Mitochondria...

Yes, there is a difference. The inter-membrane space delimits the region bound between the inner- and outer-mitochondrial membranes (hence the name). The intercristal space is also known as the mitochondrial matrix and is bound by the inner-mitochondrial membrane (also known as the cristal membrane).

This question is weird because the intracristal space is indeed the region of the intermembrane space stretched inward within a crista. The intercristal space on the other hand is between the cristae and is the matrix, as saggy said.

Temperature101 said:

I fail to see a major difference here regarding H+ concentration between #3 and # 5 (except that # 3 is just more inward) . I guess I will have to accept the answer from EK1001.

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No no, you are correct. The region within the cristae is the intracristal space, and is continuous with the intermembrane space.

In the OP you referred to the intercristal space, i.e. the area between the cristae (not enclosed by them) and this is the mitochondrial matrix contained by the inner membrane.

Seems like a typo to me.

InTERcristal space = mito matrix
InTRAcristal space = intermembrane space

Temperature101 said:

So let me get this right....
INTER = INSIDE...
INTRA = IN BETWEEN

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It really depends on your definition of inside and in between. Think about inter and intramolecular forces.

Intramolecular = within the molecule. Intermolecular = between multiple molecules.

The intramolecular forces of water molecules are polar covalent (ionic? I don't know, but this isn't the point), while the intermolecular forces of water molecules are hydrogen bonds. To say hydrogen bonds are intramolecular forces is wrong.

Temperature101 said:

So let me get this right....
INTER = INSIDE...
INTRA = IN BETWEEN

Click to expand...

Think about it like this:

Intra means within, so intracristal = within the cristae.

Inter means between, so intercristal means between the cristae.

Because the cristae are inward folds of the inner membrane, the intRAcristal space must be the region on the outward side of the inner membrane, i.e. the intermembrane space. Likewise the intercristal space is the region on the inward side of the inner membrane, i.e. the matrix.