Class 8 Science Questions and Answers: The Invisible Living World Beyond Our Naked Eye
Class 8 Science The Invisible Living World Beyond Our Naked Eye Questions and Answers | CBSE Important Questions
Meta Description: Get CBSE Class 8 Science important questions and answers for The Invisible Living World: Beyond Our Naked Eye. Includes very short answers, short answers, long answers, MCQs, assertion-reason, competency-based questions, diagram questions, HOTS and quick revision points.
This premium question-answer set is designed for CBSE Class 8 Science students preparing for school exams, unit tests and quick revision. The questions are based on the chapter The Invisible Living World: Beyond Our Naked Eye and cover cells, microscopes, microorganisms, microbes in food, decomposition, microalgae, fermentation and the basic unit of life.
Class 8 Science Questions and Answers CBSE Class 8 Science Important Questions NCERT Science Chapter Questions Competency Based Science QuestionsChapter Overview
| Particular | Details |
|---|---|
| Class | Class 8 |
| Board | CBSE |
| Subject | Science |
| Chapter | The Invisible Living World: Beyond Our Naked Eye |
| Main Concepts | Microscope, cell, plant cell, animal cell, microorganisms, fungi, bacteria, protozoa, algae, viruses, decomposition, fermentation, curd formation, biogas, Rhizobium, microalgae |
Table of Contents
Very Short Answer Questions
Question 1.
What is the basic unit of life?
The cell is the basic unit of life.
Question 2.
What are microorganisms?
Microorganisms are tiny living organisms that cannot be seen with the naked eye.
Question 3.
Name the scientist who first used the word cell in science.
Robert Hooke first used the word cell in science.
Question 4.
Who is known as the Father of Microbiology?
Antonie van Leeuwenhoek is known as the Father of Microbiology.
Question 5.
Name the outer layer of a typical cell.
The outer layer of a typical cell is the cell membrane.
Question 6.
Which part of the cell regulates cell activities and growth?
The nucleus regulates cell activities and growth.
Question 7.
Which cell part provides rigidity and strength to plant cells?
The cell wall provides rigidity and strength to plant cells.
Question 8.
Name the green pigment present in chloroplasts.
The green pigment is chlorophyll.
Question 9.
Name one unicellular fungus mentioned in the chapter.
Yeast is a unicellular fungus.
Question 10.
Name the bacterium that helps in curd formation.
Lactobacillus helps in curd formation.
Question 11.
What is decomposition?
Decomposition is the breakdown of complex substances of dead plants and animals into simpler nutrient-rich substances by microorganisms.
Question 12.
Name the bacteria found in root nodules of legumes.
Rhizobium bacteria are found in root nodules of legumes.
Short Answer Questions
Question 1.
Why was the invention of the microscope important?
The invention of the microscope was important because it helped humans see tiny living organisms and cell structures that cannot be seen with the naked eye. It opened a hidden world of microorganisms and cells.
Question 2.
Why did the letters appear larger when seen through a round-bottom flask filled with water?
The flask filled with water acted like a magnifying glass. A curved transparent surface can make small objects appear larger, just like a lens.
Question 3.
Write the three basic parts of a typical cell.
The three basic parts of a typical cell are cell membrane, cytoplasm and nucleus.
Question 4.
How is an onion peel cell different from a human cheek cell?
Onion peel cells are nearly rectangular and closely arranged. They have a cell wall in addition to the cell membrane. Human cheek cells are polygon-shaped, thin and flat, and they do not have a cell wall.
Question 5.
What is the function of the cell membrane?
The cell membrane encloses the cytoplasm and nucleus, separates one cell from another, and allows the entry of useful materials and exit of waste materials.
Question 6.
Why do nerve cells have a long and branched structure?
Nerve cells, also called neurons, carry messages in the body. Their elongated and branched structure helps them reach different parts of the body and pass messages quickly.
Question 7.
Write the correct sequence of levels of organisation in a living organism.
The correct sequence is: Cell → Tissue → Organ → Organ system → Organism.
Question 8.
