Ecosystem — Class 12 Biology Notes

Topics covered in Ecosystem

1. 1.Introduction of Ecosystem

   Short Answer

   An ecosystem is a community of living organisms interacting with each other and their non-living environment. It can be as small as a pond or as large as a forest.

   Long Answer

   An ecosystem consists of all the living things in a particular area, along with non-living components of the environment that interact with living organisms, such as air, water, and mineral soil. Ecosystems are the foundation of the biosphere and maintain the natural balance of the earth. They provide essential services like air and water purification, climate regulation, and the cycling of nutrients. Ecosystems can be classified into two main types: terrestrial (land-based) and aquatic (water-based).

   Real-life examples include a forest ecosystem, where trees, animals, insects, and microorganisms interact with each other and the environment; and a coral reef ecosystem, which includes fish, coral, seawater, and sunlight.

   Activities to understand ecosystems better can include observing a local park's flora and fauna, setting up a simple aquarium to watch aquatic life interact, or even building a terrarium to see a small-scale ecosystem in action.

   Understanding ecosystems is crucial for careers in environmental science, conservation, wildlife management, and sustainable development, as well as for informed citizenship and making choices that support the health of our planet.

2. 2.Ecosystem – Structure and Function

   Short Answer

   An ecosystem is a community of living organisms (biotic) and non-living components (abiotic) interacting as a system. These interactions involve the flow of energy and cycling of nutrients, which supports various processes like productivity, decomposition, energy flow, and nutrient cycling. For example, a pond ecosystem shows how plants, animals, and microorganisms work together with water and sunlight to create a balanced environment. Energy flows from the sun to plants (autotrophs) and then to animals (heterotrophs), with decomposers breaking down waste materials, returning nutrients to the water for plants to use again.

   Long Answer

   An ecosystem consists of all the biotic components, which include all living organisms, and abiotic components, which are the non-living elements like water, air, and minerals. These elements interact within an ecosystem to form a complex and interdependent system. The structure of an ecosystem is determined by the interaction of its biotic and abiotic components, leading to a characteristic physical structure. This includes species composition and the stratification of plants and animals at different levels.

   Ecosystem functions are critical for the balance and sustainability of the environment. These functions include:

   1. Productivity: This refers to the rate at which autotrophs (like plants and algae) convert sunlight into energy through photosynthesis. This energy is then available for use by other organisms within the ecosystem.

   2. Decomposition: Decomposers (such as bacteria and fungi) break down dead organisms and waste materials, releasing nutrients back into the ecosystem for reuse by plants.

   3. Energy Flow: Energy in an ecosystem flows from the sun to autotrophs, which convert it into usable forms for heterotrophs (animals and other consumers). Energy is transferred through the food chain but is eventually lost as heat.

   4. Nutrient Cycling: The movement and exchange of organic and inorganic matter back into the production of living matter. The nutrient cycle includes the carbon cycle, nitrogen cycle, water cycle, and more.

   Taking a pond as an example helps illustrate these concepts in a simple, understandable way. In a pond ecosystem, sunlight provides energy for algae and plants to grow (productivity). Animals like fish consume these plants or smaller animals (energy flow). When plants and animals die, decomposers break them down, returning nutrients to the water (decomposition), which plants can then use to grow (nutrient cycling). This creates a self-sustaining system where each component plays a crucial role.

   Ecosystems are essential for the survival of all living organisms, including humans, and they play a vital role in various industries such as agriculture, forestry, and fisheries. Understanding ecosystems and their functions can help us manage natural resources more sustainably and protect the environment.

3. 3.Productivity

   Short Answer

   The main reason for the low productivity of oceans compared to land is the limited availability of sunlight and nutrients in the ocean's deep waters, which restricts the growth of photosynthetic organisms, the primary producers.

   Long Answer

   In ecosystems, productivity refers to the rate at which plants (primary producers) create biomass, which is the foundation for all other life forms. This process largely depends on sunlight for photosynthesis, making it crucial for ecosystems' sustainability. Primary productivity is divided into gross primary productivity (GPP) and net primary productivity (NPP), with NPP being the actual biomass available for consumption by other organisms after the plants have used some energy for respiration.

