Maharashtra Board Class 12 Biology Chapter 14 Ecosystems and Energy flow PDF Download

Ecosystems And Energy Flow

An ecosystem is a self regulatory and self sustaining structural and functional unit of nature (biosphere). It contains both biotic and abiotic components. Biotic components interact with each other and also with the surrounding environment. Tansley (1935) coined the term ecosystem. Ecosystems vary greatly in size from a small pond to large oceans or small farmland to village. Entire biosphere can be considered as one global ecosystem, made up of many local ecosystems. Since the earth ecosystem is too big and too complex to be studied, it is divided into two basic categories, viz. terrestrial and aquatic. Forest, grassland and desert are the types of terrestrial ecosystems while lakes, wetlands, rivers and estuaries are the types of aquatic ecosystems. The ecosystems can also be classified as Natural ecosystems and Artificial ecosystems. Natural ecosystems do not require any human inputs, in other words they are self-sustainable. Artificial ecosystems e.g. a farm land, a fish tank or even a large pond used for rearing fish, require constant input in terms of energy or materials.

In this chapter, we will study and analyse the structure of the ecosystem, in order to appreciate the input (productivity), transfer of energy (food chain/web, nutrient cycling) and the output (degradation and energy loss). We will also look at the relationships, chains and webs that are created because of the energy flows within the system.

14.1 Ecosystem: Structure And Function

We have already studied the various biotic and abiotic components of the environment. We know that all these biotic and abiotic components influence each other. Let us now look at these components with an integrated approach and see how the flow of energy takes place in ecosystem. Interaction of biotic and abiotic components, results in a physical structure that is characteristic for each type of ecosystem. Identification and enumeration of plant and animal species of an ecosystem gives its species composition.

Biotic and abiotic components differ as the locations vary in space and time. The variation due to space results in spatial pattern. There are two types of spatial patterns. viz. Stratification and Zonation.

Vertical distribution of different species of plants and animals occupying different levels, is known as stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layer. Similar stratification is also observed in the open seas as epipelagic, mesopelagic, bathy-pelagic and benthic zones.

Teacher's Note

Stratification is like different floors in a building. In a forest, tall trees are on the top floor, shrubs in the middle, and small plants on the ground floor, just like how different shops are on different floors in a mall.

Exam Trick

Remember: STRATIFICATION = VERTICAL LAYERS. Think of a cake with layers. Trees are the top layer, shrubs are middle, and herbs are the bottom layer.

Points to Remember

Stratification means vertical distribution of plants and animals.
Trees occupy the top layer in a forest.
Shrubs occupy the middle layer.
Herbs and grasses occupy the bottom layer.
Stratification is also seen in oceans with different zones.

Horizontal distribution of plants and animals on land or in water, is called zonation. Zonation is observed in aquatic (wetlands) as well as terrestrial ecosystems, but it is easily seen at the junction of the two. Edges of a large lake or beach show pronounced zonation in the form of Inter-tidal, Littoral, Sub-littoral zones.

Teacher's Note

Zonation means different plants and animals live in different horizontal areas. At the seashore in India, you see different creatures and plants at the high tide area, low tide area, and mudflats area.

Exam Trick

Remember: ZONATION = HORIZONTAL ZONES. Think of layers on a beach from water to land. Different zones have different animals.

Points to Remember

Zonation is horizontal distribution of organisms.
It is seen at the edges of lakes and beaches.
Inter-tidal, Littoral, and Sub-littoral are types of zones.
Each zone has its own special plants and animals.

The biotic and abiotic components of an ecosystem are all linked together to function as an 'ecosystem unit' through various processes like, Productivity, Decomposition, Nutrient cycling and Energy flow. In fact, these are functional aspects of ecosystem.

Any ecosystem must perform these four processes for its sustainance (to be self–sustaining). The ecosystem understudy may be as small as a pond or entire biosphere as a whole. The process of productivity involves conversion of inorganic chemicals into organic material with the help of the radiant energy of the sun by the autotrophs and consumption of the autotrophs by heterotrophs. The Decomposition is the break down of dead organic material and mineralization of the dead matter. The nutrient cycling is the storage and transport of nutrients. (minerals released in decomposition process are used again by autotrophs). The energy flow is unidirectional flow of energy from producers to consumers and finally dissipation and loss as heat.

Example- Think of a small pond ecosystem. It is fairly a self-sustainable unit that explains the complex interactions which exist in any aquatic ecosystem. A pond is a shallow water body in which all the above four aforesaid basic processes of an ecosystem are observed. The abiotic component is water with all the dissolved inorganic and organic substances and also the rich soil deposit at the bottom of the pond. The solar input, the cycle of temperature, day-length and other climatic conditions regulate the rate of function of the entire pond. The producers include the phytoplankton, algae and other aquatic plants. The consumers are represented by the zooplankton, aquatic insects and fish. The decomposers are the fungi, bacteria located at the bottom of the pond.

Teacher's Note

A pond is like a small world. It has producers (plants), consumers (animals), and decomposers (fungi and bacteria) all working together. This is just like how a village has farmers, shopkeepers, and sweepers all doing their jobs.

Exam Trick

Remember: POND ECOSYSTEM = Self-contained world. It shows all four processes: productivity, decomposition, nutrient cycling, and energy flow in one place.

Points to Remember

A pond has all four basic ecosystem processes.
Abiotic components include water and soil at bottom.
Producers are phytoplankton and aquatic plants.
Consumers are zooplankton, insects, and fish.
Decomposers are fungi and bacteria at the bottom.

a. Productivity

A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Productivity refers to the rate of generation of biomass in an ecosystem. It is expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g/ m² / day). The mass unit may relate to dry matter or to the mass of carbon generated.

It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. Plants themselves use a considerable proportion of this GPP for their respiration. Hence, gross primary productivity minus respiratory losses (R) constitute the net primary productivity (NPP).

\[GPP - R = NPP\]

Teacher's Note

Productivity means how much food (biomass) an ecosystem can make. It is like measuring how much rice a farmer can grow in his field in one year.

Exam Trick

Remember: GPP is total food made by plants. NPP is food left for animals after plants eat some for themselves. Formula: GPP - R = NPP.

Points to Remember

Productivity is the rate of making biomass in an ecosystem.
It is measured in grams per square meter per day.
GPP is total organic matter made during photosynthesis.
NPP is the biomass available for consumers.
Plants use some GPP for their own respiration.

This is a preview of the first 3 pages. To get the complete book, click below.