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B2.2.9 (HL)—Vesicles in cells

Vesicles transport proteins and other cargo between organelles, the plasma membrane, and extracellular space during secretion, uptake, and intracellular delivery.

Syllabus
First assessment 2025
Objective
B2.2.9
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1

Common command terms

  • Identify

Scoring notes

Common mistake
Putting the Golgi apparatus before rough ER in the protein export route.

Recent exam appearances

May 2025Paper1A ["HL"] · TZ215[ 1 ]B2.2.9 (HL)—Vesicles in cells
May 2017Paper1 ["HL"] · TZ23[ 1 ]B2.2.9 (HL)—Vesicles in cells
Practice this objective

Coverage 2017–2025 · Updated 15 Jul 2026

Vesicles Move Cargo Without Mixing Compartments

HL only

Vesicles move membrane and soluble cargo by budding from one compartment and fusing with a specific target while keeping cargo enclosed.

Clathrin proteins assemble as a coat on the cytoplasmic face of a budding membrane, helping curve it into a coated pit and select cargo through adaptor proteins. The coat is removed before targeting and fusion.

Trace vesicle traffic: cargo selection → clathrin-coated bud → membrane scission → uncoating → target recognition → fusion and cargo delivery.

In receptor-mediated endocytosis, receptors and bound cargo cluster in a clathrin-coated pit that pinches off; in secretion, a Golgi-derived vesicle later fuses with the plasma membrane.

Clathrin helps form and select coated vesicles; it does not determine every later target by itself, and vesicle traffic is not random diffusion.

Vesicles in cells

HL only

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Identify.

Command terms

Identify

What earns marks

Build the answer around this relationship: Protein export commonly follows rough ER to Golgi apparatus to plasma membrane.

Watch for

Putting the Golgi apparatus before rough ER in the protein export route.

Representative question

Question 1

[Maximum number: 1]

What is the role of clathrin molecules in the formation of vesicles?

A

Facilitate transport of sodium and potassium ions

B

Bind together to help the membrane become indented

C

Adhere to the phospholipid bilayer to increase fluidity

D

Create a concentration gradient for uptake of substances into vesicles

Link Organelle Structure To Function

HL only

HL structure-function answers should link organelle compartments to the process they support. Mitochondria use cristae, intermembrane space, and matrix; chloroplasts use thylakoid membranes, thylakoid space, and stroma. Protein export is a route: rough ER makes entry-pathway proteins, Golgi modifies and sorts, vesicles bud and fuse with targets.

  • Mitochondrion: cristae/inner membrane for ATP synthase, intermembrane space for protons, matrix for Krebs cycle enzymes.
  • Chloroplast: thylakoid membranes for photosystems/ATP synthase, thylakoid space for protons, stroma for Calvin cycle enzymes.
  • Secretory pathway: rough ER to Golgi to vesicle to plasma membrane or another target.

Concept essentials

  • Protein export commonly follows rough ER to Golgi apparatus to plasma membrane.
  • Secretory vesicles can move enzymes out of cells by exocytosis.
  • Clathrin helps membranes indent during coated vesicle formation.
  • Vesicles link organelles, membranes, and extracellular release pathways.