Soil Formation Biology Quiz: Microbes and Roots

1. Why is the "O Horizon" (top layer) of soil usually the darkest?

It has the highest concentration of organic matter

It is burnt by the sun

It contains the most lead

It is made of pure coal

It is underwater

If the top layer receives falling leaves and dead bugs, then it has the most organic matter; if humus is dark, then that layer must be the darkest.

Explanation

If the top layer receives falling leaves and dead bugs, then it has the most organic matter; if humus is dark, then that layer must be the darkest.

2. What is the relationship between biodiversity and soil health?

Higher biodiversity usually leads to healthier, more fertile soil

Biodiversity makes soil toxic

More species mean the soil dries out faster

Biodiversity has no effect on soil

Fewer species make the soil more productive

If many species perform different roles (decomposing, aerating, fixing nitrogen), then the soil system is balanced; if balanced, then it is healthier.

Explanation

If many species perform different roles (decomposing, aerating, fixing nitrogen), then the soil system is balanced; if balanced, then it is healthier.

3. Which biological process adds oxygen to the soil pore spaces?

Animal burrowing and root growth

Photosynthesis in the deep soil

Rock melting

Water evaporation

Volcanic eruptions

If animals and roots move through soil, then they leave physical gaps; if gaps are created, then atmospheric oxygen fills those spaces.

Explanation

If animals and roots move through soil, then they leave physical gaps; if gaps are created, then atmospheric oxygen fills those spaces.

4. What would happen to soil development if all decomposers were removed?

Plant matter would pile up and nutrients would not recycle

The soil would become much richer

Rocks would turn into soil faster

Plants would grow twice as tall

The soil would turn into gold

If decomposers are gone, then dead matter cannot break down; if matter doesn't break down, then nutrients stay locked away from new plants.

Explanation

If decomposers are gone, then dead matter cannot break down; if matter doesn't break down, then nutrients stay locked away from new plants.

5. How do burrowing animals help prevent soil erosion?

By increasing the soil's ability to absorb water

By paving the surface with stones

By eating all the rain

By building tiny fences

By gluing the dirt together

If animal burrows create holes, then water enters the ground instead of running off; if runoff is reduced, then less soil is washed away.

Explanation

If animal burrows create holes, then water enters the ground instead of running off; if runoff is reduced, then less soil is washed away.

6. The process by which nutrients are removed from the soil by water is called ______.

If water moves downward through soil, then it carries dissolved minerals; if minerals are carried away from the root zone, then it is leaching.

Explanation

If water moves downward through soil, then it carries dissolved minerals; if minerals are carried away from the root zone, then it is leaching.

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7. Lichens contribute to soil formation by secreting acids that break down rock surfaces.

True

False

If lichens produce acidic chemicals, then the chemicals react with rock; if the rock reacts, then it dissolves into soil minerals.

Explanation

If lichens produce acidic chemicals, then the chemicals react with rock; if the rock reacts, then it dissolves into soil minerals.

8. Which organisms are primarily responsible for breaking down dead organic matter into humus?

Decomposers

Producers

Herbivores

Predators

Omnivores

If organisms break down dead matter, then they recycle nutrients; if they recycle nutrients into soil, then they are classified as decomposers.

Explanation

If organisms break down dead matter, then they recycle nutrients; if they recycle nutrients into soil, then they are classified as decomposers.

9. What do plants contribute to the soil when they die?

Organic matter

Plastic

Metal

Salt water

Volcanic ash

If a plant is a living thing, then its remains are organic; if these remains stay in the soil, then they provide the base for organic soil matter.

Explanation

If a plant is a living thing, then its remains are organic; if these remains stay in the soil, then they provide the base for organic soil matter.

10. What is the main role of bacteria in the nitrogen cycle within soil?

Converting nitrogen into a form plants can use

Eating the roots of healthy plants

Blocking sunlight from reaching the soil

Turning soil into sand

Making the soil stay frozen

If plants need nitrogen but cannot take it from air, then they need a soil source; if bacteria transform nitrogen, then plants can finally absorb it.

Explanation

If plants need nitrogen but cannot take it from air, then they need a soil source; if bacteria transform nitrogen, then plants can finally absorb it.

11. How do plant roots contribute to the physical weathering of rocks in soil?

By growing into cracks and wedging them apart

By absorbing all the liquid water

By releasing poisonous gases

By turning rocks into sugar

By freezing the ground

If roots grow into small rock cracks, then they exert outward pressure; if pressure increases, then the rock breaks into smaller soil particles.

