1.  Energy is never made or destroyed, it simply changes from one form to another. When we eat food, the chemicals are broken down, and energy is released. This energy is stored in your body as chemical energy, ready to be used when you need it. Energy is all around us, in many different forms. Energy is essential for life.  You can imagine that energy travels in a big cycle: it comes in from the sun as heat and light, is used by plants to produce chemical energy, which is eaten by animals and humans, then it is lost as heat and goes back into space.

3.  Humans also use energy from the sun, but not in the same way that we use chemical energy from plants and animals. The human body must stay above a certain temperature for all the organs to function properly. If the body cools down too much, you can die.  We use the sun’s energy to keep us warm. On a cold day, the body must find another way to stay warm. It uses the chemical energy it has stored up from eating food, and converts this into heat energy. So we don’t use the sun’s energy directly, but if the sun is keeping us warm, the body doesn’t have to work so hard.

4.  Lets start at the bottom of the food chain – plants. Being at the bottom does not mean that plants are not important – the exact opposite in fact. We would not be able to survive without plants. But where do plants get their energy from?  Plants take water from the soil, and carbon dioxide from the air (they also get some water from the air). Both water and carbon dioxide are essential for plants, and therefore they are essential for you to grow and be healthy.  Energy from the sun is also essential for plants to grow. They use light energy for photosynthesis. In photosynthesis, plants use the sun’s energy to turn carbon dioxide and water into glucose and oxygen.

5. Carbon dioxide Waterenergy Glucose + oxygen Glucose is a form of sugar Plants take in carbon dioxide from the atmosphere, and release oxygen.

6.  Animals and humans eat plants. Some animals eat only plants, and no meat. These are called herbivores. When animals (including humans) eat plants, they break down the chemicals, releasing energy which is then used for powering the body.  The process that takes place is called respiration, and it is the opposite of the photosynthesis reaction that takes place in plants.

7.  Photosynthesis in plants:  Respiration in animals Carbon dioxide Waterenergy Glucose + oxygen Glucoseoxygen Carbon dioxide + water + energy

8. Glucose + oxygen  Animals break down glucose, and energy is released. This energy is used to power all the processes of the body, including moving your muscles, and breathing. Animals then breathe out the carbon dioxide. Photosynthesis in plants Respiration in animals

9.  If there were no plants, there would be no photosynthesis, so no carbon dioxide would be removed from the atmosphere, and no oxygen would be produced.  Animals would keep breathing in oxygen and breathing out carbon dioxide.  Eventually all the oxygen would be used up, and there would only be carbon dioxide left. We would not be able to breathe.  It is very important that there are plants to absorb the carbon dioxide, and to produce oxygen. This is why it is important not to destroy all the forests in the world.

10.  All life on Earth depends on each other, because every animal must eat to survive. We can write lists of animals (and plants) that eat each other, and therefore depend on each other. We call this a food chain.  We will look at some examples of food chains.

11. EagleOwlFrogButterfly/caterpillarGrass  The butterfly larvae (caterpillars) eat grass  The frog eats the butterfly/caterpillar  The owl eats the frog  The eagle eats the owl  Each time one creature eats another, energy is passed up the food chain. The energy is passed right up from the grass to the eagle.

12.  Algae is a type of plant that grows in water.  The plankton eat the algae  The herring eat the plankton  The salmon eats the herring  The sea lion eats the salmon  The shark eats the sea lion SharkSea lionSalmonHerringPlanktonAlgae

13.  There are three groups of animals involved in food chains: ◦ Producers ◦ Consumers ◦ Decomposers

14.  Producers are the start of the food chain. They are plants and vegetables, and they use the sun’s light to make their own food.  The plants produce energy for the other organisms.  Photosynthesis is the process that plants use to make energy.  In the food chains that we have looked at, the producers are grass and algae.

15.  Primary consumers eat producers. Primary consumers are also called herbivores. These are animals that will only eat plants. In our food chains the primary consumers are the butterflies and the plankton. Rabbits, deer and squirrels are also primary consumers.  Secondary consumers eat primary consumers. They are called carnivores. This means ‘meat eater’. Frogs and herring are examples of secondary consumers. A cat that eats a mouse is another example of a secondary consumer.

16.  Tertiary consumers eat both primary and secondary consumers. They are also carnivores. Owls, eagles, salmon, sea lions and sharks are tertiary consumers.  Some consumers are omnivores. These are animals that can be primary, secondary or tertiary consumers. Humans are omnivores. We eat meat (so we are secondary or tertiary consumers) but we also eat plants (so we are primary consumers).

17.  When an animal at the top of the food chain (for example an eagle or a shark) dies, its body is eaten by bacteria and other organisms, such as worms and fungi.  These organisms are called decomposers.  Decomposers break the body down into chemicals, which go back into the soil and help to fertilise it. This means that plants are able to grow in the soil, because there are lots of nutrients.

18.  The decomposers break down the bodies of the animals at the top of the food chain.  So the energy that was eaten by the animal at the top of the food chain (the eagle) actually helps the plants at the bottom of the food chain to grow.  Instead of drawing the food chain as a straight line, we could have drawn it as a circle, because the energy goes right round the cycle and back to the beginning.

19. GrassButterfly/caterpillarFrogOwlEagleDecomposers