Students can keep Class 8 Science Extra Questions and Class 8th Curiosity Chapter 2 The Invisible Living World: Beyond Our Naked Eye Important Extra Question Answer handy for quick reference during exams.
Class 8 Science Chapter 2 The Invisible Living World: Beyond Our Naked Eye Extra Questions
Class 8 Science Chapter 2 Extra Questions on The Invisible Living World: Beyond Our Naked Eye
The Invisible Living World: Beyond Our Naked Eye Class 8 Very Short Question Answer
Question 1.
Name one commercial use of yeast. (NCERT Exemplar)
Answer:
Baking bread/manufacturing of alcoholic drinks.
Question 2.
Name the process in yeast that converts sugars into alcohol. (NCERT Exemplar)
Answer:
Fermentation
The Invisible Living World: Beyond Our Naked Eye Class 8 Short Question Answer
Question 1.
What is the role of Lactobacillus in curd formation?
Answer:
Lactobacillus converts lactose (milk sugar) into lactic acid, which causes the milk to thicken and form curd.
Question 2.
Why do farmers grow legumes in rotation with other crops?
Answer:
Legumes contain Rhizobium bacteria in their roots that fix nitrogen and naturally enrich the soil.
Question 3.
How does yeast make dough soft and fluffy?
Answer:
Yeast ferments the sugars in dough, releasing carbon dioxide that creates bubbles and makes the dough rise.
Question 4.
What do you observe when a bread slice is kept in a moist, warm place for 3 days? Why?
Answer:
Fungi grow on the bread due to the favorable warm and moist environment that supports microbial growth.
Question 5.
What is the purpose of using lime water in the yeast experiment?
Answer:
To test for the presence of carbon dioxide, which turns lime water milky if present.
Question 6.
Why did the balloon inflate in test tube B when yeast was added?
Answer:
The yeast fermented sugar and released carbon dioxide gas, which inflated the balloon.
Question 7.
What will happen if yeast is not added to the sugar solution in flask A?
Answer:
No fermentation occurs, so no gas is produced, and the connected test tube remains unchanged.
Question 8.
What can be inferred if curd forms in warm milk but not in cold milk?
Answer:
Warm temperatures help bacteria multiply and ferment milk, while cold temperatures slow their activity.
Question 9.
How does Rhizobium benefit legume plants?
Answer:
It converts nitrogen from the air into compounds the plant can use, improving growth without fertilizers.
Question 10.
What are microalgae, and why are they important for the Earth?
Answer:
Microalgae are tiny photosynthetic organisms that produce oxygen and are used as nutritious food and in water purification.
Question 11.
Why do microorganisms grow faster in warm, moist conditions?
Answer:
Because these conditions support their metabolism and reproduction, speeding up their growth.
Question 12.
What is the difference between unicellular and multicellular microorganisms?
Answer:
Unicellular microbes like yeast have one cell; multicellular microbes like mould have many cells.
Question 13.
Why is Spirulina called a “superfood”?
Answer:
It is rich in protein, vitamins, and minerals and is easy to digest with little fat or sugar.
Question 14.
How are microorganisms used in the food industry?
Answer:
They are used for fermentation in products like curd, bread, idlis, dosas, vinegar, and alcohol.
Question 15.
What is the role of microorganisms in the production of biogas?
Answer:
Microbes decompose organic waste without oxygen, producing biogas such as methane that can be used as fuel.
Question 16.
How can we prevent the following diseases? (NCERT Exemplar)
(a) Cholera
(b) Typhoid
(c) Hepatitis A
Answer:
(a) Cholera: By maintaining personal hygiene and good sanitation practices.
(b) Typhoid: Eating properly cooked food, drinking boiled water and getting vaccinated against the disease.
(c) Hepatitis A: Drinking boiled water and getting vaccinated against the disease.
The Invisible Living World: Beyond Our Naked Eye Class 8 Long Question Answer
Question 1.
Explain the role of microorganisms in the nitrogen cycle, about Rhizobium, and soil fertility.
