Ecology and Biomes

Grade 7 · Science · Study Guide

An overview of how living organisms interact with each other and their environments across Earth's major biomes.

Ecology is the scientific study of how organisms interact with each other and with their physical environment. These interactions happen at multiple levels: individual organisms, populations (groups of the same species), communities (different species living together), ecosystems (communities plus their physical environment), and the biosphere (all life on Earth).

A biome is a large geographic region characterized by a specific climate and the plants and animals that have adapted to live there. Earth's major biomes include tropical rainforests, temperate forests, grasslands, deserts, tundra, and aquatic biomes like oceans and freshwater lakes.

Within any ecosystem, organisms fill specific ecological roles called niches. Producers (mostly plants) capture energy from the sun through photosynthesis. Consumers eat other organisms — herbivores eat plants, carnivores eat animals, and omnivores eat both. Decomposers like fungi and bacteria break down dead matter and recycle nutrients back into the soil.

Energy flows through ecosystems in food chains and food webs. At each step up the food chain, roughly 90% of energy is lost as heat, which is why ecosystems can support far fewer top predators than primary producers. Understanding these relationships helps scientists protect biodiversity and manage natural resources sustainably.

Key terms

Ecosystem: A community of living organisms together with the nonliving components of their environment, functioning as a system.
Biome: A large naturally occurring community of plants and animals occupying a major habitat defined by climate and geography.
Food web: A complex network of feeding relationships among organisms in an ecosystem, showing who eats whom.
Producer: An organism, usually a plant or alga, that makes its own food through photosynthesis using sunlight.
Decomposer: An organism such as a fungus or bacterium that breaks down dead organic matter and returns nutrients to the environment.
Niche: The role and position a species occupies in its ecosystem, including what it eats, where it lives, and how it interacts with other species.

Flashcards

Trophic level: A step in a food chain or food web representing the position of an organism based on its feeding relationships.
Herbivore: An animal that feeds only on plants or plant material.
Carnivore: An animal that feeds primarily on other animals.
Omnivore: An animal that eats both plants and animals.
Biodiversity: The variety of life in a particular habitat or on Earth as a whole.
Abiotic factor: A nonliving component of an ecosystem such as temperature, water, sunlight, or soil.
Biotic factor: Any living component of an ecosystem, including all plants, animals, fungi, and microorganisms.
Carrying capacity: The maximum population size that an environment can sustainably support given available resources.

Questions

Which of the following correctly lists ecological organization from smallest to largest?
1. Biosphere → Ecosystem → Community → Population → Organism
2. Organism → Population → Community → Ecosystem → Biosphere
3. Population → Organism → Community → Biosphere → Ecosystem
4. Organism → Community → Population → Ecosystem → Biosphere
Show answer
Answer: Organism → Population → Community → Ecosystem → Biosphere
The correct order from smallest to largest is organism, population, community, ecosystem, biosphere — each level includes all the previous ones.
Decomposers are considered consumers because they eat dead organisms.
Show answer
Answer: False
Decomposers are their own category, not consumers. They break down dead and decaying matter rather than consuming living or freshly killed organisms.
The biome characterized by very low precipitation, extreme temperatures, and sparse vegetation is called a ______.
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Answer: desert
Deserts receive less than 250 mm of rain per year and can have extreme heat during the day and cold at night. Plants like cacti have special adaptations to survive.
Approximately how much energy is transferred from one trophic level to the next in a food chain?
1. 50%
2. 25%
3. 10%
4. 75%
Show answer
Answer: 10%
The 10% rule states that only about 10% of the energy at one trophic level is passed on to the next. The other 90% is lost as heat or used for the organism's own life processes.
A food web shows more realistic feeding relationships in an ecosystem than a single food chain.
Show answer
Answer: True
Real ecosystems are complex — most animals eat more than one thing. A food web captures these multiple feeding relationships, giving a more accurate picture than a single linear food chain.

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