Grade 6 Science Worksheet on Soil Composition and Plant Growth - 12-Year-Olds

Instructions

Read each question carefully. For the objective questions, circle the best answer or fill in the blank. For the subjective and problem-solving questions, write your answers in complete sentences in the space provided.

Part A: Objective Questions

Circle the correct answer for questions 1-10.

1. Which soil component is made from decayed plants and animals?
1. Sand
2. Clay
3. Humus
4. Bedrock
2. Which soil type has the largest particles and feels gritty?
1. Sandy soil
2. Clay soil
3. Loamy soil
4. Silt soil
3. Which soil is considered the best for growing most garden plants?
1. Sand
2. Clay
3. Rock
4. Loam
4. The process of water seeping down through the soil is called:
1. Erosion
2. Percolation
3. Weathering
4. Respiration
5. Which soil type feels sticky when wet and is used to make pottery?
1. Sandy soil
2. Loamy soil
3. Clay soil
4. Peaty soil
6. What does the 'A' horizon, or topsoil, primarily contain?
1. Solid rock
2. Humus and minerals
3. Only water and air
4. Large, unweathered rocks
7. Which of the following is NOT a primary component of healthy soil?
1. Minerals
2. Organic Matter
3. Water
4. Plastic
8. The slow breaking down of rocks into the smaller pieces that form soil is called:
1. Erosion
2. Compaction
3. Weathering
4. Irrigation
9. Why is air in the soil important for plants?
1. It helps the plant stand up straight.
2. It allows the roots to perform respiration.
3. It makes the soil lighter.
4. It keeps the soil dry.
10. Which soil would have the fastest water percolation rate?
1. Clay soil
2. Loamy soil
3. Sandy soil
4. Soil with no air spaces

Fill in the blanks for questions 11-15.

11. The removal of fertile topsoil by wind or water is known as __________________.
12. __________________ soil is a balanced mixture of sand, silt, clay, and humus.
13. The different vertical layers of soil are called soil __________________.
14. __________________ is the dark, organic material in soil, rich in nutrients.
15. Clay soil has a low __________________ rate, meaning water drains through it very slowly.

Mark questions 16-20 as True (T) or False (F).

16. ____ Sandy soil is excellent at holding lots of water for plants.
17. ____ Plants get all of their food and energy from the nutrients in the soil.
18. ____ Bedrock is the soft, topmost layer of the soil profile.
19. ____ The presence of humus helps make soil fertile.
20. ____ Loamy soil is generally not suitable for agriculture.

Part B: Subjective Questions

Write a short answer for each question.

1. What are the four main components that make up soil?


2. Explain why loamy soil is considered ideal for farming and gardening.


3. Describe the main differences between sandy soil and clay soil regarding particle size and ability to hold water.


4. What is humus and how is it formed in the soil?


5. Why is soil erosion considered a major problem for farmers?


6. List three essential nutrients that plants get from the soil.


7. How does the process of weathering contribute to the formation of soil?


8. Why do plant roots need access to air within the soil?


9. If you have a pot of clay soil and a pot of sandy soil, which one would you need to water more frequently? Explain why.


10. What is the role of earthworms and other small organisms in keeping soil healthy?

Part C: Problem-Solving Questions

Read the scenarios and answer the questions.

1. A farmer notices that water sits in puddles on his field long after it rains and doesn't sink in. His crops look weak and their roots seem rotten. What type of soil does he likely have, and what could he add to the soil to improve it?


2. You want to create the perfect soil for a vegetable garden. You have access to bags of pure sand, pure clay, and compost (which is rich in humus). Describe the kind of mixture you would create and explain why it would be good for growing vegetables.


3. An experiment is set up with three identical funnels. Funnel A contains sand, Funnel B contains clay, and Funnel C contains loam. An equal amount of water (200 ml) is poured into each. Predict which funnel will have collected the most water after 10 minutes and which will have collected the least. Justify your prediction.