Why are plants and animals called multicellular organisms?
Plants and animals are called multicellular organisms because their bodies are made up of many cells. These cells perform specialised functions and cooperate with each other.
Question 9.
Why do pickles and murabbas not get infected easily by microorganisms?
Pickles and murabbas contain high concentrations of salt or sugar. These act as preservatives and do not allow microorganisms to grow easily.
Question 10.
How does yeast make dough soft and fluffy?
Yeast respires and breaks down food to release energy. During this process, carbon dioxide is released. The carbon dioxide forms bubbles in the dough, making it soft and fluffy.
Long Answer Questions
Question 1.
Describe the structure and functions of the main parts of a cell.
A typical cell has three main parts: cell membrane, cytoplasm and nucleus.
- Cell membrane: It encloses the cytoplasm and nucleus. It separates one cell from another and allows useful materials to enter and wastes to leave.
- Cytoplasm: It is the space between the cell membrane and nucleus. It contains cell components and substances such as carbohydrates, proteins, fats and mineral salts. Most life processes occur in the cytoplasm.
- Nucleus: It regulates all activities inside the cell and also controls growth.
- Cell wall: Plant cells have an extra outer layer called the cell wall. It provides rigidity and strength to the cell.
Question 2.
Explain how microorganisms help in cleaning the environment.
Microorganisms such as bacteria and fungi act on plant and animal waste and break it down into simpler substances. This process is called decomposition.
- They decompose fallen leaves, fruit peels, vegetable peels and dead organisms.
- The waste changes into dark, nutrient-rich manure.
- The nutrients return to the soil and help plants grow better.
- Thus, microorganisms recycle waste and clean the environment naturally.
Question 3.
Explain the role of microorganisms in food preparation.
Microorganisms are very useful in food preparation.
- Yeast is used to make breads, cakes and similar food items soft and fluffy.
- Yeast releases carbon dioxide during respiration, which forms bubbles in dough.
- Some bacteria help in the fermentation of batter for idli and dosa and dough for bhatura.
- Lactobacillus converts milk into curd by fermenting lactose and producing lactic acid.
- These processes improve texture, taste and usefulness of food.
Question 4.
Why is the cell considered the basic unit of life?
The cell is considered the basic unit of life because the body of every living organism is made up of cells. A cell contains different components that help an organism perform life functions and survive. Unicellular organisms carry out all life processes within a single cell. In multicellular organisms, different cells perform specialised functions and work together. Therefore, the cell is the smallest living unit that can perform essential life processes.
Question 5.
Describe the importance of microalgae.
Microalgae are microscopic plant-like organisms found in water, soil, air and even on trees. They are important because:
- They make their own food using sunlight.
- They release oxygen and produce more than half of the Earth’s oxygen supply.
- They are rich in nutrients and serve as food for aquatic animals.
- Some microalgae such as Spirulina, Chlorella and Diatoms are used as health supplements and medicines.
- They help in cleaning water and can be used to make biofuel.
MCQs
Question 1.
Which device is used to observe microorganisms?
- A. Telescope
- B. Microscope
- C. Periscope
- D. Stethoscope
Explanation: A microscope magnifies tiny organisms and makes them visible.
Question 2.
Robert Hooke observed a thin slice of which material?
- A. Cork
- B. Leaf
- C. Cheek cell
- D. Soil
Explanation: Robert Hooke observed a thin slice of cork and called the small spaces cells.
Question 3.
Which of the following is present in plant cells but not in human cheek cells?
- A. Cytoplasm
- B. Cell membrane
- C. Nucleus
- D. Cell wall
Explanation: Onion peel cells have a cell wall, while human cheek cells do not.
Question 4.
Which microorganism helps in making curd?
- A. Rhizobium
- B. Lactobacillus
- C. Amoeba
- D. Paramecium
Explanation: Lactobacillus ferments lactose in milk and forms curd.
Question 5.
Yeast belongs to which group of microorganisms?
- A. Fungi
- B. Protozoa
- C. Algae
- D. Virus
Explanation: Yeast is a microorganism that belongs to fungi.
