1.2.1—Eukaryotic cell organelles

Eukaryotic cells divide their cytoplasm into membrane-bound organelles. Each organelle has a structure that supports a particular job, while ribosomes carry out protein synthesis but are not membrane-bound.

• Cell surface membrane: partially controls exchange between the cell and its surroundings.
• Nucleus, nuclear envelope and nucleolus: the nucleus contains chromosomes; pores in the envelope regulate traffic; the nucleolus makes ribosomal components.
• Rough and smooth endoplasmic reticulum: rough ER has ribosomes and processes proteins; smooth ER lacks ribosomes and makes lipids.
• Golgi body and vesicles: the Golgi modifies and packages cell products; vesicles transport or store them.

• Mitochondria: folded inner membranes and matrix enzymes support aerobic respiration; mitochondria also contain small circular DNA and 70S ribosomes.
• Ribosomes: 80S ribosomes occur in the eukaryotic cytoplasm; 70S ribosomes occur in mitochondria and chloroplasts; both are sites of translation.
• Lysosomes: hydrolytic enzymes digest worn-out structures, engulfed material and cell debris.

• Centrioles and microtubules: organise microtubules and support cell shape, movement and chromosome movement during division.
• Cilia: move substances across the cell surface.
• Microvilli: increase cell-surface area for absorption.

• Cell wall: provides support outside the cell-surface membrane; plant walls contain cellulose.
• Chloroplasts: thylakoid membranes and grana absorb light for photosynthesis; chloroplasts contain small circular DNA and ribosomes.
• Plasmodesmata: cytoplasmic bridges that allow transfer between neighbouring plant cells.
• Large permanent vacuole and tonoplast: the vacuole stores cell sap and supports the plant cell; the tonoplast is its partially permeable membrane.

A structure–function link is not the same as an exclusive identity: not every eukaryotic cell contains every organelle, and centrioles are not found in flowering plants and fungi. Do not describe a ribosome as membrane-bound or treat a cell wall as the membrane controlling exchange.