Fishing quotas. These are legal limits on the amount of fish that can be caught. This helps protect fish stocks by ensuring that enough adult fish are left in the sea to reproduce and maintain the population for the following season. [2 marks]

  2. 2

    Measure 2: Net size regulation. Laws specify a minimum mesh size for fishing nets. This allows smaller, immature fish to escape being caught. This is important because it gives them a chance to grow to reproductive age and have offspring, replenishing the stock. [2 marks]

Recap

  • Sustainable production provides food without harming the environment for the future.
  • Overfishing has severely depleted many of the world's fish stocks.
  • Fishing quotas limit the quantity of fish that can be caught.
  • Controlling net mesh size allows young fish to escape and reproduce.
  • Sustainable farming methods include biological control and crop rotation.

Quick check

  1. What is the purpose of setting fishing quotas?1 mark
  2. Why is it important that young fish can escape from fishing nets?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Define the term 'famine' and state two human activities that can cause it.3 marks
  2. Explain why a farmer might use fertilisers on their crops and describe one negative environmental consequence of their overuse.4 marks
  3. The world's human population is increasing. Describe the effects of this on the demand for food and on the environment.4 marks
  4. Explain how introducing a minimum mesh size for fishing nets can help to conserve fish stocks.3 marks
  5. Describe and explain the process of eutrophication in a lake.6 marks
  6. Compare the biodiversity of a natural forest with that of a field of wheat grown as a monoculture. Explain any differences.4 marks
  7. Suggest two reasons why clearing a forest to create a cattle ranch is damaging to the environment.2 marks
  8. Explain why, despite the world producing enough food to feed its entire population, millions of people still suffer from malnutrition.3 marks
  9. Evaluate the use of intensive farming methods. In your answer, you should discuss both the benefits and the drawbacks.6 marks
  10. A fish farm is set up in a lake. The fish are kept in high densities and fed large amounts of food. Explain why the water in the lake downstream of the fish farm might become low in oxygen.4 marks

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