Chapter 2, Problem 17A

Summary Introduction

To identify:

The relationship between the given terms.

Introduction : Organisms interact with each other in different ways within an ecosystem. They differ in how they derive their energy and so they are classified as autotrophs or heterotrophs based on how they obtain their food in an ecosystem. Food chains and food webs help us in studying the flow of energy from one organism to another.

Answer to Problem 17A

Autotroph, food chain and heterotroph are all part of a food web.

Explanation of Solution

Autotroph- It is an organism that can prepare its own food. They are called producers. All green plants and blue green algae are autotrophs. They trap solar energy and convert it to carbohydrates. They make energy available to all other organisms in an ecosystem. In a food web, autotrophs are at the bottom. Heterotroph- It is a living organism that cannot prepare its own food but is dependent on other organisms for food. They rely on autotrophs and other heterotrophs for food. So they are also called consumers. Examples are humans, lions, deer, etc.

Food chain- Ecologists use food chain to show the flow of energy through an ecosystem. In a food chain the first trophic level is that of autotroph, followed by heterotrophs. For example, in a grassland type of food chain, grasses are autotrophs. The grasshopper forms second trophic level as it is dependent on grass for food. This is followed by mouse as an omnivore and then snake as a carnivore.

All these three categories of organisms are linked together in a food web which is a model representing interconnected food chains. So in a food web, there are autotrophs, heterotrophs and food chains.