Living World and Classification of Microbes | Class 8 | Science | Chapter 1 | Maharashtra State Board
Explore the fascinating world of living organisms with a focus on the classification of microbes. This lesson covers the five-kingdom system, characteristics of bacteria, fungi, algae, viruses, and more, with engaging activities and detailed explanations.
Questions & Answers
1. Use Whittaker method to classify bacteria, protozoa, fungi, algae, prokaryotic, eukaryotic, microbes.
Ans.
Bacteria: Kingdom Monera
Protozoa: Kingdom Protista
Fungi: Kingdom Fungi
Algae: If unicellular, Kingdom Protista. If multicellular, Kingdom Plantae
Prokaryotic: Kingdom Monera
Eukaryotic: Any kingdom other than Monera.
Microbes: Kingdom Monera or Protista.
2. Complete the five kingdom method of classification using-living organism, prokaryotes, eukaryotes, multicellular, unicellular, protista, animals, plants, fungi.
Ans.
3. Find out my partner
A | B |
Fungi | Chlorella |
Protozoa | Bacteriophage |
Virus | Candida |
Algae | Amoeba |
Bacteria | Prokaryotic |
Ans.
A | B |
Fungi | Candida |
Protozoa | Amoeba |
Virus | Bacteriophage |
Algae | Chlorella |
Bacteria | Prokaryotic |
4. State whether the following statements are True or False. Explain your statement:
a. Lactobacilli are harmful bacteria.
Ans. False.
Explanation: Lactobacilli are useful bacteria. They are used for curdling the milk. They are also used for preparing variety of milk products.
b. Cell wall of fungi is made up of chitin.
Ans. True.
Explanation: The cell wall of the plants is made up of cellulose while the cell wall of fungi is made up of complex sugar called chitin. Inside the fungal cell wall there is cytoplasm which contains many nuclei.
c. Organ of locomotion in amoeba is pseudopodia.
Ans. True.
Explanation: Amoeba is a protozoan, primitive organism which possesses pseudopodia as the organ for locomotion.
d. Tomato wilt is a viral disease.
Ans. True.
Explanation: Tomato wilt is a viral disease. These viruses are able to infect only plant cells.
5. Give answers
a. State the merits of Whittaker’s method of classification.
Ans.
Merits of Whittaker's Classification:
Organized Framework: Divides life into five kingdoms, making it easier to categorize organisms.
Evolutionary Insight: Reflects evolutionary relationships by separating prokaryotes from eukaryotes.
Ecological Roles: Considers organisms' roles in ecosystems (producers, consumers, decomposers).
Adaptable: Can be updated with new scientific discoveries.
Simplified Understanding: Helps students and researchers grasp the diversity of life.
Demerits of Whittaker's Classification:
Oversimplification: Some groups are too broad, leading to diverse organisms being lumped together.
Unclear Boundaries: Difficulty in classifying certain organisms that don't fit neatly into one kingdom (e.g., viruses).
Limited Molecular Basis: Lacks consideration of genetic data, which is now crucial in modern classification.
Static Nature: Doesn’t always account for the continuous evolution of organisms, leading to outdated classifications.
This method, while foundational, has limitations that newer classification systems aim to address.
b. Write the characteristics of viruses.
Ans.
Viruses are extremely minute of the size range of 10 nm to 100 nm. They are on the borderline of living and non-living. They are 10 to 100 times smaller than bacteria and are visible only through the electron microscope.
Though they are not considered as living, they can make replica of their own.
They exist in the form of independent particles. They are long molecules of DNA or RNA which are covered by a protein coat.
Their survival is possible only inside the living plant or animal cells. When they infect the host cells, they produce their own proteins with the machinery of the host cell. These proteins form many replicas of the infecting virus.
This infection destroys the host cell and the virus replicas are released. These free replicas re-infect the other adjoining cells of the host.
