First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic of marine biology. It gives a broad overview of what marine biology studies. It does not refer to any previous information. Why other lines are not chosen? Paragraph 2 starts with 'These species', which refers back to something, so it is not independent. Paragraph 3 starts with 'However', which is a conjunction, so it is not independent. Paragraph 4 starts with 'As a result', which is also a conjunction, so it is not independent. Paragraph 5 starts with 'Marine biology', which is a specific subject and does not introduce a new topic.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion. It gives a conclusion about the importance of conserving marine biodiversity. It summarizes the main points made in the previous paragraphs.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): This pair connects because the second paragraph gives specific examples of what marine biology studies. It follows the broader topic of marine biology with specific details about ocean life.
• Pair 2 (Paragraph 2 → Paragraph 3): This pair connects because the second paragraph talks about the species in the ocean, and the third paragraph explains what these species do in the ecosystem. It shows a logical order from species to their roles.
• Pair 3 (Paragraph 3 → Paragraph 4): This pair connects because the third paragraph discusses the roles of species, and the fourth paragraph introduces the threats to these ecosystems. It shows a cause and effect relationship.
• Pair 4 (Paragraph 4 → Paragraph 5): This pair connects because the fourth paragraph talks about threats, and the fifth paragraph explains why it is important to conserve marine biodiversity. It shows a logical order from problem to solution.