4. A construction company clears a large, sloped area of land, removing all the trees and grass to build new houses. A few months later, a nearby river becomes very brown and muddy, especially after heavy rain. Explain the connection between the construction project and the muddy river.


5. You are growing two identical tomato plants in separate pots. Plant A is in soil that is dark, crumbly, and rich with compost. Plant B is in soil that is pale, sandy, and has very little organic matter. Both plants receive the same amount of sunlight and water. Predict which plant will grow larger and produce more tomatoes. Explain your reasoning.

Answer Key

Part A: Objective Questions

1. c) Humus
2. a) Sandy soil
3. d) Loam
4. b) Percolation
5. c) Clay soil
6. b) Humus and minerals
7. d) Plastic
8. c) Weathering
9. b) It allows the roots to perform respiration.
10. c) Sandy soil
11. Soil erosion
12. Loam / Loamy
13. horizons
14. Humus
15. percolation
16. F (False)
17. F (False - They also need sunlight and carbon dioxide for photosynthesis.)
18. F (False - Bedrock is the bottom layer.)
19. T (True)
20. F (False)

Part B: Subjective Questions

1. The four main components of soil are minerals (like sand, silt, and clay), organic matter (humus), water, and air.
2. Loamy soil is ideal because it has a balanced mixture of sand, silt, and clay. This balance allows it to hold enough water and nutrients while also draining well so that plant roots don't get waterlogged and have access to air.
3. Sandy soil has large particles and does not hold water well (high percolation). Clay soil has very small particles and holds water very well (low percolation), often becoming waterlogged.
4. Humus is the dark, organic component of soil. It is formed from the decomposition (rotting) of dead plants, animals, and other organic waste by microorganisms like bacteria and fungi.
5. Soil erosion is a problem because it removes the fertile topsoil, which contains the most nutrients (humus) necessary for crops to grow. This leads to lower crop yields and less productive farmland.
6. Three essential nutrients are Nitrogen (N), Phosphorus (P), and Potassium (K). (Other answers like calcium, magnesium are also acceptable).
7. Weathering is the process where large rocks are broken down into smaller and smaller pieces over a long time by wind, rain, ice, and temperature changes. These small rock pieces are the mineral basis of soil.
8. Plant roots need air to perform cellular respiration. Respiration is a process that releases energy from sugars, which the roots need to grow and absorb water and nutrients from the soil.
9. You would need to water the pot with sandy soil more frequently. Sandy soil has large particles with large air spaces between them, which allows water to drain through very quickly. Clay soil holds onto water for much longer.
10. Earthworms and microorganisms (like bacteria and fungi) are decomposers. They break down dead organic material to create humus, which enriches the soil with nutrients. Earthworms also create tunnels that help aerate the soil and allow water to penetrate.

Part C: Problem-Solving Questions

1. The farmer likely has heavy clay soil. Clay has very small particles that pack tightly, preventing water from draining through (low percolation), which can cause roots to rot. He could improve it by adding organic matter (like compost or manure) and sand to increase drainage and aeration.
2. I would create a mixture that is mostly loam, so I would mix a large amount of compost (humus) with some sand and a smaller amount of clay. This creates a loamy soil that is rich in nutrients from the compost, holds water well but also drains properly due to the sand, preventing the vegetable roots from rotting.
3. Most water collected: Funnel A (sand). Sand has the largest particles and largest air gaps, so water percolates through it the fastest.
   Least water collected: Funnel B (clay). Clay has the smallest particles that hold onto water tightly, resulting in the slowest percolation rate. Funnel C (loam) would be in the middle.
4. The construction company removed the vegetation (trees, grass) that held the topsoil in place with its roots. Without this vegetation cover, the soil is exposed. When it rains, the water easily washes the loose topsoil away (soil erosion), carrying it into the nearby river and making the water brown and muddy.
5. Plant A will grow larger and produce more tomatoes. The soil for Plant A is rich in compost/humus, which provides essential nutrients for healthy growth and fruit production. Plant B's sandy soil lacks these nutrients, which will stunt its growth and limit its ability to produce tomatoes, even with adequate sun and water.