Answer:
Microorganisms play a vital role in the nitrogen cycle, which is essential for plant growth. One of the key microorganisms involved is hizobium, a type of bacteria that lives symbiotically inside the root nodules of leguminous plants such as beans, peas, and pulses. Rhizobium captures nitrogen gas from the atmosphere and converts it into ammonia, a form of nitrogen that plants can absorb and use to build proteins and other vital compounds. This process is called biological nitrogen fixation. By enriching the soil with nitrogen, Rhizobium reduces the need for chemical fertilizers, promotes sustainable farming, and maintains soil health. When legume plants die, the fixed nitrogen remains in the soil, benefiting future crops planted in the same field. Hence, crop rotation with legumes helps in natural soil enrichment and increased agricultural productivity.
Question 2.
Describe the fermentation process using yeast and explain its importance in daily life, including experimental evidence.
Answer:
Fermentation is a metabolic process carried out by yeast, where it breaks down sugars into alcohol and carbon dioxide in the absence of oxygen (anaerobic conditions). In food science, yeast is commonly used in baking and brewing. When added to flour dough, yeast consumes the sugars and produces carbon dioxide gas, which forms bubbles and causes the dough to rise, making it soft and spongy. This process is also essential in making alcoholic beverages like beer and wine.
Experimentally, fermentation can be demonstrated by mixing sugar, yeast, and warm water in a flask, sealing the opening with a balloon. After some time, the balloon inflates, indicating the production of carbon dioxide. If the released gas is passed through lime water, it turns milky, confirming the presence of CO2. This experiment proves that yeast performs anaerobic respiration during fermentation. The process is temperature-sensitive and works best in warm, moist conditions. Fermentation not only improves the texture and taste of food but also preserves it and adds nutritional value.
Question 3.
Compare and contrast unicellular and multicellular microorganisms with examples and structural differences.
Answer:
Microorganisms can be either unicellular or multicellular. Unicellular microorganisms consist of a single cell that performs all life functions. Examples include bacteria, yeast, and protozoa. These organisms are microscopic and reproduce rapidly. For example, yeast is a unicellular fungus that carries out fermentation and has a well-defined nucleus and cytoplasm.
On the other hand, multicellular microorganisms are made of many cells with division of labor, meaning different cells perform specific tasks. Examples include moulds and algae like Spirogyra. Multicellular microbes often form visible colonies or structures such as filaments. Moulds, for instance, produce thread¬like structures called hyphae that help in reproduction and nutrient absorption.
Structurally, unicellular organisms often have a simpler body plan. Some, like bacteria, lack a true nucleus (prokaryotic), whereas fungi and protozoa are eukaryotic with defined nuclei. Multicellular microbes are always eukaryotic and can grow larger and survive in more complex environments. This structural difference also affects how they reproduce, respond to stimuli, and interact with the environment.
Question 4.
How do environmental factors affect microbial growth? Discuss with the help of bread mould and curd formation examples.
Answer:
Microbial growth is strongly influenced by environmental factors such as temperature, moisture, air, and food availability. Warm and moist conditions favor rapid microbial activity, while cold and dry environments inhibit it. This can be observed in the bread mould experiment. When bread is kept in a warm, moist place, it develops fuzzy, colored growth after a few days. These are colonies of mould fungi that thrive in such conditions. If the same bread is kept in a dry or refrigerated environment, mould growth is minimal or absent because moisture and warmth are lacking.
Similarly, in curd formation, warm milk curdles faster than cold milk. This is because Lactobacillus bacteria grow and multiply quickly at warmer temperatures, converting lactose into lactic acid. In cold milk, their activity slows down, delaying or preventing curdling. These examples demonstrate that microorganisms are highly sensitive to environmental factors, and this property is used in food preservation techniques such as refrigeration, drying, and adding salt or sugar to inhibit microbial growth.
Question 5.
Discuss the role of micro-organisms in sustainable development, including food, fuel, and waste manage¬ment.
Answer:
Microorganisms are key players in sustainable development due to their versatile roles in food production, energy generation, and waste recycling. In the food industry, microbes like Lactobacillus and yeast are used in fermentation to make products like curd, bread, idlis, and alcoholic drinks. These processes improve the taste, nutrition, and shelf life of food.
In terms of fuel production, microorganisms are essential for generating biogas. In anaerobic digesters, bacteria break down organic waste (like cow dung and food scraps) in the absence of oxygen, producing methane-rich gas that can be used for cooking and lighting. This renewable energy reduces dependence on fossil fuels and promotes clean energy usage.
