An ecosystem is a functional unit of nature where living organisms (biotic components) interact with each other and their non-living environment (abiotic components).
Components of an Ecosystem
- Biotic Components:
- Producers (plants)
- Consumers (herbivores, carnivores, omnivores)
- Decomposers (bacteria, fungi)
- Abiotic Components:
- Physical factors (temperature, light, water, soil)
- Chemical factors (nutrients, pH)
Ecological Pyramids
- Pyramid of Numbers
- Pyramid of Biomass: Represents the total mass of organisms at each trophic level.
- Pyramid of Energy: Represents the energy flow through each trophic level.
Ecological Succession
- Primary Succession: The development of a community in a previously barren area.
- Secondary Succession: The development of a community in a disturbed area.
Ecosystem Services
- Provisioning Services: Benefits that directly support human life, such as food, water, and fuel.
- Regulating Services: Benefits that help maintain the ecosystem’s balance, such as climate regulation and water purification.
- Cultural Services: Benefits that contribute to human well-being and quality of life, such as recreation and spiritual values.
- Supporting Services: Essential ecosystem processes that support other ecosystem services, such as nutrient cycling and pollination.
Threats to Ecosystems
- Habitat Loss
- Pollution
- Overexploitation: Excessive use of natural resources.
- Climate Change: Altering the Earth’s climate, leading to changes in ecosystems and species distributions.
Conservation Efforts
- Protected Areas
- Sustainable Practices: Promoting sustainable agriculture, forestry, and fisheries.
- Environmental Education: Raising awareness about the importance of conserving ecosystems.
Exercise
1. Fill in the blanks.
(a) Plants are called as_________because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is_________type
(c) In aquatic ecosystems, the limiting factor for the productivity is_________.
(d) Common detritivores in our ecosystem are_________.
(e) The major reservoir of carbon on earth is_________.
Ans :
(a) Producers
(b) Inverted
(c) Sunlight
(d) Earthworms, beetles, and termites
(e) Ocean sediments
2. Which one of the following has the largest population in a food chain?
(a) Producers (b) Primary consumers (c) Secondary consumers (d) Decomposers
Ans :
The answer is (a) Producers.
In a typical food chain, producers (like plants) have the largest population. As energy is transferred through the food chain, it decreases at each trophic level due to energy loss in metabolic processes. This results in a pyramid of numbers, where the number of organisms decreases at higher trophic levels.
3.The second trophic level in a lake is
(a) Phytoplankton (b) Zooplankton (c) Benthos (d) Fishes
Ans :
The second trophic level in a lake is (b) Zooplankton.
4. Secondary producers are
(a) Herbivores (b) Producers (c) Carnivores (d) None of the above
Ans : Secondary producers are (a) Herbivores.
5. What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a) 100% (b) 50 % (c) 1-5% (d) 2-10%
Ans : The correct answer is (b) 50%
6. Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity
Ans :
(a) Grazing food chain and detritus food chain
| Feature | Grazing Food Chain | Detritus Food Chain |
| Energy Source | Living organisms (producers) | Dead organic matter (detritus) |
| Flow | Linear, from producers to consumers | Non-linear, involving decomposers |
| Primary Producers | Plants | Detritus |
| Secondary Consumers | Herbivores | Detritivores (e.g., earthworms, beetles) |
| Role of Decomposers | Less significant | Crucial for nutrient cycling |
(b) Production and decomposition
| Feature | Production | Decomposition |
| Process | Conversion of inorganic matter into organic matter | Breakdown of organic matter into inorganic substances |
| Organisms Involved | Producers (plants, photosynthetic bacteria) | Decomposers (bacteria, fungi) |
| Energy Flow | Enters the ecosystem | Recycles nutrients in the ecosystem |
| Role in Ecosystem | Essential for energy flow and biomass accumulation | Critical for nutrient cycling and maintaining ecosystem balance |
| Impact on Nutrient Availability | Increases nutrient availability | Releases nutrients back into the environment |
(c) Upright and inverted pyramid
| Feature | Upright Pyramid | Inverted Pyramid |
| Shape | Pyramid-shaped | Inverted pyramid shape |
| Trophic Levels | Number of organisms decreases at higher trophic levels | Number of organisms increases at higher trophic levels |
| Common in | Terrestrial ecosystems | Aquatic ecosystems with high productivity |
| Energy Transfer | Significant energy loss at each trophic level | More efficient energy transfer |
| Examples | Grassland ecosystem, forest ecosystem | Marine ecosystems with abundant phytoplankton |
(d) Food chain and Food web
| Feature | Food Chain | Food Web |
| Structure | Linear sequence of organisms | Interconnected network of food chains |
| Complexity | Simpler | More complex |
| Focus | Single pathway of energy flow | Multiple pathways of energy flow |
| Vulnerability | Disruption of one link can have significant consequences | More resilient to disturbances |
| Examples | Grass → Rabbit → Fox | Complex interactions among various organisms in an ecosystem |
(e) Litter and detritus
| Feature | Litter | Detritus |
| Definition | Dead and decaying plant material on the ground | Organic matter that has been partially decomposed |
| Composition | Leaves, twigs, branches, etc. | Broken-down plant and animal material |
| Role in Ecosystem | Serves as a food source for decomposers | Provides nutrients for soil and plants |
| Decomposition Rate | Varies depending on factors like temperature and moisture | Contributes to nutrient cycling |
| Impact on Ecosystems | Influences soil health and nutrient availability | Essential for ecosystem productivity |
(f) Primary and secondary productivity
| Feature | Primary Productivity | Secondary Productivity |
| Definition | The rate at which organic matter is produced by producers (autotrophs) | The rate at which organic matter is produced by consumers (heterotrophs) |
| Organisms Involved | Plants, photosynthetic bacteria, and chemosynthetic bacteria | Herbivores, carnivores, and omnivores |
| Energy Source | Sunlight (photosynthesis) or inorganic compounds (chemosynthesis) | Organic matter produced by primary producers |
| Units | g/m²/year or kcal/m²/year | g/m²/year or kcal/m²/year |
| Factors Affecting | Light intensity, temperature, water availability, nutrients | Availability of food, predation, and other factors |
| Role in Ecosystem | Foundation of energy flow | Determines the amount of energy available for higher trophic levels |
