Maharashtra Board Class 8 Science Chapter 1 Living World and Classification of Microbes PDF Download

Living World and Classification of Microbes

1. What is the hierarchy for classification of living organisms?

2. Who invented 'binomial system' of nomenclature?

3. Which levels of hierarchy are considered while writing the name in binomial nomenclature?

Biodiversity and Need of Classification

Last year we learnt that all the living organism on earth have adapted according to geographic regions, food ingestion, defence etc. While adapting, many differences are observed in the organisms of same species too.

According to 2011 census, around 87 million species of living organisms are found on the earth- including land and sea. To study such a vast number, it was essential to divide them into groups. So groups and subgroups were created considering the similarities and differences among the living organisms.

This process of dividing living organism into groups and subgroups is called Biological classification.

Robert Harding Whittaker (1920-1980) was an American Ecologist. In 1969 he divided living organisms into 5 groups.

In History

Carl Linnaeus in 1735 divided living world in 2 kingdoms - Vegetabilia and Animalia.

Haeckel in 1866 considered 3 kingdoms- Protista, Plants and Animals.

In 1925 - Chatton created two groups Prokaryotes and Eukaryotes.

In 1938 Kopland divided living organisms into 4 kingdoms-Monera, Protista, Plants and Animals.

For this classification Whittaker considered following criteria

1. Complexity of cell structure: Prokaryotic and Eukaryotic.

2. Complexity of organisms: Unicellular or Multicellular.

3. Mode of nutrition: Plants - Autotrophic-Photosynthetic; Fungi- Saprophytic- Absorption from dead organisms; Animals- Heterotrophic and ingestive.

4. Life style: Plants - Producers; Animals - Consumers; Fungi - Decomposers

5. Phylogenetic relationship: Prokaryotic to Eukaryotic, unicellular to multicellular.

1.1 Five Kingdom System of Classification

Living Organisms are divided into Prokaryotes and Eukaryotes. Prokaryotes are Unicellular and form Kingdom 1. Monera. Eukaryotes are divided into Unicellular and Multicellular forms. Unicellular Eukaryotes form Kingdom 2. Protista. Multicellular Eukaryotes are further divided into three kingdoms. Kingdom 3. Fungi have cell wall present but organisms can't perform photosynthesis. Kingdom 4. Plantae have cell wall present and organisms can performs photosynthesis. Kingdom 5. Animalia have no cell wall.

Teacher's Note

Think about the five kingdoms like different neighbourhoods in your city. Just like your city has different areas for homes, shops, and parks, living things are also divided into five different groups.

Exam Trick

Remember: Monera = no nucleus (like a shop without a proper counter). All others have a nucleus (like a shop with a proper counter).

Points to Remember

Whittaker divided living things into 5 kingdoms based on cell structure and how they eat.
Monera have no real nucleus and are very small.
Protista are single cells with a real nucleus.
Fungi eat dead things and have chitin in their cell wall.
Plantae make their own food using sunlight.

Kingdom 1: Monera

Activity: Take a small drop of curd or buttermilk on a clean glass slide. Dilute it with a little water. Carefully keep a cover slip. Observe it under high power of compound microscope. What did you see?

Moving, small rod-like microbes are lactobacilli bacteria.

All type of bacteria and blue green algae are included in the kingdom Monera.

Characteristics:

1. All the organisms are unicellular.

2. They may be autotrophic or heterotrophic.

3. These are prokaryotic cells without distinct nucleus or cell organelles

Kingdom 2. Protista

Activity: Prepare a temporary mount of one drop of pond water on a glass slide. Observe it under low power and high power of microscope. You will find some motile microbes with irregular shape. These are amoebae.

Characteristic:

1. Protista are single celled organisms with well defined nucleus enclosed in a nuclear membrane.

2. They have pseudopodia or hair like cilia or whip like flagella for locomotion.

3. Autotrophs- eg. Euglena, Volvox contain chloroplast. Heterotrophs- eg. Amoeba, Paramoecium

Teacher's Note

Protista are like small creatures you can find in a puddle of water near your house. They move around in the water looking for food, just like small fish.

