Chemical elements are recycled in ecosystems. Microorganisms play a key role in recycling these elements.

In this IBDP Biology topic, you will learn about carbon cycle and nitrogen cycle.

• The role of microorganisms in the carbon and nitrogen cycles in sufficient detail to illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification.

• The importance of respiration, photosynthesis and human activity in giving rise to short-term fluctuation and long-term change in global carbon dioxide concentration.
• The roles of carbon dioxide and methane in enhancing the greenhouse effect and bringing about global warming.

• The environmental issues arising from the use of fertilizers.
• Leaching and eutrophication.

• Active Transport: Movement of a substance across a membrane from a region of low concentration to high concentration using ATP
• Aerobic: In the presence of oxygen
• Anaerobic: Without oxygen
• Biomass: Total mass of living material in a specific area at a given time, usually measured as dry mass since water value is variable
• Consumers: Organism that obtains energy by eating another
• Decomposer: An organism, e.g. fungus that breaks down organic material.
• Ecosystem: Unit in ecology made up of all interacting biotic and abiotic factors in a specific area
• Greenhouse Gas: Such as methane and carbon dioxide, they cause heat to be trapped in the atmosphere raising the Earth’s temperature
• Niches: All conditions and resources required for an organism to survive, reproduce and maintain population
• Oxidation: Chemical reaction causing the loss of electrons
• Producers: Organism that synthesises organic molecules from simple inorganic ones
• Saprobiotic Microorganisms (Saprophyte): Organism that obtains food from dead or decaying remains of other organisms

• The main source of carbon for terrestrial organisms is carbon dioxide in the atmosphere
• Photosynthetic organisms remove it from the air to form macromolecules e.g. carbohydrates, fats and proteins
• Respiration returns carbon dioxide back to the air
• The concentration of CO₂ is higher at night than day due to no photosynthesis occurring while respiration still occurs

• Natural process that occurs all the time
• Due to solar radiation from the sun reaching the earth
• Greenhouse gases trap the heat in the Earth’s atmosphere causing it to heat up

• The major greenhouse gas is CO₂ which is increasing due to human activities
• Methane is also produced when microorganisms break down organic molecules , it occurs in two situations:
• Decomposers break down dead remains of organisms
• Microorganisms in intestines of primary consumers e.g. cattle digest food

• Due to the layer of greenhouse gases building up it traps the heat from the sun causing the Earth to heat up

Consequences of global warming

• Changes in temperature and precipitation, the timing of seasons and frequency of extreme events e.g. storms
• Climate change will effect niches available due to organisms being adapted to particular niches
• Animals could migrate to new areas causing competition and loss of native species
• Melting ice gap could cause extinction of wild plants and animals e.g. polar bears and sea levels will rise
• Low land would be flooded and sea water would extend further up rivers making cultivation difficult
• Droughts could occur due to higher temperatures meaning xerophytes could only survive
• Greater rainfall would occur in some areas
• Insect lifecycles will be altered and due to them carrying human and crop pathogens tropical diseases could spread toward poles
• Benefit could be more rainfall filling reservoirs, higher temperatures causing higher rate of photosynthesis so more productivity and a larger harvest

• All living organisms require a source of nitrogen to form nucleic acids and proteins
• Plants take most of their nitrogen up via nitrate ions (NO₃-) from the soil
• The ions are absorbed by active transport from the root hairs
• Animals obtain their nitrogen compounds by eating the plants
• Nitrate ions are soluble
• When plants and animals die decomposition occurs and the nitrates are restored to the soil

• Plants require minerals for growth, nitrogen is needed for proteins and DNA
• With nitrogen plants grow taller and have a greater leaf area
• This increases the rate of photosynthesis and improves crop productivity

• Nitrogen is essential for proteins and growth and causes the increase in leaf area
• This increases the rate of photosynthesis and improves crop productivity

• Reduced species diversity as nitrogen rich soils favor growth of grasses so they out compete other species that then die
• Leaching leads to pollution of watercourses
• Eutrophication caused by leaching of fertilizer into watercourses

This is the end of the topic

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Drafted by Eva (Biology)

Photo references:

1. https://intl.siyavula.com/read/science/grade-10-lifesciences/biosphere-to-ecosystems/08-biosphere-to-ecosystems-07
2. https://www.sciencefacts.net/carbon-cycle.html
3. https://en.wikipedia.org/wiki/Greenhouse_effect
4. https://biologywise.com/nitrogen-cycle-steps