Maharashtra Board Class 11 Environmental Science Chapter 2 Ecosystems PDF Download

2: Ecosystems

2.1 Scope of Ecology

2.2 Structure And Functions Of Ecosystem

2.3 Types Of Ecosystems

2.4 Dynamics Of Ecosystem

2.5 Ecosystem Services

2.6 Species Interdependence And Interactions

2.7 Ecological Succession

To understand the proper structure and functions of various kinds of ecosystem, it is very essential to understand the scope of ecology.

The word ecology is derived from two Greek words i.e. "Oikos" meaning house and "ology" means to study. Thus, ecology is the study of organisms in their natural home i.e. habitat. It is generally defined as the study of plants and animals in reciprocal relationship with their environment.

2.1 Scope Of Ecology

Ecology deals with the interrelationship between the organisms and its environment. Therefore the scope of ecology becomes wide due to variable environmental conditions as well as abundance of plants and animals. The main function of ecology is to show the general principle under which the natural community and its various components operate. These may be applied for the interpretation of various activities of particular plants or the animals in a given region. The biota (plants and animals) of an area can be easily identified and counted. An understanding of ecology is useful for conservation of air, water, soil, wildlife etc. Ecology has practical applications in the field of agriculture, biological survey, forestry and fisheries.

Teacher's Note

Ecology helps us understand how all living things depend on each other. In your garden at home, you can see how bees visit flowers, birds eat insects, and plants grow from soil.

Exam Trick

Remember: Eco = home, ology = study. So Ecology = study of home. Just like your home has a kitchen, bedroom, and living room, an ecosystem has producers, consumers, and decomposers.

Points To Remember

Ecology is the study of organisms in their habitat.
It helps us conserve air, water, soil, and wildlife.
Ecology is useful in agriculture and forestry.
The biota means all plants and animals in an area.

2.2 Structure And Function Of Ecosystems

In nature several communities of organisms live together and interact with each other as well as with their physical environment as an ecological unit. An ecosystem is a functional unit of nature encompassing complex interaction between its biotic (living) and abiotic (nonliving) components. For example aquatic systems such as a pond, lake, river, estuary, ocean. The terrestrial ecosystems includes forest, grassland, agricultural field, desert etc.

The structure of ecosystem includes two kinds of components.

(a) Abiotic components

(b) Biotic components

Components Of Ecosystem

Teacher's Note

Every ecosystem has living and non-living things working together. In a forest, trees are living things and soil is a non-living thing, but they need each other to survive.

Exam Trick

Remember: Abiotic = A for "air, all non-living things". Biotic = B for "beings, all living things". A and B together make an ecosystem.

Points To Remember

Abiotic components are non-living things like water, air, and sunlight.
Biotic components are living things like plants, animals, and microorganisms.
Producers make their own food through photosynthesis.
Consumers eat plants or other animals for food.
Decomposers break down dead things and return nutrients to soil.

(a) Abiotic Components (Nonliving)

The abiotic component can be grouped into following three categories:

(i) Physical Factors: Sunlight, temperature, rainfall, humidity and pressure. They sustain and limit the growth of organisms in an ecosystem.

(ii) Inorganic Substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulphur, water, rock, soil and other minerals.

(iii) Organic Compounds: Carbohydrates, proteins, lipids. They are the building blocks of living systems and therefore, make a link between the biotic and abiotic components.

(b) Biotic Components (Living)

(i) Producers: The green plants manufacture food for the entire ecosystem through the process of photosynthesis. Green plants are called autotrophs, as they absorb water and nutrients from the soil, carbon dioxide from the air, and capture solar energy for this process.

(ii) Consumers: They are called heterotrophs and they consume food synthesized by the autotrophs. Based on food preferences they can be grouped into three broad categories.

a) Herbivores feed directly on plants (e.g. cow, deer and rabbit etc.)

b) Carnivores are animals which eat other animals (eg. lion, cat, dog etc.)

c) Omnivores organisms feed upon both plants and animals (e.g. human beings, pigs and crows).

(iii) Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in recycling of nutrients. They are also called detritivores or detritus feeders.

Functions Of Ecosystems

Ecosystems are complex dynamic entities which include abiotic and biotic components. They perform various functions. These are:

(i) Energy flow through food chain

(ii) Nutrient cycling (biogeochemical cycles)

(iii) Ecological succession or ecosystem development

Ponds, lakes, marshlands, grasslands, deserts and forests are examples of natural ecosystems. Many of you have seen a grassland, a garden and an agricultural field in your neighborhood. These are examples of man made ecosystems.

