ECOSYSTEMS
Nothing can survive on the planet unless it is a co-operative part of a larger global life.. ….Barry Commoner
Ecology is a branch of science that deals with the relationship between living organisms and their surrounding environment. It is nothing but study of ecosystems. It investigates the interactions among organisms, populations, communities, ecosystems, and biosphere
2.1 DEFINITION AND CONCEPT OF ECOSYSTEM
An Ecosystem was defined, by A. G. Tansley in 1935, as a unit of interaction between the living (plants, animals and micro-organisms) and the non-living components of the environment (air, water and soil). It is a structural and functional unit of ecology.
Ecosystems vary greatly in size, location, climate and the elements (biotic and abiotic) that make them, and each is a functioning unit of nature. It can be as small as a pond or as big as the entire ocean and also it can be as small as a single tree or as large as entire forest. Most ecosystems are self-regulating or sustainable. Sustainability is the ability to maintain natural ecological conditions without interruption, weakening or loss of value. All the ecosystems of earth join together to form the giant ecosystem called as biosphere. The life cycle of a plant or an animal signifies the interdependence of living organisms among themselves and their surrounding environment.
2.2 STRUCTURE OF ECOSYSTEM
In general, the structure of an ecosystem has two major components as, (1) Abiotic, and (2) Biotic. These two classes of components interact with each other to create an ideal ecosystem.
1. Abiotic Component of Ecosystems : Abiotic component of an ecosystem consists of non living substances and factors which make up the structural aspects of an ecosystem are:
(i) A large number of minerals which are required by the organisms for their proper growth and are present in soil and atmosphere e.g. calcium, sodium, potassium, nitrogen etc. The deficiency of any one of these minerals results in abnormal growth and may lead to even death. Excess of these minerals is equally harmful.
(ii) Climatic factors like rain water, carbon dioxide, temperature, light, wind, humidity, pH, etc. where crop may grow most successfully.
2. Biotic Component: The living organisms like plants, animals and micro-organisms, present in an ecosystem are called biotic component. On the basis of their role in the ecosystem the biotic components can be classified into three main groups: (i) Producers, (ii) Consumers and (iii) Decomposers or Reducers.
(i) Producers (Autotrophs) : Producers are photosynthetic plants, bacteria and algae. They convert solar energy into chemical energy by chlorophyll present in them. The chemical energy is used in building bonds of organic compounds. These plants are also called transducers because they convert solar energy into chemical energy. As the green plants manufacture their own food they are known as Autotrophs. All other organisms depend upon these plants for their supply of food and are known as heterotrophs. The process by which green plants make their food using carbon dioxide and water in the presence of sun light and chlorophyll is known as photosynthesis. This transformation is shown as
6CO2 + 6H2O C6H12O6 + 6O2
(ii) Consumers (Heterotrophs) : They are animals which cannot manufacture their own food. They obtain their food from plants or other animals for their survival. The consumers are of four types, namely:
(a) Primary Consumers (Herbivore): The animals which obtain their food from green plants e.g., deer, cow, rabbit,
mouse, goat, squirrel, cattle, grasshopper etc. They are also called first order consumers.
(b) Secondary Consumers (Primary Carnivores): The animals, which live on the flesh of the primary consumers e.g., birds, frog, fox, fishes, cats, dogs, snakes etc.
(c) Tertiary Consumers (Secondary Carnivores): These are the large carnivores which eat the flesh of the secondary consumers e.g., wolves, peacock, owl, fishes etc.
(d) Top carnivores: These are the largest carnivores, which eat the flesh of the tertiary consumers and can’t be eaten up by any other animal e.g., lion, tiger and vulture.
(iii) Decomposers (Reducers): Small animals like bacteria, fungi, insects and worms act as decomposers. They breakdown the dead organic materials of producers and consumers into smaller particles and release the simple substances as the by-products that are used by plants as nutrition. The by- products produced are water, carbon dioxide, nitrogen, phosphates, sulphates etc. They are also called reducers because they are able to degrade or remove the dead bodies of organisms. The decomposers are known as saprophytes.
Primary Consumer
Grasshopper
Frog Snake
Sun Water
Grass
Hawk Fungi Food Chain Producer
Figure 2.1 : Food Chain
2.4
2.3 FUNCTIONS OF ECOSYSTEMS:
The functioning of an ecosystem refers to the ecosystem’s analysis in terms of followings:
1. Physical (Energy flow/Energy circuits)
2. Biological (Food chains, food web, ecological succession)
3. Biogeochemical (nutrient cycling) processes.
ENERGY FLOW IN AN ECOSYSTEM
Energy flows through ecosystems by means of food chains and food webs. Solar energy is absorbed by plants and made into usable chemical energy through photosynthesis. This energy is consumed by other living organisms which in turn provide a food and energy source for other organisms. It was proposed by Lindemann in 1942 that the flow of energy occurs from one trophic level to the other at the rate of 10%. During this process, a major portion (nearly 90%) of energy stored in food, is lost in the form of heat energy. This heat is radiated into the atmosphere and cannot be reused by plants and animals. This energy flow is always unidirectional as the energy released from the sun can never be returned to the sun.
