One of the most general distinctions among organisms is between plants, which use sunlight to make their own food, and animals, which consume energy-rich foods. Some kinds of organisms, many of them microscopic, cannot be neatly classified as either plants or animals.
Learning Goal 2
Animals and plants have a great variety of body plans and internal structures that contribute to their being able to make or find food and reproduce.
Learning Goal 3a
Similarities among organisms are found in internal anatomical features, which can be used to infer the degree of relatedness among organisms.
Learning Goal 3b
In classifying organisms, scientists consider details of both internal and external structures.
Learning Goal 4
Traditionally, a species has been defined as all organisms that can mate with one another to produce fertile offspring.
Learning Goal 5
The cycles continue indefinitely because organisms are decomposed after death to return food materials to the environment.