1. 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

2. 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?

3. 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 + O H2O +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)

4. 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

5. 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

6. Water dissolves minerals rocks, soil and air

7. 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

8. 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.

9. 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─

10. 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

11. Light is the primary source of energy for the biosphere

12. The absorption spectrum of chlorophyll and accessory photosynthetic pigments (eg carotenoids)

13. It also heats up our atmosphere and keeps us much warmer than outer space (<─50C)
The Greenhouse effect

14. Organisms also need to balance their heat budgets

15. 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

16. 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.

17. Heat, water and energy budgets are coupled by diet, evaporative loss, and excretion

18. 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

19. Organisms sense a wide range of stimuli from the physical environment
The paddlefish can detect electrical impulses
Some insects see flowers differently than we do because they can detect ultraviolet light
The bat “sees” the world through high frequency sounds
rattlesnake pit organs can detect infrared radiation