Explanation

If roots grow into small rock cracks, then they exert outward pressure; if pressure increases, then the rock breaks into smaller soil particles.

12. The dark, organic material in soil formed by the decay of plant and animal matter is called ______.

If organic matter decays completely, then it forms a dark substance; if this substance provides nutrients, then it is known as humus.

Explanation

If organic matter decays completely, then it forms a dark substance; if this substance provides nutrients, then it is known as humus.

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13. Organisms that live in the soil and eat primary decomposers are known as ______ consumers.

If an organism eats a decomposer, then it is one step up the food chain; if it is one step up, then it is a secondary consumer.

Explanation

If an organism eats a decomposer, then it is one step up the food chain; if it is one step up, then it is a secondary consumer.

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14. Small animals like moles and ants hinder soil development by mixing the soil layers.

True

False

If animals burrow, then they mix nutrients and subsoil; if mixing occurs, then soil quality improves; therefore, they help rather than hinder.

Explanation

If animals burrow, then they mix nutrients and subsoil; if mixing occurs, then soil quality improves; therefore, they help rather than hinder.

15. Fungi are plants that get their energy from the sun to help soil.

True

False

If fungi do not have chlorophyll, then they cannot use the sun; if they eat dead matter instead, then they are decomposers, not plants.

Explanation

If fungi do not have chlorophyll, then they cannot use the sun; if they eat dead matter instead, then they are decomposers, not plants.

16. Earthworms help soil development by creating tunnels that allow air and water to reach plant roots.

True

False

If earthworms move through soil, then they create physical spaces; if these spaces exist, then air and water flow improves, aiding development.

Explanation

If earthworms move through soil, then they create physical spaces; if these spaces exist, then air and water flow improves, aiding development.

17. In what ways do microorganisms affect soil?

Breaking down toxins

Releasing nutrients

Binding soil particles together

Creating oxygen pockets

All of the above

If microbes process matter, then they release nutrients and toxins; if they produce sticky substances, then they bind soil; thus all roles apply.

Explanation

If microbes process matter, then they release nutrients and toxins; if they produce sticky substances, then they bind soil; thus all roles apply.

18. Which of the following are biological factors in soil formation?

Bacteria

Fungi

Earthworms

Plant roots

All of the above

If an entity is living, then it is a biological factor; if bacteria, fungi, worms, and roots are all living, then they all contribute biologically.

Explanation

If an entity is living, then it is a biological factor; if bacteria, fungi, worms, and roots are all living, then they all contribute biologically.

19. Which substances are produced by biological activity in soil?

Carbon dioxide

Organic acids

Methane

Humus

All of the above

If organisms breathe and decay, then they release gases like CO2 and methane; if they rot, then they produce acids and humus.

Explanation

If organisms breathe and decay, then they release gases like CO2 and methane; if they rot, then they produce acids and humus.

20. Tiny hair-like structures on roots that absorb water and minerals are called root ______.

If a plant needs to maximize surface area, then it grows tiny extensions; if these are on the root, then they are called root hairs.

Explanation

If a plant needs to maximize surface area, then it grows tiny extensions; if these are on the root, then they are called root hairs.

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Life in the Dirt: Soil Formation Biology Quiz

1. Why is the "O Horizon" (top layer) of soil usually the darkest?

2. What is the relationship between biodiversity and soil health?

3. Which biological process adds oxygen to the soil pore spaces?

4. What would happen to soil development if all decomposers were removed?

5. How do burrowing animals help prevent soil erosion?

6. The process by which nutrients are removed from the soil by water is called ______.

7. Lichens contribute to soil formation by secreting acids that break down rock surfaces.

8. Which organisms are primarily responsible for breaking down dead organic matter into humus?

9. What do plants contribute to the soil when they die?

10. What is the main role of bacteria in the nitrogen cycle within soil?

11. How do plant roots contribute to the physical weathering of rocks in soil?

12. The dark, organic material in soil formed by the decay of plant and animal matter is called ______.

13. Organisms that live in the soil and eat primary decomposers are known as ______ consumers.

14. Small animals like moles and ants hinder soil development by mixing the soil layers.

15. Fungi are plants that get their energy from the sun to help soil.

16. Earthworms help soil development by creating tunnels that allow air and water to reach plant roots.

17. In what ways do microorganisms affect soil?

18. Which of the following are biological factors in soil formation?

19. Which substances are produced by biological activity in soil?

20. Tiny hair-like structures on roots that absorb water and minerals are called root ______.