Ecology – Study Notes for Paramedical Entrance
(Biology – Ecology)
Goal of these notes – Give you a clear, concise overview of core ecological concepts, a step‑by‑step worked example, and a quick‑review cheat‑sheet to keep the essentials fresh before your exam.
1. Simple Explanation
Ecology is the scientific study of how living organisms interact with each other and with their physical environment. It asks:
- Who lives where?
- How do they obtain energy and matter?
- How do populations change over time?
- What are the consequences of human activity on natural systems?
Think of an ecosystem as a living network: organisms (plants, animals, microbes) form communities; those communities interact with abiotic components (soil, water, air). Energy flows through the network, while matter cycles (e.g., carbon, nitrogen) is reused.
2. Key Points
| Concept | What it Means | Why It Matters |
|---|---|---|
| Levels of Ecological Organization | Organism → Population → Community → Ecosystem → Biosphere | Helps structure ecological thinking and problem‑solving. |
| Biotic & Abiotic Factors | Biotic = living; Abiotic = non‑living (light, temperature, soil chemistry). | Determines species distribution, health, and interactions. |
| Trophic Levels | Producers → Primary consumers → Secondary consumers → Tertiary consumers → Apex predators. | Energy is transferred at each step; helps explain food webs. |
| Food Chain vs Food Web | Chain = linear; Web = network of multiple chains. | Real ecosystems are webs; more robust to disturbances. |
| Energy Flow | Primary production → Consumption → Decomposition → Respiration. | Energy is lost (12–20 % at each trophic step), limiting ecosystem size. |
| Nutrient Cycles | Carbon, Nitrogen, Phosphorus, Water, etc. | Matter is recycled; nutrient availability controls productivity. |
| Population Dynamics | Growth, Mortality, Immigration, Emigration. | Determines species abundance and community composition. |
| Human Impacts | Pollution, habitat loss, climate change, invasive species. | Drives changes in biodiversity, ecosystem services, and public health. |
| Conservation & Restoration | Protected areas, restoration ecology, sustainable use. | Maintains ecosystem services vital for health and well‑being. |
3. Worked Example – The Nitrogen Cycle in a Grassland Ecosystem
Goal: Trace the journey of a nitrogen atom from the atmosphere to a plant and back to the soil.
| Step | Process | Key Players | Outcome |
|---|---|---|---|
| 1. Nitrogen Fixation | Atmospheric N₂ → Organic N | Nitrogen‑fixing bacteria (Rhizobium in root nodules) | Forms ammonia (NH₃) or ammonium (NH₄⁺). |
| 2. Assimilation | NH₄⁺ → Plant amino acids | Plants | Plants incorporate N into proteins. |
| 3. Consumption | Plant consumption → Animal tissue | Herbivores | Animals acquire N for growth. |
| 4. Excretion & Decomposition | Animal waste / dead bodies → NH₃/NH₄⁺ | Detritivores, microbes | Nutrients return to soil. |
| 5. Nitrification | NH₄⁺ → NO₂⁻ → NO₃⁻ | Nitrifying bacteria (e.g., Nitrosomonas, Nitrospira) | Produces nitrate usable by plants. |
| 6. Denitrification | NO₃⁻ → N₂ (gas) | Denitrifying bacteria (e.g., Pseudomonas) | N₂ re‑enters atmosphere. |
| 7. Mineralization | Organic N → NH₄⁺ | Microbial decomposition | Restores inorganic N for uptake. |
Take‑away:
- The cycle is closed; nitrogen is continually recycled.
- Human actions (e.g., fertilizer use) can cause nitrification to produce excess nitrate → runoff → eutrophication.
- Paramedical relevance: Excess nitrate in water supplies poses health risks (e.g., methemoglobinemia in infants).
4. Quick Revision Summary
- Ecology = interactions between organisms & environment.
- Levels: Organism → Population → Community → Ecosystem → Biosphere.
- Trophic structure: Producers → Consumers → Decomposers.
- Energy loss: ~90 % lost as heat; limits food chain length.
- Key cycles:
- Carbon – photosynthesis → respiration → decomposition.
- Nitrogen – fixation → assimilation → excretion → nitrification/denitrification.
- Phosphorus – weathering → uptake → decay → mineralization.
- Human impacts: Pollution, habitat fragmentation, climate change, invasive species.
- Conservation strategies: Protected areas, sustainable resource use, ecosystem restoration.
- Health link: Ecosystem services (clean air, water, disease regulation) directly affect human health.
Final Tip
When you’re revising, draw a simple diagram of a food web or a nutrient cycle next to each key concept. Visuals help anchor the relationships and make recall during the exam faster and more reliable. Good luck!