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State Board · Class 8 · General Science

Lesson 1: Living World and Classification of Microbes

5 concepts · 40 practice questions with answers · Free to read

This lesson is also in: मराठी

Biodiversity and need for classification

From daily life

In a big grocery shop, rice, dal, soap and biscuits are kept in separate shelves with labels, so you find things quickly. In nature there are millions of kinds of living things, so scientists also arrange them into groups with labels.

Simple definition

Biological classification (जैविक वर्गीकरण) is dividing living organisms into groups and sub-groups on the basis of their similarities. About 87 million species live on the earth.

Number of groups in the system1234521735Linnaeus31866Haeckel21925Chatton41938Kopland51969Whittaker

In the figure : In the figure the systems of classification are shown: Linnaeus (1735) 2 kingdoms, Haeckel (1866) 3 kingdoms, Chatton (1925) 2 groups (prokaryotes and eukaryotes), Kopland (1938) 4 kingdoms and Whittaker (1969) 5 kingdoms.

Rule 1: Why classify — With so many species, we group them so that studying and remembering them becomes easy.

  • Easy : Grouping fruits together and vegetables together is a simple classification.
  • Medium : If 87 million species were put in 5 kingdoms, each kingdom would hold about 87 ÷ 5 = 17.4 million species on average.
  • Exam-type : Dogs and wolves are put in a close group because they share many features; a dog and a mango tree are put in different kingdoms.

Rule 2: History of classification — Linnaeus (1735): 2 kingdoms. Haeckel (1866): 3 kingdoms. Chatton (1925): prokaryotes and eukaryotes. Kopland (1938): 4 kingdoms. Whittaker (1969): 5 kingdoms.

  • Easy : Linnaeus's system came first, in 1735.
  • Medium : From Linnaeus to Whittaker: 1969 − 1735 = 234 years.
  • Exam-type : Number of kingdoms kept rising with knowledge: 2, 3, then 4, then 5.
Remember

87 million species. Kingdoms: Linnaeus 2, Haeckel 3, Kopland 4, Whittaker 5.

Common mistake

Mixing the years of the scientists. Remember the order 1735, 1866, 1925, 1938, 1969.

Shortcut

Memory clue: "Little Hens Can Kick Whales": Linnaeus, Haeckel, Chatton, Kopland, Whittaker (L-H-C-K-W).

Spot the difference

ScientistYearGroups
Linnaeus17352 kingdoms
Haeckel18663 kingdoms
Chatton1925Prokaryotes, eukaryotes
Kopland19384 kingdoms
Whittaker19695 kingdoms

Practice questions

Easy
  1. 1What is biological classification?
  2. 2About how many species live on the earth?
  3. 3Who proposed the two-kingdom system and when?
Medium
  1. 4How many kingdoms did Haeckel propose?
  2. 5Who divided organisms into prokaryotes and eukaryotes?
  3. 6Which classification is the most widely used and who gave it?
Challenging
  1. 7How many years passed between Chatton's (1925) and Kopland's (1938) systems?
  2. 8Why did the number of kingdoms increase from 2 to 5 over time?
Show answers (try them yourself first)
  1. 1Dividing organisms into groups and sub-groups on the basis of similarities.
  2. 2About 87 million
  3. 3Linnaeus, 1735
  4. 43
  5. 5Chatton (1925)
  6. 6The five-kingdom system by Whittaker (1969).
  7. 71938 − 1925 = 13 years
  8. 8As knowledge about organisms grew, scientists found that two groups were not enough.

Whittaker's five kingdom system

From daily life

A banyan tree makes its own food from sunlight. A cow eats grass. A mushroom on a dead log feeds on the log. How living things get their food is a good way to sort them.

Simple definition

The five kingdom system (पंचसृष्टी पद्धत) by Robert Whittaker (1969) has Monera, Protista, Fungi, Plantae and Animalia.

MoneraProtistaFungiPlantaeAnimalia

In the figure : In the figure Whittaker's five kingdoms are shown: Monera (bacteria), Protista (Amoeba), Fungi (mushroom), Plantae (plants) and Animalia (animals).

Rule 1: Criteria — The five kingdoms are based on complexity of cell structure, complexity of the organism, mode of nutrition, life style and phylogenetic (evolutionary) relationship.

  • Easy : Bacteria are in Monera.
  • Medium : An amoeba is in Protista, a mushroom in Fungi.
  • Exam-type : A mango tree (Plantae) and a goat (Animalia) are in different kingdoms because they get food in different ways.
autotrophicproducerheterotrophicconsumersaprotrophicdecomposer

In the figure : In the figure of mode of nutrition: plants are autotrophic producers, animals are heterotrophic consumers, and fungi are saprotrophic decomposers that absorb food from dead matter.

