TOPIC 1 LESSON 5

The Laws of Thermodynamics (Energy Transfer and Efficiency)

Syllabus Link 1.1.4 - Describe how the first and second laws of thermodynamics are relevant to environmental systems.

ENERGY and MATTER FLOWS through an ECOSYSTEM

Producers Consumers

decomposersInorganic nutrient pool

Sun

Heat

Heat

http://www.wisegeek.org/what-are-inorganic-nutrients.htm

The energy in all ecosystems is subject to the FIRST and SECOND

LAWS of THERMODYNAMICS

1st LAW – “CONSERVATION OF ENERGY”ENERGY IS NEITHER CREATED NOR DESTROYED

Energy can be converted from one form into another, but not consumed.Ecosystems are characterised by constant flows and transformations of energy:

Electromagnetic energy (light) transformed into

chemical energy (sugar) by photosynthesis.

Chemical energy transformed into

heat.

Chemical energy transformed into electrical energy.

Read the hand-out on Photosynthesis.

An example would be a simple food chain.

Draw a simple food chain with 5 components.

30%

50%

<1%

c. 19%

Where does the sun’s energy (that reaches Earth’s surface) go?

2nd LAW – “The ENTROPY OF AN ISOLATED SYSTEM NOT IN EQUILIBRIUM WILL INCREASE OVER TIME”.

1. What is ENTROPY?“the spreading out or dispersal of energy”

In other words, energy conversions are never 100% EFFICIENT.Some energy is transferred into WORK or WASTE HEAT.

ENERGY = WORK + HEAT (and other waste energy)

CONVERSION PROCESS

INPUT ENERGY USEFUL ENERGY (WORK)

HEAT

Each level is known as a TROPHIC LAYER.

Because of ENTROPY, the amount of energy passed to the next TROPHIC LAYER decreases.

At each layer, energy is lost as heat generated during work eg

respiration.

Calculating Efficiency

% Efficiency = work or energy produced x 100 energy consumed

1. Plants convert around 1-2% of the solar energy they receive into glucose (photosynthesis).

2. Herbivores assimilate (turn into animal matter) around 10% of plant energy they consume.

3. A carnivore’s efficiency is also around 10%.

Energy Loss in a Food Chain