BiologyChapter 15: Ecology
Carbon and Nitrogen Cycles
Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve.
Learning objectives
- Explain carbon and nitrogen cycles in clear biological language.
- Distinguish 1. carbon from 2. nitrogen.
- Use the key terms to answer a short Federal Board exam question.
Definition
Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve. Nitrogen: N2 is unusable for most; nitrogen-fixing bacteria (Rhizobium, free-living named) make ammonium; nitrifying bacteria named; plants take nitrate; animals eat; death/urea; denitrifying bacteria return N2. Lightning named as a small fixer. These are names of groups, not culture methods. Biogeochemical cycles connect living and non-living parts of ecosystems. Human activities (burning fossil fuels, fertiliser use) accelerate these cycles with environmental consequences.
Important terms
- CARBON AND NITROGEN CYCLES
- Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve.
- 1. CARBON
- Fossil fuel extra CO2: climate page.
- 2. NITROGEN
- Fixation, nitrification, assimilation, ammonification, denitrification named as five words.
Overview
Two element stories:
Carbon
Fossil fuel extra CO2: climate page. Deforestation: less uptake. Combustion vs respiration both make CO2; combustion is fast extra. Shells/limestone as long stores. CO₂ fixed in photosynthesis. Released in respiration, combustion, decomposition. Fossil fuels lock carbon for millions of years — burning releases it rapidly. Oceans absorb CO₂.
Examples Producer pulls C in · Consumer passes C · Decomposer returns C
Nitrogen
Fixation, nitrification, assimilation, ammonification, denitrification named as five words. Legume nodules. Waterlogged soil: denitrification loss (school). No industrial Haber how-to.
Examples Rhizobium named · Nitrosomonas named if the book · No bacterial-culture method
WHAT — CARBON AND NITROGEN CYCLES
Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve. Nitrogen: N2 is unusable for most; nitrogen-fixing bacteria (Rhizobium, free-living named) make ammonium; nitrifying bacteria named; plants take nitrate; animals eat; death/urea; denitrifying bacteria return N2. Lightning named as a small fixer. These are names of groups, not culture methods. Biogeochemical cycles connect living and non-living parts of ecosystems. Human activities (burning fossil fuels, fertiliser use) accelerate these cycles with environmental consequences.
WHY — Why this topic matters
CARBON AND NITROGEN CYCLES is an independent FBISE learning unit because students must connect its structures and processes with their biological functions and examples.
HOW — How it works
CARBON: Fossil fuel extra CO2: climate page. Deforestation: less uptake. Combustion vs respiration both make CO2; combustion is fast extra. Shells/limestone as long stores. CO₂ fixed in photosynthesis. Released in respiration, combustion, decomposition. Fossil fuels lock carbon for millions of years — burning releases it rapidly. Oceans absorb CO₂. Examples: Producer pulls C in; Consumer passes C; Decomposer returns C. NITROGEN: Fixation, nitrification, assimilation, ammonification, denitrification named as five words. Legume nodules. Waterlogged soil: denitrification loss (school). No industrial Haber how-to. Examples: Rhizobium named; Nitrosomonas named if the book; No bacterial-culture method. Exam N2 problem: Air is full of N2. Most organisms cannot use that gas. Fixers (and fertiliser named as human) supply usable N.
In simple words
Cycle names. No Haber plant design, no culture of fixers.
Key points
- CO2 in and out
- N2 needs fixers
- photosynthesis vs respiration + burn
- five N words
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Carbon and Nitrogen Cycles
Sticky Notes · Quick Revision
Core Idea
- Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve. Nitrogen: N2 is unusable for most; nitrogen-fixing bacteria (Rhizobium, free-living named) make ammonium; nitrifying bacteria named; plants take nitrate; animals eat; death/urea; denitrifying bacteria return N2. Lightning named as a small fixer. These are names of groups, not culture methods. Biogeochemical cycles connect living and non-living parts of ecosystems. Human activities (burning fossil fuels, fertiliser use) accelerate these cycles with environmental consequences.
1. CARBON
- Fossil fuel extra CO2: climate page. Deforestation: less uptake. Combustion vs respiration both make CO2; combustion is fast extra. Shells/limestone as long stores. CO₂ fixed in photosynthesis. Released in respiration, combustion, decomposition. Fossil fuels lock carbon for millions of years — burning releases it rapidly. Oceans absorb CO₂.
2. NITROGEN
- Fixation, nitrification, assimilation, ammonification, denitrification named as five words. Legume nodules. Waterlogged soil: denitrification loss (school). No industrial Haber how-to.
Exam Example
- Exam N2 problem:
- Air is full of N2.
- Most organisms cannot use that gas.
- Fixers (and fertiliser named as human) supply usable N.
Common Misconception
- Do not treat 1. CARBON and 2. NITROGEN as the same idea; each explains a different part of the topic.
FBISE Exam Check
- Define carbon and nitrogen cycles, explain the two key parts, and use the correct biological terms.
- Exam reminder: Exam N2 problem: Air is full of N2. Most organisms cannot use that gas. Fixers (and fertiliser named as human) supply usable N.
60-second revision
- Carbon: CO2 -> photosynthesis -> organic; respiration and burn return CO2; fossil stores; ocean dissolve.
- 1. CARBON: Fossil fuel extra CO2: climate page.
- 2. NITROGEN: Fixation, nitrification, assimilation, ammonification, denitrification named as five words.
- Exam reminder: Exam N2 problem: Air is full of N2. Most organisms cannot use that gas. Fixers (and fertiliser named as human) supply usable N.
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