Chapter 3

Food chain and food web

The Food Chain

Every living thing needs energy in order to live. Everytime animals do something (run, jump) they use energy to do so.

Animals get energy from the food they eat, and all living things get energy from food. Plants use sunlight, water and nutrients to get energy (in a process called photosynthesis). Energy is necessary for living beings to grow.

A food chain shows how each living thing gets food, and how nutrients and energy are passed from creature to creature. Food chains begin with plant-life, and end with animal-life. Some animals eat plants, some animals eat other animals.

A simple food chain could start with grass, which is eaten by rabbits. Then the rabbits are eaten by foxes.

A food chain shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. For example, a simple food chain links the trees & shrubs, the giraffes (that eat trees & shrubs), and the lions (that eat the giraffes). Each link in this chain is food for the next link. A food chain always starts with plant life and ends with an animal.

1. Plants are called producers because they are able to use light energy from the Sun to produce food (sugar) from carbon dioxide and water. The process by which plants make food is called photosynthesis.

2. Animals cannot make their own food so they must eat plants and/or other animals. They are called consumers. There are three groups of consumers.

a. Animals that eat ONLY PLANTS are called herbivores (or primary consumers).

b. Animals that eat OTHER ANIMALS are called carnivores.

§ carnivores that eat herbivores are called secondary consumers

§ carnivores that eat other carnivores are called tertiary consumers

e.g., killer whales in an ocean food web ... phytoplankton → small fishes → seals → killer whales

3. Animals and people who eat BOTH animals and plants are called omnivores.

4. Then there are decomposers (bacteria and fungi) which feed
on decaying matter.

These decomposers speed up the decaying process that releases mineral salts back into the food chain for absorption by plants as nutrients.

Image Map of the Nitrogen Cycle - What happens in the soil?

Simple food chain

The food web

A food web is a series of food chains. A food chain is a linear sequence of links in a food web starting from a trophic species that eats no other species in the web and ends at a trophic species that is eaten by no other species in the web.

A food web differs from a food chain in that the latter shows only a portion of the food web involving a simple, linear series of species (e.g.,predator, herbivore, plant) connected by feeding links.

A food web aims to depict a more complete picture of the feeding relationships, and can be considered a bundle of many interconnected food chains occurring within the community. All species occupying the same position within a food chain comprise a trophic level within the food web. For instance, all of the plants in the foodweb comprise the first or "primary producer" tropic level, all herbivores comprise the second or "primary consumer" trophic level, and carnivores that eat herbivores comprise the third or "secondary consumer" trophic level. Additional levels, in which carnivores eat other carnivores, comprise a tertiary trophic level.

A food web shows which animals eat other animals in their environment. It consists of food chains. If a particular keystone species is removed from the food web, it can cause the eco system big problems.