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Level 1 of 7 · Organism ·
Mitochondria: an oval or a tube? Why they look different here from the drawing in your book
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Hide The real tissue, on a slide A very thin slice of the lining of a cervix, stained and photographed through a light microscope. The model is traced from it.
The real tissue, through a light microscope: the slice outlined in green on the model. The model's cut face is traced from it. About 0.4 mm across.
Hide Closer, on the same slide Through a stronger lens: the lining cells, side by side.
Closer: one layer of tall cells, side by side, each with its nucleus. About 0.06 mm across. The lit-up cell in the model is a cell like these.
Hide This cell, under an electron microscope One real slice of the same cell, much thinner than a light microscope's slide.
Nucleus Endoplasmic reticulum Mitochondria
Lysosomes Endosomes Lipid droplets Cell membrane
This cell under the electron microscope: one real slice, 12 µm across, from the glass up. It crosses the box of the cell you are in. Each part the computer found is outlined in its colour in the 3D. On the left, the cell goes on, thinner and thinner.
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Eric Betzig · Nobel Prize 2014
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Who is talking? Eric Betzig , a physicist. He won the Nobel Prize in Chemistry in 2014 for microscopes that can see single molecules inside living cells.From the 632nm podcast, episode 61 (2026). He says that the pictures of cells in books are too empty: a real cell is crowded. Watch the whole episode ↗ ▶ Eric Betzig ▶ Watch the film: Eric Betzig
Topics 2–5
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Mitochondria: an oval or a tube?
Both are right. A book draws a mitochondrion as an oval, cut open so that you can see inside it. This zoom shows the mitochondria of one real cell, measured by an electron microscope: many of them are long tubes. Here is why the two look different.
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In this cell
There are 351 mitochondria. 7 in 10 are short, under 2 µm long: these look like the drawing in a book. 3 in 10 are longer tubes, from 2 µm up to 14 µm long, and they hold three quarters of all the mitochondria. Mitochondria also join together and divide again all the time, so their shapes change.
So the drawing in a book shows one short mitochondrion, cut open lengthways , so that you can see its two membranes and the folds (cristae). A photograph from an electron microscope shows one thin slice of the cell: in it, short and long mitochondria all look like ovals or circles.
In your exam
Exam questions use drawings and photographs like the ones in your book. Name a mitochondrion by what it has, not by its whole shape: two membranes, and the inner one folded (cristae).
Explore more
Measured in this cell (OpenOrganelle, jrc_hela-2). The two mitochondria in the steps, their outlines and the photograph are real: the outlines are the computer's own, from the same data as the 3D. The slice straight across the tube is imagined; its outline is worked out from the real tube. Others found the same with slices one after another: what looked like many separate mitochondria in yeast is one branched mitochondrion (Hoffmann and Avers, Science , 1973); the mitochondria of a muscle cell form a joined-up network (Glancy and others, Nature 523:617, 2015); mitochondria join and divide (Westermann, Nature Reviews Molecular Cell Biology 11:872, 2010).
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About this picture
Real: the woman's body and organs (a medical atlas), the tissue photographs, and the cell and its organelles, measured by an electron microscope .A model: the tissue, the inside of the cut organ, the cell rising from the tissue, and the molecules . Their sizes are real; where each cell and molecule sits is made up. The kinesin walks 100 times slower than in life.Three different people: the body, the tissue and the cell. The cell is a HeLa cell , grown in a laboratory.Colours are chosen: most parts of a cell are too small to have a colour. The nucleus is violet at every level.Not shown: water, most proteins and ribosomes (far too many), and movement : the cell was frozen.
Sources
The body: HuBMAP Human Reference Atlas, United Female v1.10 (Visible Human Female, US National Library of Medicine), CC BY 4.0. Since October 2026 that link opens a “Not Found” page on the atlas's website, and the atlas's 3D reference library lists the organs.
The tissue: photographs by Mikael Häggström, M.D. (Wikimedia Commons), CC0.
The cell: OpenOrganelle, jrc_hela-2 , Janelia Research Campus, CC BY 4.0 (Xu et al. 2021 and Heinrich et al. 2021, Nature 599).
The molecules: Protein Data Bank structures (CC0); HeLa protein numbers from Mueller et al. 2020, Nature 583, through PaxDb.
The film: 632nm podcast, episode 61 (8 September 2026), three swear words silenced.
The 3D models were made from these data for this hub.
Something wrong, or a suggestion? Please contact me: dmompelriera@nlcsjeju.kr . Checked against the Cambridge IGCSE Biology 0610 syllabus for 2026–2028.
Lining cells
Nucleus
Connective tissue
Small blood vessel
Crypt, cut across
One lining cell
Its nucleus
Connective tissue
Red blood cell
