Final answer:
The best method to help third graders understand new vocabulary from a science book is through direct instruction using multimedia methods to provide a rich contextual understanding of the terms.
Step-by-step explanation:
The best teaching activity to help third-grade students develop an understanding of new vocabulary words such as "chlorophyll," "germinate," and "photosynthesis" from a trade book about plants is planning direct instruction using multimedia methods to introduce words in rich contexts. This approach allows students to clearly recognize which words and ideas are new and connects them to visual and contextual clues, thereby enhancing the learning experience. Utilizing multimedia methods can also make the content more engaging and can help locate those other sources to build a deeper understanding of the terms.
Words on a word wall, while useful for reference, may not provide the context and in-depth understanding that multimedia instruction can. Asking students to assume definitions may confuse them if they make incorrect connections. Venn diagrams are helpful for categorizing, but they do not inherently teach the meaning of new words. It is important for students to have some context for the new ideas they encounter and to understand how these new words fit into the bigger picture of their science lesson.