Chapter 2: The Invisible Living World: Beyond Our Naked Eye
This comprehensive guide provides short and long questions with answers from Chapter 2 of the "Curiosity — Textbook of Science for Grade 8."
Short Questions and Answers
From Chapter Content
1. Q: What is a lens?
A: A curved piece of glass, thick in the middle and thin at the edge, that makes small things look bigger.
2. Q: Who published the book 'Micrographia' in 1665?
A: Robert Hooke.
3. Q: What did Robert Hooke observe in a thin slice of cork?
A: Small, empty spaces resembling a honeycomb, which he called 'cells'.
4. Q: Who is known as the Father of Microbiology?
A: Antonie van Leeuwenhoek.
5. Q: What are the three main basic parts of a cell?
A: Cell membrane, cytoplasm, and nucleus.
6. Q: What is the function of the cell membrane?
A: It encloses the cytoplasm and nucleus, separates one cell from another, is porous, and allows the entry of essential materials and the exit of waste material.
7. Q: Where do most of the life processes take place within a cell?
A: Within the cytoplasm.
8. Q: What is an extra outer layer found in some cells, like onion peel cells?
A: Cell wall.
9. Q: What is an organism?
A: All living beings, whether plants or animals, are called organisms.
10. Q: What are microorganisms (or microbes)?
A: Tiny living creatures that cannot be seen with the naked eye.
11. Q: Give two examples of unicellular microorganisms.
A: Bacteria, Amoeba, Paramecium (any two).
12. Q: What are viruses?
A: Microscopic and acellular entities that reproduce only when they enter a living cell.
13. Q: How do microorganisms help in cleaning the environment?
A: They decompose plant and animal waste, returning nutrients to the soil.
14. Q: What is biogas?
A: A gas (like methane) produced by some bacteria decomposing plant and animal waste in oxygen-free environments, used as fuel.
15. Q: Who developed a special bacterium to break down oil spills?
A: Ananda Mohan Chakrabarty.
16. Q: What type of microorganism is yeast?
A: A unicellular fungus.
17. Q: Which bacteria are used in curd formation?
A: Lactobacillus.
18. Q: What are microalgae?
A: Microscopic plant-like organisms that live in water and produce oxygen through photosynthesis.
19. Q: Give two examples of microalgae.
A: Spirulina, Chlorella, Diatoms (any two).
20. Q: Why is Spirulina considered a superfood?
A: It is a microalga rich in Vitamin B.
From Exercises (Fill in the Blanks)
1. Q: The invention of the __________ opened a fascinating hidden world filled with tiny living creatures.
A: Microscope.
2. Q: Robert Hooke observed a thin slice of __________ and saw it was made of many small, empty spaces.
A: Cork.
3. Q: The word __________ was first used in science to describe the basic unit of life.
A: Cell.
4. Q: Antonie van Leeuwenhoek is known as the Father of __________.
A: Microbiology.
5. Q: All living beings are made up of __________.
A: Cells.
Long Questions and Answers
From Chapter Content
1. Q: Describe the contributions of Robert Hooke and Antonie van Leeuwenhoek to the field of microbiology.
A: Robert Hooke, in 1665, published 'Micrographia,' a book containing detailed drawings of tiny things he observed through his microscope, which magnified objects 200 to 300 times. He famously observed a thin slice of cork and saw small, empty, honeycomb-like spaces, which he named 'cells,' marking the first use of this term in science to describe the basic unit of life. Around the same time in the 1660s, Antonie van Leeuwenhoek, a Dutch scientist, developed superior lenses that enabled him to build more powerful microscopes. He was the first person to clearly observe and describe various tiny living organisms, including bacteria and blood cells. Due to his pioneering work, Leeuwenhoek is widely recognized as the Father of Microbiology.
2. Q: Explain the levels of organization in a living organism with examples.
A: The body of a living organism is organized in a hierarchical manner, starting from the most basic unit. The fundamental unit of life is the cell. Similar cells group together to form a tissue, which performs a specific function. Different tissues then combine to form an organ, such as the heart or stomach, each with a specialized role. Multiple organs working together constitute an organ system, like the digestive system or circulatory system. Finally, all the organ systems collectively form a complete organism. For example, in humans, muscle cells form muscle tissue, which is part of organs like the stomach, contributing to the digestive system, and ultimately forming the human organism.
3. Q: Differentiate between plant and animal cells based on their structure.
A: Both plant and animal cells are eukaryotic cells, sharing common structures like a cell membrane, cytoplasm, and nucleus. However, they possess distinct structural differences. Plant cells have an additional rigid outer layer called the cell wall, which provides structural support and protection, a feature absent in animal cells. Plant cells also typically contain chloroplasts, which are organelles responsible for photosynthesis, allowing plants to produce their own food. Animal cells lack chloroplasts. Furthermore, plant cells usually have a large, central vacuole that stores water, nutrients, and waste, maintaining turgor pressure. Animal cells, if they have vacuoles, possess several small, temporary ones.
4. Q: Discuss the beneficial roles of microorganisms in our daily lives.
A: Microorganisms play numerous beneficial roles that are crucial for human life and the environment. In food production, bacteria like Lactobacillus are essential for fermenting milk into curd, and yeast is used to make bread rise and produce alcoholic beverages. They are vital in environmental cleaning by decomposing dead plant and animal waste, returning essential nutrients to the soil and acting as natural scavengers. This decomposition process also contributes to the formation of manure, enriching soil fertility. Some bacteria produce biogas (like methane) from organic waste in oxygen-free conditions, providing a renewable energy source for cooking and electricity generation. Microalgae, such as Spirulina, are not only a superfood rich in nutrients but also contribute significantly to oxygen production and are used in water purification processes. Additionally, microorganisms are being explored for various biotechnological applications, such as developing bacteria to clean up oil spills, demonstrating their versatility and importance.
From Exercises
1. Q: Describe an experiment to observe onion peel cells under a microscope.
A: To observe onion peel cells, first, take an onion bulb and wash it thoroughly. Cut the onion vertically and carefully pull out a thin, transparent layer from its inner surface; this is the onion peel. Place this peel in a petri dish containing a few drops of safranin stain for about 30 seconds to give the cells a pinkish color, enhancing visibility. Rinse the peel in another petri dish with water to remove excess stain. Next, carefully transfer the stained onion peel onto a clean glass slide using a thin brush, ensuring it remains flat and unfolded. Add a drop of glycerin over the peel to prevent drying and improve clarity. Slowly lower a coverslip over the peel at a 45-degree angle using a needle to avoid trapping air bubbles. Finally, gently wipe off any extra glycerin with blotting paper and observe the prepared slide under a microscope. You will see nearly rectangular, closely arranged structures, which are the onion cells.
2. Q: A student observes that when curd is left out for a day, it becomes more sour. What can be two possible explanations for this observation?
A: The increased sourness of curd left out for a day can be attributed to the continued activity of Lactobacillus bacteria. Two possible explanations are:
- Increased Lactic Acid Production: Lactobacillus bacteria, which are responsible for curd formation, continue to ferment the lactose (sugar) in the milk into lactic acid. At room temperature, these bacteria are highly active, leading to a higher concentration of lactic acid over time.
- Growth of Other Acid-Producing Microorganisms: Other acid-producing microorganisms present in the environment might also grow and contribute to the fermentation process when the curd is left out.
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