Ch 1 · Food Supply · O Level Biology 5090
Topic 1 of 4 in Human Influences on Ecosystems — O Level Biology 5090 — 48 lessons.
Introduction
The human population has passed 8 billion, and every one of those people needs feeding. Food production has kept pace so far because machines, chemicals and selectively bred crops and animals produce far more food per hectare than a century ago. But each gain has a cost to ecosystems, and food is still not shared evenly. Questions here reward balanced answers that name specific advantages and disadvantages.
Key ideas — How humans have increased food production
🧑🏫 Teacher's explanation
Imagine you are running a professional kitchen. To feed hundreds of people, you can't just pick vegetables from a garden by hand; you need high-speed food processors (machinery) and specialized ingredients to make everything grow faster (fertilisers). You also need to keep pests out of your pantry (insecticides/herbicides) and choose only the best-tasting seeds to plant next season (selective breeding).
📖 Definitions
🔍 Worked example — Easy
A farmer uses a tractor and a combine harvester to harvest a field. Calculate the percentage increase in the area harvested per hour if the farmer previously harvested 0.5 ha/hr by hand and now harvests 12 ha/hr using machinery.
🔍 Worked example — Standard
Explain why adding nitrogen-based fertilisers increases crop yield.
🔍 Worked example — Exam-style
Compare the use of insecticides and herbicides in modern agriculture.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Key ideas — Large-scale monocultures
A monoculture is a single crop species grown over a very large area, year after year.
🧑🏫 Teacher's explanation
Imagine you are playing a video game where you can only build one type of building—say, identical wooden huts—across a massive map. Because every building is exactly the same, you can build them very quickly using a single type of machine, and it is very cheap to produce them. This is the essence of a monoculture: efficiency through uniformity.
📖 Definitions
🔍 Worked example — Easy
A farmer uses a monoculture of wheat. State two economic advantages of this method.
🔍 Worked example — Standard
Explain why a monoculture is more susceptible to a single pest than a diverse ecosystem.
🔍 Worked example — Exam-style
A farmer grows maize on 50 hectares. Due to intensive monoculture, the soil nutrient level drops by 25\% in one year. If the initial nutrient concentration was 400 mg/kg, calculate the new concentration.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Describe two advantages of this change for the farmer. [2] (b) Explain two environmental disadvantages of this change. [2] [4 marks]
Key ideas — Intensive livestock production
Intensive livestock production keeps large numbers of animals at high density, often indoors, with controlled feeding.
🧑🏫 Teacher's explanation
Imagine you are running a high-speed factory that produces smartphones. To maximize profit, you pack as many machines as possible into a small room, keep the temperature perfect, and feed them constant electricity. This is 'intensive' production. In biology, we do this with animals to get the most 'output' (meat, milk, eggs) for every bit of 'input' (food, land, time).
📖 Definitions
🔍 Worked example — Easy
A farmer uses intensive methods to produce 500 kg of meat. Using traditional grazing, he would need 2000 m^2 of land. Using intensive methods, he only needs 400 m^2. Calculate the percentage reduction in land area required.
🔍 Worked example — Standard
Compare the energy efficiency of intensive livestock production versus traditional grazing in terms of food conversion.
🔍 Worked example — Exam-style
Explain how intensive livestock farming can lead to the death of fish in a nearby lake.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Key ideas — Feeding an increasing population
The growth of the human population is increasing the demand for global resources: food, water, land, energy and materials. Providing sufficient food raises social, environmental and economic issues, and a good discussion touches all three.
🧑🏫 Teacher's explanation
Imagine a massive global potluck dinner. Even if there is enough food to feed everyone in the room, some people leave hungry because they don't have the right currency to trade, or the food is being delivered to the wrong tables. This is the core of the 'social' issue: it is not just about how much food we grow, but how it is distributed.
📖 Definitions
🔍 Worked example — Easy
A farmer uses a new herbicide to kill weeds in his wheat field. State one advantage and one disadvantage of using this herbicide.
🔍 Worked example — Standard
Compare the use of traditional farming methods with intensive farming methods in terms of environmental impact.
🔍 Worked example — Exam-style
A country experiences a sudden increase in the price of imported wheat due to a drought in the exporting nation. Discuss the social and economic implications of this event.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Describe one advantage and one disadvantage of using a monoculture. [2] (b) Explain how the use of chemical fertilisers can lead to the death of aquatic organisms. [3] [5 marks]
Worked example
Question. A farmer clears an area of forest and plants it entirely with maize, which is grown every year on the same land. Discuss the advantages and disadvantages of this method of food production. [5]
🔍 Worked example — Easy
A farmer uses a specific herbicide to kill weeds in a maize field. Explain why this is more efficient in a monoculture than in a mixed-crop field.
🔍 Worked example — Standard
Calculate the percentage increase in crop yield if a farmer switches from traditional methods to intensive farming, moving from 2.5 tonnes per hectare to 6.0 tonnes per hectare.
🔍 Worked example — Exam-style
A farmer uses intensive livestock production to meet food demands. Discuss the environmental implications of this method. [4]
⚠️ Common errors
Common mistakes
Practice
Answers