Ecology: Succession & Nutrient Cycles
Ecology examines how populations interact with each other and with their abiotic environment. This guide covers how ecosystems develop over time through directional succession toward a stable climax community, alongside how saprobionts and bacteria recycle carbon and nitrogen through ecosystems.
- Pioneer Species
- The first organisms to colonize a harsh environment during primary succession, capable of surviving extreme conditions.
- Secondary Succession
- Succession that occurs on land that has been cleared of plants but still retains soil, proceeding much faster than primary succession.
- Nitrification
- The oxidation of ammonium ions to nitrites, then to nitrates, carried out by nitrifying bacteria in the soil.
Ecology: Succession & Nutrient Cycles: Enzyme Collision, Active Site & Rate Curve Lab
Drag the temperature, pH, and substrate sliders to watch how kinetic collisions, active-site binding, and denaturation change the reaction rate in real time.
Key Concepts & Exam Definitions (5)
- Pioneer Species
- The first organisms to colonize a harsh environment during primary succession, capable of surviving extreme conditions.
- Secondary Succession
- Succession that occurs on land that has been cleared of plants but still retains soil, proceeding much faster than primary succession.
- Nitrification
- The oxidation of ammonium ions to nitrites, then to nitrates, carried out by nitrifying bacteria in the soil.
- Denitrification
- The conversion of soil nitrates into nitrogen gas by denitrifying bacteria under anaerobic conditions.
- Gross Primary Production (GPP)
- The total chemical energy stored in plant biomass, in a given area or volume, over a given time.
Quick-Fire Flashcards (5)
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What type of bacteria convert nitrogen gas into ammonia?
What is meant by the term plagioclimax?
What is Net Primary Production (NPP)?
Which process removes carbon dioxide from the atmosphere in the carbon cycle?
How do pioneer species change the environment in primary succession?
Exam-Style Questions & Mark Schemes (3)
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- Q1
Describe how primary succession occurs on a newly formed volcanic island.
Click “Check Mark Scheme” to compare your answer, Pioneer species like lichens colonize the bare rock. They weather the rock and, upon death, decompose to form basic soil (humus). This makes the abiotic environment less hostile. Mosses and small plants can now grow, outcompeting the pioneer species. Soil deepens as more organic matter is added, allowing larger plants and eventually trees to grow, ultimately forming a stable climax community.
- Q2
Explain the role of bacteria in making nitrogen in dead leaves available to growing plants.
Click “Check Mark Scheme” to compare your answer, Saprobionts secrete extracellular enzymes to digest proteins and nucleic acids in dead leaves. They absorb the products and release ammonia/ammonium ions into the soil (ammonification). Nitrifying bacteria then oxidize ammonium ions to nitrites, and other nitrifying bacteria oxidize nitrites to nitrates (nitrification). Plants can then absorb these nitrates through their roots.
- Q3
Explain why keeping cattle in heated sheds and confining their movement increases farming efficiency.
Click “Check Mark Scheme” to compare your answer, Restricting movement means less energy is lost through muscle contraction/respiration. Heating the sheds means less energy is lost maintaining body temperature. Therefore, more of the energy from their food is converted into biomass (meat/milk), increasing the net productivity.
Common Exam Questions (3)
What is primary succession?
Primary succession occurs when newly exposed or newly formed bare rock or sand, with no existing soil, is colonised for the first time by hardy pioneer species such as lichens and mosses.
What is a climax community?
A climax community is the stable, self-sustaining final stage of ecological succession, usually dominated by large trees or woodland, where species composition remains relatively constant unless the environment is disturbed.
What is the role of saprobionts in the nitrogen cycle?
Saprobionts are decomposers (fungi and bacteria) that secrete enzymes onto dead organic matter and waste to digest it externally. During ammonification, they break down nitrogen-containing compounds such as proteins and urea, releasing ammonium ions back into the soil.
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