Looped Network Optimizes Water and Nutrient Flow

Biological Strategy

Lemon

Alexandra Ralevski

Image: Sami Nurmi / Flickr / Some rights reserved

Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Vein systems in leaves allow for optimal flow and resilience to damage due to a dense network of nested, interconnected loops.

In both natural and man-made systems, networks transport materials from a central source to widely distributed destinations. Branched, tree-like networks that contain repeatedly forking nodes, as are often found in river networks and sewage systems, are one of the most common network designs. Although this design allows for rapid and efficient transport through a system, it is only optimal if the flow is constant across time and space. In other systems, such as the blood vessels of the brain and the veins of leaves, networks must be optimized to quickly respond to fluctuations in load, or rapidly re-route flow in response to damage. These networks all have a common pattern of interconnected, nested loops. Loops are essential for these networks, because they allow material to follow different paths as conditions change.

For example, in leaves of the lemon tree, a main vein runs through the center, transporting water to the photosynthetic cells, and sugars away from them. Secondary veins branch off the main vein, similar to a tree-like network. However, all the veins are additionally connected to each other through a pattern of nested loops, with several smaller loops inside larger ones. This pattern of interconnected, nested loops throughout the leaf allows for flow to be quickly re-routed to any other vein in the event of injury, or when a change in flow is required. This allows the leaf to rapidly and efficiently respond to fluctuations in flow, while remaining resilient to damage.

Fluorescent dye shows how flow transport is re-routed in a lemon leaf after damage to the primary vein. Credit: National Science Foundation/Magnasco and Katifori