How a Harbor Seal Dives on One Breath

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How a Harbor Seal Dives on One Breath

Use tag data from a refuge seal survey to argue how body systems work together.

The tag data

Read the passage and Table 1, then answer the questions.

Seal H-7 Goes Fishing

1Gull Bar National Wildlife Refuge protects an estuary where a river meets the sea. The refuge, the people and the numbers here are made up, but they are based on real seal studies. Each spring, refuge biologist Dr. Henrik Valdés surveys the harbor seals that rest on the sandbars at low tide. This year, sixth grader Noemi Castellanos volunteered with the survey. Under a federal permit, the team glued small tags to the fur of a few seals. A tag records depth, heart rate and breathing, and it falls off on its own when the seal sheds its fur in summer.

2A seal named H-7 wore one of the tags. She has a mass of about 80 kg. Harbor seals hunt fish on the bottom of the estuary, and most of their dives last a few minutes. A seal usually breathes out before it dives, so it carries little air in its lungs. Instead, it dives on oxygen stored in its blood and muscles. A seal has roughly twice as much blood for its body mass as a person, and its muscle cells hold about ten times as much of an oxygen-storing protein as human muscle cells do.

3Dr. Valdés explained what the tag picks up. When receptors in a seal's face sense cold water, its brain sends signals along nerves that slow the heart within seconds. Other nerve signals narrow the blood vessels that lead to the kidneys, the stomach and the intestines, while blood keeps flowing to the brain and the heart muscle. Digesting a meal mostly waits until the seal rests on a sandbar.

4When H-7 comes back up, she breathes fast and her heart speeds up. Noemi noticed on the records that H-7 stayed at the surface longer after long dives than after short ones. The team rounded every value in the two tables.

Table 1. Seal H-7 on One Morning
What H-7 was doing	Heart (beats/min)	Breaths per min
Resting on the sandbar	90	12
Swimming at the surface	120	20
Middle of a 5-minute dive	20	0
First minute after surfacing	130	30

1.

Use Table 1.

H-7's heart rate in the middle of the dive was beats per minute lower than when she rested on the sandbar.

2.

Use Table 1.

In the first minute after surfacing, H-7's heart beat how many times as fast as in the middle of the dive? Do not round. times

3.

H-7 took 30 breaths per minute right after she surfaced. Which explanation fits the passage and Table 1 best?

A. Her heart was beating slowly, so her lungs had to push her blood around instead.B. Her blood and muscle cells had used up stored oxygen, so her lungs worked fast to reload it.C. Her lungs filled with seawater during the dive, so she breathed fast to push it out.D. Fast breathing cooled her body down after the warm water heated her during the dive.

4.

Use paragraph 3. H-7's heart slows within seconds of a dive, even though her swimming muscles are still at work. Which explanation fits best?

A. Her brain sends nerve signals that slow the heart, so her stored oxygen lasts longer.B. The cold water chills her heart muscle tissue, so it beats more slowly by itself.C. Water pressure squeezes her lungs, so they pump less blood into her heart.D. Her muscles stop using oxygen underwater, so the heart has less blood to move.

5.

Circle each statement from the passage that is evidence that H-7's nervous system changes the work of her circulatory system.

Short dives and long dives

Use Table 2 to answer the questions.

Table 2. Four of H-7's Dives
Dive length (min)	Lowest heart (beats/min)	Breathing at surface (s)
2	40	20
4	25	45
6	18	70
10	12	150

6.

After the 10-minute dive, H-7 spent s longer breathing at the surface than after the 4-minute dive.

7.

Which pattern does Table 2 show?

A. Longer dives had lower low heart rates, and she spent more time at the surface after them.B. Her lowest heart rate stayed near 25 beats/min, and surface time grew with dive length.C. Longer dives had higher low heart rates, and she spent less time at the surface after them.D. Surface time stayed near 45 s, while her lowest heart rate fell as dives got longer.

8.

Suppose H-7 makes an 8-minute dive. Based on Table 2, which values are most likely?

A. Lowest heart rate about 30 beats/min; about 30 s at the surfaceB. Lowest heart rate about 8 beats/min; about 200 s at the surfaceC. Lowest heart rate about 20 beats/min; about 45 s at the surfaceD. Lowest heart rate about 15 beats/min; about 110 s at the surface

9.

Sort each change in H-7's body by what it most likely does for her.

From cells to the whole seal

Use the passage and both tables.

10.

Use paragraph 2. How does the oxygen-storing protein in H-7's muscle cells most likely help the whole seal?

A. Her lungs can stay full of air, so she can skip breathing at the surface.B. Her muscle tissue can keep working on stored oxygen, so she can stay under longer.C. Her muscle cells can make new oxygen out of seawater while she swims.D. Her heart can stop beating during a dive, so her blood can rest until she surfaces.

11.

The refuge cares for a young seal with a lung infection, so its lungs move oxygen into its blood more slowly than a healthy seal's. When it swims in the care pool, which prediction fits the data best?

A. Its heart would likely beat more slowly at the surface, since its heart and lungs work separately.B. It would likely make longer dives, since a seal with sick lungs uses less oxygen while it swims.C. It would likely need more time at the surface after each dive, since its blood reloads oxygen slowly.D. It would likely dive the same way, since a dive draws on muscle oxygen and not on blood oxygen.

12.

A visitor at the refuge says, "Diving is just a lung job. A seal holds its breath, and the rest of its body carries on as usual." Argue against this. Write a claim, give evidence from both tables and the passage, and explain how at least three organ systems work together during and after a dive.