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Everyday science

Everyday science

Physics of carnivorous pitcher plants, daring nuclear-reactor mission in war-torn Vietnam 

08 Sep 2023 Hamish Johnston
Pitcher plant in Oxford

Carnivorous pitcher plants consist of hollow, cup-like structures that capture and then digest unsuspecting prey. Found mostly in the tropics, especially south-east Asia, pitcher plants have a slippery rim at the top, called a peristome that is covered in small ridges that collect water. This liquid film then causes the prey to skid, like an aquaplaning car, and fall into a pleasant pool of digestive juices at the bottom of the pitcher.

One mystery about these plants, however, is why they come in such a range of different shapes and sizes such as tubes, goblets and some even have “teeth” on their ridges.

Now, researchers at the University of Oxford’s Botanic Gardens teamed up with Oxford mathematicians so see what effect the shape and size had on the type of prey pitchers captured. After all, a more elaborate structure, such as being highly ornate, comes at a greater energy cost than having just a simple design that could do the same job.

The results, published in the Proceedings of the National Academy of Sciences, suggest that variations in peristome geometries have a profound effect on what the plant could catch and how much. “We were able to show that in an optimal structure, the cost of production might be offset by the extra prey that can be caught,” says mathematician Derek Moulton. For example, the geometry of highly flared peristomes appeared to be particularly suited to capturing walking insects such as ants.

Well-adapted to their prey

“Just as birds’ beaks are shaped differently to feed on nuts, seeds, or insects and so on,” says botanist Chris Thorogood, “these pitcher plants are well-adapted to the different forms of prey that exist in their environments.”

Since the Russian invasion last year, there has been much concern about the Zaporizhzhia nuclear power plant in Ukraine. The plant was seized by Russian forces in March after a battle with Ukrainians that resulted in some minor damage to the main facility. The Russians have controlled the plant ever since and appeared to have taken defensive positions near to the reactors.

The nightmare scenario of a nuclear power plant being destroyed by military action has thankfully not happened – at least for now – but this is not the first time that a reactor has been under threat by warfare.

Research reactor

In 1963, a US-supplied TRIGA reactor was switched on at Vietnam’s Dalat Nuclear Research Institute, which is about 300 km northeast of Ho Chi Minh City (called Saigon at the time). This was not a power reactor, but was used for training, research and isotope production. Despite the growing intensity of the Vietnam War, the reactor operated until 1968, when it was put into a long-term shutdown.

In 1975, the reactor was on the front line of battle as the North Vietnamese Army advanced on Saigon. To prevent the facility and its fuel rods from falling into enemy hands, the Americans briefly considered bombing the reactor – which would have caused radioactive contamination.

Instead a daring plan was hatched to snatch the reactor’s fuel rods. The physicist Wally Hendrickson volunteered for the mission and his story is told in a fascinating BBC Radio 4 programme called “Wally, the reluctant nuclear hero”.

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