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FSc Notes Biology Part 2 Chapter 25 Ecosystem Notes

FSc Notes Biology Part 2 Chapter 25 Ecosystem Notes

Environmental Biology

“The effect of the environment on the organism is called Environmental biology or Ecology.” OR “Ecology is the study of relationship between the organisms and their environment.” “Okios” means “Home life or place of living” and “logos” means “Study” The term Ecology was first introduced by a zoologist Reiter in 1885. Ecology was first of all fully defined by Ernst Hackel in 1869. As living organisms are of two types, plants and animals ecology is divided into Plant Ecology and Animal Ecology.

Levels of Ecological organization

Various levels of ecological organization are as under:
“A group of individual of the same species that live in the same area and share the same resources.” The word population has been taken from “populous” which means “people” Population size is the total number of organisms living in an area.
A group of different species of plants and animals living together in the same place is called Community. A community is composed of different populations. A forest with various trees, shrubs, herbs, animals, insects, birds, and micro – organisms is considered as a community.
A System in which living organisms and non-living live together and exchange materials between them is called Ecosystem”. The word ecosystem was first used by Tansely in 1935. Ecosystem is the basic structural and functional unit of ecology.
Ecosystem occupying broad geographical region is called Biome. Biome is characterized by distinctive vegetation as grasses, conifers or broad leaved trees etc. some major biomes of the world are forest, grassland, desert, tundra etc. combined biomes of earth together form the planetary ecosystem. It extends about 10Km into the atmosphere and also the same depth in the oceans. It consists of three parts. (i) Atmosphere (air) (ii) Lithosphere (earth) (iii) Hydrosphere (water).
Everything around the living organisms such as light, temperature and soil which affect their life is called Environment. The environment provides food, water and shelter to the organisms.
Specific locality with a particular set of environmental conditions where organisms live is called habitat.
The ecological role that a species plays with in a community is called Niche.” The term Niche was first used by Jospeh Grinnell in 1917. The habitat and the niche are closely related. Niche is the profession and habitat is the address of an organisms.

Approach to Ecology

There are two approaches to ecology
  1. Autecology
  2. Syechology
The study of relationship of a single population to its environment is called Autecology. The term Autecology was introduced by Schroter in 1896. It is also called population ecology. It involves the study of individual organisms their life histories and their relationship to their environment.
The study of the relationship of different communities to their environment is called Syechology.” It is also called community ecology. This term was also introduced by Schroter. In this case we study the structure, composition, development and distribution and their relationship to their environment.

Components of Ecosystem

Ecosystem consists of two components:

Abiotic Component:

Abiotic components are the non-living materials of ecosystem. These are the , light, water, Temperature, Atmosphere, Fire, Soil, Inorganic material, Topographic factor, Gravity.
Sunlight is the source of energy for all ecosystems. Light affects the living organisms in three
ways i.e. quality, intensity and duration of light.
Light influences the growth and distribution of organisms. Of the total light reaching the earth’s surface, only 1% is used in photosynthesis. Light also control the structural and behavioural characteristics of the organisms. In lower organism the locomotion is influenced by light. Plants growing in weak light do not develop chlorophyll. Light duration affects the growth and flowering. Light also play important role in animals migration. Light also determine the periods of activity of animals. According to tolerance to light intensity plants are divided into two groups.
  1. Heliophytes: Heliophytes are the light loving plants. They grow best in high intensity of light. They have thick cuticle, more branches with short internodes.
  2. Sciophytes: They are shade loving plants. They grow best in dim light. They have thin cuticle, few branches with long internodes.

Water is essential for all living organisms on land. It covers more than 70% of the earth’s surface. Water acts as a universal solvent. It is used as a raw material in photosynthesis. It is most essential for almost all the metabolic chemical reactions in the body. On the basis of availability of water the plants are divided into three groups.
  1. Hydrophytes: Grow in or near water e.g. Thypha.
  2. Mesophytes: Grow in areas with moderate water e.g. Crops
  3. Xerophytes: Grow in dry and arid conditions e.g. Acacia.
Protozoa have contractile vacuoles to get rid of excess of water. Fished have water proof exoskeleton which prevent absorption of water through body surface.

Temperature controls the growth, and distribution of animals and plants. life functions generally within a temperature range of 10 – 45 degree Celsius. At 0 degree Celsius water freezes in the cells and the cells rupture. Above 45 degree Celsius the protoplasm, proteins and enzymes denature. The temperature at which the activities of the organisms are at maximum is called optimum temperature is called thermal migration. At high temperature some animals become inactive called Aestivation. At low temperature some animals become inactive called Hibernation. On the basis of temperature tolerance plants are divided into Megatherm, Microtherm and Mesotherm. Temperature also determines the breeding seasons of most animals.

