8.3 3.1.4 ecosystems  (Page 3/6)

For example, plants use photosynthesis to manufacture sugar (glucose) from carbon dioxide and water. Using this sugar and other nutrients (e.g., nitrogen,phosphorus) assimilated by their roots, plants produce a variety of organic materials. These materials include: starches, lipids, proteins and nucleicacids. Energy from sunlight is thus fixed as food used by themselves and by consumers.

The consumers are classed into different groups depending on the source of their food. Herbivores (e.g. deer, squirrels) feed on plants and are known as primaryconsumers. Carnivores (e.g. lions, hawks, killer whales) feed on other consumers and can be classified as secondary consumers. They feed on primaryconsumers. Tertiary consumers feed on other carnivores. Some organisms known as omnivores (e.g., bears, rats and humans) feed on both plants and animals.Organisms that feed on dead organisms are called scavengers (e.g., vultures, ants and flies). Detritivores (detritus feeders, e.g. earthworms, termites,crabs) feed on organic wastes or fragments of dead organisms.

Decomposers (e.g. bacteria, fungi) also feed on organic waste and dead organisms, but they digest the materials outside their bodies. The decomposersplay a crucial role in recycling nutrients, as they reduce complex organic matter into inorganic nutrients that can be used by producers. If an organicsubstance can be broken down by decomposers, it is called biodegradable.

In every ecosystem, each consumer level depends upon lower-level organisms (e.g. a primary consumer depends upon a producer, a secondary consumer depends upon aprimary consumer and a tertiary consumer depends upon a secondary consumer).

Activity:

Let's study an example of an ecosystem:

(a) What is a forest?

A forest is much more than a large area of land covered with trees. Shrubs, vines, ferns, mosses and toadstools live in the shade of trees. The forest alsoswarms with birds, mammals, reptiles, amphibians and insects. A forest is therefore all these plants and animals living together.

The animals depend on plants for food, while plants use sunlight, carbon dioxide, water and minerals to make food for themselves and other organisms inthe forest.

The living organisms (plants and animals) together with the non-living environment (air, water, sun and soil) constitute an ecosystem.

(b) Tabulate an example of each of the following found in a forest.

(c) Now sketch these five examples in the drawing to complete it!

(d) The Ecosystem concept

The organism-environment interaction leads to the ecosystem concept, elaborating the interaction between matter, energy and organism.

(e) How big is an ecosystem?

An ecosystem can be of any size, from a puddle of water on the pavement to the entire rain forest in the Amazon or an even larger area.

A forest with its trees, plants, insects, birds, etc., is an ecosystem of certain kinds of organisms that occupy a certain environment. On the otherhand, a rock in the shade of a forest with its mosses and other rock plants, insect larvae and centipedes, is also an ecosystem. The system is thereforeintegrated, with parts that are intimately related to one another. Anything affecting a part of the system will also affect the rest.