Though, each plant or animal can be linked to several other plants or animals through several different linkages, these inter-linked chains can be depicted as a complex food web. This is, therefore, called the ‘web of life’ that shows that there are thousands of interrelationships in nature. The energy in the ecosystem can be depicted in the form of a food pyramid or energy pyramid or ecological pyramid.
Food Chains:
The various sequences of transfer of food energy and matter from one organism to another (through a series of action of eating and being eaten) are known as food chains. Every organism needs to obtain energy in order to live. Food chains in ecosystem help to maintain the biodiversity of nature, flow of energy and transfer of nutrients. For example, the grasshopper eats grass, the frog eats the grasshopper, the snake eats the frog, and the eagle eats the snake. At each step, energy is lost to the extent of 90%.
Types of food chains
Generally, food chains are classified in two types: 1. Grazing food chain and 2. Decomposer food chain.
1. Grazing food chain: Grazing food chain begins with green plants and algae, and from there the energy passes through various levels of consumers. Humans belong to a grazer chain as either a primary or secondary consumer usually.
2. Detritus or Decomposer food chain: Detritus food chains begin with dead organic matter called ‘detritus’, which mainly include fallen leaves, plant parts or dead animal bodies. These are consumed by insects, worms and bacteria etc. These organisms are responsible for decomposition of the waste and return of its nutrients to the environment for reuse by plants.
The interlocking pattern formed due to interaction of various food chains are known as food webs. It consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiple food chains. Each food chain is one possible path that energy and nutrients may take as they move from one organism to other through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web.
Figure 2.2 : Grazing Food Chain
Figure 2.3 : Decomposer Food Chain Food Web
Ecological succession is a process through which ecosystems tend to change over a period of time. Succession can be related to seasonal environmental changes, which create changes in the community of plants and animals living in the ecosystem. Other succession events may take much longer periods of time extending to several decades. If a forest is cleared, it is initially colonized by a certain group of species of plants and animals, which gradually change through an orderly process of community development. One can predict that an opened up area will gradually be converted into grassland, a shrub land and finally woodland and a forest, if permitted to do so without human interference. There is a tendency for succession to produce a more or less stable state at the end of the succession stages. Developmental stages in the ecosystem, thus, consist of a pioneer stage, a series of changes known as seral stages, and finally, a climax stage. The successive stages are related to the way in which energy flows through the biological system. The most frequent example of succession changes occur in a pond ecosystem where it fluctuates from a dry terrestrial habitat to the early colonisation stage by small aquatic species after the monsoon, which gradually passes through to a mature aquatic ecosystem, and then reverts back to its dry stage in
Figure 2.4 : Food Web
summer where its aquatic life remains dormant. Therefore, ecological succession describes the process by which a sequence of increasingly complex communities develops over time. The climax community is reached when succession has ended and the community has all of its characteristics. There are two main types of succession, 1. Primary, and 2. Secondary.
1. Primary Succession
Occurs when succession starts on entirely new land without any established soil - this may occur at river deltas, sand dunes or on exposed rock.
As the organisms which first colonise a region (pioneer community) die and decompose, they establish a layer of soil for future organisms to utilise.
On exposed rock, lichen and moss may initially colonise the area and provide a layer of soil for seeds to germinate, increasing species diversity.
2. Secondary Succession
Occurs when succession starts on existing soil following a natural or artificial upheaval of the primary succession.
Secondary succession occurs when the existing biota is removed from soil that is already formed - such as following a bushfire or earthquake.
During secondary succession, dominance is usually achieved by the fastest growing plants.
The cycling of matter (carbon, hydrogen, nitrogen, oxygen, phosphorus, water, calcium, iron etc.) through an ecosystem is known as biogeochemical cycle. Some important cycles are discussed in this chapter.
Water Cycle
The cycle that involves change of water into water vapour and then back to water is called water cycle. The water cycle helps to maintain the supply of fresh water on earth. This cycle describes the continuous movement of water between the earth and the atmosphere.
The process of water cycle first starts by evaporation or transpiration. The sun, which drives the water cycle, heats up water in oceans and seas. Water evaporates as water vapours into the air. This process of changing of water into water vapour is called evaporation. During transpiration plants absorb
ENVIRONMENTAL SCIENCE
water from the soil and as the water reaches the leaves, some of it evaporates and goes into the air. In the atmosphere, the water vapour cools and forms millions of tiny droplets. These droplets come together to form clouds. This process is called condensation. On further cooling, clouds lose their water as rain or snow, which is called precipitation. The flow of liquid water and ice transports minerals across the globe. A part of the rainwater percolates into the ground. This water is known as ground water. Some groundwater finds openings in the land surface and comes out as freshwater springs. Over time, the water returns to the ocean, to continue the water cycle.