   The lower productivity of oceans, despite their vast size, can be attributed to several factors:

   1. Light Availability: Sunlight penetrates only the top layers of the ocean, limiting photosynthesis mainly to the surface area known as the euphotic zone. Below this zone, darkness prevails, making photosynthesis impossible.
   2. Nutrient Limitation: Essential nutrients for photosynthesis, such as nitrogen, phosphorus, and iron, are often scarce in the ocean's surface waters. These nutrients are more abundant near coastlines and upwelling zones but are limited in the vast open ocean.
   3. Water Depth and Stratification: The ocean's depth and its stratified layers prevent the mixing of water, which means nutrients from the deep waters do not easily reach the surface where sunlight is available for photosynthesis.
   4. Type of Producers: The primary producers in oceans are phytoplankton, which have a rapid turnover rate but are limited by the factors mentioned above, unlike land plants which can tap into deeper soil layers for nutrients and have a larger biomass.

   Real-Life Example: Consider a forest and the open ocean. A forest has deep-rooted trees that access nutrients from various soil layers and have a dense canopy that captures sunlight efficiently. In contrast, phytoplankton in the ocean are limited to surface waters where light is available but might not always find the necessary nutrients.

   Application in Careers/Industries: Understanding productivity is crucial in fields like environmental science, marine biology, agriculture, and fisheries management. It helps in managing ecosystems, conserving biodiversity, and ensuring sustainable practices in agriculture and fisheries.

4. 4.Decomposition

   Short Answer

   Decomposition is the process by which decomposers like bacteria and fungi break down complex organic matter into simpler inorganic substances such as carbon dioxide, water, and nutrients. Earthworms, referred to as the farmer's friend, play a crucial role in this process by fragmenting detritus, thus aiding in soil aeration and nutrient recycling.

   Long Answer

   Decomposition is a fundamental ecological process where dead organic matter is broken down into simpler inorganic forms. This process is essential for recycling nutrients in ecosystems and involves several key steps:

   1. Fragmentation: Detritivores, such as earthworms, break down large pieces of organic matter into smaller particles, making it easier for decomposers to access and process the material.

   2. Leaching: Water carries soluble inorganic nutrients deeper into the soil, where they can be absorbed by plant roots or precipitate as salts, becoming temporarily unavailable to organisms.

   3. Catabolism: Bacterial and fungal enzymes degrade the detritus further into simple substances. This step is crucial for the conversion of complex organic materials into forms that can be easily assimilated by plants and other organisms.

   4. Humification: This process results in the formation of humus, a dark, amorphous material that is resistant to decomposition and acts as a nutrient reservoir in the soil.

   5. Mineralisation: Finally, some microbes decompose humus, releasing inorganic nutrients back into the soil, making them available for uptake by plants.

   Real-Life Example: Consider a fallen leaf in a forest. Over time, it undergoes fragmentation by insects and earthworms, leaching by rainwater, catabolic breakdown by microbes, and eventually becomes part of the humus-rich soil, contributing to the nutrient cycle.

   Application in Careers/Industries: Knowledge of decomposition is vital in waste management, agriculture, soil science, and environmental conservation. In agriculture, for example, understanding how to manage soil health through composting and the use of biofertilizers can enhance crop yield and sustainability.

   Decomposition is influenced by the detritus's chemical composition and environmental conditions such as temperature and moisture. Warmer, moist environments accelerate decomposition, while cold, dry conditions slow it down. This understanding helps in managing ecosystems, agricultural practices, and in mitigating climate change impacts by managing carbon storage in soils.

5. 5.Energy Flow

   Short Answer

   In ecosystems, energy flows from the sun to plants and then to consumers in a unidirectional manner. Plants, which capture a small fraction of solar energy, are the primary producers. This energy supports the entire ecosystem, moving from producers to consumers (herbivores, then carnivores) through food chains and webs. The flow of energy aligns with the first law of thermodynamics, emphasizing conservation of energy, but ecosystems still follow the second law, indicating the need for constant energy input to maintain order and support life. Decomposers play a key role in recycling nutrients back into the ecosystem, forming a detritus food chain that complements the grazing food chain.

