2.2 Cell Structure & Function

Structure fits function

An organelle's structure matches its job. Cells with high energy demands (like muscle) hold many mitochondria; cells that secrete lots of protein have extensive rough ER and Golgi. Internal membranes fold to pack more working surface into a small space.

Membranes maximize surface area

Folded membranes increase surface area for reactions. The inner mitochondrial membrane folds into cristae to boost ATP output; chloroplast thylakoids stack to capture more light. Prokaryotes lack membrane-bound organelles and a nucleus, so their reactions happen in the cytoplasm or on the plasma membrane.

Key terms

Structure–function relationship

An organelle's shape and amount match the cell's needs (e.g., many mitochondria in muscle).

Cristae

Folds of the inner mitochondrial membrane that increase surface area for ATP production.

Thylakoid

Stacked chloroplast membranes that increase surface area for the light reactions.

Prokaryote vs. eukaryote

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both.

Compartmentalization

Membranes divide the cell so different reactions can run at once.

Try an AP-style question

The inner mitochondrial membrane is highly folded into cristae. What is the functional advantage?

1. It stores extra glucose so glycolysis can run inside the matrix
2. It lets the mitochondrion divide more quickly by binary fission
3. It separates the mitochondrial DNA from the mitochondrial ribosomes
4. It increases surface area for electron transport chains and ATP synthase