Q.What is common to the techniques

Biodiversity conservation operates through two broad strategies: in situ (protecting species in their natural habitats) and ex situ (conserving them outside their natural environments). The three techniques mentioned—in vitro fertilisation, cryopreservation, and tissue culture—all fall squarely into the ex situ category because they involve maintaining genetic material or organisms away from their wild settings.

In vitro fertilisation allows fertilisation to occur in controlled laboratory conditions, producing embryos that can later be implanted. Cryopreservation freezes gametes, embryos, or seeds at ultra-low temperatures for long-term storage of genetic diversity. Tissue culture propagates plants from small tissue samples under sterile conditions. Each technique removes the biological material from nature and works with it in artificial environments—laboratories, gene banks, or culture facilities. …

When we talk about conserving biodiversity, the fundamental divide is between in situ and ex situ strategies. In situ conservation means protecting species in their natural habitats — think national parks, wildlife sanctuaries, biosphere reserves where organisms live, breed, and evolve in the wild. Ex situ conservation, on the other hand, takes organisms or their genetic material out of their natural homes and preserves them in artificial, controlled environments.

All three techniques mentioned in the question fall squarely into the ex situ category, and here's why each one does:

In vitro fertilisation involves fertilising an egg with sperm outside the body, in a laboratory dish or test tube (literally "in glass"). For endangered species, this technique allows scientists to produce offspring even when natural mating is difficult or impossible. The embryos can then be implanted into surrogate mothers or cryopreserved for future use. The entire process happens in a lab, far removed from the organism's natural environment.

Cryopreservation is the freezing and storage of biological material — gametes (sperm and eggs), embryos, seeds, or even tissue samples — at ultra-low temperatures, typically in liquid nitrogen at around –196°C. This technique essentially puts life on pause, preserving genetic diversity for decades or even centuries. Gene banks, seed banks, and sperm/egg banks are all forms of cryopreservation. Again, this is entirely artificial storage, not conservation in the wild.

Tissue culture (or micropropagation) involves growing plants from small tissue samples — a few cells, a leaf fragment, or a shoot tip — in sterile, nutrient-rich media under controlled laboratory conditions. It's a powerful tool for rapidly multiplying rare or endangered plant species, producing thousands of genetically identical individuals from a single parent plant. The whole process unfolds in culture flasks and growth chambers, not in forests or grasslands.

Sort each technique by where it physically happens: fertilising an egg in a dish, freezing gametes, growing plant tissue in …