Trace the endomembrane pathway
Rough and smooth endoplasmic reticulum, the Golgi body and lysosomes have distinct structures and linked roles.
Section 1.2 · Cells as the basic units of living organisms
AS Level · Cambridge International Biology 9700, 2028–2030. Interpret only the structures supported by the provided image or description. Written practice is self-checked; it does not demonstrate practical microscopy competence.
Before you begin
- Recognise that organisms are made of cells and that a light microscope produces a magnified image.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which structure has ribosomes attached to its surface?
What you will learn
- Recognise rough and smooth endoplasmic reticulum, Golgi body and lysosomes
- Relate each structure to its main role in a eukaryotic cell
Two forms of endoplasmic reticulum
Rough endoplasmic reticulum is a membrane network with ribosomes attached to its surface. It is involved in processing and transporting proteins made by those ribosomes. Smooth endoplasmic reticulum lacks attached ribosomes and is involved in lipid synthesis and other cell-specific processes.
The Golgi body is a stack of flattened membrane sacs. It modifies, sorts and packages substances, including proteins and lipids, for transport or secretion. The rough endoplasmic reticulum and Golgi body are separate structures linked by vesicle transport.
Lysosomes contain digestive enzymes
Lysosomes are membrane-bounded vesicles containing enzymes that digest material within the cell. They can break down substances taken into the cell and recycle components. Their exact appearance and abundance depend on cell type and activity.
A small circular vesicle should not be labelled a lysosome from shape alone. Use context and the level of detail in the image. The roles described here are the core distinctions; avoid claiming that every protein follows an identical route.
Pause and explain
Which organelle modifies, sorts and packages substances?
Worked example
A cell image shows flattened membranes with ribosomes attached, a stack of curved sacs and small enzyme-containing vesicles. Relate each to a role.
Show the worked solution
- Attached ribosomes identify rough ER.
- A stack of sacs is consistent with Golgi.
- Enzyme-containing vesicles are lysosomes.
Answer The ribosome-studded membranes are rough endoplasmic reticulum, which processes and transports newly made proteins. The stack is the Golgi body, which modifies, sorts and packages substances. The enzyme-containing vesicles are lysosomes, which digest material inside the cell.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare rough and smooth endoplasmic reticulum by one structural and one functional difference.
Give me a hint
Use attached ribosomes and typical roles.
Compare my reasoning
- Rough ER has attached ribosomes; smooth ER does not.
- Rough ER processes proteins; smooth ER is involved in lipid synthesis.
Rough ER has ribosomes attached and is involved in processing and transporting proteins. Smooth ER lacks attached ribosomes and is involved in lipid synthesis and other cell-specific processes.
Look for these in your work
- Structural difference
- Functional distinction
A cell secretes a protein. Outline a possible route through the organelles in this lesson.
Give me a hint
Do not treat the route as a single uninterrupted organelle.
Compare my reasoning
- Ribosomes on rough ER make the protein.
- Vesicles carry it to the Golgi for modification and packaging.
Ribosomes associated with rough ER make the protein; the rough ER processes and transports it in vesicles to the Golgi body, where it can be modified, sorted and packaged for secretion.
Look for these in your work
- Rough ER included
- Golgi role correctly described
A student says lysosomes produce ATP because they contain enzymes. Correct the error.
Give me a hint
Enzymes have many roles; identify this organelle’s function.
Compare my reasoning
- Lysosomal enzymes digest material.
- ATP production is associated mainly with respiration in mitochondria.
Lysosomes contain digestive enzymes and break down material within the cell. They are not the organelle mainly associated with ATP production during respiration; that role is associated with mitochondria.
Look for these in your work
- Lysosome role
- ATP organelle distinguished
Common mistakes
- Calling smooth ER ribosome-studded
- Treating Golgi stacks as part of the nucleus
- Describing lysosomes as energy-producing organelles
What can you explain now?
Which structure has ribosomes attached to its surface?
Compare with the explanation
Rough endoplasmic reticulum
Attached ribosomes give it a rough appearance.
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Make it stick
How do rough ER, smooth ER, the Golgi body and lysosomes differ?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.