9th Class Biology · Punjab Board · Complete learning guide
Chapter 2Biodiversity
Every topic, every MCQ and every exercise question, explained step by step in simple language. Written for the Punjab Board new-syllabus Biology book, English medium.
Biodiversity means the variety of organisms in a particular area. Biodiversity of an area is measured by considering the number of different kinds of organisms and the variation within each kind.
Biologists have discovered and classified almost two million kinds of organisms. Biodiversity is not evenly spread out; it depends on factors like climate, altitude and soil type. Tropical regions have more biodiversity than polar regions.
Importance of biodiversity
Benefit
How (from the book)
Ecosystem stability
maintains the balance of ecosystems; plays a role in biogeochemical cycles (carbon, nitrogen)
Climate regulation
plants and algae absorb carbon dioxide, keeping the climate balanced
Natural resources
food, medicine, building materials, fuel
Economic benefits
supports agriculture, tourism and pharmaceuticals
Did you know?
The United Nations has designated May 22nd as International Biodiversity Day, to promote the protection of biodiversity.
Exam tip
Some people respect biodiversity only because it is useful to humans; others respect it on aesthetic and moral grounds. Both are good answers to "why protect biodiversity?"
Topic 2
Classification
Definition
Classification
The process in which organisms are divided into groups and subgroups on the basis of similarities and differences found in them.
Biologists have identified about 2 million kinds of organisms: about 0.5 million kinds of plants and 1.5 million kinds of animals. To better study such a large collection of organisms, biologists classify them.
Aims of classification
To determine similarities and differences among organisms so that they can be studied easily.
To find the evolutionary relationships among organisms.
Biologists classify organisms on the basis of similar physical characteristics; in recent times they also take help from genetics.
Advantages of classification
Groups similar organisms together, making it easier to identify and understand their characteristics, relationships and evolutionary history.
Provides a framework for studying and comparing species.
Explains the inter-relationship amongst organisms.
Helps in the identification of new species.
Provides a common language for biologists around the world.
Topic 3
Taxonomic ranks
Definition
Taxonomic ranks (taxa)
The groups into which organisms are classified are known as taxonomic ranks or taxa (singular "taxon").
The Swedish botanist Carl Linnaeus devised the Linnaean system of taxonomic ranks in 1735, with seven ranks: kingdom, phylum (division), class, order, family, genus and species. In 1977, the rank of domain was added.
Fig 2.1 (redrawn): taxonomic ranks, from domain to species.
Rank
Meaning (from the book)
Domain
highest rank; three domains: Archaea, Bacteria, Eukarya
Kingdom
domains are divided into kingdoms (Eukarya: Animalia, Plantae, Fungi, Protista)
Phylum / Division
each kingdom divided into phyla (division is used for plants and fungi)
Class
each phylum divided into classes
Order
each class divided into orders
Family
each order broken into families
Genus
each family divided into genera
Species
lowest level: similar organisms that can interbreed and produce fertile offspring
Rank
Fruit fly
Human
Pea
Domain
Eukarya
Eukarya
Eukarya
Kingdom
Animalia
Animalia
Plantae
Phylum / Division
Arthropoda
Chordata
Magnoliophyta
Class
Insecta
Mammalia
Magnoliopsida
Order
Diptera
Primates
Fabales
Family
Drosophilidae
Hominidae
Fabaceae
Genus
Drosophila
Homo
Pisum
Species
Drosophila melanogaster
Homo sapiens
Pisum sativum
Exam tip
Memory line for the order: "Do Kings Play Chess On Fine Glass Sets?" (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species).
Topic 4
History of classification
Early scientists
Aristotle (384–322 BC): first to classify organisms into two groups: plants and animals.
Al-Jahiz (781–869 AD): described the characteristics of 350 species of animals; wrote a lot about the life of ants.
Andrea Caesalpinio (1519–1603): divided plants into fifteen groups and called them genera.
Tournefort (1656–1708): introduced the taxa of class and species.
Carl Linnaeus (1707–1778): taxonomic hierarchy of seven taxa.
Did you know?
Ibn Rushd (Averroes) translated Aristotle's book "de Anima" into Arabic.
Fig 2.2 (redrawn): different classification systems.
(a) Two-kingdom system
The earliest system: organisms that prepare their own food (autotrophs) were placed in kingdom Plantae and those that cannot (heterotrophs) in kingdom Animalia. Bacteria, archaea and fungi were in Plantae. It was unworkable because Euglena has plant-like (chlorophyll) and animal-like (heterotrophic in darkness, no cell wall) characteristics; it also did not separate prokaryotes from eukaryotes.
(b) Three-kingdom system
In 1866, the German zoologist Ernst Haeckel proposed a third kingdom, Protista, for Euglena-like organisms, and included prokaryotes in it. Fungi stayed in Plantae, though fungi are heterotrophs that absorb food and have chitin, not cellulose, in their walls. In 1937, Chatton suggested the terms "prokaryotic" for bacteria and "eukaryotic" for protists, fungi, animals and plants.