Question 6.
Which gas makes dough soft and fluffy?
- A. Oxygen
- B. Nitrogen
- C. Carbon dioxide
- D. Hydrogen
Explanation: Yeast releases carbon dioxide, which forms bubbles in the dough.
Question 7.
Which bacteria live in root nodules of legumes?
- A. Lactobacillus
- B. Rhizobium
- C. Amoeba
- D. Yeast
Explanation: Rhizobium traps nitrogen from air and helps plants grow better.
Question 8.
Which structure is found in bacteria instead of a well-defined nucleus?
- A. Chloroplast
- B. Nucleoid
- C. Vacuole
- D. Cell wall only
Explanation: Bacteria do not have a well-defined nucleus. They have a nucleoid region.
Question 9.
Which of the following can reproduce only inside a host organism?
- A. Virus
- B. Yeast
- C. Algae
- D. Amoeba
Explanation: Viruses multiply only after entering a living cell.
Question 10.
Which of the following is a microalga called a superfood?
- A. Spirulina
- B. Bread mould
- C. Rhizobium
- D. Paramecium
Explanation: Spirulina is rich in protein and vitamin B12 and is known for health benefits.
Assertion and Reason Questions
Question 1.
Assertion: A microscope helps us observe microorganisms.
Reason: Microorganisms are too small to be seen with the naked eye.
Explanation: Microorganisms need magnification for observation because they are invisible to the unaided eye.
Question 2.
Assertion: Plant cells have a cell wall.
Reason: The cell wall provides rigidity and strength to plant cells.
Explanation: The cell wall helps plant cells remain firm and compactly arranged.
Question 3.
Assertion: Yeast is used in making bread and cakes.
Reason: Yeast releases carbon dioxide during respiration.
Explanation: Carbon dioxide bubbles make dough soft and fluffy.
Question 4.
Assertion: Bacteria have a well-defined nucleus.
Reason: Bacteria have a nucleoid region instead of a well-defined nucleus.
Explanation: Bacteria lack a well-defined nucleus and nuclear membrane.
Question 5.
Assertion: Microorganisms are always harmful.
Reason: Some microorganisms help in decomposition, curd formation and fermentation.
Explanation: Microorganisms can be beneficial or harmful. Many are useful in food preparation and environmental cleaning.
Case Study / Competency-Based Questions
Case Study 1: Yeast and Dough
A student took two bowls, A and B. In both bowls, she added flour, sugar and warm water. In bowl A, she added yeast. In bowl B, she did not add yeast. After keeping both bowls in a warm place for a few hours, the dough in bowl A became fluffy and had a different smell.
Question 1. Which microorganism was added to bowl A?
Yeast was added to bowl A.
Question 2. Why did the dough in bowl A rise?
Yeast released carbon dioxide during respiration. The gas formed bubbles and made the dough rise.
Question 3. Why was warm water used?
Yeast grows well in warm conditions, so warm water helps yeast activity.
Question 4. Why did bowl B not show the same change?
Bowl B did not contain yeast, so carbon dioxide was not produced in the same way.
Question 5. Name two food items made using this property of yeast.
Bread and cakes are made using this property of yeast.
Case Study 2: Manure Formation
A student added fruit and vegetable peels into a container half-filled with garden soil. She covered the waste with another layer of soil and left it for 2-3 weeks. After this period, the waste turned into a dark-coloured material rich in nutrients.
Question 1. What is the dark-coloured material called?
It is called manure.
Question 2. Which microorganisms help in this process?
Bacteria and fungi help in this process.
Question 3. What is the process of breaking down waste called?
It is called decomposition.
Question 4. How does manure help plants?
Manure adds nutrients to the soil and increases soil fertility.
Question 5. What conditions help manure formation?
Optimal temperature and appropriate moisture level help manure formation.
Diagram-Based Questions
Question 1.
In a diagram of onion peel cells, which parts should be labelled?
The important labels are cell wall, cell membrane, cytoplasm and nucleus.
Question 2.
