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Lecture #2: Stuff

BE/Bio 105. What is role of leaf morphology?. Why is alder shaped like this?. Why do/don’t trees fall down?. Lecture #2: Stuff. Central question: how do things work?. Why is oak tree shaped like this?. Why/How do kangaroos hop on two legs…?. when wombats don’t. How is locomotion

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Lecture #2: Stuff

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  1. BE/Bio 105 What is role of leaf morphology? Why is alder shaped like this? Why do/don’t trees fall down? Lecture #2:Stuff Central question: how do things work? Why is oak tree shaped like this?

  2. Why/How do kangaroos hop on two legs…? when wombats don’t. How is locomotion of kangaroos & wombats related to their skeletal structure? Lecture #2:Stuff All these questions basically asking, ‘how do these things work?’ or ‘how can I build one?’ = REVERSE ENGINEERING

  3. Lecture #2:Stuff Outline: Part 1: From whence come mechanical properties of stuff? Part 2: What is biological stuff made from? Part 3: How do we mechanically classify stuff? force length stuff

  4. square beam structures steel materials We will define material properties We will define structural properties solid cylinder wood Part 1: From whence come mechanical properties of stuff? I-beam For any structure (e.g. I-beam, tree) we can define and measure mechanical properties: e.g. stiffness, strength, toughness, resiliance tree But how do these structures ‘get’ these properties? It is convenient to separate material properties from structural properties:

  5. Cellulose is a polymer of the sugar hexose Part 1: From whence come mechanical properties of stuff? This dichotomy is sometime absurd when considering biological structures. consider wood:

  6. Part 2: What is biological stuff made from? • Biological entities composed of 4 components: • Carbohydrates • bun, lettuce, onion, tomato • Lipids • cheese, mayo • Proteins • burger • Inorganic crystals • salt

  7. termite gut symbiont (Trychonympha) Part 2: What is biological stuff made from? 1. Carbohydrates = sugars, often as polymers e.g. chitin – structure molecule of arthropods and fungi e.g. cellulose – structure molecule of plants both chitin and cellulose virtually indigestable

  8. Part 2: What is biological stuff made from? 2. Lipids = Fats polar hydrophilic region non-polar hydrophobic region form stable, but fluid Bi-lipid membranes Highest energy-to-weight ratio. Thus best energy storage material

  9. NH2 amino acid chains helix sheet turn structural motifs Part 2: What is biological stuff made from? 3. Proteins = encode amino acid chains ‘central dogma’

  10. Part 2: What is biological stuff made from? Proteins can function like little machines: Myosin (molecular motor) Note also: genome can only encode proteins. Therefore enzymatic role of proteins is critical for synthesizing lipids and carbohydrates.

  11. calcite dolomite hydroxyapatite Part 2: What is biological stuff made from? 4. inorganic crystals and salts Calcium-based crystals are essential for making hard bits. e.g. CaCo3 calcite Ca2(PO4)3(OH) hydroxyapatite CaMg(CO3)2 dolomite SiO2(H2O)N silicas Many biological materials are composites of carbos, proteins, lipids, and inorganics!

  12. force length stuff ‘stuff’ tester Part 3: How do we mechanically classify stuff? Three general types of responses: slope=k 1. Force = constant x length Hooke’s Law of elasticity F= k1xL k1 = spring constant Units: M T-2 = SOLID (elastic material) force length slope=k 2. Force = constant x rate of length change F= k2xd(L)/dt k2 = viscosity or damping constant k2 = M T-1 = FLUID (viscous material) force d(length)/dt

  13. Hookian hysteresis force force decays over time length force length time Part 3: How do we mechanically classify stuff? 3. Force = constant x length + constant x rate of length change F= k1xL + k2xd(L)/dt = Viscoelastic material initially stiff force length time

  14. extension compression Part 3: How do we mechanically classify stuff? Difference between gas and liquid (both are fluids): Liquids will resist both compression and extension Gas will resist compression, but it always ‘trying’ to expand. Why is it hard to ‘pull’ a vacuum ? stuff Gas molecules will expand to fill any arbitrary volume high pressure = 1 atmosphere modified ‘stuff’ tester low pressure liquid molecules will remain within cohesive mass pushing against atmosphere, not pulling against vacuum

  15. force length stuff Things have material properties and structural properties. Biological materials are composed of carbohydrates, lipids, proteins and inorganic crystals. Materials can be divided into solids, liquids, and gases. Lecture #2:Stuff

  16. Lecture #3:Jumping Fleas

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