(c) Five-kingdom system
In 1969, the American ecologist Robert Whittaker introduced the five-kingdom system: Monera, Protista, Fungi, Plantae, Animalia. It is based on levels of cellular organization (prokaryotic, unicellular eukaryotic, multicellular eukaryotic) and modes of nutrition (photosynthesis, absorption, ingestion). In 1988, Margulis and Schwartz modified it, also considering genetics.
(d) Three-domain system
In 1977, the American microbiologist Carl Woese added the domain above kingdom: Archaea, Bacteria and Eukarya. It divided the prokaryotes into two domains, based on the differences between Archaea and Bacteria; all eukaryotes were placed in Eukarya.
Check your book
The book spells the German zoologist "Ernst Hackel"; the usual spelling is Haeckel.
Topic 5
Domains of living organisms
Fig 2.4 (redrawn): the three domains.
1. Domain Archaea
These are the most primitive organisms on Earth. They are prokaryotes but their cell wall does not contain peptidoglycan; it is made of various polypeptides and proteins. Their rRNA resembles eukaryotes more than bacteria. Their cell membrane contains unique lipids which enable them to live in extreme environments, e.g. hot springs, salt lakes and acidic or alkaline waters. Some obtain energy from inorganic compounds such as sulphur or ammonia; others photosynthesise but do not produce oxygen.
Archaebacteria (one kingdom)
Lives in / does
Methanogens
produce methane as a by-product
Halophiles
extremely salty environments
Thermophiles
hot springs
Acidophiles
extremely acidic environments
2. Domain Bacteria
Contains bacteria and cyanobacteria. They are prokaryotes with a cell wall of peptidoglycan, found in all environments (soil, water, air, bodies of organisms). They are unicellular; many live solitary, some form chains, clusters or colonies. Most are heterotrophic but some have chlorophyll and photosynthesise. One kingdom: Eubacteria (true bacteria). Some cause diseases; decomposer bacteria recycle nutrients.
3. Domain Eukarya
Includes all unicellular and multicellular eukaryotes, with complex cells having a nucleus and other membrane-bound organelles. It contains kingdoms Protista, Fungi, Plantae and Animalia.
Eukaryotes which are unicellular or colonial or filamentous or simple multicellular (without multicellular sex organs). Three types:
Type
Features
Examples
Plant-like protists (algae)
cellulose walls, chlorophyll in chloroplasts, autotrophs
Euglena, diatoms
Animal-like protists (protozoa)
no cell wall, heterotrophs, ingest food
Amoeba, Paramecium
Fungus-like protists
absorb nutrients from decaying matter; walls of cellulose, not chitin
slime molds, water molds
Common protists (drawn after Fig 2.5).
Did you know?
Certain protists are parasitic: Plasmodium causes malaria and Entamoeba causes amoebic dysentery.
(b) Kingdom Fungi
Fungi are heterotrophic; they do not ingest food but absorb it from decaying matter in their surroundings. They are eukaryotic with a cell wall made of chitin (a polysaccharide). Most are multicellular (mushrooms, rusts, smuts, molds); a few are unicellular (yeast).
Remember
Some fungi are used in making bread, cheese and beer. The antibiotic penicillin is derived from the fungus Penicillium.
(c) Kingdom Plantae
Plants are eukaryotic, multicellular, with cell walls of cellulose. They are autotrophic and prepare food through photosynthesis. All plants have multicellular sex organs and form embryos during sexual reproduction; asexual reproduction through vegetative parts is common. Examples: mosses, ferns, conifers and flowering plants.
(d) Kingdom Animalia
Animals are eukaryotic, multicellular and heterotrophic. They develop from embryos, ingest food and digest it within their bodies. Vertebrates and invertebrates are included.
Kingdom
Cells
Cell wall
Nutrition
Multicellular
Protista
eukaryotic
present in some
autotroph, heterotroph or both
absent in most
Fungi
eukaryotic
chitin
absorptive heterotroph
present in most
Plantae
eukaryotic
cellulose
autotroph
present in all
Animalia
eukaryotic
absent
ingestive heterotroph
present in all
Topic 7
Status of viruses in classification
Viruses are ultramicroscopic creatures at the borderline of living and non-living. They are acellular: not made of cells and without organelles. A virus consists of nucleic acid (DNA or RNA) surrounded by a protein coat. They cannot run metabolism; to make their proteins and multiply, they become parasites in organisms (plants, animals and bacteria). Viruses are not included in the classification system because they lack any of the characteristics of the three domains of life.
Fig 2.8 (redrawn): a bacteriophage and an influenza virus.
