[00:00.00]NARRATOR: Listen to a conversation between a student and his biology professor.
[00:05.99]MALE STUDENT: Well, you know, I am writing that paper about whales and the path they travel as they swim through the ocean, their migration patterns.
[00:14.44]FEMALE PROFESSOR: Yes. I remember.
[00:15.62]MALE STUDENT: And well, I was thinking about it and I realized I don't understand how they hold their breath underwater. [00:20.50]It's a little crazy for me to be writing about migration patterns without actually knowing how they stay underwater for so long.
[00:27.21]FEMALE PROFESSOR: Did you do any research to find out how they do it?
[00:29.92]MALE STUDENT: Yeah, I did. [00:31.00]I searched on the internet and there was a lot of information about whales, their habitats, the way they communicate, you know, their songs. [00:37.21]But if there was anything about whales and how they hold their breath, I missed it. [00:41.29]I've got a bunch of books. [00:43.04]Actually, I have got so much information, it's a little overwhelming.
[00:46.00]FEMALE PROFESSOR: I am surprised there is nothing about it in any of those books. [00:49.16]MALE STUDENT: Well, to be honest, l've only skimmed them so far. [00:51.77]I am still working on finding sources.
[00:54.08]FEMALE PROFESSOR: OK. I know I encourage everyone in class to look at a substantial number of sources, but I don't want you to get overwhelmed. [01:01.48]Looking at a number of sources gives you a good knowledge base, but students only have a limited amount of time to work on each paper. [01:07.92]I don't expect you to read a dozen books on whales for this assignment. [01:11.69]Focus on just a few.
[01:12.89]MALE STUDENT: Ok. Thanks.
[01:14.10]FEMALE PROFESSOR: You know, since you are already here. [01:16.06]I can give you a quick summary of how whales hold their breath underwater. [01:19.72]It's just a matter of certain adaptations in their anatomies, specifically in their circulatory system.
[01:25.05]MALE STUDENT: So the blood flow is what makes the difference?
[01:27.20]FEMALE PROFESSOR: Yes, and in a couple of ways.[01:29.05] First, blood makes up a larger share of a whale's weight than in other mammals.
[01:33.26]MALE STUDENT: So they can store more oxygen because they have more blood?
[01:36.23]FEMALE PROFESSOR: Yes, but that's only part of it.[01:38.03]They also have a greater capacity than land animals to store oxygen in their blood.
[01:43.25]MALE STUDENT: So how does having more oxygen in their blood help them stay underwater longer?
[01:47.31]FEMALE PROFESSOR: It's the way the whale's blood carries oxygen to the rest of its body. [01:51.18]Whales carefully conserve their oxygen when underwater in a couple of ways. [01:55.46]When a whale dives, its metabolic rate drops, causing its heartbeat to slow down. [02:00.58]And the blood flow to its muscles and some of its non-vital organs, like its kidneys, is also cut off. [02:07.02]A whale's muscles and non-vital organs are able to function without oxygen for an extended period of time. [02:12.69]MALE STUDENT: I see... Well, now I can concentrate on my topic!
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