   Long Answer

   Understanding Energy Flow in Ecosystems:

   1. 1. The Source of Energy:

      • The sun is the primary source of energy for all ecosystems on Earth, except for unique environments like deep-sea hydrothermal ecosystems. Plants and certain bacteria (autotrophs) use sunlight to make food through photosynthesis, capturing only 2-10% of the photosynthetically active radiation (PAR) from the sun.

   2. 2. Unidirectional Energy Flow:

      • Energy flows in one direction: from the sun to producers (plants) and then to various levels of consumers (herbivores, carnivores). This pattern supports the first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed.

   3. 3. Role of Producers and Consumers:

      • Producers, such as green plants in terrestrial ecosystems and phytoplankton in aquatic ecosystems, are at the base of the energy pyramid. Consumers are organisms that depend on producers (directly or indirectly) for their energy needs, classified as primary, secondary, or tertiary consumers based on their diet.

   4. 4. Food Chains and Webs:

      • Energy transfer among organisms is depicted through food chains and webs, illustrating how organisms are interdependent. Energy that is captured by a producer is either passed on to a consumer or released back into the ecosystem upon the organism's death, marking the start of the detritus food chain.

   5. 5. Decomposers and Detritus Food Chain:

      • Decomposers, including fungi and bacteria, break down dead organic matter, releasing simple inorganic materials back into the ecosystem. This detritus food chain plays a crucial role in energy flow, especially in terrestrial ecosystems where a significant portion of energy flows through decomposers.

   6. 6. Energy Flow and Thermodynamics:

      • While the first law of thermodynamics highlights the conservation of energy in ecosystems, the second law emphasizes that ecosystems require a constant energy supply to maintain structure and function against the universal trend towards disorder.

   7. 7. Trophic Levels:

      • Organisms occupy specific trophic levels based on their source of nutrition. Producers are at the first level, primary consumers (herbivores) at the second, and secondary consumers (carnivores) at the third, illustrating the structured energy flow in ecosystems.

   Real-Life Application and Careers: Understanding energy flow in ecosystems is crucial for careers in environmental science, ecology, wildlife conservation, and sustainable agriculture. It helps in designing conservation strategies, managing natural resources, and developing sustainable practices to maintain biodiversity and ecosystem health.

6. 6.Ecological Pyramids

   Short Answer

   Ecological pyramids show the relationship between organisms at different trophic levels in terms of number, biomass, or energy. There are three types: pyramid of numbers, pyramid of biomass, and pyramid of energy. These pyramids help understand how energy and matter flow through ecosystems, highlighting that energy decreases and becomes less available as it moves up the trophic levels. The pyramid of energy is always upright because energy lost as heat at each step cannot be recovered.

   Long Answer

   Ecological pyramids visually represent the relationship between different trophic levels within an ecosystem in terms of their number, biomass, or energy content. Here’s a detailed look at each type:

   1. 1. Pyramid of Numbers: This shows the number of organisms at each trophic level. It can vary in shape; usually, it's upright but can be inverted or even diamond-shaped, depending on the ecosystem.

   2. 2. Pyramid of Biomass: This illustrates the total biomass at each trophic level. Biomass is the mass of living biological organisms. This pyramid can be upright in terrestrial ecosystems, where the biomass of producers is higher than that of consumers. However, it can be inverted in aquatic ecosystems, where the biomass of consumers (like fish) exceeds that of producers (like phytoplankton).

   3. 3. Pyramid of Energy: This is always upright because it depicts the flow of energy from one trophic level to the next, with energy decreasing and becoming less available as it moves up the trophic levels. Energy is lost as heat at each step due to the second law of thermodynamics, which states that energy transformations are not 100% efficient.

   Real-life example: In a grassland ecosystem, grass (producer) has the most biomass and number, followed by herbivores like rabbits, and then by carnivores like foxes at the top. The energy pyramid for this ecosystem would show the largest amount of energy at the grass level, decreasing at the rabbit level, and the smallest amount at the fox level.

   Application: Understanding ecological pyramids is crucial for fields like conservation biology, environmental management, and sustainable agriculture, as they help in assessing the health of ecosystems, planning conservation efforts, and managing resources more sustainably.

   Activity for better understanding: Draw your own ecological pyramids based on a local ecosystem, such as a garden or a pond. Note the different organisms you can see or know exist in that ecosystem and try to classify them into producers, primary consumers, secondary consumers, etc., to understand the flow of energy and matter