Science Practice Challenge Questions

29.1 Types of Skeletal Systems


Biomimetics is the design of engineering solutions guided by biological solutions to similar problems. Support materials in biological systems must be tough, flexible, and light. Engineers define a tough material as one that can absorb energy without fracturing. Flexibility is the ability to deform elastically but able to return to the original shape. Size of in both biological and designed system is often determined by many factors. Density of a material becomes important when size cannot be adjusted but lightness is needed. An analysis of several biological materials in terms of these parameters (Wegst and Ashby, Philosophical Magazine, 84, 2004) shows that selection has conserved a bounding value in the product of these parameters; the square root of all of the ratios of toughness and elasticity lie above the dashed line. Patterns like this lead to new science but, in applications to biomimetics, they can also lead to improved technologies.

This graph plots the log of toughness on the y-axis versus the log of 1/elasticity on the x-axis. A straight line runs diagonally from 10 on the y-axis to 100 on the x-axis. A label indicates that along this line, the square root of toughness divided by elasticity is equal to point one. A variety of biopolymers and biominerals appear above this line. Biopolymers, including collagen and cork, are in the upper left corner. Biominerals, including hydroxyapatite and calcium carbonate, are in the lower right c
Figure 29.39

Biopolymers like collagen have higher toughness and higher elasticity. Biominerals like enamel have lower toughness but provide rigidity. Some organisms support soft tissue by combining biopolymers and biomaterials. Some rely more on biopolymers. Note that this is a logarithm scale not a linear scale. So that the difference in toughness of keratin and bone is roughly 100 and the difference in rigidity of these to materials is nearly that large.

  1. Use this graph to pose questions about the fitness of various biological solutions to the problem of capturing, storing, and using free energy. (Remember that engineers define “toughness” as the ability to absorb energy without fracturing.)
  2. Refine this representation by identifying an important property of a biomaterial that is missing and explain its importance in terms of free energy acquisition and use.
  3. Explain how this data indicates that the properties of biopolymers will lead to a better biomimetic design of the humanoid robot than is imagined in C3PO of Star Wars fame.

29.4 Muscle Contraction and Locomotion


An investigation of the evolution of muscle was made by Steinmetz et al (Nature, 487, 2012), and a sample of data is presented in the following diagram. Below the accepted phylogeny of major groups are rows with families of genes that code for different muscle proteins, including actin and myosin. Shared genes are shown where the cell is darkened. Samples of genes associated with striated and smooth muscle and the Z-disc that terminates the actin-myosin pair are clustered. These are shown in the diagram below, where groups in which muscle cells occur lie within the box whose edges are dashed lines.

This diagram indicates which muscle proteins are present in plants, fungi, and various animals. The diagram also notes that all of animals except the sponge possess muscle cells and that fungi and plants do not possess muscle cells. The muscle proteins are divided into three groups: striated and smooth proteins, striated proteins, and disc proteins. The four striated proteins are actin, myosin heavy chain, myosin light chain, and tropomyosin. The three striated proteins are paramyosin, troponin, and tropo
Figure 29.40
  1. Analyze these data in terms of evidence of common ancestry and evidence of the convergent evolution of the muscle cell.

    Molecular phylogenetics has provided many insights into the evolution of genes. Because this work is framed by the central organizing principle of evolution it is possible to forget that there are people living today who need evidence that speciation and extinction have occurred throughout Earth’s history.
  2. Describe in broad outline a plan using molecular databases for either protein or DNA sequences that you could help those who are in need of evidence construct it.