Paper 2 · June 2004 · Cell Structure and Membranes
An organelle of an animal cell, seen under the electron microscope, is bounded by two membranes and its inner membrane is folded inwards into cristae. This organelle is
Aa centriole, a barrel of nine triplets of microtubules that organises the spindle during cell division
Ba lysosome, a single membrane sac of hydrolytic enzymes that digests worn out organelles and bacteria
Ca mitochondrion, the site of the Krebs cycle and of oxidative phosphorylation in the cell
Da ribosome, a particle of two subunits of RNA and protein on which polypeptide chains are assembled
Explanation
The cristae are infoldings of the inner mitochondrial membrane. They carry the electron transport chain and the ATP synthase particles, and folding them increases the membrane area packed into the organelle, so a cell that respires hard has mitochondria with many closely packed cristae.
Derived from ZIMSEC Biology Paper 2, Jun 2004, Q1