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🧬 NEET Biology❓ Question

If CFCs are used everywhere, why does the ozone hole sit over Antarctica? And what does UV-B actually damage?

Riya Singh12th Sample

10 Oct 2026 · 1 min read

I was writing a late-night poem about the sky wearing a thin blanket when I realised I don't actually understand the thing I'm writing about 🙃

Ozone depletion in NCERT: ozone in the stratosphere absorbs harmful UV; its formation and breakdown are balanced naturally, but CFCs disturb that. UV in the stratosphere acts on CFCs and releases chlorine atoms, which then degrade ozone to oxygen. Then it says the depletion is "particularly marked over the Antarctic region" and calls it the ozone hole.

My questions:

  1. CFCs are used in cities across the world. Why is it Antarctica that gets the hole?
  2. The chlorine atom "is not consumed" in the reaction. How does one atom destroy so much ozone, and what is the reaction?
  3. What does UV-B actually do to us? I remember skin cancer, but NCERT also lists something about the eye.

The second part of the chapter, deforestation, is where I have fewer questions but I still don't remember the forest cover numbers from the National Forest Policy and what Joint Forest Management is. A short summary of both would help me finish this chapter before my brain melts.

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7 answers & replies

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  • [+]Nisha Verma12thSample· 9d ago

    Reaction first. UV on O2 splits it into two oxygen atoms, each of which combines with an O2 to make ozone: O2→O+OO_2 \rightarrow O + O, O+O2→O3O + O_2 \rightarrow O_3. Ozone breaks down again to O2 and O, so there's a balance.

    CFC under UV releases Cl. Then: Cl+O3→ClO+O2Cl + O_3 \rightarrow ClO + O_2 ClO+O→Cl+O2ClO + O \rightarrow Cl + O_2 The Cl atom is regenerated at the end, so it acts as a catalyst and is not used up. The same Cl can go around the cycle again and again, which is why a small amount of CFC can damage a large amount of ozone.

  • [+]Pooja Iyer12thSample· 9d ago

    ahh the hole is a literal hole, riya!! it's over Antarctica because CFCs are only used in cold countries, that's why only the cold poles have the problem. So ozone is zero in that circle and UV pours in!!

    • [+]Zoya Khan12thSample· 9d ago

      Pooja, CFCs were used all over the world and they spread through the atmosphere, they don't stay where they are released. The Antarctic is special because of its extremely cold winter stratosphere (polar stratospheric clouds form and help the chlorine reactions run faster when the sunlight returns in spring), so the depletion is much more severe there. And "hole" means a large area of thinned ozone layer, not a place where ozone is exactly zero.

      • [+]Riya Singh12thSample· 9d agoAuthor

        thank you both. the "spreads everywhere but the polar spring does the damage" bit makes so much more sense than my first guess. I'm changing my poem's line from "a hole in the sky" to "a thinning" 🌙

        • [+]Pooja Iyer12thSample· 9d ago

          oops I was so confident 😭 and I'm now going to edit the notes I posted to my friends

  • [+]Siddharth RaoDropperSample· 9d ago

    UV-B: it damages DNA, and mutations may follow. In skin it causes ageing, damage of skin cells and various types of skin cancers. In the eye, high doses cause inflammation of the cornea, called snow-blindness, which can lead to permanent damage to the cornea, and cataract is also mentioned. The ozone layer absorbs most of this UV, so thinning of it increases the amount reaching the earth.

    Also: the Montreal Protocol (1987) was the international treaty to control emission of ozone-depleting substances. Direct-recall for NEET.

  • [+]Kavya NaikDropperSample· 9d ago

    Deforestation quick-fire:

    • Deforestation = conversion of forested area to non-forested area.
    • National Forest Policy (1988) recommends 33% forest cover for the plains and 67% for the hills.
    • Slash and burn agriculture (jhum cultivation in the north-eastern states) is one of the causes, with the forest burned and cleared for a few seasons and then left.
    • Effects: more CO2 in the air, loss of biodiversity, hydrological cycle disturbed, soil erosion, desertification.
    • Joint Forest Management (JFM): introduced by the government around 1990 (after the 1988 forest policy), local communities work with the forest department to protect and manage forests, and in return get forest products like fruits, gum, rubber, medicines and so on, along with the satisfaction of protecting the forest.

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