Microbes also contribute to waste management and soil health. Decomposer organisms such as fungi and bacteria break down plant and animal remains, converting them into simple nutrients that return to the soil. This process not only keeps the environment clean but also supports agriculture by maintaining soil fertility.
Moreover, microalgae like Spirulina serve as nutrient-rich superfoods, requiring minimal resources to grow, making them sustainable food options. Overall, microorganisms support a circular, eco-friendly system and are critical to achieving long-term environmental and economic sustainability.
The Invisible Living World: Beyond Our Naked Eye Class 8 Case Based Questions
Question 1.
In a school laboratory experiment based on the textbook, three test tubes were prepared:
- Test Tube A contained only sugar solution and water.
- Test Tube B contained sugar solution, water, and a pinch of yeast.
- Test Tube C contained yeast and water only.
All three test tubes were sealed with balloons on top and left undisturbed for 2 days. After the observation period, the balloon on Test Tube B was inflated. When the gas collected from this tube was passed into lime water, it turned milky.
(a) What gas caused the balloon on Test Tube B to inflate?
(b) Why was there no balloon inflation in Test Tube A and Test Tube C?
(c) What chemical reaction caused lime water to turn milky?
(d) What is the process called in which yeast converts sugar into alcohol and carbon dioxide?
(e) What conclusion can you draw about the role of sugar in this experiment?
Answer:
(a) Carbon dioxide (CO2)
(b) Test Tube A had no yeast to perform fermentation, and Test Tube C had no sugar as food for yeast, so no gas was produced.
(c) CO2 reacted with lime water (calcium hydroxide) to form calcium carbonate, a white precipitate, making it milky.
(d) Fermentation
(e) Sugar is essential as an energy source for yeast to carry out fermentation and produce CO2.
Question 2.
A farmer decides to stop using chemical fertilizers and instead uses a compost pit made from kitchen waste, vegetable peels, and dry leaves. He also starts planting leguminous crops such as gram and beans between cereal crop seasons. Over time, he notices improved soil fertility and better plant growth.
(a) Which types of microorganisms are responsible for breaking down kitchen waste in the compost pit?
(b) Why is it important to add both dry and wet waste to the compost pit?
(c) Which specific microorganism helps leguminous plants fix nitrogen in the soil?
(d) How does growing leguminous crops reduce the need for chemical fertilizers?
(e) What environmental benefit does composting offer over using synthetic fertilizers?
Answer:
(a) Decomposer microorganisms like fungi and bacteria.
(b) Dry waste adds carbon and balances moisture, while wet waste provides nitrogen; both are needed for efficient decomposition.
(c) Rhizobium bacteria.
(d) Rhizobium fixes atmospheric nitrogen into forms plants can use, naturally enriching the soil with nutrients.
(e) Composting recycles organic waste, reduces landfill use, and avoids harmful chemical runoff into water bodies.
The Invisible Living World: Beyond Our Naked Eye Extra Questions for Practice
Question 1.
How do viruses differ from other microorganisms, such as bacteria?
Question 2.
Write the name of a microorganism that is multicellular.
Question 3.
Which microorganism lives alone?
Question 4.
Which microorganism is utilized in making curd from milk?
Question 5.
What do you mean by fermentation?
Question 6.
What are pathogens?
Question 7.
What are microorganisms?
Question 8.
Name two types of microorganisms.
Question 9.
How are microorganisms important to us?
Question 10.
What is the difference between luminous and non-luminous objects?
Question 11.
Explain why we cannot see most cells with our naked eye.
Question 12.
Explain the role of microorganisms in the environment.
Question 13.
Describe the different ways in which microorganisms can be harmful.
Question 14.
Discuss the importance of studying microorganisms.
Question 15.
How does light make objects visible to us?
Question 16.
Explain the difference between viruses and bacteria.
Question 17.
If a farmer avoids using chemical fertilizers and instead grows legume crops repeatedly, what long-term benefits and risks might this have on soil health and crop yield? Explain using microbial interactions.
Question 18.
In the yeast-lime water experiment, what would you conclude if the lime water does not turn milky, even though the balloon inflates? Suggest possible reasons and corrections.