Question 1

What is the difference between a double-membrane and a single-membrane organelle?

Accepted Answer

Mitochondria and plastids are surrounded by two membranes, called an envelope. Peroxisomes and glyoxysomes are microbodies surrounded by one membrane. This boundary difference is a central feature of their classification.

Question 2

Why are mitochondria and plastids called semi-autonomous organelles?

Accepted Answer

They contain their own circular DNA and 70S-type ribosomes, so they can make some of their own proteins. They still depend on the nucleus and the wider cell for many components, which is why they are called semi-autonomous.

Question 3

What is the function of mitochondrial cristae?

Accepted Answer

Cristae are folds of the inner mitochondrial membrane. They increase membrane surface area for respiratory machinery associated with ATP synthesis, while the matrix remains the space inside the inner membrane.

Question 4

How are grana and stroma lamellae related in a chloroplast?

Accepted Answer

Grana are stacks of thylakoid membranes. Stroma lamellae are membranous channels that connect different grana. Together they form an internal membrane system surrounded by the stroma, which contains the Calvin-cycle enzymes.

Question 5

How do peroxisomes differ from glyoxysomes?

Accepted Answer

Peroxisomes occur in animal tissues and contain catalase for breaking down hydrogen peroxide. Glyoxysomes are especially found in germinating oil-rich seeds and contain enzymes involved in converting fatty acids into carbohydrates through the glyoxylate cycle.

Membrane-Bounded Organelles — Mitochondria, Plastids & Microbodies

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