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, with some lost as heat at each step along a food chain.

Behavioural objectives

1. Define energy and state how energy is lost in the ecosystem.
2. State the first and second laws of thermodynamics.
3. Give an example of the first law of thermodynamics.
4. Apply the two laws to a food chain.
5. Apply the two laws to a pyramid of energy and to energy flow.

What are the key terms?

• Energy: the ability to do work.
• Energy transformation: the change of energy from one form to another, for example light to chemical energy.
• Thermodynamics: the study of heat and how it changes into other forms of energy.
• Producer: a green plant that makes its own food by photosynthesis, such as grass or maize.
• Consumer: an organism that feeds on other organisms, such as a goat, a toad or an eagle.
• Food chain: a line showing who feeds on whom, for example grass, grasshopper, toad, snake.
• Trophic level: the feeding position of an organism in a food chain.

What are the common forms of energy in nature?

The forms of energy met most often in living things are light, chemical, kinetic and heat energy.

• Light energy: energy from the sun, which green plants capture.
• Chemical energy: energy stored in food such as starch and glucose.
• Kinetic energy: energy of movement, as in a running goat.
• Heat energy: energy given off from the body during respiration and movement.

What forms of energy change occur in living things?

Living things change energy in photosynthesis, feeding, respiration and muscle movement.

How is energy lost in the ecosystem?

Energy is lost in the ecosystem mainly as heat, and through waste and dead remains that are not passed on.

Where does food energy come from?

• Source of food energy: all organisms get energy from food, and the food is made by green plants.
• Dependence on plants: other organisms depend on the plants, directly or through other animals.

How is energy lost?

• Capture by producers: only a small part of the solar energy reaching a plant is captured in photosynthesis.
• Respiration and metabolic activities: organisms use part of their energy for living processes, and some escapes as heat.
• Heat loss: some chemical energy is constantly lost as heat from the body of every organism.
• Waste and dead remains: energy in faeces, dead bodies and uneaten parts is not passed to the next level, and decomposers use it instead.

What are the laws of thermodynamics?

There are two laws of thermodynamics, and heat is a form of energy that follows both in living organisms.

First law of thermodynamics

• Statement: energy can neither be created nor destroyed, although it can be changed from one form to another.
• Meaning: the total amount of energy stays the same, only its form changes.
• 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

• Statement: in any conversion of energy from one form to another, there is always a decrease in the amount of useful energy.
• Meaning: no transformation of energy from one state to another is ever 100 percent efficient.
• Example: during metabolic activities, some chemical energy is lost as heat from the body of an organism.

How do the two laws compare?

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

In a food chain, the first law explains the transfer of energy and the second law explains the loss at each level.

First law in a food chain

• Transfer: energy from the sun passes from the producer to the final consumer.
• Total energy: the total energy remains constant, because heat lost to the surroundings is not destroyed.

Second law in a food chain

• Heat loss: as energy moves from one trophic level to the next, part of it becomes heat and is lost.
• Result: there is a progressive drop in energy at each successive trophic level.

Worked example: grass, grasshopper, toad, snake

1. Grass captures light energy and stores it as chemical energy in its tissues.
2. The grasshopper eats the grass. Part of the energy is used and lost as heat, and the rest is stored in its body.
3. The toad eats the grasshopper and receives less energy than the grasshopper took from the grass.
4. The snake eats the toad and receives less energy again.

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

A pyramid of energy is a diagram showing the amount of energy at each trophic level, with producers at the base.

• First law: the energy of the producers at the base is highest, and it is gradually transformed to other trophic levels.
• Second law: as energy is transferred from one level to the next, part of it is converted to heat.
• Shape: because of this loss, each level is smaller than the one below it, so the diagram is a pyramid.

How do the laws of thermodynamics apply to energy flow?

Energy flow is the movement of energy from producers through the consumers in one direction only.

First law and energy flow

• Path of energy: energy flows from producers to primary consumers, then to secondary consumers and finally to tertiary consumers.
• Direction: energy flow in a food chain is in one direction only.
• Reason for one direction: heat lost to the surroundings cannot be used by organisms to make food, so energy does not return to the producers.

Second law and energy flow

• Transfer: energy transfer between trophic levels is not 100 percent.
• Producers: green plants have the highest amount of energy.
• Herbivores: when herbivores feed on plants, the energy level is reduced.
• Carnivores: when carnivores eat the herbivores, the energy level is reduced again.
• Number of organisms: higher levels have less useful energy, so they support fewer organisms.

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

State the two laws of thermodynamics, then use them to explain the food chain and pyramid of energy for a chain of your choice.