Final answer:
To teach first graders about living things, illustrating with a tree is essential because it expands their understanding beyond animals, showing that plants are also living organisms that perform vital life processes and play crucial roles in ecosystems.
Step-by-step explanation:
When teaching first graders the concept of living things, after presenting examples that include themselves, a cat, a dog, a lizard, a fish, and a bird, the most important additional example to show them would be a tree. This is because the previous examples are all animals, and it is crucial to illustrate that living things also include plants. A tree is a living organism that grows, reproduces, responds to its environment, and carries out other life processes just like animals do, but in different ways. For instance, while animals might move around to seek sunlight, water, or food, a tree will grow towards the sunlight and spread its roots to access water and nutrients from the soil.
The examples provided so far to the students are all animals, which are easier to recognize as living organisms. However, it's necessary for students to understand that living organisms can also be plants. Besides providing oxygen, which is essential for animal life, trees represent a large category of living organisms that are crucial for the environment and the planet's ecosystems. Highlighting a tree as a living thing challenges students to broaden their understanding of what is included in the category of living organisms and also introduces concepts like photosynthesis and the interdependence between plants and animals.