GSEB Class 7 Science Solutions Chapter 9 ભૂમિ

Select the correct option for the textbook questions: (for questions 1 and 2)

Question 1. What components is soil made of?
(a) Stones, topsoil
(b) Air and water
(c) Mineral salts, organic matter, air, and water
(d) Water, air, and plants
Answer: (c) Mineral salts, organic matter, air, and water
In simple words: Soil is made up of many things like tiny rock pieces (minerals), plant and animal remains (organic matter), air pockets, and water. These all mix together.

Exam Tip: Remember the four main components of soil: minerals, organic matter, air, and water. This forms the foundation of soil science.

Question 2. Water holding capacity is highest in ..........
(a) Sandy soil
(b) Clayey soil
(c) Porous soil
(d) Mixture of sand and silt
Answer: (b) Clayey soil
In simple words: Clayey soil can hold the most water because its tiny particles are packed closely together, leaving less space for water to drain away.

Exam Tip: Understand that the size of soil particles directly influences water retention. Smaller particles in clay soil lead to higher water holding capacity.

Question 3. Match the details given in Column I with Column II.
Column I
(1) Home of organisms
(2) Topsoil / A-horizon
(3) Sandy soil
(4) Subsoil / B-horizon
(5) Clayey soil
Column II
(a) Large particles
(b) All types of soil
(c) Dark colored
(d) Small particles and tight bonding
(e) Low silt content
Answer:
(1) → (b)
(2) → (c)
(3) → (a)
(4) → (e)
(5) → (d)
In simple words: Match the description from the first list with the best-fitting word or phrase from the second list. For example, "Home of organisms" matches with "All types of soil" because many living things live in different soils.

Exam Tip: Pay close attention to the characteristics of each soil type and layer. This ensures you make the correct matches. For instance, clayey soil's small particles give it tight bonding.

Question 4. Explain how soil is formed.
Answer: Water, wind, and climate play a vital role in the formation of soil. Extreme heat and cold cause cracks in rocks. River flow, ocean waves, and rainwater erode rocks. The wearing down of rocks makes them break. Over time, these form small pebbles. Later, sand is created from these pebbles. When dead organic materials mix with it, soil is formed. Thus, the formation of soil occurs by the breaking of rocks (stones) by water, wind, and atmosphere. This process is called weathering.
In simple words: Soil is formed through a process called weathering. Rocks slowly break down over time due to sun, rain, wind, and ice. These tiny rock pieces mix with dead plants and animals to become soil.

Exam Tip: When explaining soil formation, remember to highlight the key agents of weathering (water, wind, climate) and the role of organic matter in the process.

Question 5. How is clayey soil useful for crops?
Answer: Clayey soil has a high water-holding capacity. Since it has more organic matter, it is fertile land. These conditions are very suitable for crop growth. Because of this, good crops can be obtained by growing them in clayey soil.
In simple words: Clayey soil is good for crops because it holds a lot of water and has many nutrients. These two things help plants to grow well.

Exam Tip: Focus on water retention and nutrient content when discussing the benefits of clayey soil for agriculture. These are the primary reasons for its fertility.

Question 6. Give the difference between clayey and sandy soil.
Answer:

Exam Tip: When differentiating, always focus on particle size, compaction, air space, and water retention. These are the key distinguishing features between soil types.

Question 7. Draw a longitudinal section of soil and name its layers.
Answer:
In simple words: A soil profile shows different layers of soil from the surface down to the bedrock. Each layer has different properties like color, texture, and composition.

Exam Tip: Ensure your diagram clearly shows distinct layers, is neatly drawn, and each layer is correctly labeled with its name and corresponding horizon.

Question 8. Razia performed a percolation rate experiment for her field. She observed that it takes 40 minutes for 200 ml of water. Find the percolation rate.
Answer:
Amount of water \( = 200 \) ml
Percolation time \( = 40 \) minutes
Percolation rate \( = \frac { \text{Amount of water (in ml)} }{ \text{Percolation time (in minutes)} } \)

\( \implies \) Percolation rate \( = \frac { 200 \text{ ml} }{ 40 \text{ minutes} } \)

\( \implies \) Percolation rate \( = 5 \text{ ml / minute} \)
In simple words: To find out how fast water goes through soil, you divide the amount of water by the time it takes. So, 200 ml in 40 minutes means 5 ml of water goes through every minute.

Exam Tip: Always remember the formula for percolation rate: `Volume of water / Percolation time`. Ensure units are consistent (ml/minute or ml/hour).

Question 9. How can soil pollution and soil erosion be prevented?
Answer:
Measures to prevent soil pollution are as follows:
1. The use of plastic and polythene bags should be restricted, or care should be taken to ensure that plastic and polythene waste is not buried in the soil.
2. Industrial chemical waste and chemicals should be treated to make them neutral before being released into the soil.
3. The use of chemical fertilizers in agriculture should be reduced.
Measures to prevent soil erosion are as follows:
1. More trees should be planted. Deforestation should be stopped.
2. Grass should be grown on barren land.
3. The soil should be plowed to make it level.
4. Bunds should be built around fields, fences should be installed, and trees should be planted.
In simple words: To stop soil pollution, we should use less plastic, treat factory waste, and reduce chemical fertilizers. To prevent soil erosion, we need to plant more trees, grow grass on bare ground, level fields, and build small walls around them.

Exam Tip: For prevention questions, categorize your points clearly (e.g., pollution vs. erosion) and provide actionable steps. Focus on sustainable practices like afforestation and responsible waste management.

Question 10. Solve the given puzzle with the help of English words from the clues below.
Given words: EARTHWORM, SANDY, WIND, WHEAT, CLAY, EROSION, POLYTHENE, PROFILE
Across clues:
2. Afforestation will prevent this.
6. Soil used for pottery.
7. Organisms found in soil.
Down clues:
1. Soil erosion in deserts.
3. Sticky and porous soil suitable for crops.
4. This type of soil holds very little water.
5. A name for all layers of soil.
Answer:
Across:
2. EROSION
6. CLAY
7. EARTHWORM
Down:
1. WIND
3. WHEAT
4. SANDY
5. PROFILE
In simple words: You need to fill in the crossword puzzle grid using the given words. Each clue helps you find the right word that fits across or down in the grid.

Exam Tip: For crossword puzzles, always read all clues first, then fill in the most obvious answers. Use the given word bank to help identify the correct terms for each clue, ensuring they fit the letter count.