Prions and viroids
Prions are made of protein only and viroids of circular RNA only. They are also acellular, are not classified, and cause infectious diseases in certain plants; they are also a cause of cancer.
COVID-19
Coronavirus was identified in late 2019 in Wuhan, China; it caused a pandemic of respiratory illness called COVID-19. It spreads through respiratory droplets and contaminated surfaces. Symptoms: fever, cough, shortness of breath, fatigue, body aches, loss of taste or smell, sore throat, headache. Prevention: masks, washing hands with soap for at least 20 seconds or sanitizer with at least 60% alcohol, and vaccination.
Topic 8
Binomial nomenclature
Definition
Binomial nomenclature
The system of scientific naming of organisms, in which the scientific name consists of two parts: the first part is the name of the genus and the second part the name of the species. Carl Linnaeus was its founder.
Common name
Scientific name
Onion
Allium cepa
Potato
Solanum tuberosum
Tomato
Solanum esculentum
Honeybee
Apis cerana
Tiger
Panthera tigris
Human being
Homo sapiens
Significance
Two organisms cannot have the same name. Words are taken from Latin (spoken by no country), so no country is favoured; the name is the same anywhere in the world: a standard way of communication.
Common names vary: onion is "piyaz", "ganda", "bassal" or "vassal" in different parts of Pakistan.
One common name may mean many organisms: "blue bell" is used for dozens of plants; "black bird" for crow and raven.
Common names have no scientific basis: silver fish, cray fish, jellyfish and star fish are not fish.
Rules
Words are taken from the Latin language.
Every scientific name has two parts: genus name first, then species name.
Every scientific name must be unique.
Genus name begins with a capital letter; species name with a small letter.
When printed, it is typed in italics.
When handwritten, the two parts are underlined separately.
The wording follows published solved exercises and every answer was re-checked by hand, so the wording or the order of options may differ slightly from your print.
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Set A: Textbook exercise 10 MCQs
The multiple-choice questions at the end of Chapter 2 in your book, in the book's option order.
Q2.1Classification and Taxonomic Ranks
Which of the following taxonomic ranks represents the broadest rank?
Answer(d) Domain
Step by step
Domain > kingdom > phylum > class > order > family > genus > species.
Why the others are wrong
(a) the lowest rank.
(b) just above species.
(c) below domain.
Remember
Domain is on top (added in 1977).
Q2.2Domains of Life
Which characteristic is unique to organisms in the domain Archaea?
Answer(c) Ability to live in extreme environments
Step by step
Peptidoglycan walls belong to bacteria.
Archaea are prokaryotes: no nucleus.
All cells have ribosomes.
Why the others are wrong
(a) that is bacteria; archaeal walls have no peptidoglycan.
(b) archaea are prokaryotes.
(d) archaea have ribosomes.
Remember
Archaea = extreme lovers.
Q2.3Domains of Life
Which of these statements is NOT related to bacteria?
Answer(d) Have chlorophyll in their chloroplast.
Step by step
No nucleus, peptidoglycan wall, mostly heterotrophic: all true of bacteria.
Why the others are wrong
(a) true of bacteria.
(b) true of bacteria.
(c) true of bacteria.
Remember
Prokaryote = no chloroplast.
Q2.4Domains of Life
Which of these organisms belongs to the domain Eukarya?
Answer(b) Yeast
Step by step
Fungi → kingdom Fungi → domain Eukarya.
Why the others are wrong
(a) a bacterium (domain Bacteria).
(c) viruses are not classified.
(d) yeast fits.
Remember
Yeast has a nucleus.
Q2.5Domains of Life
Which of the following is a key characteristic that distinguishes eukaryotic cells from prokaryotic cells?
Answer(b) Presence of a nucleus
Step by step
Eu = true, karyon = nucleus.
Why the others are wrong
(a) plants and fungi (eukaryotes) have walls.
(c) both have ribosomes.
(d) eukaryotic cells are larger.
Remember
Eukaryote = true nucleus.
Q2.6Kingdoms of Eukarya
Which kingdom includes organisms that are primarily unicellular, eukaryotic, and often heterotrophic?
Answer(b) Protista
Step by step
Archaea are prokaryotes; fungi are mostly multicellular; plants are multicellular autotrophs.
Why the others are wrong
(a) prokaryotes.
(c) mostly multicellular.
(d) multicellular autotrophs.
Remember
Protista = mostly single-celled eukaryotes.
Q2.7Kingdoms of Eukarya
Why are fungi included in heterotrophic organisms?
Answer(d) Cannot prepare food
Step by step
Heterotroph = cannot make food.
Absorption is how fungi feed.
Why the others are wrong
(a) a wall feature, not about food.
(b) HOW they feed, not why they are heterotrophs.
(c) reproduction.
Remember
Hetero = depends on others for food.
Q2.8Status of Viruses
Why is it impossible to classify viruses within traditional biological kingdoms?