Atmosphere and Wind:
Atmosphere is the gaseous envelop surrounding the earth. It contain nitrogen (78%) Oxygen (21%) Co2 (0.03%). Plants take nitrogen from the soil in the form of nitrates. CO2 is used in photosynthesis as raw material. Oxygen is required for respiration of organisms. Fast moving atmosphere is called wind. Wind leads to excessive transpiration which produces desiccation. It also causes soil erosion and uprooting of trees. Wind also help in pollination, dispersal of sees and fruits.

Soil is the upper layer of earth’s crust. It consists of two layers i.e. topsoil and subsoil. Top soil is the surface soil which is 20 – 30 cm thick. It is dark brown in colour due to the presence of humans. Topsoil supply nutrients to the plants. Subsoil lies below the topsoil. It is light brown in colour and contains large rock particles. Soil which is good for agriculture is called loam. Soil is important to plants because it provide Anchorage water and nutrients. Air to roots for respiration.

Inorganic Nutrients:
It includes nitrates, phosphates and various other salts. A small portion of these nutrients available in solution form. Most of them remain reserved in rocks. Organism depends on these nutrients for their body maintenance.

Behavior and structure of earth’s surface like, hill, slope, elevation is called Topography. Topography has no direct effect on organisms. But it modifies other factors like, atmosphere, temperature. Slope affects the drainage and stability of soil. Steeper slope support less vegetation.

At higher altitudes:
Radiation increases, Atmosphere is thin, Temperature is low, Rainfall is high, and Winds are strong.

Gravity is the most constant factor affecting an ecosystem. Plants and animals have some structural modification to overcome the pull of gravity. It acts as an external stimulus in the grow response of plants. Root grows towards gravity while stem grow away from gravity. Xylem cells in plant lifting water to the upper parts of the plants. Birds have light bones and wings to overcome the gravitational pull.

Biotic Components

Biotic components are the living organisms of ecosystem. These components are of three types:
  1. Producers
  2. Consumers
  3. Decomposer
Green plants are the producers. They prepare their own food and are called Autotrophs. Phytoplanktons are the producers of aquatic ecosystem. Rooted plants are producers of land ecosystem. A part of this prepared food is utilized by plant themselves. Remaining part is utilized by consumers.
(ii) Consumers:
Consumers are mostly animals which get their food from producer. Consumers are all heterotrophs. Consumers are of the following three types:
  1. Primary Consumers: Primary consumers feed directly on green plants. They are also called herbivores. The primary consumers of land ecosystem are insects, cow, rabbits, sheep, and goats. The Primary consumers of aquatic ecosystem are mollusks, crustaceans (arthropods) and some fishes.
  2. Secondary Consumers: They feed on herbivores and green plants. Secondary consumer which feed on herbivores is called carnivores e.g. lion, tiger, hawk etc. some consumers eat both herbivores, carnivores and green plants and are called Omnivores.
  3. Tertiary Consumers: These are the top carnivores. They get their good from primary and secondary consumers. e.g. lion, tiger, for, hawks etc.
(iii) Decomposers:
They are also called saprophytes or scavengers. They get their energy from the decomposition of dead bodies of plants and animals. Decomposers act as cleaners of ecosystem. Decomposers help in the recycling of nutrients in the ecosystem. Bacteria and fungi are chief decomposers of ecosystem.

Cycling of Nutrients in Ecosystem

The cyclic movements of chemical elements of the biosphere between the organism and the environment are called Biogeochemical cycles.” The chemical elements essential for life in living organisms are called biogenic elements or nutrients elements. These are of two types.
  1. Macronutrients: These nutrients are needed in large amount like, water, oxygen, nitrogen, hydrogen.
  2. Micronutrients: these nutrients are needed in very small amount like , zinc, iron, molybdenum etc.

