Background: The lungs of mammals are unique in having alveoli . These are tiny, sac-like structures. Each alveolus is surrounded by a network of very small blood vessels (see Figure below ). Because there are millions of alveoli in each lung, they greatly increase the surface area for gas exchange between the lungs and bloodstream. Human lungs, for example, contain about 300 million alveoli. They give the lungs a total surface area for gas exchange of up to 90 square meters (968 square feet). That’s about as much surface area as one side of a volleyball court!

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read more about alveoli?
Answer: Paul

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read less about alveoli?
Answer: Pete

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read less about a network of very small blood vessels?
Answer: Pete

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read more about a network of very small blood vessels?
Answer: Paul

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read more about human lungs?
Answer: Paul

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read less about human lungs?
Answer: Pete

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read less about gas exchange between the lungs and bloodstream?
Answer: Pete

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read more about gas exchange between the lungs and bloodstream?
Answer: Paul

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read more about the total surface area for gas exchange?
Answer: Paul

Situation: Two friends read about respiratory systems. Paul read more about the lungs of mammals, while Pete read more about the lungs of frogs.

Question: Which student read less about the total surface area for gas exchange?
Answer: Pete

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned more about the lungs of mammals?
Answer: Dan

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned less about the lungs of mammals?
Answer: Lori

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned less about alveoli?
Answer: Lori

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned more about alveoli?
Answer: Dan

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned more about a network of very small blood vessels?
Answer: Dan

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned less about a network of very small blood vessels?
Answer: Lori

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned less about gas exchange between the lungs and bloodstream?
Answer: Lori

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned more about gas exchange between the lungs and bloodstream?
Answer: Dan

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned more about tiny, sac-like structures?
Answer: Dan

Situation: Two six graders learned about the lives of animals. Lori learned more about fish, while Dan learned more about mammals.

Question: Which student learned less about tiny, sac-like structures?
Answer: Lori

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned more about alveoli?
Answer: Dana

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned less about alveoli?
Answer: Barry

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned less about tiny, sac-like structures?
Answer: Barry

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned more about tiny, sac-like structures?
Answer: Dana

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned more about a network of very small blood vessels?
Answer: Dana

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned less about a network of very small blood vessels?
Answer: Barry

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned less about surface area for gas exchange between the lungs and bloodstream?
Answer: Barry

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned more about surface area for gas exchange between the lungs and bloodstream?
Answer: Dana

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned more about the number of alveoli?
Answer: Dana

Situation: Two students learned about respiratory systems in animals. Dana learned more about mammalian lungs, while Barry learned more about the lungs of birds.

Question: Which student learned less about the number of alveoli?
Answer: Barry

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned more about the lungs of mammals?
Answer: One

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned less about the lungs of mammals?
Answer: Two

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned less about alveoli?
Answer: Two

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned more about alveoli?
Answer: One

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned more about alveoli being surrounded by a network of very small blood vessels ?
Answer: One

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned less about alveoli being surrounded by a network of very small blood vessels ?
Answer: Two

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned less about the surface area for gas exchange between the lungs and bloodstream?
Answer: Two

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned more about the surface area for gas exchange between the lungs and bloodstream?
Answer: One

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned more about human lungs?
Answer: One

Situation: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system.

Question: Which group of students learned less about human lungs?
Answer: Two