ENERGY AND LIFE

The capture and use of energy in living systems is dominated by two processes: photosynthesis and respiration. Through these two processes living organisms are able to capture and use all of the energy they require for their activities.

Photosynthesis

Plants can capture the electromagnetic energy from the Sun by a chemical process called photosynthesis. This chemical reaction can be described by the following simple equation:

6CO2 + 6H2O + light energy >>> C6H12O6 + 6O2

The product of photosynthesis is the carbohydrate glucose and oxygen which is released into the atmosphere. All of the sugar glucose is produced in the specialized photosynthetic cells of plants and some other organisms. Glucose is produced by chemically combining carbon dioxide and water with sunlight. This chemical reaction is catalyzed by chlorophyll acting in concert with other pigment, lipid, sugars, protein, and nucleic acid molecules. 

ENERGY, TEMPERATURE, AND HEAT

We have learned that energy can take on many forms. One important form of energy, relative to life on Earth, is kinetic energy. Simply defined, kinetic energy is the energy of motion. The amount of kinetic energy that a body possesses is dependent on the speed of its motion and its mass. At the atomic scale, the kinetic energy of atoms and molecules is sometimes referred to as heat energy.

Kinetic energy is also related to the concept of temperature. Temperature is defined as the measure of the average speed of atoms and molecules. The higher the temperature, the faster these particles of matter move. At a temperature of -273.15° Celsius (absolute zero) all atomic motion stops. Heat is often defined as energy in the process of being transferred from one object to another because of difference in temperature between them. Heat is commonly transferred around our planet by the processes of conduction, convection, advection, and radiation.

Some other important definitions related to energy, temperature, and heat are:

• Heat Capacity - is the amount of heat energy absorbed by a substance associated to its corresponding temperature increase.
• Specific Heat - is equivalent to the heat capacity of a unit mass of a substance or the heat needed to raise the temperature of one gram (g) of a substance one degree Celsius. Water requires about 4 to 5 times more heat energy to raise its temperature when compared to an equal mass of most types of solid matter. This explains why water bodies heat more slowly than adjacent land surfaces.
• Sensible Heat - is heat that we can sense. A thermometer can be used to measure this form of heat. Several different scales of measurement exist for measuring sensible heat. The most common are: Celsius scale, Fahrenheit scale, and the Kelvin scale.Latent Heat - is the energy needed to change a substance to a higher state of matter. This same energy is released from the substance when the change of state (or phase) is reversed. The diagram below describes the various exchanges of heat involved with 1 gram of water.

Figure 6c-1: Latent heat exchanges of energy involved with the phase changes of water.

Figures 6c-2 and 6c-3 show the net absorption and release of latent heat energy for the Earth's surface for January and July, respectively. The highest values of flux or flow occur near the subtropical oceans where high temperatures and a plentiful supply of water encourage the evaporation of water. Negative values of latent heat flux indicate a net release of latent energy back into the environment because of the condensation or freezing of water. Values of latent heat flux are generally low over landmasses because of a limited supply of water at the ground surface.

Figure 6c-2: Mean January latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations). 

Figure 6c-3: Mean July latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations).

CITATION:  Pidwirny, M. (2006). "Energy, Temperature, and Heat". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

MEASUREMENT OF ENERGY

In the previous discussion (Characteristics of Energy Matter), we developed the concept of energy. We now must be able to measure and quantify it, using a standard set of units. Worldwide, two systems of units of measurement are commoly used today: the Metric System (Systeme International) and the British System. The units of energy described in these systems are derived from a technical definition of energy used by physicists. This definition suggests that energy can be represented by the following simple equation:

Work = Force x Distance

Similar to the definition given in the previous topic, physicists view energy as the ability to do work. However, they define work as a force applied to some form of matter (object) multiplied by the distance that this object travels. Physicists commonly describe force with a unit of measurement known as a newton (after Sir Isaac Newton). A newton is equal to the force needed to accelerate (move) a mass weighting one kilogram one meter in one second in a vacuum with no friction. The work or energy required to move an object with the force of one newton over a distance of one meter is called a joule.

Some other definitions for the energy measurement units that you may come across in this textbook are as follows:

• Calorie - equals the amount of heat required to raise 1 gram of pure water from 14.5 to 15.5° Celsius at standard atmospheric pressure. 1 calorie is equal to 4.1855 joules. The abreviation for calorie is cal. A kilocalorie, abbreviated kcal, is equal to a 1000 calories. 1 kilocalorie is equal to 4185 joules.
• Btu - also called British thermal unit is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.
• Watt (W/m2 or Wm-2) - a metric unit of measurement of the intensity of radiation in watts over a square meter surface. One watt is equal to one joule of work per second. A kilowatt (kW) is the same as 1000 watts.

CITATION: Pidwirny, M. (2006). "Measurement of Energy". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

CHARACTERISTIC OF ENERGY MATTER

Energy is defined simply by scientists as the capacity for doing work. Matter is the material (atoms and molecules) that constructs things on the Earth and in the Universe. Albert Einstein suggested early in this century that energy and matter are related to each other at the atomic level. Einstein theorized that it should be possible to convert matter into energy.

 From Einstein's theories, scientists were able to harness the energy of matter beginning in the 1940s through nuclear fission. The most spectacular example of this process is a nuclear explosion from an atomic bomb. A more peaceful example of our use of this fact of nature is the production of electricity from controlled fission reactions in nuclear reactors.Einstein also suggested that it should be possible to transform energy into matter.

Energy and matter are also associated to each other at much larger scales of nature. Later on in this chapter, we will examine how solar radiation provides the energy to create the matter that makes up organisms. Organisms then use some of this matter to power their metabolism.