FYFD

Tag: biology

  • Prehistoric Filter Feeders

    Prehistoric Filter Feeders

    Earth’s earlier ages are filled with enduring mysteries about the plants and creatures that lived and died long before humanity. Many of these organisms, like the aquatic Ernietta shown above, are known only from scattered fossil remains. Yet fluid dynamics is helping us understand how Ernietta lived and fed some 545 million years ago.

    Ernietta were sack-like organisms consisting of stitched-together tubular elements. They had no way to move around and no obvious method for transporting nutrients into their bodies. Scientists hypothesized that they likely used one of two feeding methods: either Ernietta relied on its surface area to extract nutrients directly from the water or its shape enabled it to trap larger particles to feed on from the flow. To decide between these modes, scientists turned to computational fluid dynamics.

    By modelling both single Ernietta and small groups, they found that the shape of the organism generates a rotating current inside the bag that pulls flow down along one side and back up the other. Moreover, being near one another enhanced this effect, helping downstream Ernietta catch more particles than they otherwise would. All in all, the results suggest not only Ernietta’s likely feeding method but also that they lived in colonies and practiced one of the earliest known examples of communal feeding! (Image credit: D. Mazierski, source; research credit: B. Gibson et al.; via ArsTechnica; submitted by Kam-Yung Soh)

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    “-N- Uprising”

    Although Thomas Blanchard’s latest short film, “-N- Uprising”, is less overtly fluid dynamical, fluids underlie almost every aspect of it. The blossoming of flowers is often driven by osmosis and water pressure. Spiders rely on hydraulic pressure to move their limbs, and many insects first unfurl their wings by pumping hemolymph through the network of veins that lace them. Even when hidden beneath the surface, fluid dynamics is everywhere. (Video credit: T. Blanchard; via Colossal)

  • Using Bubbles to Keep Clean

    Using Bubbles to Keep Clean

    Keeping produce clean of foodborne pathogens is a serious issue, and delicate fruits and vegetables like tomatoes cannot withstand intense procedures like cavitation-based cleaning. But a new study suggests that simple air bubbles may have the power to keep our produce free of germs.

    In particular, researchers studied air bubbles injected into water as they bounced and slid along an inclined solid surface. They found that as a bubble approaches a tilted surface, it squeezes a thin film of liquid between itself and the surface. That flow creates a shear stress that pushes contaminants like E. coli away from the point of impact. When the bubble bounces away, fluid gets sucked back into the void left behind, creating more shear stress. In their experiments and simulations, the team measured shear stresses greater than 300 Pa, more than double what’s needed to remove foodborne bacteria like Listeria. (Image credit: Pixabay; research credit: E. Esmaili et al.)

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    Active Foam

    Geometrically, biological tissues and two-dimensional layers of foam share a lot of similarities. To try and understand how active changes in one cell affect neighbors, researchers are studying how foams shift when air is injected (below) at one or more sites. When a foam cell expands, it forces topological changes in neighboring cells, which researchers built an algorithm to track in real-time. 

    With some processing, they can actually visualize the radially-expanding waves of strain that pass through the foam (bottom image). This allows them to visualize the effects and interaction of multiple injection sites at once, hopefully helping unlock the mechanics behind both the foam’s shifts and those that occur in tissues. (Image and video credit: L. Kroo and M. Prakash)

  • Bubble Break-Up

    Bubble Break-Up

    When bubbles burst, they spray a myriad of tiny droplets into the air. In general, the older a bubble gets, the thinner it is, thanks to gravity draining its liquid away. When older bubbles burst, they create tinier and more numerous droplets (upper right) compared to a younger bubble (upper left). But there are more forces than just gravity at play.

    Bubbles also undergo evaporation – most effectively at the apex. Evaporation cools the cap of the bubble, increasing its surface tension and triggering a Marangoni flow that helps restore fluid to the bubble film. This stabilizes an aging bubble. 

