IGCSE Biology - Ecology + Human Influence

The sun is the principle source of energy input into biological systems.

Energy flow is non-cyclical, meaning it does not repeat itself, because it is comsumed and used.

An ecosystem is a unit containing all the organisms and their environment, interacting together in a given area.

In the water cycle, water in lakes and seas evapourates.  This water vapour condenses in the atmosphere to snow and rain.  Some of this water is taken up via plants for photosynthesis but lost through transpiration.  Some water is taken in by animals but is lost by respiration and excretion.  All remaining water in organisms is lost after death and decay.  This water forms underground streams which return it to the lakes and rivers.

In a sigmoid curve, the lag phase occurs as the organism is adapting to its environment, hence the birth rate is only slightly higher than the death rate.  The log (or exponential) phase occurs when the birth rate is significantly higher than the death rate so the population size grows rapidly.  However as food becomes more scarce and the organisms become affected by their own pollution, they enter the stationary phase where the birth rate is equal to the death rate.  As these factors become more severe, the death phase occurs.

Deforestation leads to the extinction of organisms as their habitat is destroyed, soil erosion, flooding (because soil is more compact without roots and water runs on top of it) and carbon dioxide buildup.

Water pollution comes from sewage and bacteria.  The sewage consists of human excretions which could contain harmful, infectious microbes and bacteria.  Chemicals can also have adverse effects.

Air pollution is caused by sulphur dioxide and nitrous oxides in the air…