Some symbiotic relationships, like those between certain fungi and plant roots (mycorrhizae), are so crucial that the organisms involved can't survive without each other.elaborate
The term "regeneration" in biology can refer to the regrowth of a severed limb in some animals, but it's not a simple process; the complexity varies wildly, even between closely related species. Some salamanders regrow limbs perfectly, while others can only manage a less-functional stump.
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