Plants have no lungs, so how does O2 reach the cells of a thick trunk or a deep root for respiration?

7 answers & replies

• [+][–]Tanvi Deshmukh12thSample· 1mo ago

  ok this is a very NCERT-line-heavy topic so let me give you the three reasons the book gives!!

  1. Each plant part handles its own gas exchange, very little gas is transported from one part to another.
  2. Plants don't have big demands for gas exchange. Roots, stems, leaves respire at rates far lower than animals. Only during photosynthesis are large volumes exchanged, and the leaf is built to handle that (and O2 is released inside the cell then, so no shortage).
  3. The distance for diffusion is short. In a stem the living cells are in thin layers just under the bark, and the bark has lenticels. The inside of a trunk is mostly dead (mechanical support only). In a leaf, the spongy mesophyll has big air spaces, so cells face an air space.

  So basically almost every LIVING cell has some surface touching air. No lungs needed!

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• [+][–]Siddharth RaoDropperSample· 1mo ago

  On substrate: carbohydrates are the usual one, yes, but fats and proteins can be used too. They don't first turn into glucose though, that's the thing I got wrong last year. They get broken into their own building blocks and plug in at different points of the same pathway. Fats go to fatty acids and glycerol, the fatty acids become acetyl CoA and glycerol goes in as PGAL. Proteins go to amino acids, which are deaminated and enter the cycle at different points.

  That is also why RQ differs for different substrates (you'll hit that later in the chapter). So glucose is the textbook model, not the only fuel.

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• [+][–]Pooja Iyer12thSample· 1mo ago

  omg wait I love this one 😭 simple version: stomata are THE gateway for plants, so oxygen enters through stomata of leaves and then goes down the stem to the root!! that's why plants in waterlogged pots die, the gas pipeline gets blocked by water. Pipeline = stomata. Pipeline blocked = dead plant. Dramatic but true

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  • [+][–]Kavya NaikDropperSample· 1mo ago

    Pooja the stem-to-root pipeline is not what happens. Roots take O2 from the air spaces between soil particles, they don't get it from leaves. Waterlogged soil kills plants because those air spaces fill with water, so roots get very little O2. That is also why mangrove plants have pneumatophores, roots that stick up out of the mud to take in air.

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    • [+][–]Pooja Iyer12thSample· 1mo ago

      ohh 😭 yes yes pneumatophores, I even have it in my notes under adaptations. deleting my pipeline lol. thank you kavya

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• [+][–]Nisha Verma12thSample· 1mo ago

  Respiration does NOT stop in the day. Every living cell respires 24 hours, otherwise it would have no ATP. In the day the leaf is doing photosynthesis which makes more O2 than respiration uses and uses more CO2 than respiration produces, so the net exchange looks like O2 out, CO2 in. At night photosynthesis stops (no light), so only respiration is visible: O2 in, CO2 out.

  So your answer should have been: respiration goes on all the time, in all living cells. In the test they probably asked about net gas exchange or you said "only". "Only" is the trap word.

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  • [+][–]Yash Tiwari11thSample· 1mo agoAuthor

    "Only" is the trap word, noted bhai 😂 thanks all, now the lenticel thing makes sense, the inside of the trunk is dead anyway so nobody needs oxygen there.

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