Rule 2: Modes of nutrition — Plants are autotrophic (make their own food) producers. Animals are heterotrophic, ingestive consumers. Fungi are saprotrophic: they absorb food from dead matter and are decomposers.

  • Easy : Plant: autotroph (producer).
  • Medium : Animal: heterotroph (consumer).
  • Exam-type : A mushroom on a dead log takes food from the log: saprotroph.
Remember

Kingdoms: Monera, Protista, Fungi, Plantae, Animalia. Plants = producers, animals = consumers, fungi = decomposers.

Common mistake

Thinking fungi are plants. Fungi do not make their own food.

Shortcut

Memory clue: "My Pet Fish Plays Alone": Monera, Protista, Fungi, Plantae, Animalia.

Spot the difference

KingdomNutritionRole
PlantaeAutotrophicProducers
AnimaliaHeterotrophicConsumers
FungiSaprotrophicDecomposers

Practice questions

Easy
  1. 1Who proposed the five-kingdom system?
  2. 2Name the five kingdoms.
  3. 3What is an autotroph?
Medium
  1. 4Which kingdom has decomposers?
  2. 5Name two criteria used in the five-kingdom system.
  3. 6Where do saprotrophs get their food?
Challenging
  1. 7A mushroom grows on a rotting log. Name its kingdom and its nutrition type.
  2. 8Why are animals called consumers while plants are called producers?
Show answers (try them yourself first)
  1. 1Robert Whittaker
  2. 2Monera, Protista, Fungi, Plantae, Animalia.
  3. 3An organism that makes its own food.
  4. 4Fungi
  5. 5Mode of nutrition and complexity of cell structure.
  6. 6From dead matter.
  7. 7Fungi; saprotrophic.
  8. 8Plants make their own food; animals depend on others for food.

Kingdoms Monera, Protista and Fungi

From daily life

Curd, bread and the green layer on a pond all have tiny living things in them. Bacteria live in the curd, yeast makes the dough rise, and Amoeba floats in pond water. These belong to the first three kingdoms.

Simple definition

Monera are prokaryotic unicellular organisms. Protista are single-celled with a well-defined nucleus. Fungi are non-green, eukaryotic heterotrophs with a chitin cell wall.

Prokaryotic cellno distinct nucleusEukaryotic celldistinct nucleus

In the figure : In the figure Monera have prokaryotic cells (no distinct nucleus or organelles). The cells of Protista, Fungi, Plantae and Animalia are eukaryotic, with a well-defined nucleus.

Rule 1: Monera — Monera include bacteria and blue green algae. They are unicellular and prokaryotic.

  • Easy : Bacteria: Monera.
  • Medium : Prokaryotic means no well-defined nucleus and no membrane-bound organelles.
  • Exam-type : Of bacteria, Amoeba and mushroom, only the bacteria have no distinct nucleus.
AmoebaParamoeciumEuglenaVolvox

In the figure : In the figure Protista move by pseudopodia (Amoeba), cilia (Paramoecium) or a flagellum (Euglena). Euglena and Volvox are autotrophs; Amoeba and Paramoecium are heterotrophs.

Rule 2: Protista — Single-celled organisms with a well-defined nucleus. They move by pseudopodia, cilia or flagella. Euglena and Volvox are autotrophs; Amoeba and Paramoecium are heterotrophs.

  • Easy : Amoeba moves by pseudopodia.
  • Medium : Paramoecium moves by cilia and Euglena by a flagellum.
  • Exam-type : Euglena has chlorophyll and makes its own food, so it is autotrophic.
YeastPenicilliumMushroom

In the figure : In the figure fungi are non-green eukaryotes with a cell wall of chitin and are mostly saprotrophs. Examples are yeast, Penicillium (a mould) and mushrooms.

Rule 3: Fungi — Fungi are non-green, eukaryotic, heterotrophic and mostly saprotrophic, with a chitin cell wall. Examples: yeast, Aspergillus, Penicillium and mushrooms.

  • Easy : Yeast and mushrooms are fungi.
  • Medium : The cell wall of fungi has chitin, not cellulose like plants.
  • Exam-type : Bread left in a damp place grows a fuzzy layer: a fungus (mould) feeding on the bread.
Remember

Monera: prokaryotic. Protista, Fungi, Plantae, Animalia: eukaryotic.

Common mistake

Thinking Euglena is only a plant or only an animal. It is a Protist: autotrophic but single-celled and mobile.