7. Describe the components of an ecosystem.
Ans :
An ecosystem is a functional unit of nature where living organisms (biotic components) interact with each other and their non-living environment (abiotic components).
Here’s a breakdown of the main components of an ecosystem:
Biotic Components
- Producers: Organisms that can produce their own food through photosynthesis (plants) or chemosynthesis (bacteria). They are the base of the food chain.
- Consumers
They can be classified as:
- Primary consumers: Herbivores that feed on plants.
- Secondary consumers: Carnivores that feed on herbivores.
- Tertiary consumers
- Decomposers
Abiotic Components
- Physical factors:
- Temperature
- Light
- Water
- Soil
- Air
- Chemical factors:
- Nutrients (e.g., nitrogen, phosphorus, potassium)
- pH
- Salinity
8. Define ecological pyramids and describe with examples, pyramids of number and biomass.
Ans :
Ecological pyramids are graphical representations that show the distribution of energy, biomass, or numbers of organisms at different trophic levels in an ecosystem. They help visualize the flow of energy and matter through a food chain.
Pyramid of Numbers
- Definition: A pyramid that shows the number of organisms at each trophic level.
- Example: In a grassland ecosystem, the pyramid of numbers is often upright, with a large number of producers (grass) at the base, followed by fewer primary consumers (rabbits), and even fewer secondary consumers (foxes).
Pyramid of Biomass
- Definition: A pyramid that shows the total mass of organisms at each trophic level.
- Example: In a marine ecosystem, the pyramid of biomass can be inverted, with a small number of large predators (e.g., whales) at the top and a large mass of primary producers (phytoplankton) at the base. This is due to the rapid turnover rate of phytoplankton and the relatively long lifespan of larger predators.
9. What is primary productivity? Give brief description of factors that affect primary productivity.
Ans :
Primary productivity is the rate at which organic matter is produced by autotrophs (organisms that can produce their own food) in an ecosystem. It is a key measure of the efficiency of energy transfer and nutrient cycling in an ecosystem.
Factors that affect primary productivity:
- Light: The availability of sunlight is essential for photosynthesis, the process by which plants and other autotrophs produce organic matter. More sunlight generally leads to higher primary productivity.
- Temperature: Optimal temperatures for plant growth vary depending on the species.
- Water: Water is essential for plant growth and photosynthesis. Adequate water availability is crucial for high primary productivity.
- Nutrients: The availability of these nutrients can limit primary productivity in certain ecosystems.
10. Define decomposition and describe the processes and products of decomposition
Ans :
Decomposition is the process by which organic matter is broken down into simpler inorganic substances by decomposers. Decomposers, such as bacteria, fungi, and detritivores, play a crucial role in nutrient cycling and the decomposition of dead organisms and waste products.
Processes of decomposition:
- Fragmentation
- Lysis: The rupture of cell membranes and the release of cellular contents.
- Hydrolysis: The breakdown of complex organic molecules into simpler molecules by the addition of water.
- Mineralization: The conversion of organic matter into inorganic nutrients, such as nitrogen, phosphorus, and carbon.
Products of decomposition:
- Inorganic nutrients: Released into the soil, where they can be absorbed by plants.
- Carbon dioxide: Released into the atmosphere, where it is a key greenhouse gas.
- Water: Released into the environment.
- Simple organic compounds: May be produced as intermediate products during decomposition.
11. Give an account of energy flow in an ecosystem.
Ans :
Energy Flow in an Ecosystem
Energy flows through an ecosystem in a linear fashion, from producers to consumers and ultimately to decomposers. This is often represented by an ecological pyramid.
- Producers: Plants and other photosynthetic organisms capture solar energy and convert it into chemical energy stored in organic molecules (glucose). This is called primary production.
- Primary Consumers: Herbivores consume producers, obtaining energy from the organic molecules they ingest.
- Secondary Consumers: Carnivores that eat primary consumers obtain energy from their prey.
- Tertiary Consumers: Carnivores that eat secondary consumers.
Decomposers: Bacteria, fungi, and other decomposers break down dead organisms and waste products, releasing nutrients back into the ecosystem.