Most of the viruses are pathogenic, they cause diseases in plants and animals.
c. Explain the nutrition in fungi.
Ans.
Most of the fungi are saprophytic in their nutrition. They absorb the nourishment from dead and decaying matter. By taking the organic matter from dead bodies of plants and animals, fungi survive. In this process they degrade the organic matter completely.
d. Which living organisms are included in the kingdom Monera?
Ans.
All the living organisms belonging to Kingdom Monera are unicellular.
The mode of nutrition in them is either autotrophic or heterotrophic.
All of them are prokaryotic and thus they do not have well-formed nucleus. The nuclear membrane and the cell organelles are absent in them.
Kingdom Monera consists of different types of bacteria and blue-green algae. E.g. Bacteria Clostridium titani, Vibrio choleri, Treponema pallidum, Streptococcus pneumoniae, Legionella pneumoniae, Salmonella typhi, Staphylococcus aureus, Clostridium botulinum.
6. Who am I ?
a. I don’t have true nucleus, cell organelles or plasma membrane.
Ans. Microbe from Monera
b. I have nucleus and membrane bound cell organelles.
Ans. Protozoan from Protista/I am any one of Eukaryote
c. I live on decaying organic matter.
Ans. Fungus
d. I reproduce mainly by cell division. (*Binary fission)
Ans. Bacteria and some Protozoa.
e. I can produce my replica.
Ans. Virus
f. I am green, but don’t have organs.
Ans. Algae
7. Draw neat and labelled diagrams.
a. Different types of bacteria:
Ans.
b. Paramoecium:
Ans.
c. Bacteriophage
Ans.
8. Arrange the following in ascending order of size Bacteria, Fungi, Viruses, Algae.
Ans.
Viruses, Bacteria, Fungi, Algae.
E X T R A
1. Fill in the blanks.
1. The process of dividing living organism into groups and subgroups is called ………… .
Ans. Biological classification.
2. Organisms with cell wall but not able to perform photosynthesis are called ………… .
Ans. Fungi.
3. Most of the fungi are …………… .
Ans. saprotrophic.
4. Viruses can be seen only with …………… .
Ans. electron microscope.
5. …………… viruses attack bacteria.
Ans. Bacteriophage
6. In fungi the cell wall is made up of j tough and complex sugar called …………… .
Ans. ‘Chitin’.
2. State whether the following statements is True or False. Explain your statement:
Plasmodium causes dysentery.
Ans.False.
Explanation: Plasmodium causes malaria. Entamoeba histolytica causes amoebic dysentery or amoebiasis.
3. Name the following/ Give examples
1. Three organs of locomotion in Protista
Ans.
Pseudopodia
Cilia
Flagella
2. Two autotrophic Protista
Ans.
Euglena
Volvox
3. Institute in India which is involved in research on viruses
Ans.National Institute of Virology, Pune
4. Two methods of asexual reproduction in Fungi
Ans.
Binary fission
Budding
5. Two pathogenic protozoans and the diseases caused by them
Ans.
Entamoeba histolytica causes amoebiasis
Plasmodium vivax – causes malaria.
4. Answer the following questions in one sentence:
1. What are the types of living organisms according to their lifestyle?
Ans.
Producers, consumers and decomposers are the types of living organisms according to their lifestyle.
2. What are the characteristics of prokaryotic cells?
Ans.
Absence of nuclear membrane, well- formed nucleus and lack of cell organelles are the characteristics of the prokaryotic cells.
3. When do virus destroy the host cells?
Ans.
After synthesising their own proteins and creating numerous replica of their own type, then the virus destroys the host cells.
5. Give answers:
1. Which criteria were considered for classification method of Whittaker?
Ans.
The criteria considered for classification by Whittaker are as follows:
Complexity of cell structure: Whether the cells of the organisms are prokaryotic or eukaryotic.
Complexity of organisms Whether the organisms are unicellular or multicellular is considered.