In a human cheek cell diagram, name the three main parts visible.
The visible parts are cell membrane, cytoplasm and nucleus.
Question 3.
What is the main difference between the labelled diagrams of plant cell and animal cell?
A plant cell has a cell wall, chloroplasts and a large vacuole. An animal cell does not have a cell wall or chloroplasts, and vacuoles are usually absent or small.
Question 4.
In a bacterial cell diagram, what is the nucleoid?
The nucleoid is the region in a bacterial cell that contains genetic material. Bacteria do not have a well-defined nucleus.
Question 5.
In the experimental set-up of yeast with sugar solution and lime water, what change is expected in lime water?
Lime water turns milky because yeast produces carbon dioxide, which reacts with lime water.
HOTS / Application-Based Questions
Question 1.
What would happen if microorganisms did not exist on Earth?
Dead plants, animals and waste materials would not decompose properly. Nutrients would not return to the soil, natural manure formation would stop, and the environment would become filled with waste.
Question 2.
Why do farmers grow legumes such as beans, peas and lentils in rotation with other crops?
Legumes have root nodules containing Rhizobium bacteria. These bacteria trap nitrogen from air and make it useful for plants, naturally increasing soil fertility for the next crop.
Question 3.
Why does curd form faster in warm milk than in cold milk?
Lactobacillus bacteria grow well in warm conditions. In warm milk, they multiply and ferment lactose faster, producing lactic acid and forming curd.
Question 4.
Why is the shape of a cell related to its function? Explain with two examples.
Cell shape helps a cell perform its function efficiently. Nerve cells are long and branched, so they can carry messages quickly to different body parts. Muscle cells are spindle-shaped, thin and flexible, so they can contract and relax to produce movement.
Question 5.
Why should microalgae be conserved?
Microalgae produce a large amount of Earth’s oxygen, serve as food for aquatic animals, help clean water, and are useful as health supplements, medicines and biofuel sources. Their conservation helps maintain environmental balance.
Quick Revision Points
Final Exam Tips
- Revise the difference between plant cell, animal cell and bacterial cell.
- Learn the functions of cell membrane, cytoplasm, nucleus, cell wall, vacuole and chloroplast.
- Practise diagrams of onion peel cell, human cheek cell, plant cell, animal cell and bacterial cell.
- Prepare examples of useful microorganisms: yeast, Lactobacillus, Rhizobium and microalgae.
- For competency-based questions, focus on experiments related to yeast fermentation, curd formation and manure formation.
Conclusion
The chapter The Invisible Living World: Beyond Our Naked Eye helps students understand that many living organisms and cell structures are too small to be seen without a microscope. It explains cells as the basic units of life, the difference between plant, animal and bacterial cells, and the useful role of microorganisms in food, agriculture, decomposition, biogas and oxygen production. These CBSE Class 8 Science Important Questions are useful for quick revision, school exams and concept-based preparation.
Additional Very Short Answer Questions
Question 13.
What is a lens?
A lens is a curved piece of glass that can make small things appear bigger.
Question 14.
Why was a lens named so?
It was named lens because it was shaped like a lentil seed, thick in the middle and thin at the edge.
Question 15.
Name the book published by Robert Hooke in 1665.
Robert Hooke published a book called Micrographia.
Question 16.
What did Robert Hooke observe in a thin slice of cork?
He observed many small empty spaces that looked like a honeycomb.
Question 17.
What are cheek cells?
Cheek cells are polygon-shaped cells that form the inner lining of the mouth.
Question 18.
Which stain is used to observe onion peel cells?
Safranin is used to stain onion peel cells.
Question 19.
Which stain is used to observe human cheek cells?
Methylene blue is used to stain human cheek cells.
Question 20.
What is the function of glycerin while preparing a slide?
Glycerin prevents the cells from drying and improves clarity during observation.
Question 21.
What are plastids?
Plastids are tiny rod-shaped structures present in plant cells.
Question 22.
Name the plastids that contain chlorophyll.
Chloroplasts contain chlorophyll.
Question 23.