Answer(a) They lack cellular structure and organelles.
Step by step
Many organisms are parasites or non-photosynthetic and are still classified.
Why the others are wrong
(b) animals cannot either.
(c) size is not the reason.
(d) many classified organisms are parasites.
Remember
No cell → no kingdom.
Q2.9Binomial Nomenclature
Which of the following is the correct way for writing the scientific name of humans?
Answer(a) Homo sapiens (in italics)
Step by step
Homo (capital H) + sapiens (small s), italic.
Why the others are wrong
(b) a printed scientific name must be in italics.
(c) species name starts with a small letter.
(d) genus name starts with a capital letter.
Remember
Capital genus, small species, italic.
Q2.10Binomial Nomenclature
Which information can you get if you know the scientific name of an organism?
Answer(c) Genus and species
Step by step
Homo sapiens: genus Homo, species sapiens.
Why the others are wrong
(a) Wrong.
(b) Wrong.
(d) Wrong.
Remember
Binomial = two names: genus + species.
Set B: More MCQs from this chapter 14 MCQs
Extra questions on the same ideas, of the kind set in board papers and class tests.
QB1Biodiversity
Biodiversity means:
Answer(c) the variety of organisms in a particular area
Step by step
Bio = life, diversity = variety.
Why the others are wrong
(a) palaeontology.
(b) Wrong.
(d) Wrong.
Remember
Variety of life.
QB2Biodiversity
Which regions have more biodiversity?
Answer(a) Tropical regions
Step by step
Warmth and rain support more kinds of life.
Why the others are wrong
(b) less.
(c) dry, less.
(d) very little.
Remember
Tropics teem with life.
QB3Biodiversity
International Biodiversity Day is celebrated on:
Answer(c) 22nd May
Step by step
5 June is World Environment Day; 22 April is Earth Day.
Why the others are wrong
(a) Environment Day.
(b) Earth Day.
(d) World Food Day.
Remember
Biodiversity: 22 May.
QB4Classification and Taxonomic Ranks
The Linnaean system of seven taxonomic ranks was devised in:
Answer(a) 1735
Step by step
1866 Haeckel; 1969 Whittaker; 1977 Woese.
Why the others are wrong
(b) Haeckel's third kingdom.
(c) Whittaker's five kingdoms.
(d) Woese's domains.
Remember
Linnaeus 1735.
QB5Classification and Taxonomic Ranks
A group of similar organisms that can interbreed and produce fertile offspring is a:
Answer(d) species
Step by step
Fertile offspring is the test of one species.
Why the others are wrong
(a) a group of related species.
(b) Wrong.
(c) Wrong.
Remember
Interbreed → same species.
QB6Classification and Taxonomic Ranks
The order to which humans belong is:
Answer(b) Primates
Step by step
Diptera is the order of the fruit fly; Fabales of the pea; Chordata is a phylum.
Why the others are wrong
(a) fruit fly.
(c) pea.
(d) phylum, not order.
Remember
Humans are primates.
QB7History of Classification
Euglena made the two-kingdom system unworkable because it:
Answer(a) has both plant-like and animal-like characteristics
Step by step
Neither plant nor animal fits.
Why the others are wrong
(b) eukaryote.
(c) unicellular.
(d) no cell wall.
Remember
Euglena = half plant, half animal.
QB8History of Classification
The five-kingdom classification system was introduced by:
Answer(d) Robert Whittaker
Step by step
Haeckel 1866 three kingdoms; Woese 1977 domains.
Why the others are wrong
(a) three kingdoms.
(b) three domains.
(c) two groups.
Remember
Whittaker → five.
QB9History of Classification
Who described the characteristics of 350 species of animals and wrote a lot about the life of ants?
Answer(c) Al-Jahiz
Step by step
Ibn Rushd translated Aristotle; Tournefort introduced class and species; Caesalpinio made 15 plant groups.
Why the others are wrong
(a) translated Aristotle's "de Anima".
(b) class and species taxa.
(d) fifteen plant genera.
Remember
Jahiz: 350 animals, ants.
QB10Domains of Life
Archaebacteria that produce methane as a by-product of metabolism are called:
Answer(a) Methanogens
Step by step
Methano-gen = methane-making.
Why the others are wrong
(b) heat.
(c) salt.
(d) acid.
Remember
Name tells the habit.
QB11Kingdoms of Eukarya
The cell wall of fungi is made of:
Answer(b) chitin
Step by step
Chitin is also in the skeleton of insects.
Why the others are wrong
(a) plants and algae.
(c) bacteria.
(d) Wrong.
Remember
Fungi = chitin.
QB12Kingdoms of Eukarya
Which protist causes amoebic dysentery?
Answer(b) Entamoeba
Step by step
Euglena and Paramecium are free-living.
Why the others are wrong
(a) malaria.
