Chapter 1: Living World and Classification of Microbes
Solved textbook questions with step-by-step explanations.
Grade 8 Q&A: Chapter 1: Living World and Classification of Microbes
Welcome to the Questions and Answers section for Grade 8 Science, Chapter 1: "Living World and Classification of Microbes." This chapter introduces you to the vast diversity of life on Earth, the necessity of classifying organisms, and the fascinating world of microscopic living beings. We will explore the different kingdoms of life and delve into the characteristics and types of various microbes.
Important Questions and Answers
Q1: What is meant by 'biodiversity'?
Answer: Biodiversity refers to the variety of living organisms in a specific area or on Earth, including their genetic diversity, species diversity, and ecosystem diversity.
Q2: Why is classification of living organisms necessary?
Answer: Classification is necessary to study the vast number of living organisms systematically, to identify them easily, to understand their similarities and differences, and to know their evolutionary relationships.
Q3: Who is known as the 'Father of Taxonomy' and what was his major contribution?
Answer: Carl Linnaeus is known as the 'Father of Taxonomy'. His major contribution was developing the binomial nomenclature system for naming organisms and a hierarchical system of classification.
Q4: Who proposed the Five Kingdom Classification system? When?
Answer: The American ecologist Robert Whittaker proposed the Five Kingdom Classification system in 1969.
Q5: List the five kingdoms according to Whittaker's classification.
Answer: The five kingdoms are: Monera, Protista, Fungi, Plantae, and Animalia.
Q6: What are the main criteria used by Whittaker for his classification?
Answer: Whittaker used five main criteria:
- Complexity of cell structure (Prokaryotic or Eukaryotic)
- Complexity of organisms (Unicellular or Multicellular)
- Mode of nutrition (Autotrophic, Heterotrophic, or Saprotrophic)
- Life style (Producers, Consumers, or Decomposers)
- Phylogenetic relationship (evolutionary history)
Q7: Describe the key characteristics of Kingdom Monera with examples.
Answer: Kingdom Monera consists of unicellular, prokaryotic organisms (lacking a true nucleus and membrane-bound organelles). They can be autotrophic or heterotrophic. Examples include various types of bacteria (e.g., *E. coli*, *Clostridium*) and cyanobacteria (blue-green algae).
Q8: What are the distinguishing features of Kingdom Protista? Give examples.
Answer: Kingdom Protista includes unicellular, eukaryotic organisms. They show diverse modes of nutrition (autotrophic, heterotrophic). Many have structures for locomotion like pseudopodia, cilia, or flagella. Examples are Amoeba, Paramoecium, Euglena, and Volvox.
Q9: How do organisms in Kingdom Fungi obtain their nutrition? Give examples.
Answer: Organisms in Kingdom Fungi are eukaryotic and mostly multicellular (except yeast, which is unicellular). They are saprotrophic, meaning they obtain nutrition by absorbing organic matter from dead and decaying organisms. Their cell wall is made of chitin. Examples include yeast, mushrooms, *Penicillium*, and *Aspergillus*.
Q10: What is the main difference between prokaryotic and eukaryotic cells?
Answer: Prokaryotic cells (found in Monera) lack a true nucleus and other membrane-bound organelles, while eukaryotic cells (found in Protista, Fungi, Plantae, Animalia) have a well-defined nucleus and various membrane-bound organelles.
Q11: Define 'microbes' or 'microorganisms'.
Answer: Microbes or microorganisms are living organisms that are too small to be seen with the naked eye and can only be observed under a microscope. They include bacteria, fungi, protozoa, algae, and viruses.
Q12: List the major types of microorganisms.
Answer: The major types of microorganisms are Bacteria, Fungi, Protozoa, Algae, and Viruses.
Q13: Describe the general characteristics of bacteria, including their shapes.
Answer: Bacteria are unicellular, prokaryotic organisms. They can exist independently or as parasites. They come in various shapes: cocci (spherical), bacilli (rod-shaped), spirilla (spiral), and vibrio (comma-shaped). They reproduce mainly by simple binary fission.
Q14: What are protozoa? Where are they typically found and how do they move?
Answer: Protozoa are unicellular, eukaryotic microorganisms. They are heterotrophic and are typically found in soil, fresh water, sea water, or as parasites in the bodies of other organisms. They move using pseudopodia, cilia, or flagella. Examples include Amoeba and Paramoecium.