What is the largest known cell in the living world?
The yolk of an ostrich egg is the largest known cell in the living world.
Question 24.
What are microbes?
Microbes are very small living beings that cannot be seen with the naked eye.
Additional Short Answer Questions
Question 11.
Why are stains used while observing cells under a microscope?
Stains are used to improve the visibility of cells under the microscope. They increase contrast and make cell parts such as the nucleus easier to observe.
Question 12.
Why should no air bubbles be trapped while placing a coverslip?
Air bubbles can disturb the clear view of the specimen. They may hide cell parts and make microscopic observation difficult.
Question 13.
Why are onion peel cells compared with bricks in a wall?
Onion peel cells are closely arranged without much space, just like bricks in a wall. This shows how cells form a compact structure in plants.
Question 14.
How do vacuoles help plant cells?
Vacuoles help plant cells store important substances, remove waste and maintain the shape of the cell. They also provide strength and support to the plant.
Question 15.
How are vacuoles different in plant and animal cells?
Plant cells usually have a large vacuole. In animal cells, vacuoles are usually absent, and if present, they are small.
Question 16.
Why are muscle cells suitable for movement?
Muscle cells are thin, flexible and spindle-shaped. These features help them contract and relax, making movement possible.
Question 17.
How do muscle cells help in digestion?
Muscle cells in the food pipe contract and relax in a wave-like manner to push food down to the stomach. Muscle cells in the stomach wall help churn the food.
Question 18.
Why are microorganisms found in pond water and soil suspension?
Microorganisms are present all around us, including water and soil. Pond water and soil suspension contain tiny living organisms that can be observed only with a microscope.
Question 19.
Why do fruits sometimes show cotton-like or powdery growth?
Fruits may show cotton-like or powdery growth because they get infected by microbes present in air, water, soil or surrounding surfaces.
Question 20.
Why is a foldable paper microscope useful?
A foldable paper microscope is low-cost and makes the microscopic world accessible to many people, though it may not show as much detail as a high-powered laboratory microscope.
Additional Long Answer Questions
Question 6.
Explain the contribution of Robert Hooke and Antonie van Leeuwenhoek in the discovery of the microscopic world.
Robert Hooke and Antonie van Leeuwenhoek played important roles in revealing the microscopic world.
- In 1665, Robert Hooke published a book called Micrographia.
- He used a microscope to observe tiny objects and made detailed drawings of them.
- He observed a thin slice of cork and saw many small empty compartments.
- These compartments reminded him of a honeycomb, and he called them cells.
- Antonie van Leeuwenhoek made better lenses and more useful microscopes.
- He was the first person to clearly see and describe tiny living things such as bacteria and blood cells.
- He is known as the Father of Microbiology.
Question 7.
Describe the procedure to prepare and observe an onion peel slide.
- Take an onion bulb and wash it properly.
- Cut the onion vertically into pieces.
- Pull out a thin transparent layer from the inner surface using forceps. This is called the onion peel.
- Place the peel in a petri dish containing safranin for about 30 seconds.
- Transfer the peel to water to remove extra stain.
- Place the stained peel carefully on a clean glass slide.
- Add a drop of glycerin to prevent drying.
- Place a coverslip gently using a needle so that no air bubbles are trapped.
- Remove extra glycerin with blotting paper.
- Observe the slide under a microscope.
Nearly rectangular, closely arranged cells are observed.
Question 8.
Explain the differences between plant cells and animal cells.
| Plant Cell | Animal Cell |
|---|---|
| Plant cells have a cell wall. | Animal cells do not have a cell wall. |
| Plant cells have chloroplasts in green parts. | Animal cells do not have chloroplasts. |
| Plant cells usually have a large vacuole. | Animal cells usually have no vacuole, or small vacuoles if present. |
| Plant cells are often more firm due to the cell wall. | Animal cells are generally more flexible in shape. |
Question 9.
Explain the structure and importance of bacterial cells.
