Differentiate between food chain and food web. In a food chain consisting of deer, grass and tiger, if the population of deer decreases, what will happen to the population of organisms belonging to the first and third trophic levels?

Q: Differentiate between food chain and food web. In a food chain consisting of deer, grass and tiger, if the population of deer decreases, what will happen to the population of organisms belonging to the first and third trophic levels?

### 1. Difference between Food Chain and Food Web: | Feature | Food Chain | Food Web | | :--- | :--- | :--- | | **Definition** | A single, straight-line series of organisms where each organism feeds on the preceding one. | A complex network of several interconnected food chains showing branching feeding relationships. | | **Complexity** | Simple, linear, and unidirectional. | Highly complex with multiple branching lines. | | **Alternative Food Sources** | An organism has only one specific source of food at the next lower level. | An organism has multiple alternative food sources, which increases ecosystem stability. | --- ### 2. Impact of Decrease in Deer Population: In the given food chain: $$\text{Grass (1st Trophic Level)} \rightarrow \text{Deer (2nd Trophic Level)} \rightarrow \text{Tiger (3rd Trophic Level)}$$ If the population of **deer** (herbivores/primary consumers at the second trophic level) decreases: - **First Trophic Level (Grass/Producers):** The population of grass will **increase**. Since deer are the primary consumers that feed on grass, a reduction in their numbers means less grazing pressure, allowing the grass to grow and reproduce unchecked. - **Third Trophic Level (Tiger/Secondary Consumers):** The population of tigers will **decrease**. Tigers are carnivores that depend directly on deer for food. A shortage of deer will lead to starvation, lower reproduction rates, and a decline in the tiger population, or force them to migrate in search of food.

Our Environment

Food Chains and Webs

Official Answer

1. Difference between Food Chain and Food Web:

Feature	Food Chain	Food Web
Definition	A single, straight-line series of organisms where each organism feeds on the preceding one.	A complex network of several interconnected food chains showing branching feeding relationships.
Complexity	Simple, linear, and unidirectional.	Highly complex with multiple branching lines.
Alternative Food Sources	An organism has only one specific source of food at the next lower level.	An organism has multiple alternative food sources, which increases ecosystem stability.

2. Impact of Decrease in Deer Population:

In the given food chain:

$\text{Grass (1st Trophic Level)} \rightarrow \text{Deer (2nd Trophic Level)} \rightarrow \text{Tiger (3rd Trophic Level)}$

If the population of deer (herbivores/primary consumers at the second trophic level) decreases:

First Trophic Level (Grass/Producers): The population of grass will increase. Since deer are the primary consumers that feed on grass, a reduction in their numbers means less grazing pressure, allowing the grass to grow and reproduce unchecked.
Third Trophic Level (Tiger/Secondary Consumers): The population of tigers will decrease. Tigers are carnivores that depend directly on deer for food. A shortage of deer will lead to starvation, lower reproduction rates, and a decline in the tiger population, or force them to migrate in search of food.

Food chainFood weblinearinterconnectedfirst trophic levelthird trophic levelincreasedecreaseproducerscarnivores

Marking Scheme

11.5 marks for differentiating between food chain and food web (at least two valid points of difference).
20.75 marks for stating that the population of the first trophic level (grass) will increase with a brief reason.
30.75 marks for stating that the population of the third trophic level (tiger) will decrease with a brief reason.

Hint

Identify the trophic levels: Grass is 1st, Deer is 2nd, Tiger is 3rd. Think about what happens to the food of tigers and the consumer of grass if deer numbers drop.

Quick Oral Answer

A food chain is a single linear pathway of energy flow, while a food web is a network of interconnected food chains. If deer decrease, grass (1st level) increases due to less grazing, and tigers (3rd level) decrease due to lack of food.

Analysis & Explanation

This question tests the understanding of trophic dynamics and ecological balance. A food chain represents a simplified, linear flow of energy, whereas a food web represents the realistic, complex branching relationships in nature. In a three-step food chain (Grass $\rightarrow$ Deer $\rightarrow$ Tiger), the deer act as a crucial link. A decrease in the intermediate herbivore population has a dual effect: it removes the predatory pressure on the producers (causing grass to overgrow) and deprives the top carnivores of their primary energy source (causing tigers to starve and decrease in number). This demonstrates how ecosystems are tightly balanced and interdependent.

Common Mistakes

1Students sometimes write that the grass population will decrease, thinking that a disturbance always decreases everything.
2Confusing the trophic levels (e.g., calling deer the first trophic level instead of second).

Interesting Facts

In real ecosystems, because of food webs, if one prey species like deer decreases, predators like tigers might switch to other prey, preventing immediate collapse. This is why food webs provide greater ecological stability than simple food chains.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 3 marks in the CBSE Class 10 Science 2024 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Our Environment" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Food Chains and Webs" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2024 paper?

This is a Short Answer question from Section C in the CBSE Class 10 Science 2024 paper.