(c) free-living alga.
(d) free-living.
Remember
Ent-amoeba → amoebic dysentery.
QB13Kingdoms of Eukarya
The antibiotic penicillin is derived from:
Answer(d) the fungus Penicillium
Step by step
Penicillin from Penicillium (a mould).
Why the others are wrong
(a) Wrong.
(b) Wrong.
(c) Wrong.
Remember
Name gives it away.
QB14Status of Viruses
A virus consists of:
Answer(c) nucleic acid surrounded by a protein coat
What are the seven taxonomic ranks used in the Linnaean system?
Answer
Kingdom, phylum (division), class, order, family, genus and species. (Domain was added above kingdom in 1977.)
Short Q 2.4
Write the taxonomic ranks of lion and corn.
Answer
Rank
Lion
Corn (maize)
Domain
Eukarya
Eukarya
Kingdom
Animalia
Plantae
Phylum / Division
Chordata
Magnoliophyta
Class
Mammalia
Liliopsida (monocots)
Order
Carnivora
Poales
Family
Felidae
Poaceae
Genus
Panthera
Zea
Species
Panthera leo
Zea mays
Short Q 2.5
What are the basic differences between archaea and bacteria?
Answer
Archaea
Bacteria
cell wall without peptidoglycan (polypeptides and proteins)
cell wall of peptidoglycan
rRNA resembles eukaryotes
rRNA typical of bacteria
unique membrane lipids; live in extreme environments
found in all environments
kingdom Archaebacteria
kingdom Eubacteria
Short Q 2.6
What are the shortcomings of the three-kingdom classification system?
Answer
Fungi were placed in Plantae, although they are heterotrophs that absorb food and have chitin, not cellulose, in their walls.
Prokaryotes (bacteria, archaea) were placed with eukaryotic Protista, ignoring the basic difference between prokaryotic and eukaryotic cells.
Short Q 2.7
Which kingdom includes organisms that are multicellular and heterotrophic, and lack cell walls?
Answer
Kingdom Animalia. Animals are eukaryotic, multicellular, heterotrophic, have no cell wall, and ingest food.
Short Q 2.8
Enlist the distinguishing characteristics of fungi.
Answer
Eukaryotic; most multicellular (mushrooms, molds), a few unicellular (yeast).
Cell wall made of chitin.
Heterotrophic: absorb food from decaying matter (do not ingest).
No chlorophyll.
Short Q 2.9
List the three domains that encompass all living organisms.
Answer
Archaea, Bacteria and Eukarya.
Short Q 2.10
Why cannot we classify viruses in any kingdom?
Answer
Viruses are acellular: not made of cells and without organelles; they cannot run metabolism. They lack any of the characteristics of the three domains of life, so they are not included in the classification system.
Short Q 2.11
How does binomial nomenclature facilitate communication about organisms across different languages?
Answer
The scientific name is in Latin (spoken by no country) and is the same anywhere in the world, so a biologist speaking Chinese, Arabic, Spanish or English uses the same name; no two organisms share a name, unlike common names which differ by region.
Set B: More short questions 37 questions
The book's in-text exercises first, then short questions on every topic of the chapter (SLO-based), as asked in board papers.
In-text boxes
SQ 2.1
When is International Biodiversity Day celebrated and why?
Answer
On May 22nd, as designated by the United Nations, to promote the protection of biodiversity.
SQ 2.2
On what grounds do some people respect biodiversity?
Answer
Some respect it only because it is useful to humans; others respect biodiversity on aesthetic and moral grounds.
SQ 2.3
What are prions and viroids?
Answer
Acellular particles not included in classification: prions are composed of protein only and viroids of circular RNA only. They cause infectious diseases in certain plants.
SQ 2.4
How does COVID-19 spread and how can it be prevented?
Answer
By respiratory droplets and contaminated surfaces. Prevention: mask, washing hands with soap for 20 seconds or 60% alcohol sanitizer, and vaccination.
Define biodiversity. On what factors does it depend?
Answer
The variety of organisms in a particular area. It depends on climate, altitude and soil type; tropical regions have more than polar regions.
SQ 2.7
How many kinds of organisms have been identified?
Answer
About 2 million: about 0.5 million kinds of plants and 1.5 million kinds of animals, a small percentage of the total.
SQ 2.8
Define classification. Write its aims.
Answer
Dividing organisms into groups and subgroups on the basis of similarities and differences. Aims: to study organisms easily and to find their evolutionary relationships.
SQ 2.9
Write three advantages of classification.
Answer
Easier identification and understanding of organisms.
A framework for comparing species and finding inter-relationships.
A common language for biologists worldwide; helps identify new species.
Taxonomic ranks
SQ 2.10
What are taxa?
Answer
The groups into which organisms are classified, i.e. taxonomic ranks (singular: taxon).
SQ 2.11
Define species.
