Energy & Cycles

I. Energy Flow (not cycle!) A. The Earth is an open system to energy Energy flows in as solar radiation Energy leaves as Infra-red radiation (heat) B. Food Webs show the flow of energy through living things 1. Autotrophs convert solar energy & inorganic carbon into chemical energy in organic compounds 2. Heterotrophs break down organic compounds to release energy to make ATP.

II. Efficiency of Energy Capture by Plants A. Plants capture solar energy using pigments 1. Different pigments use different wavelengths of light 2. Chlorophyll a absorbs violet/blue and red light best 3. Accessory pigments absorb other wavelengths a. Chlorophyll b absorbs blue & orange b. Carotenoids absorb violet, blue & green B. Only about 1% of visible light that strikes plants is captured

III. Primary Productivity: A) = the amount of light E converted to chemical E in form of organic compounds per unit of time B) Gross Primary Productivity (GPP)= total C) Net Primary Productivity (NPP) = total – Ra (Ra = autotroph respiration) D) NPP = GPP – Ra (NPP usually about ½ of GPP)

IV. Calculating Productivity A. GPP measured as Biomass produced/area/time (g/m/year) or as oxygen produced B. Ra = measured by how much oxygen is consumed by cellular respiration C. 1 ml of O2 = .536 mg of Carbon assimilated D. NPP = GPP – Ra

V. Efficiency of Energy Capture by Animals A.  Assimilation = (Ingestion - Excretion). B. Efficiency: 1. 15-50% if the food is plant material 2. 60-90% if the food is animal material.  C. Much of the energy assimilated is used to produce ATP D. Only 10% of energy consumed is stored in animals body E. Only 10% of consumed energy is available to next trophic level

This is why food chains are limited to 3 or 4 trophic levels

VI. Energy Use A. Smaller body mass = higher metabolic rate: more E use B. Extra energy used to.. 1. grow 2. reproduce C. Energy deficit = weight loss and death D. ∆ available E can ∆ population size & disrupt ecosystem

VI. Nitrogen CYCLES A. Atmospheric N2 only used by N-fixing bacteria 1. bacteria ‘fix’ N make it usable to other organisms a. ammonium/ ammonia b. added to soil or water c. produced in root nodules of legumes B. Nitrifying bacteria convert NH4+/NH3 to nitrates/nitrites B. Plants assimilate N compounds from soil/water C. Animals ingest N compounds in their food D. waste & dead animals/plants return N to soil/water E. Denitrifying bacteria return N to atmosphere

Key point: only bacteria add/remove N to/from atmosphere

VII.Human Impact on N cycle A. Enrichment: too much N in ecosystem 1. industrial nitrogen fixation : fertilizer production 2. concentrated animal waste: stock yards/farms B. N in water causes algal blooms 1. algae cover surface of water & block light 2. benthic organisms die 3. decomposition depletes oxygen C. Eutrophication/ dead zones

VIII. Phosphorous Cycle A. Phosphorous erodes out of rock B. Plants assimilate P C. Animals ingest P D. Decomposition returns P to soil/water E. P in nucleotides proteins F. Returned to sedimentary rock by deposition F. Human impact: enrichment by fertilizer use

IX. Carbon Cycle

X. Water Cycle Human Impact: Salination: water evaporation/absorption leaves salt behind 1. Irrigation with saline ground water 2. replacing native shrubs with crops a. reduces evapotransporation b. rain water seeps down to clay & runs to low spots c. collects salt as it runs to low spots 3. Ingress of sea water a. removal of fresh ground water lowers water table b. water table below sea level lets salt water in