Human Influences on the Environment
Explore how human activities impact ecosystems through agriculture, pollution, and resource management.
🎯 Learning Objectives
By the end of this lesson, you will be able to:
- Describe how glasshouses and polytunnels increase crop yield
- Explain how fertilisers increase crop yield
- Compare pesticides and biological control methods
- Identify greenhouse gases and their effects
- Understand pollution consequences on ecosystems
- Explain eutrophication from fertiliser runoff
As human population grows exponentially, we place increasing demands on the environment for food, materials, fuel, and space. Modern farming is a managed ecosystem where humans control many factors to maximise yield.
Population Growth & Agriculture
Human population has grown exponentially, creating unprecedented demands on our environment.
📈 Exponential Population Growth
Human population remained relatively stable for thousands of years, but has grown exponentially since the Industrial Revolution. By 2050, the global population is projected to reach 10 billion people.
This creates increasing demands for:
🌾 Modern Farms as Managed Ecosystems
A modern farm is a managed ecosystem where humans control many interactions that occur naturally. Crop plants act as producers, livestock as primary consumers, and humans as top consumers.
The food web on a farm is simplified compared to natural ecosystems, but follows the same energy flow principles.
Crop plants are producers because they make food through photosynthesis.
Humans are primary consumers in the farm food web.
Cattle convert plant material into protein for humans.
Glasshouses & Controlled Environments
Farmers control environmental factors to maximise crop yield using glasshouses and polytunnels.
🏠 How Glasshouses Increase Yield
Glasshouses (greenhouses) and polytunnels create controlled conditions for optimal plant growth. They allow farmers to manipulate factors that limit photosynthesis.
🌞 Light Control
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Transparent walls allow natural light. Additional lighting extends "day" during winter months.
🌡️ Temperature
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Greenhouse effect traps heat. Short-wave infrared converts to long-wave that can't escape.
💨 CO₂ Enrichment
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Burning fuels releases CO₂ and heat. Higher CO₂ increases photosynthesis rate.
💧 Humidity
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Water vapour maintains moisture, reducing water loss by transpiration.
Heating glasshouses to the optimum temperature for photosynthesis maximises yield. Heating above this wastes money with no further increase in yield.
| Factor | Primary Effect |
|---|---|
| Soil nitrates | |
| Soil structure | |
| Soil pH | |
| CO₂ levels |
Nitrogen Cycle & Fertilisers
Nitrogen is essential for plant protein synthesis. Farmers must replace nitrogen lost when crops are sold.
🔄 The Nitrogen Cycle on Farms
When crops and livestock are sold off the farm, nitrogen is lost. Farmers must replace this nitrogen through:
- Growing legumes (peas, beans, clover) with nitrogen-fixing bacteria
- Adding organic fertilisers (farmyard manure)
- Adding inorganic fertilisers (NPK)
🌿 Organic Fertilisers
Made from animal faeces mixed with straw (farmyard manure).
- Contains decaying matter
- Improves soil structure
- Only replaces some lost nitrogen
🧪 Inorganic Fertilisers
Chemical compounds like potassium nitrate (NPK).
- Provides precise nutrient amounts
- Can replace all lost minerals
- Does NOT improve soil structure
Pest Control Methods
Pests reduce crop yield. Farmers use chemical and biological methods to control them.
In Britain, about 30% of the potential maize crop is lost to weeds, insects, and fungal diseases each year.
🐛 What is a Pest?
A pest is any organism that reduces the yield of crop plants or stock animals. Pests include weeds, insects, fungi, bacteria, and viruses.
Pests harm crops by: damaging leaves (reducing photosynthesis) and affecting appearance (making crops unsuitable for sale).
🧪 Types of Pesticides
Pesticide
Target Pest
🐞 Biological Control
Biological control uses natural predators, parasites, or pathogens to reduce pest populations. For example, introducing ladybirds to control aphids.
Water vapour
Carbon dioxide (CO₂)
Nitrogen (N₂)
Methane (CH₄)
Summary & Final Assessment
Review the key concepts and test your understanding.
Population Growth
Exponential growth creates demands for food, materials, fuel, and space.
Controlled Environments
Glasshouses control light, temperature, CO₂, and humidity for maximum yield.
Nitrogen Cycle
Lost nitrogen replaced with organic or inorganic fertilisers.
Pest Control
Chemical pesticides vs biological control - each with pros and cons.