Energy Transformation in Nature – SS1 Biology Lesson Note (Second Term)

Energy transformation in nature is the change of energy from one form to another as it passes through living things. At each step along a food chain, some energy is lost as heat. Two laws of thermodynamics describe this: energy is never created or destroyed, and no transformation of energy is 100 percent efficient.

Behavioural objectives

By the end of the lesson, students should be able to:

• define energy and state how energy is lost in the ecosystem;
• state the first and second laws of thermodynamics;
• give an example of the first law of thermodynamics;
• apply the two laws to a food chain, a pyramid of energy and energy flow.

How is energy lost in the ecosystem?

Energy is the ability to do work. All living organisms obtain energy from the food they eat. The food is produced by green plants, and other organisms depend on the plants.

As energy is passed from one organism to another along the food chain, it is progressively lost through respiration (energy used for various metabolic activities) and heat. In most ecosystems, only about 1 – 10% of the solar energy may be available to photosynthetic producers.

What are the laws of thermodynamics?

Thermodynamics simply means heat change. Heat is a form of energy, and its change in living organisms is governed by two laws.

First law of thermodynamics

The first law states that energy can neither be created nor destroyed, although it can be changed from one form to another. For example, chemical energy in food is converted to kinetic energy and heat energy in our muscles when we walk or run.

Second law of thermodynamics

The second law states that in any conversion of energy from one form to another, there is always a decrease in the amount of useful energy, i.e. no transformation of energy from one state to another is ever 100 percent efficient.

During metabolic activities, some chemical energy is constantly lost as heat energy from the body of an organism. As energy is converted from one form to another, there will always be a loss.

How do the laws of thermodynamics apply to a food chain?

First law: in a food chain, energy from the sun is transferred from the producer to the final consumer, and the total energy remains constant.

Second law: as energy is transformed from one trophic level to another, part of it is converted into heat and lost. This causes a progressive drop in energy in successive trophic levels.

How do the laws of thermodynamics apply to the pyramid of energy?

1. First law: the energy of the producers at the base of the pyramid is higher, and it is gradually transformed to other trophic levels.
2. Second law: as energy is transferred from one trophic level to another, part of the energy is converted to heat.

How do the laws of thermodynamics apply to energy flow?

1. First law: energy flows from producers to primary consumers, then to secondary consumers and finally to tertiary consumers in a food chain. The energy flow in a food chain is therefore in one direction only.
2. Second law: energy transfer between trophic levels is not 100%. Successive levels have less useful energy and so can only support fewer organisms. Producers (green plants) have the highest amount of energy. When herbivores feed on the plants, the energy level is reduced. When carnivores consume the herbivores, the energy level is reduced again.

Evaluation

1. What is energy?
2. State the first law of thermodynamics and give one example.
3. Why is no energy transformation 100 percent efficient?
4. Why does energy decrease along a food chain?
5. Why is energy flow in a food chain in one direction only?

Assignment

1. State the laws of thermodynamics and explain them.
2. Explain the pyramid of energy and food chain using the laws of thermodynamics.