Class 9 Biology Notes – Chapter 2

Chapter 2: Biodiversity

Textbook Exercise Solution

A. Select the Correct Answers for the Following Questions

1. Which of the following taxonomic ranks represents the broadest rank?

(a) Species
(b) Genus
(c) Kingdom
(d) Domain

Answer: (d) Domain

2. Which characteristic is unique to organisms in the domain Archaea?

(a) Cell walls made of peptidoglycan
(b) Presence of a nucleus
(c) Ability to live in extreme environments
(d) Lack of ribosomes

Answer: (c) Ability to live in extreme environments

3. Which of these statements is NOT related to bacteria?

(a) Do not have a nucleus
(b) Cell wall made of peptidoglycan
(c) Most are heterotrophic
(d) Have chlorophyll in their chloroplasts

Answer: (d) Have chlorophyll in their chloroplasts

4. Which of these organisms belongs to the domain Eukarya?

(a) Escherichia coli
(b) Yeast
(c) Coronavirus
(d) None of these

Answer: (b) Yeast

5. Which of the following is a key characteristic that distinguishes eukaryotic cells from prokaryotic cells?

(a) Lack of a cell wall
(b) Presence of a nucleus
(c) Absence of ribosomes
(d) Smaller size

Answer: (b) Presence of a nucleus

6. Which kingdom includes organisms that are primarily unicellular, eukaryotic, and often heterotrophic?

(a) Archaea
(b) Protista
(c) Fungi
(d) Plantae

Answer: (b) Protista

7. Why are fungi included among heterotrophic organisms?

(a) They have chitin in their cell walls
(b) They absorb nutrients
(c) They reproduce by spores
(d) They cannot prepare their own food

Answer: (d) They cannot prepare their own food

8. Why is it impossible to classify viruses within traditional biological kingdoms?

(a) They lack cellular structure and organelles
(b) They cannot perform photosynthesis
(c) They are smaller in size than bacteria
(d) They are parasites

Answer: (a) They lack cellular structure and organelles

9. Which of the following is the correct way to write the scientific name of humans?

(a) Homo sapiens
(b) Homo sapiens
(c) Homo Sapiens
(d) homo sapiens

Answer: (a) Homo sapiens

10. What information can you obtain from the scientific name of an organism?

(a) Kingdom and phylum
(b) Phylum and genus
(c) Genus and species
(d) Class and species

Answer: (c) Genus and species

B. Write Short Answers

1. What is the term used to describe the variety of organisms in ecosystems?

Answer: The term used to describe the variety of life forms within a species, ecosystem, or biome is biodiversity (biological diversity).

2. How is biodiversity crucial for humans and planet Earth?

Answer: Biodiversity provides essential resources such as food, timber, fibres, and medicines. It maintains ecosystem stability and nutrient cycling, controls soil erosion, helps regulate the climate, purifies air and water, and improves ecosystem resilience against environmental changes.

3. What are the seven taxonomic ranks used in the Linnaean system?

Answer: The seven main taxonomic ranks, arranged from the broadest to the most specific, are:

Kingdom
Phylum (or Division in plants)
Class
Order
Family
Genus
Species

4. Write the taxonomic ranks of lion and corn.

Answer:

Lion (Panthera leo)

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Panthera
Species: Panthera leo

Corn (Zea mays)

Kingdom: Plantae
Division: Tracheophyta (vascular plants)
Class: Liliopsida (monocots)
Order: Poales
Family: Poaceae
Genus: Zea
Species: Zea mays

5. What are the basic differences between Archaea and Bacteria?

Answer:

Archaea:

Their cell walls lack peptidoglycan.
They possess unique ether-linked membrane lipids.
Some live in extreme environments, while others inhabit ordinary environments.
Their genetic and protein-synthesis machinery has certain similarities to that of eukaryotes.

Bacteria:

Their cell walls usually contain peptidoglycan.
They possess ester-linked membrane lipids.
They inhabit a wide variety of environments.
Their genetic and ribosomal characteristics differ from those of Archaea.

