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 0How many electrons are taken up by each C during photosynthesis?

We keep track of the e- transfer using Oxidation numbers (Ox#)

For each e- transferred the Ox# changes by 1

2H2 + O2 2H2O0 0 +1 -2

Some rules for Oxidation numbers1. In free elements Ox# =02. For ions with one atom Ox# = charge. eg H+ Ox# of H+ = 13. 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)

How to assign Oxidation numbers

•organisms are mostly water•take up nutrients from water•discharge wastes into water•regulate their water content

Water is the primary medium for life

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 ( max at 4oC)•powerful solvent—H-bonding•stores a lot of heat—high specific heat•high viscosity—resists deformation, drag•high density—buoyancy

Buoyant fat droplets prevent sinking

Streamlined shape reduces dragSwim bladder regulates buoyancyVery light skeleton

Small size and filamentous projections retard sinking

Water contains enough soluble nutrients to support small algae

Water dissolves minerals rocks, soil and air

Dissolved matter is taken up by diffusion in aquatic organisms

Tiny algae have high surface/volume ratios to offset slow diffusion in water

When the boundary layer becomes stagnant molecular diffusion rates can •limit algal photosynthesis•limit animal or microbial metabolism

Most organisms highly sensitive to the H+ ion

Indicator species can be used to back-calculate pH through history in mud cores.

Hydrogen ions (pH) play a major role in dissolving minerals from rocks

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─

• both water and CO2 can be important limiting factors for plant growth

Air poses special problems for plants because it contains so little CO2 and so little water vapour

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

For poikilotherms metabolic rate approximately doubles for each 10oC rise in temperature

The metabolism of organisms is very sensitive to temperature because heat makes molecules move faster and speeds up chemical reactions

Thermal images of Canada geese

Geese lose most heat through their head, neck and legs, and little from their down insulated bodies.

Warm blooded animals maintain very high metabolic rates even in cold climates, but this requires physiological adaptations to regulate their body temperatures.

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