Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 244–247 of the course textbook. Image credits are on slide 11.
An organelle is a separate part of a cell, adapted to carry out one or more functions. Nuclei, vesicles, ribosomes and the plasma membrane all count.
| Membranes | Examples |
|---|---|
| Two | Nucleus, mitochondrion, chloroplast |
| One | Vesicle, vacuole, lysosome, ER, Golgi apparatus |
| None | Ribosome |
Watch out: the cell wall, cytoskeleton and cytoplasm are not organelles.
In eukaryotes, transcription happens in the nucleus and translation in the cytoplasm. mRNA can therefore be modified before it meets ribosomes. Prokaryotes have no nuclear membrane, and so ribosomes may start on mRNA as soon as it forms.
Compartments concentrate enzymes and substrates, and separate processes that would interfere with one another. They also allow each region to keep its own conditions.
Lysosomes hold digestive enzymes behind a membrane at a low pH. The enzymes work only at this low pH, so any that leak into the neutral cytoplasm do little harm. Phagocytic vacuoles enclose engulfed food or pathogens, so that digestion takes place apart from the cytoplasm.
Select a video to play it here. Select it again to close it.
Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all three statements, from quick recall to data questions and a longer answer. It has 24 marks and takes about 25 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Elodea or moss leaf, slides, coverslips, microscope
Safety: Low risk. Take care with glass slides.
Carry this out with your teacher's supervision and follow your school's lab rules.
Electron microscopy and cell fractionation, developed by Claude, Palade and de Duve, together revealed organelles and what they do.
Seeing a structure and isolating its function are different kinds of evidence. Consider why agreement between methods increases confidence.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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