2.1 Energy Flow in an Ecosystem
An ecosystem consists of several communities that interact with one another and with non-living components in an environment.
Producers, Consumers, and Decomposers
- Producers: Autotrophic organisms (mainly green plants) that produce their own food through photosynthesis using sunlight.
- Primary Consumers: Herbivores or omnivores that feed on producers (e.g., caterpillars, rabbits).
- Secondary Consumers: Carnivores or omnivores that feed on primary consumers (e.g., frogs, small birds).
- Tertiary Consumers: Apex carnivores that feed on secondary consumers (e.g., eagles, snakes, tigers).
- Decomposers: Microorganisms (fungi, bacteria) that break down dead complex organic materials into simpler substances to be absorbed by plants.
Food Chains and Food Webs
Energy flows through an ecosystem from producers to consumers. A food chain shows the linear transfer of energy, while a food web consists of interconnected food chains.
Energy Loss: About 90% of energy is lost at each trophic level through heat, respiration, excretion, and movement. Only about 10% of energy is passed to the next trophic level.
2.2 Nutrient Cycles in an Ecosystem
Nutrients are continuously recycled through ecosystems via biological and physical processes.
1. Water Cycle
Water evaporates from bodies of water and transpires from plant leaves (evapotranspiration) to form clouds (condensation), returning as precipitation (rain). Organisms consume water and release it back through respiration, excretion, and transpiration.
2. Carbon and Oxygen Cycles
- Processes that consume oxygen and release carbon dioxide: Respiration, combustion of fossil fuels, decomposition, and rusting.
- Processes that consume carbon dioxide and release oxygen: Photosynthesis (the primary pathway balancing atmospheric carbon and oxygen).
Human Activities Disturbance to Nutrient Cycles
- Uncontrolled logging and deforestation reduce carbon dioxide absorption.
- Excessive burning of fossil fuels increases atmospheric carbon dioxide, leading to the greenhouse effect and global warming.
- Overuse of fertilizers causes water pollution and eutrophication.
2.3 Species, Population, Community, Habitat, and Ecosystem
Ecological Definitions
- Species: A group of similar organisms that can interbreed to produce fertile offspring.
- Population: A group of organisms of the same species living in the same habitat at the same time.
- Community: Several populations of different organisms living and interacting together in a shared habitat.
- Habitat: The natural living place or environment of an organism.
- Ecosystem: A community of organisms interacting with each other and their non-living environment (abiotic factors).
Interactions Between Organisms
| Interaction Type |
Description |
Example |
| Prey-Predator |
One organism (predator) hunts and eats another (prey). |
Eagle and mouse, Lion and zebra |
| Symbiosis: Mutualism |
Both organisms benefit from the relationship (+/+). |
Sea anemone and clownfish, Lichen (alga + fungus) |
| Symbiosis: Commensalism |
One organism benefits while the other is unaffected (+/0). |
Remora fish and shark, Bird's nest fern on trees |
| Symbiosis: Parasitism |
One organism (parasite) benefits while harming the host (+/-). |
Tapeworm in human intestine, Flea on dog |
| Competition |
Organisms compete for limited resources (food, space, mates). |
Plants competing for sunlight, Lions competing for prey |
| Biological Control |
Using natural predators or parasites to control pest populations instead of chemicals. |
Owls used in oil palm plantations to hunt rats |
2.4 Role of Humans in Maintaining Balanced Ecosystems
A balanced ecosystem is one where the interactions between living organisms and non-living factors remain stable without human interference or environmental degradation.
Effects of Human Activities
- Deforestation: Causes soil erosion, flash floods, habitat loss, and global warming.
- Industrial Pollution: Causes acid rain, water pollution, and air contamination.
- Overfishing: Disrupts aquatic food chains and depletes marine populations.
Steps to Solve Environmental Issues
- Enforcing environmental laws and timber logging quotas.
- Reforestation (replanting trees) and establishing forest reserves.
- Practicing 3R (Reduce, Reuse, Recycle).
- Promoting public education on environmental protection.