What soil is made of Cambridge IGCSE Environmental Management revision
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In plain words
Soil looks like dirt. It is closer to a city: bits of ground-up rock for the buildings, air and water in the streets between them, and billions of living things going about their business. Take away any one part and crops struggle.
8 things to know
- Soil has four parts: mineral particles, organic content, gases and water.
- Mineral particles come from weathered rock. There are three sizes. Sand is the largest and feels gritty. Silt is in between and feels smooth. Clay is the smallest and feels sticky when wet.
- Organic content has two parts. One is the living organisms: plant roots, animals such as earthworms, fungi and bacteria. The other is organic matter from the decomposition of dead plants and animals.
- The gaps between particles are called pore spaces. They hold the gases and the water. Roots and soil organisms need the oxygen in them for respiration.
- Soil water has mineral ions dissolved in it, and roots take the ions in with the water.
- Sandy soil has large particles and large pore spaces. Water drains through quickly and there is plenty of air. It holds little water, and nutrients are washed out of it.
- Clay soil has tiny particles and tiny pore spaces. It holds water and nutrients well. It drains badly, has little air when wet, and is heavy to dig.
- Bacteria and fungi are decomposers. They break down dead material, which releases mineral ions that plants can use. Earthworms mix the soil, and their burrows let in air and water.
Worked example
Water is poured onto a sandy soil and a clay soil. It drains through the sand in seconds and sits on top of the clay. Explain the difference.
- Sand particles are large, so the pore spaces between them are large.
- Water passes easily through large pore spaces.
- Clay particles are tiny and pack closely, so the pore spaces are very small and water can hardly move through them.
Tips and tricks
- Order of size, largest first: sand, silt, clay. Clay is the smallest, even though a lump of it feels solid.
- Organic content means the living organisms and the dead, decomposed matter. Give both when asked.
It lands in your notebook with its questions as flashcards.
What soil is made of: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which mineral particle is the smallest?
Clay particles are too small to see.
What fills the pore spaces in soil?
The balance between air and water matters to roots.
Which organisms decompose dead material in soil?
Decomposers release mineral ions from dead material.
Which describes a clay soil?
Tiny pore spaces hold on to water.
Why do roots need air in the soil?
Roots are living cells and respire.
A soil feels gritty and dries out a day after rain. Which particle does it mostly contain?Stretch
Gritty feel and fast drainage both point to large particles.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 9 marks. Write your answers on paper, then check them.
What soil is made of
Cambridge IGCSE Environmental Management 0680 · 9 marks · papermunch.org
Name ______________________________ Date ______________
State the four components of soil.[4]
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Mineral particles, organic content, gases (air) and water.
Describe the two parts of the organic content of soil.[2]
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Living organisms, such as plants, animals, fungi and bacteria. Organic matter from the decomposition of dead plants and animals.
Explain why crops in a sandy soil may be short of water and nutrients.[3]
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Sand has large pore spaces, so water drains through quickly. Little water is held for roots. Nutrients are dissolved in the water and are washed out with it.
Answers: What soil is made of
- 1. Mineral particles, organic content, gases (air) and water.
- 2. Living organisms, such as plants, animals, fungi and bacteria. Organic matter from the decomposition of dead plants and animals.
- 3. Sand has large pore spaces, so water drains through quickly. Little water is held for roots. Nutrients are dissolved in the water and are washed out with it.