Exam Trick

Remember: Protista have a nucleus. Amoeba can change its shape like water changes shape in a bottle.

Points to Remember

Protista are single-celled and have a real nucleus.
Some Protista are green and make their own food.
Some Protista eat other tiny living things.
They move using pseudopodia, cilia, or flagella.
You can see them in pond water under a microscope.

Kingdom 3. Fungi

Activity: Take a moist piece of bread or bhakri and keep it in a container with lid for 2-3 days. After 2-3 days a fine cotton thread like tuft is found growing on the surface of the bread. Prepare a temporary mount of few threads from this culture and observe it under the microscope.

Characteristics:

1. These are non-green, eukaryotic, heterotrophic organisms.

2. Most of them are saprotrophs. They feed upon decaying organic matter.

3. Their cell wall is made up of tough and complex sugar called 'Chitin'.

4. Some fungi are thread like and many nuclei are present in the cytoplasm.

5. Examples- Baker's yeast, Aspergillus (Fungus on corn), Penicillium, Mushrooms.

Though many systems of classification are introduced after the Whittaker's, his five kingdom system is widely accepted.

Teacher's Note

Fungi are like nature's garbage collectors. When you see mold on old bread or mushrooms in the forest, those are fungi eating dead things and making the soil rich for new plants to grow.

Exam Trick

Remember: Fungi = food from dead things. Like a vulture that eats dead animals, fungi eat dead plants.

Points to Remember

Fungi cannot make their own food like plants do.
Fungi eat dead and decaying things from nature.
Their cell wall is made of chitin, not cellulose.
Fungi include mushrooms, yeast, and mold.
Fungi are eukaryotic organisms with a nucleus.

Institutional Work: National Institute of Virology, Pune is involved in research on viruses. This institute has been founded in 1952 under the jurisdiction of Indian Council of Medical Research.

1.2 Organisms from Kingdom Monera

The image shows different types of bacteria including Clostridium tetani, Treponema pallidum, Vibrio choleri, Salmonella typhi, Staphylococcus aureus, Legionella pneumoniae, Streptococcus pneumoniae, and Clostridium botulinum.

1.3 Organisms from Kingdom Protista

The image shows Volvox, Paramoecium, Euglena, and Amoeba.

1.4 Fungi

The image shows the structure of a fungus with parts labeled including Sporangium, Columella, Apophysis, Hypha, Sporangiophore, and Rhizoids.

Classification of Microorganisms

Prokaryotes include Bacteria. Eukaryotes include Protista, Fungi, and Algae.

Among the living organisms, microorganisms are largest in number. Hence they are classified as follows.

1. Bacteria (size – 1 μm to 10 μm)

1. Unicellular, independent / parasitic organisms. Sometimes many bacteria together form colonies.

2. Bacterial cell is prokaryotic with cell wall, but distinct nucleus or cell organelles are absent.

3. They reproduce by simple binary fission.

4. In favourable conditions, bacteria grow vigorously and can double their number in 20 minutes.

Teacher's Note

Bacteria are everywhere - in curd, soil, and even in your stomach helping you digest food. Some are good helpers, but some can make you sick.

Exam Trick

Remember: Bacteria = no nucleus. Like a simple house with no rooms inside, bacteria have no nucleus inside.

Points to Remember

Bacteria are very small single cells.
Bacteria do not have a real nucleus like bigger cells do.
Bacteria can be helpful or harmful to humans.
Bacteria multiply very quickly in good conditions.
Some bacteria need air, and some do not need air to survive.

With reference to size of microbes, remember 1 meter = 10^6 micrometer (μm) and 1 meter = 10^9 nanometer (nm).

1.6 Classification of Microorganisms

Microorganisms are divided into two main types: Prokaryotes and Eukaryotes. Prokaryotes include Bacteria. Eukaryotes include Protista, Fungi, and Algae.

Use Your Brain Power

Explain merits and demerits of Whittaker's classification.

1.7 Some Bacteria

The image shows different shapes of bacteria: Coccus (round), Cocco-bacillus (round-rod shaped), Bacillus (rod shaped), Vibrio (Comma shaped), and Spirillum (spiral shaped).