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Topic 4.2 Energy Flow
IB BiologyR. Price
v. 1 2015
Allott 213
#1: Most ecosystems rely on a supply of energy from sunlight
• Initial source of energy in most biological communities is sunlight• Producers like plants, eukaryotic
algae, & cyanobacteria use photosynthesis (autotrophs)• Consumers, detrivores, &
saprotrophs use the carbon in their food (heterotrophs)
Allott 214
#2: Light energy is converted to chemical energy in carbon compounds by photosynthesis
• Producers absorb sunlight using chlorophyll & other photosynthetic pigments• Converts light energy to
chemical energy• Chemical energy (ATP) used to
make carbs, lipids, and all other carbon compounds in producers
#3: Chemical energy in carbon compounds flows through food chains by means of feeding
• Food chain is a sequence of organisms, each of which feeds on the previous one• Two – five organisms in a chain is
normal• Producers always first• Producer -> primary consumer ->
secondary consumer -> tertiary consumer• Arrow indicate the direction of
energy flow
#3: Chemical energy in carbon compounds flows through food chains by means of feeding
• Consumers obtain energy from the carbon compounds in the organism on which they feed
#4: Energy released by respiration is used in living organisms and converted to heat
• Organisms use chemical energy for life processes (ATP)• Cells produce ATP by cell
respiration.• Carbohydrates & lipids are
oxidized and the chemical energy is transferred to ATP• Energy transformation is not
100% efficient. Some is lost as heat
Allott 216
#5: Living organisms cannot convert heat to other forms of energy
Living orgamisns can perform various energy conversions• Light energy to chemical energy in
photosynthesis• Chemical energy to kinetic energy in
muscle contraction• Chemical energy to electrical energy in
nerve cells• Chemical energy to heat energy in heat
generating adipose tissueCannot convert heat energy into any other form of energy
#6: Heat is lost from ecosystems
• Heat passes from hotter to cooler bodies (laws of thermodynamics)• Heat produced in living organisms
(including plants) is lost to the abiotic environment• Heat is radiated from the
environment into the atmosphere• All energy released by respiration
will be ultimately lost from an ecosystem
• By Arno (www.nutscode.com) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons
Infrared image of fruit bat
#7: Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels
Loss of energy between trophic levels:1. Most energy in digest food used in
respiration and lost as heat2. Consumers may not eat the entire
plant or animal, such as roots, hairs, or bones
3. Not all ingested food is digested and absorbed. Indigestible food passes in feces
Around 10% of energy of biomass in one trophic level is available to next
Allott 218
Allott 219
Sources
Content Allott, Andrew, and David Mindorff. Biology: Course Companion. 2014 ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.
Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge: Cambridge UP, 2014. Print.
ImagesUnless otherwise noted, images are obtained from Pixabay (www.pixabay.com) and used under the CC0 Public Domain license.