Shortcut

Memory clue: "Prokaryote = Primitive, no Proper nucleus"; Eukaryote = Excellent nucleus.

Spot the difference

KingdomCell typeExamples
MoneraProkaryoticBacteria, blue green algae
ProtistaEukaryotic, single cellAmoeba, Euglena
FungiEukaryotic, chitin wallYeast, mushroom

Practice questions

Easy
  1. 1Which kingdom has prokaryotic organisms?
  2. 2Name two members of Monera.
  3. 3How do Amoeba, Paramoecium and Euglena move?
Medium
  1. 4Which Protista are autotrophs?
  2. 5What is the cell wall of fungi made of?
  3. 6Give three examples of fungi.
Challenging
  1. 7A damp piece of bread grows a fuzzy layer. Which kingdom does it belong to, and why is it not a plant?
  2. 8How is Protista different from Monera?
Show answers (try them yourself first)
  1. 1Monera
  2. 2Bacteria and blue green algae.
  3. 3By pseudopodia, cilia and flagellum respectively.
  4. 4Euglena and Volvox.
  5. 5Chitin
  6. 6Yeast, Penicillium and mushroom.
  7. 7Fungi; it has no chlorophyll and takes food from the bread.
  8. 8Protista cells have a well-defined nucleus; Monera cells do not.

Classification of microbes

From daily life

A drop of pond water, a curd culture and mouldy bread each hold different tiny living things. Doctors need to know which one causes which disease, so microbes are grouped by size, shape and way of living.

Simple definition

Microbes (सूक्ष्मजीव) are grouped into bacteria, protozoa, fungi, algae and viruses.

CoccusBacillusSpirillumVibrio

In the figure : In the figure the shapes of bacteria are: coccus (round), bacillus (rod), spirillum (spiral) and vibrio (comma-shaped).

Rule 1: Bacteria — Bacteria (1-10 micrometres) are prokaryotic. They multiply by binary fission, and some can double in 20 minutes. Shapes: coccus, bacillus, spirillum and vibrio.

  • Easy : A round bacterium is a coccus.
  • Medium : A rod-shaped bacterium is a bacillus.
  • Exam-type : Cholera is caused by a comma-shaped bacterium (vibrio).
0 min20 min40 min60 min80 min

In the figure : In the figure some bacteria double in about 20 minutes, so 1 bacterium becomes 2, 4, 8 and 16 after 20, 40, 60 and 80 minutes.

Rule 2: Doubling — In binary fission one cell divides into two. If a bacterium doubles every 20 minutes, the number is 2n after n doublings.

  • Easy : After 1 hour (3 doublings): 2 × 2 × 2 = 8 bacteria.
  • Medium : After 2 hours (6 doublings): 26 = 64 bacteria.
  • Exam-type : After 3 hours (9 doublings): 29 = 512. This is why food spoils quickly if left out in the warmth.
AB

In the figure : In the figure algae are aquatic, eukaryotic and autotrophic; each cell has chloroplasts (A). Spirogyra is a green filament, and B marks one of its cells.

Rule 3: Protozoa, fungi and algae — Protozoa (about 200 µm) are unicellular eukaryotes: Plasmodium causes malaria and Entamoeba causes amoebiasis. Fungi (10-100 µm) are saprotrophs and reproduce by cell division and budding. Algae (10-100 µm) are aquatic, with chloroplasts, and make their own food.

  • Easy : Plasmodium causes malaria.
  • Medium : Spirogyra is an alga and has chloroplasts.
  • Exam-type : Yeast reproduces by budding, a small bud grows out of the parent cell.
10 nm100 nm1 µm10 µm100 µm1 mmViruses 10 – 100 nmBacteria 1 – 10 µmFungi 10 – 100 µmAlgae 10 – 100 µmProtozoa about 200 µm

In the figure : In the figure sizes on a log scale: viruses are the smallest (10 to 100 nm), then bacteria (1 to 10 µm), fungi and algae (10 to 100 µm) and protozoa (about 200 µm).

Rule 4: Size order — Virus (10-100 nm) is smaller than bacteria (1-10 µm), which are smaller than fungi and algae (10-100 µm), which are smaller than protozoa (about 200 µm).

  • Easy : Smallest microbe: virus.
  • Medium : 1 µm = 1000 nm, so a 5 µm bacterium is 5000 nm.
  • Exam-type : A 100 nm virus is 0.1 µm, while a 5 µm bacterium is 5 ÷ 0.1 = 50 times larger.
Remember

Size order: virus smaller than bacteria, smaller than fungi and algae, smaller than protozoa.

Common mistake

Thinking bacteria are the smallest microbes. Viruses are smaller.