Bacteria are microorganisms that may be spherical, comma-shaped, spiral-shaped or rod-shaped. They have a cellular structure but do not have a well-defined nucleus. Instead, they contain a nucleoid region. Some bacteria have one long hair-like structure and many small hair-like projections around the cell.
Bacteria are important because some of them help in digestion, curd formation, decomposition and increasing soil fertility. For example, Lactobacillus helps in curd formation and Rhizobium helps legumes by trapping nitrogen from air.
Question 10.
Explain how microorganisms are both useful and harmful.
Microorganisms can be both useful and harmful.
- Useful roles: Some microbes decompose plant and animal waste and clean the environment.
- Some microorganisms help in making manure by breaking down fruit and vegetable peels.
- Yeast helps in making bread, cakes and other fermented foods soft and fluffy.
- Lactobacillus helps convert milk into curd.
- Rhizobium helps increase soil fertility by trapping nitrogen.
- Microalgae release oxygen, provide food for aquatic animals and help clean water.
- Harmful roles: Some microbes infect food and cause it to rot. Viruses may infect plants, animals or bacteria and may cause disease.
Additional MCQs
Question 11.
Which stain is used for onion peel cells?
- A. Methylene blue
- B. Safranin
- C. Iodine vapour
- D. Lime water
Explanation: Safranin gives a pinkish colour to onion peel cells and makes them easier to observe.
Question 12.
Which stain is used for human cheek cells?
- A. Safranin
- B. Methylene blue
- C. Glycerin
- D. Sugar solution
Explanation: Methylene blue increases contrast and helps in observing cheek cells clearly.
Question 13.
Which cell part controls all activities inside the cell?
- A. Cell wall
- B. Cytoplasm
- C. Nucleus
- D. Vacuole
Explanation: The nucleus regulates all activities that occur within the cell and also regulates growth.
Question 14.
Which of the following is the correct order of organisation in living organisms?
- A. Tissue → Cell → Organ → Organism
- B. Cell → Tissue → Organ → Organ system → Organism
- C. Organism → Organ → Cell → Tissue
- D. Organ → Tissue → Cell → Organ system
Explanation: Cells form tissues, tissues form organs, organs form organ systems and organ systems form an organism.
Question 15.
Which cells form a protective lining on the inner surface of the cheek?
- A. Nerve cells
- B. Muscle cells
- C. Cheek cells
- D. Root cells
Explanation: Inner cheek cells are thin and flat and form a protective lining.
Question 16.
Which cells carry messages in the body?
- A. Nerve cells
- B. Onion peel cells
- C. Bread mould cells
- D. Root nodule cells
Explanation: Nerve cells, also called neurons, carry messages in the body.
Question 17.
Which of the following is observed in pond water?
- A. Amoeba
- B. Paramecium
- C. Algae
- D. All of these
Explanation: Amoeba, Paramecium and algae may be observed in pond water.
Question 18.
Which microorganism is described as single-celled, moving and irregular in shape?
- A. Amoeba
- B. Bread mould
- C. Rhizobium
- D. Spirulina
Explanation: Amoeba is a unicellular protozoan with an irregular shape.
Question 19.
Which microorganism is described as branched filament without chlorophyll?
- A. Algae
- B. Fungi
- C. Bacteria
- D. Paramecium
Explanation: Bread mould and mould are fungi with branched filaments and without chlorophyll.
Question 20.
Which of the following conditions helps curd formation?
- A. Very cold conditions
- B. Warm conditions
- C. Complete dryness
- D. Absence of bacteria
Explanation: Lactobacillus grows well in warm conditions and helps milk turn into curd.
Additional Assertion and Reason Questions
Question 6.
Assertion: Safranin is used while preparing an onion peel slide.
Reason: Safranin stains the cells and helps us see them clearly.
Explanation: Safranin gives colour to onion peel cells, improving visibility under the microscope.
Question 7.
Assertion: Nerve cells are long and branched.
Reason: Their shape helps them carry messages to different parts of the body quickly.
Explanation: The structure of nerve cells is related to their function of carrying messages.
Question 8.
Assertion: Plant cells usually have a large vacuole.
