Biology
Nutrient cycles
How carbon and nitrogen travel through nature, why nothing is lost, and the role decomposers play in it.
In nature no substance is lost. The building blocks of life are used again and again: they move from the air into the plant, from the plant into the animal, and finally back into the soil. Because this path keeps starting over, we call it a cycle.
The carbon cycle
Carbon is part of every living thing. Plants take it from the air as and use it to build sugar in . Animals eat the plants and take up the carbon. When they breathe, animals and plants release carbon dioxide back into the air. In this way the carbon keeps going around.
Eats: nothing, it is a producer
Eaten by: Hare, Mouse, Beetle
If it disappears: Without grass all herbivores lose their food and the whole web collapses.
The nitrogen cycle
Living things need nitrogen to build proteins. About 78 out of 100 parts of the air are nitrogen, but plants cannot use it in that form. Special bacteria in the soil and on the roots of plants like clover change it into a form that plants take up through their roots. Through food the nitrogen then reaches the animals.
Decomposers close the cycle
When a living thing dies or an animal leaves droppings, the step in. Fungi, bacteria, and small soil creatures break the remains down into their building blocks. They return part of these nutrients to the soil, and they breathe part of the carbon out into the air as carbon dioxide. From the soil the plants take the building blocks up again, and the cycle starts over.
Why cycles matter
Without cycles the nutrients would soon be used up. Because they are returned again and again, the soil stays fertile and life can continue. When a cycle loses its balance, for example through too much carbon dioxide in the air, this has consequences for all of nature.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
Which living things break down dead remains and return the nutrients to the soil?
In which form do plants take carbon from the air?
A nutrient cycle first passes through air or soil, then through plants and animals, then through the decomposers. How many stops is that?
Follow a carbon atom through the cycle. Put the steps in the correct order.
- 1When breathing, the animal releases carbon dioxide back into the air
- 2A plant takes carbon dioxide from the air
- 3An animal eats the plant and takes up the carbon
A leaf contains 8 units of carbon. When it is decomposed half of that reaches the soil. How many units is that?
Match each living thing to its role in the nutrient cycle.