Biological systems are

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Biological systems are highly ordered, and yet,
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Disorder reigns! Entropy rules! Everythings
falling apart!
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• The Second Law of Thermodynamics
• The total disorder (entropy) always increases.
• Examples of entropy increasing
• Solutes diffuse from areas of higher to lower
  concentration.
• Heat flows from a warmer body to a cooler one.
• Complex structures degrade into simpler parts.
• Batteries lose their charge over time

castles made of sand, fall into the sea,
eventually Jimi Hendrix

• A process can happen spontaneously, (without the
  input of energy), if it increases the entropy of
  the system and its surroundings.

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• Things change spontaneously so as to reduce the
  capacity
• for further change.
• Temperature gradients tend to dissipate
• Complex structures tend to fall apart into
  simpler pieces
• Solute concentration tends to become equal
  everywhere
• Equilibrium
• A system is at equilibrium when it has no
  capacity for further spontaneous change.

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• Diffusion - a spontaneous process leading to the
  net movement of a substance from a region of
  higher to lower concentration.
• Diffusion results from the random thermal motions
  of molecules
• Diffusion is involved in many plant processes
• gas exchange by leaves
• nutrient movement to root surface
• the leaking of solutes out of the vacuole
• osmosis, the movement of water from regions of
• higher to lower water concentrations

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Figure 3.7
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So, if disorder is the natural tendency, how do
biological systems maintain such highly ordered
states?
They use energy to do the work of maintaining
order!
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• Energy is required to counter the universal
  tendency for disorder (entropy) to increase.
• to maintain solute concentration gradients
• to maintain thermal or electrical gradients
• to rebuild complex structures and molecules

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• What is energy?
• 1) The capacity to do work
• 2) That which is required to displace an object
  against
• a force - mechanical, electrical, osmotic,
  chemical potential
• Work and Energy have the same units calories or
  Joules
• Some examples of the work that plants do (the
  ways they use energy).
• Growing roots through soil - mechanical work
• Raising water against gravity - mechanical work
• Moving charged solutes against membrane
  electrical gradients
• Concentrating solutes in a compartment - osmotic
  work
• Synthesizing complex molecules - chemical work

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• Units of energy are joules, J
• How much is 1 Joule?
• about 1/4 calorie
• enough energy to heat 1/4 gram of water 10C
• Plants convert sunlight energy into chemical
  energy (ATP), then use that energy to do work.
• The different compounds made by plants and
  animals
• have different energy contents.
• proteins and carbohydrates 17 kJ/g
• fats 37 kJ/g
• Why do great white sharks (usually) spit out
  surfers but eat seals?

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Yuck, another skinny human
Yum, energy dense blubber!
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More on units Well use the International System
of Scientific Units Distance in meters not feet
or inches! Mass in kilograms not pounds or
ounces! Time in seconds So area is m2, volume is
m3, velocity is m s-1
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Temperatures will be in either Celsius (0C) or
Kelvin (absolute temperature scale, 0K 0C
273) Water freezes at 32oF, 00C, or 273 0K.
For quantity well use moles. A mole is 6.02 x
1023 of anything. For concentration well use
moles/volume (liters m3, etc.). Molarity, M, is
moles per liter
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Exponents are your friends! milli,
m 10-3 millimeter, 1/1000 m micro,
µ 10-6 microgram, a millionth gram kilo,
k 103 kiloliter, 1000 liters mega,
M 106 megabyte, a million bytes
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Some important derived units Variable
name fundamental units also expressed
as force Newton, N 1 kg m s-2 energy joule,
J kg m2 s-2 force times
distance (work) N . m pressure pascal,
Pa kg m-1 s-2 force per area N
m-2 power watt, W kg m2 s-3 energy per
time J s-1
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• Example applications
• Energy
• How much energy does a plant expend in pumping
  nutrient ions from the soil solution into root
  cells?
• Whats a better strategy for dealing with
  herbivores - making
• chemical defenses or suffering the losses and
  regrowing leaves?
• How much energy is in a photon of light? Does it
  matter what
• color the light is?
• Power
• What is the power (energy/time) of light striking
  a leaf in full sun?
• How does this compare to the rate of energy
  production as carbohydrates are made in the
  chloroplast?
• Pressure
• What positive pressure (turgor) is required to
  expand a plant cell?
• At what pressure does a leaf wilt?
• What negative pressures (tension) exist in the
  xylem cells of a transpiring plant?
• At what tension do embolisms form?

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The gas constant, R Remember PV nRT? R is the
constant that makes the relationship among P, V,
n, and T work. Values and units for R 8.314 J
mol-1 K-1 8.314 m3 Pa mol-1 K-1 Well use R a
lot!