Food chain diagram illustrating energy transfer from grass to grasshopper, frog, snake, and bird.

Problem Analysis:

The task involves understanding ecological concepts, specifically food chains, trophic levels, and energy flow in ecosystems. Let's break down each part of the problem and solve it step by step.

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Task 1: Fill in the blanks

#### (a) What is an ecosystem?
An ecosystem is a community of living organisms (plants, animals, and microbes) interacting with their non-living environment (air, water, soil, sunlight). It includes all the biotic (living) and abiotic (non-living) components in a specific area.

Answer:
An ecosystem is a community of living things interacting with their environment.

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#### (b) What are the following things called in an ecosystem?
1. Plants that make their own food using sunlight: These are called producers because they produce their own food through photosynthesis.
2. Animals that eat other animals: These are called carnivores because they consume meat.
3. Organisms that feed on dead plants and animals: These are called decomposers because they break down dead organic matter.

Answers:
1. Producers
2. Carnivores
3. Decomposers

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Task 2: Study the diagram and answer the following question

The diagram shows a food chain involving a plant, a rabbit, a snake, and an eagle. The arrows indicate the direction of energy flow (who eats whom).

#### Question:
Who does the eagle eat in this ecosystem?

From the diagram:
- The plant is eaten by the rabbit.
- The rabbit is eaten by the snake.
- The snake is eaten by the eagle.

Thus, the eagle eats the snake.

Answer:
Snake

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Task 3: Which of the following is absent in an ecosystem?

Options:
1. Plants
2. Birds and rabbits
3. Air, water, and soil
4. Animals
5. Bacteria

In an ecosystem, all living (biotic) and non-living (abiotic) components are present. This includes:
- Plants (producers)
- Animals (consumers)
- Microorganisms (e.g., bacteria, decomposers)
- Non-living components like air, water, and soil (abiotic factors)

Since all these components are essential for an ecosystem to function, none of them can be absent. However, if we interpret the question as asking which component is not directly listed in the options, the correct answer would be "Bacteria," as it is often overlooked but crucial for decomposition and nutrient cycling.

Answer:
Bacteria

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Task 4: From the following food chain, which organism can be classified as a predator?

Food chain: Grass → Grasshopper → Frog → Snake → Hawk

#### Explanation:
- Grass: Producer (makes its own food through photosynthesis).
- Grasshopper: Primary consumer (herbivore, eats grass).
- Frog: Secondary consumer (carnivore, eats grasshoppers).
- Snake: Tertiary consumer (carnivore, eats frogs).
- Hawk: Apex predator (top carnivore, eats snakes).

A predator is an organism that hunts and eats other organisms. In this food chain, the hawk, snake, and frog are predators because they consume other animals.

Answer:
Snake

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Final Answers:

1. Ecosystem definition: An ecosystem is a community of living things interacting with their environment.
2. Blanks in the ecosystem:
- Plants that make their own food: Producers
- Animals that eat other animals: Carnivores
- Organisms that feed on dead plants and animals: Decomposers
3. Who does the eagle eat? Snake
4. Absent in an ecosystem? Bacteria
5. Which organism is a predator? Snake

Boxed Final Answer:
\[
\boxed{\text{Snake}}
\]