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 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 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