Reason: Vacuoles help in storage, waste removal and maintaining cell shape.
Explanation: A large vacuole gives support and helps plant cells maintain shape.
Question 9.
Assertion: Curd forms better in cold milk than in lukewarm milk.
Reason: Lactobacillus grows well in warm conditions.
Explanation: Curd forms better in lukewarm milk because Lactobacillus grows well in warm conditions.
Question 10.
Assertion: Viruses are acellular.
Reason: Viruses multiply only when they enter a living cell.
Explanation: Viruses are microscopic and acellular. They multiply inside living cells and may cause diseases.
Additional Case Study / Competency-Based Questions
Case Study 3: Observing Cells Under a Microscope
A teacher demonstrated how to observe onion peel cells. She stained the onion peel with safranin, placed it on a slide, added glycerin and carefully placed a coverslip. Under the microscope, students observed rectangular structures arranged closely together.
Question 1. What were the rectangular structures observed by the students?
They were onion peel cells.
Question 2. Why was safranin used?
Safranin was used to stain the cells and make them clearly visible.
Question 3. Why was glycerin added?
Glycerin was added to prevent the cells from drying and to improve clarity.
Question 4. Name one extra outer layer present in onion peel cells.
The extra outer layer is the cell wall.
Question 5. Why do onion peel cells look firm and compact?
They look firm and compact because the cell wall provides rigidity and strength.
Case Study 4: Curd Formation
A student took two bowls. Bowl A contained lukewarm milk and bowl B contained cold milk. She added a small spoonful of curd to both bowls. Bowl A was kept in a warm place, while bowl B was kept in a cool place. After a few hours, bowl A turned into curd, while bowl B did not curdle properly.
Question 1. Which bacterium helps in curd formation?
Lactobacillus helps in curd formation.
Question 2. What sugar is present in milk?
The sugar present in milk is lactose.
Question 3. What acid makes curd sour?
Lactic acid makes curd sour.
Question 4. Why did bowl A form curd faster?
Bowl A formed curd faster because Lactobacillus grows well in warm conditions.
Question 5. Why did bowl B not curdle properly?
Bowl B was kept in a cool place, which slowed the growth and activity of Lactobacillus.
Additional Diagram-Based Questions
Question 6.
In the diagram of a plant cell, which labelled part contains chlorophyll?
Chloroplast contains chlorophyll.
Question 7.
In a plant cell diagram, which part maintains the shape of the cell and stores substances?
The vacuole maintains the shape of the cell and stores substances.
Question 8.
In the diagram of levels of organisation, what comes after tissue?
Organ comes after tissue.
Question 9.
In a diagram of pond water organisms, which organism has an irregular shape?
Amoeba has an irregular shape.
Question 10.
In a root nodule diagram of a legume plant, which bacteria are present in the nodules?
Rhizobium bacteria are present in the root nodules.
Additional HOTS / Application-Based Questions
Question 6.
A student observes that bread kept in a moist place develops cotton-like growth. Which microorganisms may be responsible and why?
Fungi such as bread mould may be responsible. Moist conditions support the growth of microorganisms, and fungi can grow as cotton-like or powdery structures on food.
Question 7.
Why should fruit and vegetable peels not always be thrown away as waste?
Fruit and vegetable peels can be converted into manure by microorganisms. This manure is rich in nutrients and improves soil fertility.
Question 8.
Why can a single cell like an egg develop into a multicellular organism?
The egg has the ability to divide repeatedly. Through repeated division, it forms many cells that later organise into tissues, organs and organ systems.
Question 9.
A farmer wants to improve soil fertility naturally. Which crop type should he grow and why?
He should grow legumes such as peas, beans or lentils because their root nodules contain Rhizobium bacteria. These bacteria trap nitrogen from air and enrich the soil.
Question 10.
Why is it incorrect to say that all tiny organisms are harmful?
It is incorrect because many tiny organisms are useful. Microorganisms help in decomposition, manure formation, curd formation, fermentation, nitrogen enrichment, water cleaning, oxygen production and biofuel production.
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