Nitrogen Cycle

The cyclic movement of atmospheric nitrogen from air into the soil and back from the soil into the atmosphere is called nitrogen cycle. In the atmosphere nitrogen occurs in three different states:
  1. Dinitrogen molecule: e.g. N2
  2. Nitrogen oxides: e.g. nitrite (No2) and nitrates (No3)
  3. Reduced nitrogen: e.g. ammonia (NH3) and ammonium (NH+
  4. The chief reservoir of nitrogen is the atmosphere. In air the nitrogen is about 78%. But it can not be used in free state by plants or animals. It cannot be functional unless it is converted into NH3. Most plants absorb nitrogen from oil as NO-

Stages of Nitrogen Cycle:

Nitrogen cycle complete in the following way:
  1. Decomposition of dead bodies.
  2. Nitrogen fixation
  3. Thunder storms
  4.  Dentirification

Decomposition of dead bodies:
Dead bodies are decomposed by fungi and bacterial into simpler compounds. There are two steps in this process.
Ammonification: The process in which the nitrogenous compounds are decomposed by fungi and bacteria into ammonia (NH3) or ammonium ion (NH+4) is called Ammonification. These micro organisms use the protein and amino acid.
Nitrification: The conversion of ammonia and ammonium ion into nitrites and nitrate by the actively nitrifying bacteria is called Nitrification. Two groups of nitrifying bacteria are responsible for nitrification.
  • Nitrosomonas: converts ammonia to nitrites.
  • Nitrobacteria: converts nitrites into nitrates.
Although the plants can utilize ammonium directly, nitrate is the form in which most nitrogen moves from the soil into the roots.

Nitrogen Fixation:
The conversion of atmospheric nitrogen into simpler compounds, nitrite and nitrate with the help of some living organisms is called Nitrogen Fixation. The organisms which help in nitrogen fixation are rhizobium bacteria and blue green algae. There are two types of nitrogen fixation.
  • Non – symbiotic nitrogen fixation
  • Symbiotic nitrogen fixation.
Non-Symbiotic nitrogen fixation:
This type of nitrogen fixation is carried out by some bacteria like Azotobacter and Clostridium, and Nostoc. These organisms live freely in the soil. They do not form any useful combination with plants.
Symbiotic nitrogen fixation:
This types of nitrogen fixation is carried out by the microorganisms like Rhizobium that live symbiotically in the root nodules of leguminous plants.

Thunder Storms:
During thunder storm nitrogen combines with oxygen to form nitric oxide. This nitric oxide dissolved in water forming nitrates and nitric acids. These acids are transferred to the soil by rain. In the soil these acids combine with mineral salts to form nitrates which are used by the plants.

Some soil bacterial (pseudomonas) in the absence of oxygen break down nitrates releasing nitrogen back into the atmosphere, this is called denitrification. Oxygen released in the process is used by bacteria in respiration.

Nitrogen Depletion And Its Remedies

The lose of nitrogen from the soil is called nitrogen depletion. It is lost due soil erosion and activity of some bacteria. Nitrogen depletion also occurs by the continuous production of crops in the soil.
Following are few important measures to overcome the shortage of nitrogen in the soil:
  • Nitrogen fertilizers should be added to the soil.
  • Use of organic manure.
  • Crop rotation should be practiced.
  • In rice fields Nostoc are added.
  • Legumes crops (pea, beans etc) should be grown.
  • Farmland may not be cultivated for a few years.

Energy Flow in The Ecosystem

Energy is required by all organisms for their vital activities. Sun is the main source of energy for all ecosystems. Green plants trap the sun energy and convert it to food. During this process some of the energy is lost as heat during respiration. Plants are eaten by herbivores and the energy is transferred to them. Here some energy is also lost as heat during metabolic process. Only a small energy is stored in the body of herbivores. Then a sequence of eating and being eaten starts. Finally the energy reaches the top consumers. Top consumers die and are decomposed by bacteria and fungi. A small amount of energy is used by decomposes and rest is lost as heat to the environment. Thus at each step in the transfer of energy from one organisms to another a large amount of energy it lost. This energy does not return to the living organisms. The organism must obtain fresh supply of energy for its use. In ecosystem the flow of energy occur in only one direction and does not complete a circle.

Interaction And Interdependence of Organism

Living world needs a regular flow of energy. Organisms interact and inter-dependence between organisms may be:
Useful to both partners
One partner get benefit and other is harmed.
Beneficial for one partner and other remain unaffected.
Interaction and interdependence between organisms may be of following type:
  • Predation
  • Parasitism
  • Symbiosis
  • Grazing

When members of one species eat those of another or same species is called Predation. An animal that preys on other animals for food is called predator. The animal that is caught and eaten is called prey. A predator animal is often larger than its prey. Predators select food on the basis of size and strength of prey. If prey population increases it will support more predators. If the prey is killed in large number, the predator’s population will also decrease. Predation maintain the biological fitness of the two populations and stability of ecosystem. The presence of prey in an area without its predator is disastrous.

