Our Environment: questions with answers

Sunlight is a non-living physical factor, so it is an abiotic component of the ecosystem. Plants, being living organisms, are biotic components that use it.

Producers make food and release oxygen. Without them, the fish's food and oxygen are not renewed.

The rabbit does not make its own food; it eats another organism (grass) for energy and matter. Organisms that feed on other organisms are consumers, not producers.

Decomposers break down complex organic remains into simpler substances that return nutrients to the soil and water. Plants can then use these recycled nutrients again.

A persistent toxin is not broken down, so it passes on and adds up at each feeding step. Its concentration therefore rises from one trophic level to the next and is highest in top consumers.

DDT persists in bodies, so its concentration rises at each higher trophic level. Glucose is used up for energy, so it does not build up along the chain.

A food chain begins with a producer and moves to the organism that eats it, and then to the next consumer. Grass is the producer, the goat eats grass, and the human eats the goat, giving the order grass, goat, human.

The producer, grass, is at the first trophic level. The insect that eats grass is at the second level, and the frog that eats the insect is at the third level.

A food web is several food chains that are linked together because they share organisms. A single chain, like grass to deer to tiger, is only one path within the web, not the whole web.

With no predators left, their prey increase in number and overuse the level below them, so the whole chain becomes unbalanced.

Only about ten percent of the energy at one trophic level passes to the next. Ten percent of 500 J is 50 J, so about 50 J reaches the fourth trophic level.

Stratospheric ozone absorbs harmful ultraviolet radiation before much of it reaches Earth's surface. If ozone is depleted, more harmful UV reaches the surface.

The ozone decline in the 1980s was caused by chemicals called CFCs, released from products like refrigerators and aerosol sprays, which destroy ozone in the upper atmosphere.

Glass is not broken down by microbes, so it is non-biodegradable. Peels and paper are broken down by decomposers.

Reusing the jar avoids waste without processing it, so this is reuse. Reducing consumption and reusing products prevent waste before recycling is even needed; recycling only recovers material afterwards.