Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 248–255 of the course textbook. Image credits are on slide 13.
A double membrane separates aerobic respiration from the cytoplasm. The inner membrane is folded into cristae, giving a large surface area for electron transport chains and ATP synthase. Protons are pumped into the small intermembrane space, so a steep gradient builds quickly. The matrix holds the Krebs cycle enzymes and substrates together at a suitable pH.
Stacked thylakoid membranes (grana) give a large surface area for photosystems, so much light is absorbed. Protons pumped into the small volume inside the thylakoids quickly make a steep gradient for ATP synthase. The stroma holds the Calvin cycle enzymes, such as rubisco, and their substrates, separate from the light-dependent reactions.
The two membranes of the nuclear envelope keep DNA apart from the cytoplasm. They join at the nuclear pores, which control traffic: mRNA leaves; nucleotides, proteins and ATP enter. The outer membrane is continuous with the rough ER. At the start of mitosis and meiosis the envelope breaks into vesicles, so spindle microtubules can reach the chromosomes; afterwards the vesicles re-form a nucleus around each set.
Both are 80S ribosomes. Free ribosomes make proteins that stay in the cytoplasm, or are imported into the nucleus, mitochondria or chloroplasts. Ribosomes bound to the rough ER make proteins for secretion, for lysosomes or for the plasma membrane; these enter the ER lumen and travel on in vesicles. Several ribosomes on one mRNA (a polysome) make many copies at once.
A stack of flattened sacs (cisternae). Vesicles from the rough ER fuse with the side facing the ER. Proteins pass from cisterna to cisterna, where enzymes modify them, for example by adding sugars (glycosylation) or phosphate. These changes label proteins for their destination. Vesicles bud from the far side and carry the proteins to the plasma membrane for secretion, or to lysosomes.
Vesicles are small sacs of membrane that carry materials between compartments and across the plasma membrane. In receptor-mediated endocytosis, a substance binds receptors and clathrin proteins link into a cage on the inner face of the membrane, pulling it into a coated pit that pinches off as a vesicle. Cells take in LDL cholesterol this way, and many viruses use it to enter.
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A printable worksheet covering all six statements, from quick recall to data questions and a longer answer. It has 30 marks and takes about 30 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Public-domain electron micrographs of a mitochondrion and a chloroplast, ruler
Safety: No practical hazards.
Carry this out with your teacher's supervision and follow your school's lab rules.
Camillo Golgi described his apparatus in 1898, but many thought it was a staining artefact until electron microscopes confirmed it.
Consider what kinds of evidence persuade us that a structure is real, and not a product of the method used to see it.
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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