Life in soil

Question 1

Describe the main components of soil

Answer 1

• different sized mineral particles
• dead material
• living organisms
• air
• water.

Question 2

Describe a typical food web in a soil

Answer 2

• herbivores such as slugs, snails and wire worms
• detritivores such as earthworms, millipedes and
springtails
• carnivores such as centipedes, spiders and
ground beetles.

Question 3

Describe the role of bacteria and fungi

Answer 3

decomposers

Question 4

Explain why soil is important for the majority of plants

Answer 4

plants need soil to grow. Soil provides them with:

• a source of minerals, e.g. nitrates, phosphates
• water for photosynthesis and transpiration
• anchorage for roots to hold the plant upright

Question 5

what can earthworms do?

Answer 5

Iimprove soil structure and fertility

Question 6

Explain why earthworms are important to soil

structure and fertility

Answer 6

• burying organic material for decomposition by
bacteria and fungi
• aerating and draining the soil
• mixing up soil layers
• neutralising acidic soil

Question 7

Explain the importance of humus in the soil

Answer 7

• decomposition to release minerals

* increasing the air content

Question 8

Describe the difference between a sandy soil and a

clay soil in terms of particle size

Answer 8

sandy - large mineral particles

clay - small mineral particles

Question 9

what is loam?

Answer 9

a soil that contains a mixture of clay and sand

Question 10

what is humus?

Answer 10

dead material in soil that is largely decomposed

Question 11

Describe a simple experiment to compare the humus of different soils

Answer 11

1. take dry soil from previous experiment and heat strongly with Bunsen burner to incinerate humus
2. weigh and record sample
3. continue steps 1 and 2 after string soil sample. Repeat process until there is no further loss in mass.

1st mass - 2nd mass = mass of humus

Question 12

Describe a simple experiment to compare the water content of different soils

Answer 12

1. weigh and record soil sample
2. heat soil in oven for 25 hours to evaporate water and then re-weigh
3. heat soil for further 24 hours and re-weigh

Question 13

Explain why some life in soil depends on a supply of

oxygen and water

Answer 13

when there is too much water in the soil, it leads to waterlogging - the water fills all the air spaces and excludes oxygen.

Question 14

Explain how particle size affects the air content and

permeability of soils

Answer 14

the larger the particle size, the larger the air spaces. This in turn will allow water to pass through more quickly.

Question 15

Explain why aerating and draining will improve soils

Answer 15

helps to drain the excess water from the soil also pushing holes into the soil aerates it so allows oxygen to penetrate into it

Question 16

Explain why neutralising acidic soils and mixing up

soil layers is important

Answer 16

Naturally acidic soils cause a problem for certain organisms that cannot survive in acidic conditions. So plants aren’t able to absorb minerals easily. So farmers and gardeners add lime to acidic soil to neutralise it.

Question 17

Recognise the part played by Charles Darwin
in highlighting the importance of earthworms in
agriculture

Answer 17

• an organic humus layer is formed on top of the soil as a result of decomposition
• nutrients are released from the decomposing material,
• nutrients are taken down into the deeper soil layers by earthworms. This prevents the nutrients from being washed away and also aerates the soil and breaks it up