Topic 4.2 Energy Flow

QOD Why did the hippy girl say that all humans should be vegetarians?

Energy in Ecosystems Initial source of energy is the sun (in most ecosystems) = photosynthesis Deep ocean trenches rely on chemosynthesis

Energy in Food Chains Chemical energy in carbon compounds flow through food chains by means of feeding Food chains show direct flow of energy from one feeding level to the next Each feeding level is called a trophic level Arrows drawn in food webs represent the direction of energy transfer Most of the energy consumed is lost

Food Chain 10% if ingested food is converted to new organic molecules 3-5 organisms in each food chain

Food Webs Collection of food chains Many organisms feed on a variety of things Complex feeding interactions

Trophic Levels A feeding level in a food chain or food web Represent organism’s position in the food chain/web Trophic levels include the following: Producers (autotrophs) Primary consumers (herbivores) Secondary consumers (omnivores or carnivores) Tertiary consumers (omnivores or carnivores)

What eats what Herbivores – eat only plants Omnivores – eat both plants and meat Carnivores – eat meat

Pyramid of energy

Biomass The total mass of a group of organisms Biomass decreases at each trophic level Reasons for this trend Most of the energy in food that is digested and absorbed by organisms in a trophic level is released by them in respiration for use in cell activities. So only chemical energy is available at the next level Organisms in trophic levels are not usually entirely consumed Not all parts of food ingested by organisms are digested and absorbed Biomass diminishes due to loss of CO2, H20, and other waste products(urea)

Respiration & Energy Release Energy released by respiration is used in living organisms and converted to heat Living organisms need energy for the following Synthesizing large molecules like DNA, RNA and proteins Pumping molecules or ions across membranes by active transport Moving things inside the cell, or muscles ATP supplies energy for these activities

ATP production ATP produced by cellular respiration Carbon compounds are oxidized This is exothermic and energy is released, this is used in endothermic reactions to make ATP Cell respiration transfers chemical energy from glucose to ATP

2nd law of Thermodynamics Energy transformations are never 100% efficient Not all is transferred to ATP the rest becomes heat.

Heat Energy in Ecosystems Living organisms cannot convert heat to other forms of energy Perform various energy conversions Light energy to chemical energy in photosynthesis Chemical energy to kinetic energy in muscle contractions Chemical energy to electrical energy in nerve cells Chemical energy to heat energy in heat-generating adipose tissue

Heat losses from Ecosystems Heat passes from hotter to cooler bodies Heat produced in living things is all eventually lost to the abiotic environment Heat may remain for a while but will ultimately be lost