Living organisms all interact with the physical world
do work against it/use energy to decrease entropy
•
move weight against gravity
•
transport solute against concentration gradients
•
exclude/eliminate waste substances
All living processes take place within limits set by the physical world
Carbon and Oxygen play a major role in biological
energy transformations
Oxidation means giving up electrons, and reduction means taking on
electrons (─)
The oxidation state of C in CO2 is +4, in Carbohydrates is 0
How many electrons are taken up by each C during photosynthesis?
How to assign Oxidation numbers
We keep track of the e- transfer using Oxidation numbers (Ox#)
For each e- transferred the Ox# changes by 1
2H2 + O2
0
0
2H2O
+1 -2
Some rules for Oxidation numbers
1. In free elements Ox# =0
2. For ions with one atom Ox# = charge. eg H+ Ox# of H+ = 1
3. Ox# of O in most compounds is -2,
4. Ox# of H in most compounds is +1,
5. For a complex ion like SO4-2 , the net Ox# = charge (Thus S=+6)
Water is the primary medium for life
•organisms are mostly water
•take up nutrients from water
•discharge wastes into water
•regulate their water content
Life first evolved in water
•primary limiting factor for terrestrial organisms
water is of primary importance to human society
Water has many unique properties essential for life on earth
•liquid at ambient temperatures
•ice floats on water (r max at 4oC)
•powerful solvent—H-bonding
•stores a lot of heat—high specific heat
•high viscosity—resists deformation, drag
•high density—buoyancy
Small size and filamentous projections retard sinking
Water contains enough soluble nutrients
to support small algae
Streamlined shape reduces drag
Swim bladder regulates buoyancy
Very light skeleton
Buoyant fat droplets prevent sinking
Water dissolves minerals rocks, soil and air
Dissolved matter is taken up by diffusion in aquatic organisms
When the boundary layer
becomes stagnant molecular
diffusion rates can
•limit algal photosynthesis
•limit animal or microbial
metabolism
Tiny algae have high
surface/volume ratios to
offset slow diffusion in
water
Hydrogen ions (pH)
play a major role in
dissolving minerals
from rocks
Most organisms
highly sensitive to
the H+ ion
Indicator species
can be used to
back-calculate pH
through history in
mud cores.
At high pH, bicarbonate ion is more abundant than CO2, and commonly
used as the major carbon source by aquatic plants.
It exists in chemical equilibrium with dissolved CO2
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3─
Air poses special problems for plants because it contains
so little CO2 and so little water vapour
• both water and CO2 can be
important limiting factors for
plant growth
Opening the stomates to take up CO2 means losing a lot of water
Light is the primary source of energy for the biosphere
The absorption spectrum of chlorophyll and
accessory photosynthetic pigments (eg carotenoids)
It also heats up our atmosphere and keeps us
much warmer than outer space (<─50C)
The Greenhouse effect
Organisms also need to balance their heat budgets
The metabolism of organisms is very sensitive to temperature because
heat makes molecules move faster and speeds up chemical reactions
For poikilotherms metabolic rate approximately doubles for
each 10oC rise in temperature
Warm blooded animals maintain very high metabolic rates even in
cold climates, but this requires physiological adaptations to regulate
their body temperatures.
Thermal images of Canada geese
Geese lose most heat through their head, neck and legs,
and little from their down insulated bodies.
Heat, water and energy budgets are coupled by diet, evaporative
loss, and excretion
Why are the shearwater eggs so much more sensitive to the
thermal environment than those of the tern?—water availability
The sooty tern tolerates extreme heat exposure because its
diet is very water rich, but the wedge-tailed shearwater cannot
Organisms sense a wide range of stimuli from the physical environment
The paddlefish can detect electrical impulses
The bat “sees” the
world through high
frequency sounds
Some insects see flowers differently than we do
because they can detect ultraviolet light
rattlesnake pit organs can
detect infrared radiation