Answer
The lowest level of classification: a group of similar organisms that can interbreed and produce fertile offspring.
SQ 2.12
Which is the highest rank? When was it added?
Answer
Domain, added in 1977 (by Carl Woese).
SQ 2.13
Write the classification of human.
Answer
Eukarya → Animalia → Chordata → Mammalia → Primates → Hominidae → Homo → Homo sapiens.
SQ 2.14
What is the difference between phylum and division?
Answer
Both are the same rank below kingdom; "division" is used for plants and fungi, "phylum" for animals and others.
History of classification
SQ 2.15
Who first classified organisms and how?
Answer
Aristotle (384–322 BC) classified organisms into two groups: plants and animals.
SQ 2.16
What was the contribution of Al-Jahiz?
Answer
He described the characteristics of 350 species of animals and wrote a lot about the life of ants.
SQ 2.17
Why was the two-kingdom system found unworkable?
Answer
Euglena has both plant-like (chlorophyll) and animal-like (heterotrophic in darkness, no cell wall) characteristics; the system also did not separate prokaryotes from eukaryotes.
SQ 2.18
On what basis did Whittaker classify organisms into five kingdoms?
Answer
Levels of cellular organization (prokaryotic, unicellular eukaryotic, multicellular eukaryotic) and modes of nutrition (photosynthesis, absorption, ingestion).
SQ 2.19
Name the five kingdoms.
Answer
Monera, Protista, Fungi, Plantae and Animalia.
Classification systems.
SQ 2.20
Who proposed the three-domain system and on what basis?
Answer
Carl Woese (1977), based on the differences between Archaea and Bacteria; he split the prokaryotes into two domains.
Domains and kingdoms
SQ 2.21
Why are archaea called the most primitive organisms?
Answer
They are considered the most ancient forms of life; prokaryotes adapted to extreme conditions like those on the early Earth.
Prokaryotes with peptidoglycan cell walls, found in all environments, unicellular (some in chains or colonies); most heterotrophic, some photosynthetic. Kingdom Eubacteria.
Fungus-like protists have cell walls of cellulose; fungi have chitin.
SQ 2.27
Give the characteristics of kingdom Plantae.
Answer
Eukaryotic, multicellular, cellulose cell walls, autotrophic (photosynthesis), multicellular sex organs, form embryos.
SQ 2.28
How do animals differ from fungi in nutrition?
Answer
Animals ingest food and digest it inside the body; fungi absorb food from decaying matter.
SQ 2.29
Name some uses of fungi.
Answer
Making bread, cheese and beer; the antibiotic penicillin from Penicillium.
Viruses
SQ 2.30
Why are viruses at the borderline of living and non-living?
Answer
Outside a host they are inert particles that cannot run metabolism; inside a host cell they reproduce, which is a sign of life.
SQ 2.31
What is the structure of a virus?
Answer
Nucleic acid (DNA or RNA) surrounded by a protein coat.
Viruses.
SQ 2.32
What is a bacteriophage?
Answer
A virus which attacks bacteria.
Binomial nomenclature
SQ 2.33
Define binomial nomenclature. Who founded it?
Answer
The system of scientific naming in which each name has two parts, genus and species. Carl Linnaeus founded it.
SQ 2.34
Why are scientific names taken from Latin?
Answer
Latin is spoken by no country, so no country is favoured and the name is the same everywhere.
SQ 2.35
Why are common names not suitable for science?
Answer
They vary by region (onion: piyaz, ganda, bassal), one name may mean several organisms (black bird), and they have no scientific basis (jellyfish is not a fish).
SQ 2.36
Write the scientific names of onion, potato and tiger.
Answer
Allium cepa, Solanum tuberosum, Panthera tigris.
SQ 2.37
How is a scientific name written by hand?
Answer
Genus with a capital letter, species with a small letter, and the two parts underlined separately.
These test whether you really understand. Give a reason every time.
CRQ 2.1
(Inquisitive) How might placing an organism in the incorrect taxonomic group affect conservation or scientific studies?
Answer
Wrong conservation status: if a rare species is lumped with a common one, its numbers seem large and it may get no protection until it is lost.
Wasted protection: money may go to a group that is not actually threatened.
Wrong predictions: biologists predict features (diseases, medicines, behaviour) from relatives; a wrong group gives wrong predictions, e.g. testing a drug source in the wrong plant family.
Confused communication: other scientists build on the wrong grouping, and research results cannot be compared.
Wrong evolutionary picture: classification aims to show evolutionary relationships; a misplaced organism distorts the family tree.
CRQ 2.2
(Inquisitive) Imagine you discover a new organism. What steps would you take to classify and name it according to the principles of binomial nomenclature?
Answer
Observe and record its structure: cells (prokaryotic or eukaryotic), cell wall, nutrition, body organisation; photograph and preserve a specimen.