Teacher's Note

In your school garden, you can see all three types of organisms. Plants are producers, insects and birds are consumers, and fungi in soil are decomposers working together.

Exam Trick

Remember: Producers make food, Consumers eat food, Decomposers recycle everything. This is like a perfect team in your home.

Points To Remember

Producers are green plants that make their own food.
Consumers are animals that eat plants or other animals.
Decomposers break down dead matter and recycle nutrients.
Herbivores eat only plants, carnivores eat only animals, omnivores eat both.
Ecosystems have three main functions: energy flow, nutrient cycling, and succession.

2.3 Types Of Ecosystems

Ecosystems are broadly classified as follows:

(I) Natural Ecosystems

(II) Man Made Ecosystems

(I) Natural Ecosystems

Natural ecosystem are totally dependent on solar radiation e.g. forests, grasslands, oceans, lakes, rivers and deserts. They provide food, fuel, fodder and medicines.

Pond Ecosystem

A pond is an example of natural ecosystem. It is convenient to study its basic structure and functions. It works on solar energy and maintains its biotic community depending on the seasons. If you collect a glass full of pond water or a scoop full of mud from bottom of the pond, it consists of a mixture of plants, animals, microorganisms, inorganic and organic materials.

The following components are found in a pond ecosystem.

(a) Abiotic (Non Living) Components Of Pond Ecosystem

(i) Sunlight: Solar radiation provides energy that controls the entire system. Penetration of light depends on transparency of water, amount of dissolved or suspended particles in water and the number of plankton. On the basis of extent of penetration of light a pond can be divided into euphotic (eu=true, photic = light), mesophotic and aphotic zones. Plenty of light is available to plants and animals in euphotic zone. No light is available in the aphotic zone.

(ii) Inorganic Substances: These are water, carbon, nitrogen, phosphorus, calcium and a few other elements like sulphur depending on the location of the pond. O\(..._{2}\) and CO\(..._{2}\) are in dissolved state in water. All plants and animals depend on food and exchange of gases in the water. Other inorganic salts are held in reserve in bottom sediment and inside the living organisms.

(iii) Organic Compounds: The commonly found organic matter in the pond area are amino acids, humic acids and the breakdown products of dead animals and plants. They are partly dissolved in water and partly suspended in water.

(b) Biotic (Living) Components Of Pond Ecosystem

(1) Producers Or Autotrophs: Synthesize food for all the heterotrophs of the pond. They can be categorized into two groups:

(a) Floating Microorganisms: Small green plants (algae) and blue green algae are called phytoplanktons ("phyto" = plants, "plankton" = floating). They are microscopic organisms. Sometimes they are so abundant in pond that they impart green colour to pond water. Such a condition is called algal bloom or water bloom e.g. Spirogyra, Ulothrix, Cladophora, Diatoms, Volvox.

(b) Rooted Plants: These are arranged in concentric zones from periphery to the deeper layers. Three distinct zones of aquatic plants can be seen with increasing depth of water in the following order:

i) Zone Of Emergent Vegetation: e.g. Typha and Sagittaria

ii) Zone Of Rooted Vegetation With Floating Leaves: eg. Nymphaea

iii) Zone Of Submergent Vegetation: eg. All under water vegetation like Hydrilla, Vallisnaria etc.

(2) Consumers (Heterotrophs): These are the animals which feed directly or indirectly on autotrophs eg. Tadpole, snails, some variety of fish.

Pond animals can be classified into the following groups

(a) Zooplanktons are floating animals. Cyclops, Cypris, Daphnia etc.

(b) Nektons are the animals that can swim and navigate eg. fishes

(c) Benthic Animals are the bottom dwellers e.g. beetle, mites, molluscs and some crustaceans.

(3) Decomposers: They are distributed throughout the pond, but are most abundant in the sediment. There are bacteria and fungi. (Rhizopus, Penicillium, Cladosporium) found at the bottom of the pond.

Teacher's Note

A pond near your home is a complete ecosystem. Green plants give food, fish and insects are consumers, and bacteria at the bottom are decomposers breaking down dead things.

Exam Trick

Remember: In a pond, phytoplankton floats like tiny plants, zooplankton floats like tiny animals, nektons swim like fish, and benthic animals live at the bottom like snails.

Points To Remember

Pond has producers like algae and water plants.
Consumers in pond include fish, insects, and tadpoles.
Decomposers are bacteria and fungi at the bottom.
Sunlight, water, and nutrients are non-living parts of pond.
Pond ecosystems depend on sunlight for energy.

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