A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first line because it introduces the main topic. It tells us when and who first used the term 'biosphere'. This is an important starting point for the text. It does not refer to any previous information, so it stands alone. Why other lines are not chosen? Paragraph 2 starts with 'Since this initial formulation', which means it needs the first paragraph for context. Paragraph 3 starts with 'Today', which also needs earlier information. Paragraph 4 uses 'The biosphere', which assumes we know what it is. Paragraph 5 starts with 'The biosphere is thought', needing prior context. Paragraph 6 starts with 'Each of the plants', which also needs earlier sentences to understand.

Concluding sentence: Why this is the last line? This paragraph is the last line because it wraps up the ideas about the biosphere. It shows how all parts work together. This gives a clear ending to the discussion about the biosphere.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it continues the idea of the term 'biosphere'. It shows how the term has changed since it was first used. This is a logical order of ideas.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 links to Paragraph 2 because it gives more details about what the term 'biosphere' includes. It explains the interactions of living things, which is a specific point following the broader idea in Paragraph 2.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it talks about the history of the biosphere. It explains when the biosphere began, which is a logical next step after discussing what it includes.
• Pair 4 (Paragraph 4 → Paragraph 5): Paragraph 5 links to Paragraph 4 because it discusses current ideas about the biosphere. It shows how scientists think about the biosphere today, which follows the historical context given in Paragraph 4.
• Pair 5 (Paragraph 5 → Paragraph 6): Paragraph 6 connects to Paragraph 5 because it explains how each part of the biosphere works together. It gives an example of the idea presented in Paragraph 5.