Compare it with known organisms using keys, museum specimens and published descriptions; use genetic (DNA) comparison as biologists now do.
Place it in the ranks from domain down to genus: e.g. eukaryotic → Eukarya; multicellular, ingests food → Animalia; and so on.
Check it is new: it must not interbreed or match any existing species.
Name it: a Latin genus name (capital letter) + a new species name (small letter), unique, printed in italics, e.g. "Panthera …".
Publish a description in a scientific journal so that the name is accepted internationally.
Set A: Textbook comprehensive questions 7 questions
The long questions at the end of the chapter in your book.
Long Q 2.1
Discuss biodiversity and its significance in maintaining the health of ecosystems.
Answer
Biodiversity
Biodiversity means the variety of organisms in a particular area, measured by the number of kinds of organisms and the variation within each kind. It is not evenly spread out: it depends on climate, altitude and soil; tropical regions have more than polar regions.
Significance
Ecosystem stability: biodiversity maintains the balance of ecosystems and plays an important role in biogeochemical cycles such as the carbon and nitrogen cycles.
Climate regulation: plants and algae absorb carbon dioxide and keep the climate balanced.
Natural resources: food, medicine, building materials and fuel.
Economic benefits: agriculture, tourism and pharmaceutical industries depend on it.
More kinds of organisms mean more links in food webs, so an ecosystem recovers better if one species is lost. The UN marks 22 May as International Biodiversity Day to promote its protection.
Long Q 2.2
Explain the importance of classification in biology and how it helps us understand the relationships between different organisms.
Answer
Classification
The process in which organisms are divided into groups and subgroups on the basis of similarities and differences. About 2 million kinds are known, so they must be grouped to be studied.
Aims
To determine similarities and differences so that organisms can be studied easily.
To find the evolutionary relationships among organisms.
Importance
Groups similar organisms, making it easier to identify and understand them.
A framework for studying and comparing species.
Explains the inter-relationships among organisms: members of one genus are closer than members of one family.
Helps identify new species and understand their evolution.
Provides a common language for biologists.
Understanding relationships
The ranks show how close organisms are: the human and the fruit fly share only domain and kingdom; the human and lion share domain to class (Mammalia). In recent times, genetics is used to confirm these relationships.
Long Q 2.3
Describe the Linnaean system of classification in detail, stating the seven taxonomic ranks and their relationships.
Answer
The Swedish botanist Carl Linnaeus devised the Linnaean system in 1735 with seven taxonomic ranks: kingdom, phylum (division), class, order, family, genus and species. In 1977 the rank of domain was added.
The ranks nest inside one another.
Kingdom: a domain is divided into kingdoms (Eukarya: Animalia, Plantae, Fungi, Protista).
Phylum (division for plants and fungi): each kingdom divided into related phyla.
Class: each phylum divided into related classes.
Order: each class into related orders.
Family: each order into related families.
Genus: each family into related genera.
Species: the lowest level; organisms that interbreed and produce fertile offspring.
Relationship between ranks
Each rank contains one or more ranks below it. Moving down, the groups get smaller and their members share more characteristics. Example: Human — Eukarya, Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, Homo sapiens.
Long Q 2.4
Compare and contrast the domains Archaea and Bacteria, focusing on their key characteristics.
Answer
Similarities
Both are prokaryotes: no nucleus or membrane-bound organelles.
Mostly unicellular, with a cell wall.
Some of both can photosynthesise.
Differences
Feature
Archaea
Bacteria
Cell wall
no peptidoglycan; polypeptides and proteins
peptidoglycan
rRNA
resembles eukaryotes
bacterial
Membrane lipids
unique; allow life in extremes
ordinary
Habitat
hot springs, salt lakes, acid/alkaline waters; also soil, oceans
all environments, including bodies of organisms
Energy
some from sulphur or ammonia; photosynthesis without oxygen
mostly heterotrophic; some photosynthetic (cyanobacteria)
Describe the distinctive characteristics of the four kingdoms within the domain Eukarya.
Answer
Kingdom Protista
Unicellular, colonial, filamentous or simple multicellular eukaryotes. Plant-like (algae: Euglena, diatoms), animal-like (protozoa: Amoeba, Paramecium), fungus-like (slime and water molds).
Kingdom Fungi
Eukaryotic heterotrophs that absorb food from decaying matter; cell walls of chitin; mostly multicellular (mushrooms, rusts, smuts, molds), some unicellular (yeast).
Kingdom Plantae
Multicellular, cellulose walls, autotrophic by photosynthesis, multicellular sex organs, form embryos. Mosses, ferns, conifers, flowering plants.
Kingdom Animalia
Multicellular heterotrophs without cell walls; develop from embryos; ingest food and digest it within their bodies. Vertebrates and invertebrates.
Examples of protists.
Long Q 2.6
Discuss the challenges of classifying viruses within the traditional three domains of life.
