Human Influence on the Ecosystem

(Section B11 from the curriculum)

What you need to know (from the curriculum)

List the undesirable effects of deforestation (to include extinction, loss of soil, flooding, carbon dioxide build up).

Explain how increases in greenhouse gases (carbon dioxide and methane) are thought to cause global warming.

Describe the undesirable effects of overuse of fertilisers (to include eutrophication of lakes and rivers).

Describe the undesirable effects of pollution to include:

  • water pollution by sewage and chemical waste,

  • air pollution by greenhouse gases (carbon dioxide and methane) contributing to global warming.

Discuss the causes and effects on the environment of acid rain, and the measures that might be taken to reduce its incidence.

Describe the need for conservation of:

  • species and their habitats,

  • natural resources (limited to water and non-renewable materials including fossil fuels).


Real World Context

Deforestation is one of the main themes of the UN Climate change conference in New York 2014 (happening at the time of writing). This conference was opened by the UN Ambassador for Peace (Leonardo DiCaprio).
Leonardo DiCaprio's 2014 UN Climate Summit Speech


Some guiding questions for today

  • What are the causes and reasons for so much deforestation?
  • What are the undesirable consequences of deforestation?
  • What is the greenhouse effect....

The causes

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The undesirable effects of deforestation

Burning the rainforest

  • One method of clearing the rainforest is burning.
  • This is how CO2 is added to the atmosphere
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Bio (meaning life) and diversity (meaning variety) together make up biodiversity, which refers to the variety of life.

Rainforests have a high biodiversity and this is an important reason to protect them.

What effect does deforestation have on biodiversity?

Biodiversity in tropical rainforest

Deforestation and the carbon cycle

Below is the carbon cycle, how do you think removing large areas of rainforest will impact on the level of atmospheric carbon dioxide?
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Causes of deforestation

  • Trees used for fuel
  • Trees used to make paper and furniture products
  • We need a huge amount of space to grow crops and raise animals for food (think of what the average person consumes!)

Undesirable consequences of deforestation

  • Loss of fertile soil
  • Increased flooding
  • More CO2 in the atmosphere (when trees/vegetation are burned)
  • Extinction of species

The greenhouse effect

Fossil fuels, greenhouse gases, carbon dioxide, methane, renewable energy are all words that are associated with the greenhouse effect and are words that we need to be able to use and understand. The below video clip from the UN visualises these words...

What is the greenhouse effect and why is it described as 'greenhouse'?

Firstly, it is important to know that WE NEED THE GREENHOUSE EFFECT! Without it the average temperature on Earth would be a very chilly -18 degrees centigrade.

The greenhouse effect is a process where certain compounds in the atmosphere retain heat from the sun, the main gases we need to know are carbon dioxide and methane

Key Words

  • Visible light - light emitted from the sun (that we can see) that strikes the Earth
  • Infra-red radiation - some visible light is converted to infra-red radiation when it strikes the Earth and this generates HEAT.
  • Re-radiate - when the infra-red radiation is reflected from the ground but it is then re-reflected back towards the ground from greenhouse gases (CO2 and CH4) in the atmosphere.
  • CO2 (carbon dioxide)
  • CH4 (methane)

How the greenhouse effect works



What is it?

Eutrophication is a biological process that causes a significant increase in the growth of algae, it can be caused by using fertilisers.

Fertilisers are highly soluble - they dissolve in water easily, rainfall washes fertilisers out of the soil.

It is caused when fertilisers (used to increase crop production) are washed into rivers, lakes and seas from farmland.

The overuse of fertiliser is responsible for eutrophication.

Why does it happen?

Fertilisers contain nutrients to increase plant yield, and they contain many essential nutrients to enhance plant growth;

Nitrates - (NO3-) required to make protein

Phosphorus - (P) needed for healthy cell division and protein synthesis.

Potassium - (K) facilitates plant growth through a variety of life processes

Fertilisers containing these minerals are known as NPK fertilisers.

Another undesirable consequence of over-using fertilisers is that plants can become damaged.

When there is too much fertiliser around the roots of the plant it can cause the plant to lose water by osmosis leading to wilting and then death of the plant.

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Exam style question

Describe what will happen to the organisms in the lake when nitrates leak from a nearby factory (4)
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Mark scheme

  • Algae on the surface will undergo rapid growth

  • They block sunlight to photosynthetic plants below

  • Causing plants underneath to decrease in number/die

  • Decomposers in the lake break down these dead plants (using up oxygen)

  • Other organisms will decrease in number/die due to a lack of oxygen.


Sewage can be treated and
Sewage can result in eutrophication in a similar way to overuse of fertilisers.

This is because sewage contains high levels of nutrients such as phosphates, organic matter and bacteria. The phosphates act as fertilisers for algae, while the bacteria feed on the organic matter and reproduce rapidly, using up O2 in respiration.

If sewage is untreated before disposal it can lead to disease organisms such as cholera and typhoid being transmitted in the water.

Acid Rain

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Addition of Lime

In Sweden one method to try to reduce the impact of acid rain in lakes is to add lime (an alkali), this is to try to neutralise the acidity of the water to prevent damage to the species that liver there.

Conservation of species and their environments