Q15: How do algae differ from other microbes in terms of nutrition? Give examples.
Answer: Algae are unique among microbes because they are autotrophic, meaning they can produce their own food through photosynthesis, similar to plants, due to the presence of chlorophyll. They can be unicellular or multicellular and are mostly aquatic. Examples include *Chlamydomonas* and *Spirogyra*.
Q16: Why are viruses considered unique and often described as being at the boundary of living and non-living things?
Answer: Viruses are unique because they are acellular (not made of cells) and can only reproduce by living inside the cells of other organisms (host cells). Outside a host cell, they behave like non-living particles, but inside, they replicate and show characteristics of life. This makes them boundary organisms.
Q17: Give two examples of beneficial bacteria.
Answer: Two examples of beneficial bacteria are *Lactobacillus* (used in making curd/yogurt) and *Rhizobium* (helps in nitrogen fixation in leguminous plants).
Q18: Name two diseases caused by bacteria in humans.
Answer: Two diseases caused by bacteria in humans are Tuberculosis (TB) and Typhoid.
Q19: How are fungi beneficial to humans?
Answer: Fungi are beneficial in several ways:
- Decomposition of organic matter.
- Food production (e.g., yeast in bread, mushrooms as food).
- Production of antibiotics (e.g., Penicillin from *Penicillium*).
Q20: Name two diseases caused by fungi in humans.
Answer: Two diseases caused by fungi in humans are ringworm and athlete's foot.
Q21: Give two examples of diseases caused by protozoa.
Answer: Two diseases caused by protozoa are Amoebiasis (dysentery caused by *Entamoeba histolytica*) and Malaria (caused by *Plasmodium*).
Q22: What is binomial nomenclature?
Answer: Binomial nomenclature is a formal system of naming species, where each species is given a name composed of two parts: the first part indicates the genus, and the second part indicates the specific epithet (species). For example, *Homo sapiens* for humans.
Q23: What is the role of decomposers in the environment?
Answer: Decomposers (like bacteria and fungi) break down dead organic matter, recycling nutrients back into the ecosystem. This process is crucial for maintaining soil fertility and cleaning up the environment.
Q24: How does yeast help in bread making?
Answer: Yeast (a type of fungus) ferments sugars in the dough, producing carbon dioxide gas. This gas gets trapped in the dough, causing it to rise and become soft and porous.
Q25: Why are algae considered important producers in aquatic ecosystems?
Answer: Algae are important producers in aquatic ecosystems because they perform photosynthesis, converting sunlight into energy. They form the base of the food chain, providing food for aquatic animals.
Q26: What is the cell wall of fungi made of?
Answer: The cell wall of fungi is primarily made of a complex carbohydrate called chitin.
Q27: How do bacteria reproduce?
Answer: Bacteria primarily reproduce asexually by binary fission, where one bacterial cell divides into two identical daughter cells. In unfavorable conditions, they form endospores.
Q28: Give an example of a virus that affects plants.
Answer: An example of a virus that affects plants is the Tobacco Mosaic Virus (TMV).
Q29: What is the approximate size range of bacteria and viruses?
Answer: Bacteria are typically 1 µm to 10 µm in size, while viruses are much smaller, ranging from 10 nm to 100 nm.
Q30: What is the significance of endospores in bacteria?
Answer: Endospores are highly resistant structures formed by some bacteria during unfavorable conditions. They allow bacteria to survive extreme temperatures, desiccation, and chemical exposure, enabling them to remain dormant until conditions become favorable again.
Exercise Solutions (From Screenshot Page 5)
Q1: Fill in the blanks.
- Whittaker's classification is based on complexity of cell structure, complexity of organism, mode of nutrition, life style and phylogenetic relationship.
- Fungi are saprotrophic to decaying organic matter.
- The cell wall of fungi is made up of complex carbohydrate called chitin.
- Viruses are acellular organisms.
Q2: Find out my partner (Match the pairs).
(Note: As an AI, I cannot create interactive matching. I will provide the correct pairs.)
- Fungi - Candida
- Protozoa - Amoeba
- Algae - Chlorella
- Bacteria - Vibrio
- Virus - HIV
Q3: State whether the following statements are True or False. Explain your statement.
- There are more than 100 million species of living organisms on the earth.
Statement: False.