Answer
What a virus is
Viruses are ultramicroscopic and at the borderline of living and non-living. A virus is nucleic acid (DNA or RNA) in a protein coat.
A bacteriophage and an influenza virus.
Challenges
Acellular: the three domains are defined by cell type (prokaryotic or eukaryotic), but viruses have no cells.
No organelles, no metabolism: they cannot make proteins or energy on their own.
Obligate parasites: they reproduce only inside host cells (plants, animals, bacteria), using the host's machinery.
Not clearly alive: outside a host they behave like chemical particles.
Therefore viruses are not included in the classification system, because they lack any of the characteristics of the three domains of life. Prions (protein only) and viroids (RNA only) are likewise unclassified.
Long Q 2.7
Explain the rules and guidelines for suggesting scientific names to organisms.
Answer
The scientific naming of organisms (binomial nomenclature) follows international rules:
For scientific naming, words are taken from the Latin language.
Every scientific name has two parts: genus name first, followed by the species name.
Every scientific name has to be unique; the same name cannot be used for two organisms.
Genus name begins with a capital letter; species name with a small letter.
At the time of printing, it is typed in italics.
When handwritten, the two parts are underlined separately.
Writing the name correctly.
Examples: Allium cepa (onion), Solanum tuberosum (potato), Homo sapiens (human).
Set B: More important long questions 3 questions
Long questions often set in board papers from this chapter, answered in the same full style.
Imp. LQ 1
Describe the history of classification from the two-kingdom to the three-domain system.
Answer
Classification systems compared.
Early workers
Aristotle (plants and animals), Al-Jahiz (350 animals), Caesalpinio (15 plant genera), Tournefort (class and species), Linnaeus (seven ranks, 1735).
Two kingdoms
Plantae (autotrophs, including bacteria and fungi) and Animalia (heterotrophs). Failed with Euglena and did not separate prokaryotes.
Three kingdoms (Haeckel, 1866)
Protista added for Euglena-like organisms and prokaryotes. Fungi still wrongly in Plantae.
Five kingdoms (Whittaker, 1969)
Monera, Protista, Fungi, Plantae, Animalia, on cellular organization and mode of nutrition; modified by Margulis and Schwartz (1988) using genetics.
Three domains (Woese, 1977)
Archaea, Bacteria, Eukarya: prokaryotes split into two domains; six kingdoms in all.
Imp. LQ 2
Write a note on the significance of binomial nomenclature over common names.
Answer
Uniqueness: two organisms cannot have the same scientific name.
Universal: Latin is spoken by no country, so the name is the same everywhere: a standard way of communication.
Common names vary by region: onion is piyaz, ganda, bassal or vassal.
One common name, many organisms: "blue bell" for dozens of plants; "black bird" for crow and raven.
Common names are unscientific: silver fish, cray fish, jellyfish and star fish are not fish (a fish has a backbone, fins and gills).
Scientific names.
Imp. LQ 3
Describe the domain Archaea and its kingdom.
Answer
Archaea are the most primitive organisms. They are prokaryotes whose cell wall lacks peptidoglycan and is made of polypeptides and proteins. Their rRNA resembles eukaryotes. Unique membrane lipids let them live in extreme environments (hot springs, salt lakes, acidic or alkaline waters), though some live in soil and oceans. Some obtain energy from sulphur or ammonia; others photosynthesise without producing oxygen.
DNA or RNA in a protein coat; acellular; not classified
Scientific name
Genus (capital) + species (small), italic / underlined separately
Biodiversity Day
22 May
Key definitions 4 terms
Biodiversity
Biodiversity means the variety of organisms in a particular area. Biodiversity of an area is measured by considering the number of different kinds of organisms and the variation within each kind.
Classification
The process in which organisms are divided into groups and subgroups on the basis of similarities and differences found in them.
Taxonomic ranks (taxa)
The groups into which organisms are classified are known as taxonomic ranks or taxa (singular "taxon").
Binomial nomenclature
The system of scientific naming of organisms, in which the scientific name consists of two parts: the first part is the name of the genus and the second part the name of the species. Carl Linnaeus was its founder.
Kingdom of mostly unicellular eukaryotes?Show answer
Protista
Why are fungi heterotrophs?Show answer
They cannot prepare food
Why are viruses not classified?Show answer
No cells or organelles
Scientific name gives?Show answer
Genus and species
Who gave five kingdoms?Show answer
Robert Whittaker (1969)
Wall of fungi?Show answer
Chitin
Scientific name of onion?Show answer
Allium cepa
Amoebic dysentery is caused by?Show answer
Entamoeba
Final self-test
Final self-test: all 24 MCQs, no answers
Give yourself 25 minutes. Pick one option for each question, then submit to see your score and which questions to revise. Any question you get wrong tells you which topic to read again.