Shortcut

Memory clue: "V-B-F/A-P": Viruses, Bacteria, Fungi/Algae, Protozoa from small to large.

Spot the difference

MicrobeSizeKey point
Bacteria1-10 µmBinary fission
ProtozoaAbout 200 µmMalaria, amoebiasis
Fungi10-100 µmBudding
Algae10-100 µmChloroplasts, autotrophic

Practice questions

Easy
  1. 1What are the four shapes of bacteria?
  2. 2How do bacteria multiply?
  3. 3Which protozoa cause malaria and amoebiasis?
Medium
  1. 4How do fungi reproduce?
  2. 5Why are algae autotrophic?
  3. 6A bacterium doubles every 20 minutes. How many are there after 2 hours?
Challenging
  1. 7A bacterium is 5 µm long. Express this in nanometres.
  2. 8Arrange viruses, protozoa, bacteria and algae from smallest to largest and say how many times larger a 5 µm bacterium is than a 100 nm virus.
Show answers (try them yourself first)
  1. 1Coccus, bacillus, spirillum, vibrio.
  2. 2By binary fission.
  3. 3Plasmodium and Entamoeba.
  4. 4By cell division and budding.
  5. 5They have chloroplasts and make their own food.
  6. 66 doublings: 26 = 64
  7. 75 × 1000 = 5000 nm
  8. 8Viruses, bacteria, algae, protozoa; 5 µm = 5000 nm, 5000 ÷ 100 = 50 times.

Viruses

From daily life

Polio, flu and the common cold are caused by something even smaller than bacteria. It cannot eat, grow or move on its own outside a living body, yet it can make a person very sick.

Simple definition

A virus (विषाणू) is a tiny particle of DNA or RNA covered by a protein coat that multiplies only inside living cells.

ABC10 – 100 nm

In the figure : In the figure a virus is a long molecule of DNA or RNA (B) covered by a protein coat (A). It is 10 to 100 nm in size and is seen only with an electron microscope.

Rule 1: Virus — Viruses (10-100 nm) are seen only with an electron microscope. They are not cells. Examples: polio, influenza and HIV in humans; tomato wilt virus in plants. National Institute of Virology, Pune was founded in 1952.

  • Easy : Polio is caused by a virus.
  • Medium : Viruses are not cells; a bacterium is.
  • Exam-type : The National Institute of Virology, Pune was founded in 1952, which is 2026 − 1952 = 74 years ago.
ABCD

In the figure : In the figure a bacteriophage is a virus that attacks bacteria: A head holding the DNA or RNA, B tail, C tail fibres that hold it on the bacterium D.

Rule 2: Edge of living and non-living — A virus shows no life outside a cell but multiplies inside the living cells of a host, so it is said to be at the edge of living and non-living. A bacteriophage attacks bacteria.

  • Easy : Outside a cell, a virus shows no sign of life.
  • Medium : Inside a host cell, it multiplies.
  • Exam-type : Antibiotics kill bacteria but do not work on viruses, because viruses live inside our own cells.
PQ

In the figure : In the figure a virus shows no life outside a cell (P) but multiplies inside the living cells of a host (Q).

Remember

Virus: DNA or RNA + protein coat; multiplies only inside a living cell.

Common mistake

Calling a virus a cell. It has no cell structure.

Shortcut

Memory clue: "Virus = Visitor inside cells": it comes alive only in a host.

Spot the difference

PointVirusBacterium
Cell?NoYes (prokaryotic)
Size10-100 nm1-10 µm
MultipliesOnly inside living cellsOn its own

Practice questions

Easy
  1. 1What is a virus made of?
  2. 2What is the size of viruses?
  3. 3Which microscope is needed to see viruses?
Medium
  1. 4Name two human diseases caused by viruses.
  2. 5What is a bacteriophage?
  3. 6When was the National Institute of Virology, Pune founded?
Challenging
  1. 7Why is a virus said to be at the edge of living and non-living?
  2. 8A friend has a viral cold and wants to take antibiotics. What would you tell him?
Show answers (try them yourself first)
  1. 1DNA or RNA covered by a protein coat.
  2. 210 to 100 nm
  3. 3Electron microscope
  4. 4Polio and influenza.
  5. 5A virus that attacks bacteria.
  6. 61952
  7. 7It shows no life outside a cell but multiplies inside living cells.
  8. 8Antibiotics do not work on viruses; he should see a doctor.

Quick revision

  • Five kingdoms: Monera, Protista, Fungi, Plantae, Animalia (Whittaker, 1969).
  • Size order: viruses < bacteria < fungi and algae.
  • Viruses are not cells and reproduce only inside host cells.