Explanation: While the Earth has a vast diversity of living organisms, the number of *identified* species is currently estimated to be around 8.7 million. Many more species are yet to be discovered and identified, but the figure of "more than 100 million" is an overestimation based on current scientific understanding. - Viruses are smaller than bacteria.
Statement: True.
Explanation: Bacteria typically range from 1 to 10 micrometers (µm) in size, whereas viruses are much smaller, ranging from 10 to 100 nanometers (nm). Since 1 µm = 1000 nm, viruses are indeed significantly smaller than bacteria. - Robert Whittaker classified living organisms into two kingdoms.
Statement: False.
Explanation: Robert Whittaker proposed the Five Kingdom Classification system in 1969, classifying living organisms into Monera, Protista, Fungi, Plantae, and Animalia. - The cell wall of fungi is made up of chitin.
Statement: True.
Explanation: Fungi possess a rigid cell wall, which is primarily composed of a complex carbohydrate called chitin, providing structural support and protection to the fungal cells.
Q4: Answer the following questions.
- What are the characteristics of Monera?
Answer: Monera are unicellular, prokaryotic organisms lacking a true nucleus and membrane-bound organelles. They can be autotrophic or heterotrophic and reproduce mainly by binary fission. Examples include bacteria and cyanobacteria. - What are the characteristics of Protista?
Answer: Protista are unicellular, eukaryotic organisms with a well-defined nucleus. They show diverse modes of nutrition (autotrophic or heterotrophic) and often possess structures for locomotion like pseudopodia, cilia, or flagella. Examples include Amoeba and Paramoecium. - What are the characteristics of Fungi?
Answer: Fungi are eukaryotic organisms, mostly multicellular (except yeast), and are saprotrophic, absorbing nutrients from dead and decaying organic matter. Their cell wall is made of chitin, and they reproduce by budding or spores. - Explain the hierarchy of classification of living organisms.
Answer: The hierarchy of classification, from broadest to most specific, is:- Kingdom: The largest group (e.g., Animalia, Plantae).
- Phylum (or Division for plants): A major subdivision within a kingdom.
- Class: A group of related orders.
- Order: A group of related families.
- Family: A group of related genera.
- Genus: A group of closely related species.
- Species: The most specific group, consisting of organisms that can interbreed and produce fertile offspring.
- What are the characteristics of Algae?
Answer: Algae are unicellular or multicellular, eukaryotic organisms that are autotrophic due to the presence of chlorophyll. They perform photosynthesis and are mostly aquatic, forming an important part of aquatic food chains. - What are the characteristics of Viruses?
Answer: Viruses are extremely small, acellular particles consisting of genetic material (DNA or RNA) enclosed in a protein coat. They are obligate intracellular parasites, meaning they can only reproduce inside living host cells, and are considered at the boundary between living and non-living things.
Q5: Give reasons.
- Classification of living organisms is necessary.
Reason: Classification of living organisms is necessary because it helps in organizing the vast diversity of life into manageable groups, making it easier to study, identify, and understand the relationships, characteristics, and evolutionary history of different organisms systematically. Without classification, studying millions of species would be chaotic and inefficient. - Viruses are considered at the boundary of living and non-living things.
Reason: Viruses are considered at the boundary of living and non-living things because they exhibit characteristics of life (like reproduction and genetic material) only when they are inside a living host cell, utilizing the host's machinery. Outside a host cell, they exist as inert, non-living particles, unable to perform any metabolic activities independently. - Fungi are called saprotrophs.
Reason: Fungi are called saprotrophs because they obtain their nutrition by secreting digestive enzymes onto dead and decaying organic matter (like dead plants and animals) and then absorbing the digested nutrients. They do not perform photosynthesis (like plants) or ingest food (like animals). - Bacteria are important decomposers.
Reason: Bacteria are important decomposers because they play a crucial role in breaking down complex organic compounds from dead organisms and waste products into simpler inorganic substances. This process of decomposition recycles essential nutrients (like carbon, nitrogen, and phosphorus) back into the soil and environment, making them available for producers and thus maintaining the nutrient cycle and ecological balance.
References
- Maharashtra State Board Science and Technology Standard Eight Textbook (Specific Edition/Year) - Chapter 1: Living World and Classification of Microbes.
- Maharashtra State Board 8th Standard Science Syllabus.
- Balbharati Science and Technology Textbook.