Parasitism is a one sided relationship between two dissimilar organisms in which one is benefited and the other is harmed. The organism which get food, and shelter is called parasite. The organisms which provide food and shelter is called host. In parasitism the weak takes benefit from the strong. The parasite may or may not harm the host. Diseases in living organism caused by parasites are called infestation. Most parasite infect only a specific host. Parasite may be:
  • Viral Parasites: Such as plant and animals viruses.
  • Microbial Parasites: Such as bacteria, fungi, protozoan etc.
  • Phytoparasites: Such as plant parasites.
  • Zooparasites: Such as animal parasites.
  • Ectoparsites: They live outside the host’s body e.g. leeches
  • Endoparasites: They live inside the host’s body e.g. liver, fluke.
  • Partialparasites: They spend only a part of their life cycle as parasite.
  • Permanent parasites: They spend their entire life as parasite.

Symbiosis is an association between two dissimilar organisms which live together for mutual benefit. Symbiosis means “living together” This type of association may be continuous or transitory obligate or facultative. There are two types of symbiosis.
  1. Mutualism
  2. Commensalism
Mutualism: The symbiotic association in which both the partners get benefit and neither can survive without the other is called Mutualism.
Following are some of the examples of mutualism.
  1. Root Nodules: in root nodules of legume plants nitrogen fixing bacteria (Rhizobium) live. The bacterial fix atmospheric nitrogen for the roots. The root provide food and shelter to the bacteria.
  2. Pollination: Certain insects such as bees and butterflies get food from the nectar of plants and in return bring about cross pollination.
  3. Lichens: The symbiotic association between algae and fungi is called lichen. The fungus absorbs water and minerals. Algae prepared food by photosynthesis. Neither of the two can grow independently.
  4. Cellulose Digestion: A flagellate protozoan Trichonympha lives in the intestine of wood eating termites where it digests cellulose. The protozoan gets food and shelter from termite. A similar relationship occurs between cow and bacteria.
Commensalism: In this type of relationship only one partner get benefit while the other member neither benefited nor harmed. Following are same of the examples of commensalism.
  1. Epiphytes: Epiphytes are the plants growing on other plants. They use other plants only as support. Tree is neither harmed nor benefited.
  2. Barnacles and whales: Barnacles attached to the backs of whales and turtles, get a free ride to better feeding places.
  3. Crabs and Sea mussels: certain crabs live in the mantle cavities of sea mussels for protection.
  4. Sharks and Remoras: Remoras are small fish which attached to the body of shark. As the shark feeds, the remoras pick up the scraps. The remoras benefit from this relationship the shark is not affected at all.
Grazing: Grazing is the relationship between herbivores and the grasses of grassland. Animals that feed on grasses are called grazers. Cows, sheep, horses etc, are all grazers. Significance: Grazing is useful as well as harmful. Some of its effect is as under. Grazing help is shaping the grassland ecosystem. Grazing removes the seeding and reduces the competition in grassland. It provides secondary productivity like meat and milk from the sheep, goat etc. Overgrazing destroys the grassland ecosystem and converts it to desert. Trampling by grazing animals make the soil compact and makes it unsuitable for vegetation.


A long term process of gradual changes in the community structure over a period of time is called Succession. The term succession was first used by Hult in 1885. Cowles in 1899 laid the foundation of successional studies. Clements elaborated the principles and theory of succession. Succession is unidirectional process. Succession is initiated by hardy invaders called pioneers. These species are gradually replaced by others. In succession the final stable and mature community is called climax.

Causes of Succession:
The causes of succession may be:
  • Climatic: Such as flood, fire, erosion, volcanic activity.
  • Biotic: such as activity of organisms like overgrazing, human activities.
All these causes destroy the existing populations in an area.

Types of Succession:
The succession may be of the following two types.
  1. Primary Succession
  2. Secondary Succession
Primary Succession:
The succession occurring for the first time on an originally bare area is called primary succession. It start on bare rock, river delta, glacial debris etc.
Secondary Succession:
The kind of succession occurs in the area where the vegetation has been destroyed is called secondary succession. It usually starts after forest fire, cutting of the trees, flood and erosion. The pace of the secondary succession is faster than the primary succession. Depending on the habitat succession may be.

Hydrosere: Succession that starts in aquatic environment
Mesosers: Succession that starts in area with sufficient moisture.
Xerosere: Succession that starts on a dry soil or habitat.

Written by: Asad Hussain