Key Concept 1: Organisms interact with both living and nonliving things to survive in their ecosystems.
An ecosystem is a community of living and nonliving things in their environment.
The living or biotic components of an ecosystem are: the plants, animals (including humans), fungi, and microorganisms living within a particular geographic area. For example, in a desert, the cactus, sagebrush, desert grasses, wildflowers, coyotes, snakes, lizards, desert mice, birds, scorpions, bacteria, etc, represent the living part of a desert ecosystem. The living parts of an environment provide a source of food, a way to reproduce, and protection. For some creatures, other living things may be their habitat
(home) or their social group. When other organisms are competitors or predators, that living part of the environment becomes a survival challenge. As energy from the Sun is transferred from producers to consumers and finally to decomposers, all of nature becomes interdependent. The study of human impact on living things has led to ecofriendly or “green” practices to lessen the harmful effects of human activity and technology on ecosystems.
Living things can be studied at increasing levels of interaction: the response of a single organism, a population of similar organisms, or a community of different organisms that live together in an ecosystem.
The nonliving or abiotic components of an ecosystem are: sunlight, atmosphere and weather, temperature, soil, rock, landforms, bodies of water, glaciers, volcanoes, manmade structures, etc. For example, in a desert, the sand, Sun, lack of water, rocks, hot air, etc., represent the abiotic elements in that ecosystem. The nonliving parts of an environment supply the sunlight, water, oxygen, carbon dioxide, nitrogen, minerals, and shelter necessary for life. Nonliving elements can also present survival challenges when they threaten life such as flooding, drought (dry spells), or pollution caused by human activity.
Life within an ecosystem is interdependent. A delicate balance exists in nature so that all living things must interact with other organisms and with their environment in order to survive and reproduce. As energy from the Sun is transferred from producers to consumers and finally to decomposers, all of nature becomes interdependent. Any change to a single component in that ecosystem can have profound impact on the entire ecosystem.

Key Concept 2: Plants interact with living things such as animals and other plants in complex ways and also require nonliving things, such as carbon dioxide, water, and sunlight.
Plants need nonliving things to survive such as carbon dioxide in the air, sunlight from above, and water brought up by their roots to survive. Through the process of photosynthesis, plants, as producers, change sunlight, carbon dioxide (produced by animals), and water to make glucose or plant food. As a by-product, plants release oxygen which animals need.
Plants interact with living things. Energy, minerals, and nutrients stored in plants are transferred to the animals when plants are eaten. Animals like insects or birds also pollinate flowers by spreading pollen grains that fertilize plant seeds. Animals also end up spreading seeds that get stuck to their fur or inside fruit carried off to be eaten and left on the ground. These loose seeds end up taking root under the right conditions and grow new plants and flowers.
Key Concept 3: Animals depend on other living things, such as plants and other animals, and nonliving things, such as air and water, to survive.

Animals breathe the oxygen in the air produced by plants. Animals use this oxygen carried in blood to cells and exchanged for carbon dioxide which is released (which plants will use). Animals also depend on other nonliving elements for survival such as water, the correct temperature from the Sun, and soil/rocks/landforms for shelter. The energy, minerals, and nutrients stored in plants are transferred to the animals when plants are eaten. Some plants provide more than food for animals; plants can also serve as shelter. For example, tree trunks or flowers can become a habitat for birds, mammals, or insects.
Animals that depend on different kinds of living things for food are grouped into herbivores (animals that eat plants), carnivores (animals that eat other animals), omnivores (animals that eat both plants and animals), and decomposers (bacteria and fungi that break down dead organisms for food).
Animals that hunt other animals are called predators. Animals that are hunted are called prey.