Maharashtra Board Class 9 Science Chapter 7 Energy Flow in an Ecosystem PDF Download

Energy Flow In An Ecosystem

We will learn about three main topics in this chapter: Food chain and food web, The energy pyramid, and Bio-geo-chemical cycle - Carbon, oxygen and nitrogen cycles.

Looking Back

1. What is meant by 'ecosystem'?

2. Which are the different types of ecosystems?

3. How do interactions take place between biotic and abiotic factors of an ecosystem?

Energy Flow In An Ecosystem

We have already learnt the classification of living organisms according to the mode of nutrition into producers, consumers, saprotrophs (saprophytes) and decomposers. Consider the various trophic levels of the ecosystem around you as given below.

Primary Consumers (Herbivores)

Example: Grasshopper, squirrel, elephant, etc. They are directly dependent on autotrophs (producers).

Secondary Consumers (Carnivores)

Example: Frog, owl, fox, etc. These consumers use herbivores as their food.

Apex Or Top Consumers (Carnivores)

Example: Tiger, lion, etc. These consumers use herbivores and carnivores as their food. No other animals feed on top consumers.

Omnivores (Mixed Consumers)

Example: Humans, bear, etc. Feed on herbivores and carnivores.

Food Chain And Food Web

Observe

Observe figure 7.1 and explain the relationship between the components.

Construct four chains like the one shown in figure 7.1.

Interactions go on continuously between producers, consumers and saprophytes. There is a definite sequence in these interactions which is called the food chain. Each chain consists of four, five or more links. An ecosystem consists of many food chains that are interconnected at various levels. Thus a food web is formed.

Use Your Brain Power

Explain the food chains of various ecosystems which you have studied last year.

Teacher's Note

A food chain shows how energy passes from plants to animals. For example, in India, grass is eaten by a goat, and the goat is eaten by a tiger.

Exam Trick

Remember: Food chain = one path. Like from grass to grasshopper to frog to snake to eagle. Each arrow shows who eats whom!

Points To Remember

Food chain is the order of who eats whom in nature.
Each living thing is at one level in the food chain.
Plants are always at the start of a food chain.
Energy moves from one animal to the next animal in the chain.
A food web has many food chains mixed together.

An organism may be the prey for many other organisms. For example, an insect feeds upon leaves of various plants but the same insect is the prey for different animals like frog, wall lizard, birds, etc. If this is to be shown in a figure, it will form an intricate web instead of a linear food chain. Such an intricate network is called a 'Food Web'. Generally, food webs are found everywhere in nature.

Teacher's Note

A food web is like a spider web in nature. One animal eats many foods. For example, in India, a crow eats seeds, insects, and leftover food from humans.

Exam Trick

Remember: Web = many chains together. Like a real spider web - it has many lines connected. Food web also has many paths!

Points To Remember

A food web shows many food chains at the same time.
One animal can be food for many different animals.
One animal can eat many different foods.
A food web is more complete than a single food chain.
Most animals in nature are part of a food web, not just one chain.

The Energy Pyramid

Trophic Level

Each level in the food chain is called a trophic level. A trophic level is the step at which the organism obtains its food in the chain. The amount of matter and energy gradually decreases from producers at lowest level to top consumers at the highest level.

Trophic Levels:

Producers: All producers in the ecosystem (Plants)

1st Trophic Level: Herbivores

2nd Trophic Level: Carnivores

3rd Trophic Level: Omnivores

Use Your Brain Power

Make a list of the various consumers of the ecosystems around you and classify them according to mode of nutrition. Pictures of various organisms are given in fig. 7.2. Construct a food web from those pictures.

1. Is the number of consumers in a food web fixed?

2. What will be the effect on an ecosystem if only one type of organism in it forms the food for several different consumers in that ecosystem?

3. Why is balance or equilibrium necessary in a food web?

Research

Lindeman, In 1942 studied the food chain and energy flow through it. Charles Elton, a British scientist first proposed the concept of the Ecological Pyramid in 1927 after his study of the Tundra Ecosystem of the Beer islands in England. Hence, this pyramid is also called the Eltonian Pyramid.

Teacher's Note

The energy pyramid shows that producers have the most energy and top predators have the least. For example, many plants are needed to feed one tiger in an Indian forest.

Exam Trick

Remember: Energy pyramid = energy decreases going up. Like 10,000 kilos of grass makes 1000 kilos of goat, which makes 100 kilos of lion. Use the 10% rule!

Points To Remember

Energy decreases at each trophic level going up the pyramid.
Plants have the most energy in the ecosystem.
Top predators have the least energy in the pyramid.
About 10% of energy passes to the next level.
That is why there are fewer top predators than herbivores.

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