Mode of nutrition Whether the organism is autotrophic and is performing photosynthesis on its own or it is heterotrophic is considered. Plants are autotrophic, fungi are saprotrophic while animals use food from plants or other animals and hence they are heterotrophic.
Lifestyle According to nutrition, every living organism is at certain trophic level. This is called lifestyle. Plants are producers, animals are consumers while fungi are decomposers.
Phylogenetic relationship When the evolution proceeded gradually, there was transition from prokaryotes to eukaryotes, unicellular to multicellular. In this order the different groups of living organisms were evolved. This is known as phylogenetic relationship.
6. Write short notes:
1. Characteristics of Fungi.
Ans.
The organisms which are placed in kingdom Fungi are multicellular, heterotrophic, non-green, and eukaryotic in nature.
Most of the fungi are saprophytic and they sustain on the dead and decaying organic matter.
The cell wall of the fungal cells is made up of chitin. Chitin is the tough and complex sugar.
Fungi have thread like body. The cytoplasm of the fungal cells contain many nuclei.
The reproduction in Fungi is either sexual or asexual. Asexual reproduction is by fission or by budding.
Examples Baker’s yeast, Candida, Mushroom, Aspergillus (Fungus on corn), Penicillium
2. Characteristics of Bacteria.
Ans.
Bacteria are microscopic, unicellular, prokaryotic organisms belonging to the kingdom Monera.
Some bacteria are solitary with independent existence. Some are colonial forms.
The bacterial cell lacks well-formed nucleus with nuclear membrane and cell organelles.
Reproduction is by binary fission.
In favourable conditions, bacteria duplicate with a great speed. Within 20 minutes they can double in number.
Bacteria may be round as in Cocci, elongated as in Bacillus, comma shaped as in Vibrio and spiral shaped as in Spirillum.
3. Characteristics of Protozoa.
Ans.
Protozoa are unicellular, eukaryotic organisms belonging to kingdom, Protista.
They are microscopic of the size of about 200 pm.
They have different organs of locomotion such as pseudopodia, cilia and flagella.
Reproduction is by asexual method, usually by binary fission. .
Protozoa are seen in varied habitats such as soil, fresh water and marine water.
Some protozoans are parasitic and cause various types of illness in hosts. E.g. Entamoeba histolytica is a species of amoeba that causes amoebiasis. Malaria is caused by Plasmodium vivax.
Protozoa show different modes of nutrition. E.g. Euglena is autotrophic as it does photosynthesis with the help of 5 chloroplasts present in its body. Amoeba and Paramoecium are heterotrophic and free living seen in contaminated water.
7. Complete the paragraph using the words given in the brackets
[Monera, Euglena, autotrophic, cell organelles, chitin, nuclear, prokaryotic, viruses, replicas, saprotrophic, viral particles]
In Kingdom ……….. bacteria were included but not ………….. Viruses are on the border line of living and non-living. Do we really call them living? If they are making …………. of their own type, are they not considered as living? Throughout the world they spread hazardous epidemics. Antibiotics do not act on ………… However, bacteria can be controlled by antibiotics. All the living organisms belonging to Monera are with …………… cell. They do not have ………….. membrane and neither they have ……………… But a nice nucleus is seen in …………….., Euglena is ………… protist. The fungi with cell wall of …………….. are ………….. in their mode of nutrition.
Ans.
In Kingdom Monera bacteria were included but not viruses. Viruses are on the border line of living and non-living. Do we really call them living? If they are making replicas of their own type, are they not considered as living? Throughout the world they spread hazardous epidemics. Antibiotics do not act on viral particles. However, bacteria can be controlled by antibiotics. All the living organisms belonging to Monera are with prokaryotic cell. They do not have nuclear membrane and neither they have cell organelles. But a nice nucleus is seen in Euglena. Euglena is autotrophic protist. The fungi with cell wall of chitin are saprotrophic in their mode of nutrition.
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