If a water molecule passes through the outer membrane of a chloroplast, how many more membranes will it have to move through to be in the stroma?

Question

A.  1
B.  2
C.  3
D.  4

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you know about the structure of a chloroplast? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  1

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the location of the stroma in a chloroplast.
· What type of thinking is required?
        o You are being asked to apply your knowledge of the structure of a chloroplast to explain how many membranes are present.
· What key words does the question contain and what do they mean?
        o Outer membrane of a chloroplast – A chloroplast has two membranes, much like a mitochondria.  However, unlike a mitochondria, inside of a chloroplast there are thylakoid disks which are made up of a third membrane.
        o Stroma – this is the fluid filled space inside the chloroplast which contains the thylakoid.

Gather Content
· What do you know about the structure of a chloroplast? How does it relate to the question?
        o A chloroplast has two membranes much like a mitochondria, an outer membrane and an inner membrane.  Inside of the chloroplast is the stroma and within it are sub-organelles called thylakoids.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o The water molecule has crossed the outer membrane, so it is in the inter-membrane space between the outer and inner membranes.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The water molecule only needs to cross the inner membrane to be in the stroma, so it must cross one membrane.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply your understanding of the structure of a chloroplast to explain the movement of water across its membranes. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall the structure of the chloroplast and that it contains an outer membrane, an inner membrane and a thylakoid membrane?  Did you remember where the stroma was in the chloroplast?  Did youthink that the question asked how many total membranes were in a chloroplast?