Energy Flow in an Ecosystem
What is an Ecosystem?
An ecosystem is a community of living organisms (plants, animals, microbes) interacting with their environment (air, water, soil).
Types of Ecosystems:
- Natural: Forests, ponds, deserts.
- Artificial: Aquariums, farms.
Interactions:
- Biotic factors (living, like plants and animals) and abiotic factors (non-living, like sunlight and water) interact to keep the ecosystem balanced.
Energy Flow in an Ecosystem
Trophic Levels:
- Producers: Plants (autotrophs) make their own food using sunlight (e.g., grass).
- Primary Consumers (Herbivores): Animals that eat plants (e.g., grasshopper, squirrel).
- Secondary Consumers (Carnivores): Animals that eat herbivores (e.g., frog, fox).
- Apex Consumers (Top Carnivores): Animals that eat other consumers but aren’t eaten (e.g., lion, tiger).
- Omnivores: Eat both plants and animals (e.g., humans, bears).
- Decomposers: Microbes like fungi and bacteria that break down dead organisms (e.g., fungi on dead logs).
Food Chain and Food Web
- A food chain is a simple sequence showing who eats whom, like grass → grasshopper → frog → snake.
- It has 4-5 links, showing the flow of energy from one organism to another.
Food Web
- A food web is a network of many food chains connected together.
- Example: An insect eats plants, but is eaten by a frog, lizard, and bird, forming a web.
- Food webs show the complex feeding relationships in nature.
Key Points:
- The number of consumers in a food web isn’t fixed; it depends on the ecosystem.
- If one organism (e.g., insect) is food for many others, its removal can disrupt the web.
- Balance in a food web is needed to ensure no species overgrows or disappears.
The Energy Pyramid
Trophic Levels
- Each step in a food chain is a trophic level (e.g., producers at level 1, herbivores at level 2).
- Energy decreases as you move up from producers to apex consumers.
Pyramid of Energy
- Shows how energy reduces at each level in an ecosystem.
- Example: In an aquatic ecosystem:
- Phytoplankton (producers): 10,000 kcal.
- Zooplankton (herbivores): 1,000 kcal.
- Fish (carnivores): 100 kcal.
- Humans (apex consumers): 10 kcal.
- Only about 10% of energy transfers to the next level; the rest is lost as heat.
History:
- Charles Elton (1927) proposed the ecological pyramid after studying the Tundra Ecosystem.
- Lindeman (1942) studied energy flow in food chains, calling it the Eltonian Pyramid.
Energy Flow:
- The sun is the main energy source.
- Plants store solar energy as food; this energy moves to consumers.
- Decomposers release some energy as heat while breaking down dead organisms.
- Energy flow is one-way-it doesn’t return to the sun.
Role of Decomposers:
- After apex consumers die, decomposers (fungi, bacteria) break down their bodies.
- They convert remains into simple compounds (like carbon) that mix with soil, air, and water.
- Plants reuse these compounds, restarting the cycle.
- Without decomposers, energy would stay trapped, and nutrients wouldn’t recycle.
Bio-Geo-Chemical Cycles
What are They?
- Bio-geo-chemical cycles are the recycling of nutrients (like carbon, oxygen, nitrogen) in an ecosystem.
- Nutrients move between biotic (living) and abiotic (non-living) parts through the biosphere (lithosphere, atmosphere, hydrosphere).
Why Cyclic?
- Unlike energy (one-way), nutrients are reused in a cycle to maintain balance in nature.
The Carbon Cycle
Process:
- Plants take in carbon dioxide (CO2) during photosynthesis to make food (carbohydrates: 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2).
- Herbivores eat plants, carnivores eat herbivores, and apex consumers eat carnivores, passing carbon along.
- During respiration, animals and plants release CO2 (C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy).
- After death, decomposers break down organisms, releasing CO2 back into the air.
Abiotic Sources:
- CO2 is also released by burning fossil fuels (coal, oil), wood, forest fires, and volcanic activity.
Impact:
- More CO2 in the air (from human activities) increases atmospheric temperature, causing global warming.
The Oxygen Cycle
Overview:
- Oxygen (O2) makes up 21% of the atmosphere and is found in water (H2O) and CO2.
- It’s a complex cycle because oxygen reacts with many elements.
Process:
- Plants release oxygen during photosynthesis.
- Animals and plants use oxygen for respiration to break down food (e.g., sugar).
- Oxygen is used in combustion (burning), decomposition, rusting, and corrosion.
- Ozone (O3) is made from oxygen in the atmosphere.
Microbes:
- Aerobes need oxygen for respiration; anaerobes don’t.
- Oxygen helps make proteins, carbohydrates, and fats.
The Nitrogen Cycle
Overview:
- Nitrogen (N2) is 78% of the atmosphere and is vital for proteins and nucleic acids (DNA).
- It’s inactive, so most organisms can’t use it directly.
Processes:
1. Nitrogen Fixation: Nitrogen gas turns into nitrates and nitrites (by lightning, industries, or microbes like rhizobium).
2. Ammonification: Decomposers release ammonia from dead organisms and waste.
3. Nitrification: Ammonia turns into nitrites, then nitrates, which plants use.
4. Denitrification: Nitrogen compounds turn back into nitrogen gas, returning to the air.
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