    Contamination plays a role as well. The bright spots in the bottom image reveal bacteria in the bubble’s cap. Compared to a clean bubble, these contaminated ones can survive far longer and, when burst, produce 10 times as many droplets as a clean bubble of the same age. That has major implications for disease transmission, especially for bacteria that spend a significant portion of their life cycle in liquids. (Image and research credit: S. Poulain and L. Bourouiba; see also Physics Today)

  • How Rain Can Spread Pathogens

    How Rain Can Spread Pathogens

    Rainfall can help spread pathogens from an infected plant to healthy ones. This transfer can happen both through droplets and by dry-dispersal of pathogen spores (top). When a raindrop hits a leaf, its initial spread triggers a vortex ring of air that can lift thousands of dry spores into a swirling trajectory (bottom). That boost in height carries spores beyond the slower wind speeds of the plant’s boundary layer and into faster air streams that disperse it toward healthy plants. (Image and research credit: S. Kim et al.)

  • Plant Week: Bunchberry Dogwood

    Plant Week: Bunchberry Dogwood

    The bunchberry dogwood, unlike its taller relatives, is a low-lying subshrub that spreads along the ground. But it sports some of the fastest action of any plant, requiring 10,000 frames per second to capture! When young buds form in the bunchberry flower, their four petals are fused, completely hiding the stamens. As the plant matures, the pollen-carrying stamens grow faster than the petals, causing them to peek out the sides of the bud. But the petals stay attached at the tip, holding the stamens in while pressure inside the stamens creates a store of elastic energy.

    When disturbed, the petals break loose and the stamens spring up and out. The anthers at their tips hold the pollen in place until the stamen reaches its maximum vertical velocity, at which point the anthers swing out to release the pollen upward. In essence, the flower works in the same manner as a trebuchet, flinging pollen with an acceleration 2,400 times greater than gravity. That’s enough to coat pollen onto nearby insects and to launch the remainder high enough for the wind to catch it. (Image and research credit: D. Whitaker et al., source; via Science News; submitted by Kam-Yung Soh)

    And with that, FYFD’s Plant Week is a wrap! Missed one of the previous posts? You can catch up with them here.

  • Plant Week: Jumping Spores

    Plant Week: Jumping Spores

    You might think that plants are pretty stationary, but they have evolved a myriad of ways of moving, especially when it comes to spreading their seeds and spores. Shown above is the spore of the horsetail plant, a spherical pod with four, ribbon-like elators that are moisture-sensitive. When exposed to water, the elators curl around the spore, but as they dry out, they unfurl (top). Repeated cycles of this allows the spores to “walk” short distances (middle). And, if the elators deploy quickly, the spore can even “jump” (bottom). Researchers recorded jumps high enough for the spores to catch a breeze and disperse further. For similar moisture-driven plant action, check out this seed that buries itself! (Image and research credit: P. Marmonttant et al., source; via Science News; submitted by Kam-Yung Soh)

    We’re celebrating botanically-based physics all this week with Plant Week. Check out our previous posts on the ultra-fast suction of carnivorous bladderworts and the incredible flight of dandelion seeds.

  • Plant Week: Bladderworts

    Plant Week: Bladderworts

    Carnivorous plants live in nutrient-poor environments, where clever techniques are necessary to keep their prey from getting away. The aquatic bladderwort family nabs their prey through ultra-fast suction. This starts with a slow phase (top) in which water is pumped out of the trap. Because the internal pressure is lower than the external hydrostatic pressure, this compresses the walls of the trap, and it leaves the trap’s door narrowly balanced on the edge of stability. A slight perturbation to the trigger hairs around the door will cause it to buckle. 

    That’s when things get fast. As the door buckles and the trap expands to its original volume, water gets sucked in, pulling whatever prey was nearby with it. The door reseals as the pressure inside and outside the trap equalizes, and, in only a couple milliseconds total, the bladderwort has its snack. It secretes digestive enzymes to break down what it’s caught, and over many hours, it pumps out the trap to reset it. (Image and research credit: O. Vincent et al.; submitted by David B.)

    All this week, FYFD is celebrating Plant Week. Check out our previous post on how dandelion seeds fly tens of kilometers.

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    Plant Week: Dandelions in Flight

    To kick off Plant Week here on FYFD, we’re taking a closer look at that ubiquitous flower: the dandelion. Love ‘em or hate ‘em, these little guys manage to get just about everywhere, thanks in part to their amazing ability to stay windborne for up to 150 km! To do that, the dandelion uses a bristly umbrella of tiny filaments, known as a pappus, that can generate more than four times the drag per area of a solid disk. Its porosity – all that empty space between the filaments – is also key to its stability; it helps create and stabilize a separated vortex ring that the seed uses to stay aloft. Check out the full video below! (Image and video credit: N. Sharp)