Figure 2.5 : Water Cycle
Human impact on water cycle
Excessive use of pesticides and fertilisers and other pollutants in agriculture and industries lead to increase in their concentration in water which results into change of ecological balance that purifies water. Large scale urbanisation covers the land with buildings, concrete etc. This reduces infiltration of water to the ground and increases the runoff resulting into flood risks, soil erosions and landslides. Misuse of fresh water and lack of water harvesting may result in acute shortage of fresh water.
Carbon cycle
Carbon is a building block of both plant and animal tissues. In the atmosphere, carbon exists in the form of carbon dioxide (CO2). During photosynthesis, plants absorb carbon dioxide and form carbohydrates and other organic substances. In this process, plants release oxygen into the atmosphere maintaining the balance of percentage of Oxygen and Carbon dioxide. Through food chain it moves to the animals and finally all organic carbon present in
dead matter is converted into carbon dioxide by micro-organism. Some of the dead plants and animals are converted into coal, oil and natural gas being buried for millions of years into the earth. The fossil fuel produces carbon dioxide on burning. Nowadays, levels of carbon dioxide in atmosphere have increased due to excessive burning of these fossil fuels and tree leaves etc. This has created a serious problem of global warming in the world. Carbon is also stored in Ocean as carbonates and bicarbonates. These oceans exchange carbon dioxide with atmosphere, maintaining atmospheric CO2 level of 0.032 per cent. The ocean contains almost 50% more CO2 in dissolved state than the atmosphere.
Human impact on carbon cycle
Cutting of trees and plants that absorb CO2 and burning of fossil fuels like, coal and wood increase the average temperature of the earth due to release of CO2 to the atmosphere. This increase of temperature may result into global warming which can affect food production, wildlife habitats and rain pattern etc.
Oxygen cycle
Oxygen, like carbon and hydrogen, is a basic element of life. In addition, in the form of O3, ozone, it provides protection of life by filtering out the sun’s UV rays as they enter the stratosphere. In addition to constituting about 21% of the atmosphere, oxygen is present in water and rocks. It also occurs in combination as oxides in the Earth’s crust and mantle (about 30%), and as water in the oceans.
Figure 2.6 : CO2 Cycle
Environmental Science | Theory into Practice (I & II)
AUTHOR : SANJAY KUMAR BATRA, KANCHAN BATRA, HARPREET KAUR
PUBLISHER : TAXMANN
DATE OF PUBLICATION : APRIL 2025
EDITION : 8TH EDITION
ISBN NO : 9789364559331
NO. OF PAGES : 460
BINDING TYPE : PAPERBACK
DESCRIPTION
Environmental Science – Theory into Practice (I & II) is a student-friendly textbook that aligns with the National Education Policy (NEP) and the Undergraduate Curriculum Framework (UGCF). The book thoroughly covers the Years I & II Environmental Science syllabus in universities across India, including the University of Delhi, NCWEB, and SOL. It seamlessly blends theoretical foundations with practical insights, making core environmental concepts accessible and applicable.
This book is intended for the following audience:
• Undergraduate Students
• Educators and Instructors
• Competitive Exam Aspirants
• Environmental Enthusiasts
The Present Publication is the 8th Edition, authored by Dr Sanjay Kumar Batra, Dr Kanchan Batra & Prof. Harpreet Kaur, with the following noteworthy features:
• [NEP-aligned & UGCF-based] Exhaustive coverage of crucial concepts following the latest NEP guidelines
• [Complete Syllabus Coverage] Includes Years I & II modules for universities nationwide
• [Topic-focused Content] Covers vital themes such as ecosystems, resources, pollution, biodiversity, and global environmental policies
• [Up-to-date Policy Insights] Features discussions on current issues like the G20 Summit and human population growth
• [Point-wise Format] Systematic breakdown of each topic for quick revision and retention
• [Practical/Experiential Approach] Offers hands-on exercises, outreach activities, and case studies for practical application
• [Exam-oriented] Contains a variety of questions (subjective, objective, past papers) for thorough preparation
• [Case Studies & Practical Examples] Showcases both Indian and global scenarios to illustrate environmental concepts
• [Author Expertise] Benefits from decades of teaching, research, and publishing experience
• [Regular Updates] Reflects emerging challenges and current policy developments
• [Inclusive Approach & User-friendly] Clear language and format cater to diverse learners
• [Interactive Learning] Practical exercises foster critical thinking and problem-solving
