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Mold spores sometimes have the same shape as platelets in blood. If I were designing a spore it would probably be spherical. Is there any advantage to this cup-like shape?

Maybe there is some advantage in flow properties in fluid or air? And maybe the physics of structures on that scale differ from that of everyday objects?

Thanks.

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The functional implications of the biconcave shape of human red blood cells are not fully understood. Several hypotheses have been suggested as explanations, including bending energy (1) and effects on oxygen transport (2). More recently, it has been hypothesized that the shape is important for the flow properties of the blood cells in capillaries. Uzoigwe (3) states that

The deleterious nature of turbulent flow on the cardiovascular system suggests that the biconcave disc form has evolved out of a necessity to maximise laminar flow, minimise platelet scatter which in turn suppress atherogenic activity in the large vessels.(...) The biconcave profile of the discocyte means that much of the mass is distributed in the periphery. This increases the moment of inertia of the cell and subsequently renders the erythrocyte less prone to rotation during flow in the large vessels. Here it is suggest that this reduction in rotation promotes laminar flow and discourages platelet scattering by minimising the "Eddy currents" and it thus anti-atherogenic. A number of pathological mutations result in the red blood cell adopting a spherical shape as opposed to the biconcave disc profile. The sphere has a smaller moment of inertia when compared to the discocyte, as much of the mass is distributed round the centre. The spherocyte is hence much more prone to rotation during flow in the large vessels.

The advantages of various structures do depend on the scale of the system, as you say. For red blood cells, the size of capillaries and veins are of importance. The shape of red blood cells differ in animals that have blood transport systems with different structures than humans. Thus, the red blood cell shape is likely optimized with respect to movement in the human blood transport system, with oxygen diffusion also being a possible factor. To determine what advantages a specific shape of spores would give, you would need to consider the expected environment the spores would live in and their typical lifecycle.

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