6. What are the shortcomings of the three-kingdom classification system?

Answer: The three-kingdom classification system had several shortcomings:

It failed to distinguish clearly between prokaryotes and eukaryotes.
It grouped unicellular photosynthetic algae with plants and heterotrophic protozoans with animals.
It incorrectly grouped fungi with plants, although fungi lack chlorophyll and obtain nutrients by absorption.

7. Which kingdom includes organisms that are multicellular and heterotrophic and lack cell walls?

Answer: Kingdom Animalia.

8. Enlist the distinguishing characteristics of fungi.

Answer:

Fungi are eukaryotic and heterotrophic organisms.
They absorb nutrients from their surroundings.
Their cell walls are made of chitin.
Their bodies usually consist of thread-like structures called hyphae, which collectively form a mycelium.
They are generally non-motile.
They store reserve food in the form of glycogen.

9. List the three domains that encompass all living organisms.

Answer:

Domain Archaea
Domain Bacteria
Domain Eukarya

10. Why cannot viruses be classified in any kingdom?

Answer: Viruses are acellular entities that lack cellular structures such as cytoplasm and ribosomes, as well as independent metabolic machinery. They can reproduce only inside suitable host cells. Outside a host cell, they remain inactive and cannot carry out independent life processes.

11. How does binomial nomenclature facilitate clear communication about organisms across different languages?

Answer: Binomial nomenclature assigns each organism a standardized, two-part scientific name that is recognized internationally. It reduces confusion caused by regional common names, language differences, and the use of multiple names for the same organism.

C. Write Answers in Detail

1. Discuss biodiversity and its significance in maintaining the health of ecosystems.

Answer:

Biodiversity: Biodiversity refers to the variety of living organisms, their genetic differences, and the ecological systems of which they are a part.

Ecological Health: Biodiversity supports essential ecosystem functions, including crop pollination, decomposition of organic matter, maintenance of soil fertility, oxygen production, water filtration, and carbon storage.

Ecosystem Stability: Diverse ecosystems often contain different species that perform similar ecological functions. If one species declines because of disease or environmental stress, other species may partly maintain those functions. This helps preserve food webs and ecosystem stability.

2. Explain the importance of classification in Biology and how it helps us understand relationships between different organisms.

Answer:

Importance of Classification: Millions of species exist on Earth. Classification organizes this great variety of organisms into manageable groups based on shared characteristics, including physical features, genetic similarities, and evolutionary relationships.

Evolutionary Relationships: Modern classification, particularly phylogenetic classification, groups organisms according to their evolutionary history and common ancestry. Organisms sharing lower taxonomic ranks, such as genus and family, generally have closer evolutionary relationships than organisms that share only a broad rank, such as kingdom or domain.

3. Describe the Linnaean system of classification in detail, stating the seven taxonomic ranks and their relationships.

Answer: Developed by Carl Linnaeus, the Linnaean system arranges organisms into a hierarchical structure. Each higher rank includes one or more groups from the rank below it.

The seven taxonomic ranks are:

Kingdom: A broad grouping containing related phyla.
Phylum: A group of related classes that share important characteristics.
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 of these seven ranks. Under the biological species concept, a species consists of organisms that can interbreed naturally and produce fertile offspring, although this definition does not apply to every organism.

4. Compare and contrast the domains Archaea and Bacteria, focusing on their key characteristics.

Answer:

Similarities:

Both Archaea and Bacteria are generally unicellular and prokaryotic.
Neither possesses a membrane-bound nucleus.
Neither has typical membrane-bound organelles such as mitochondria.
Both reproduce mainly through cell division.

Differences:

Cell Wall Composition: Bacterial cell walls usually contain peptidoglycan, whereas archaeal cell walls lack peptidoglycan and may contain proteins, polysaccharides, or other materials.

Membrane Lipids: Archaea possess ether-linked membrane lipids with branched hydrocarbon chains, whereas Bacteria generally possess ester-linked lipids with unbranched fatty acid chains.

Habitat: Archaea include methanogens, extreme halophiles, and extreme thermophiles, but they also inhabit ordinary environments. Bacteria occur in a wide variety of habitats worldwide.

Genetic Machinery: Some aspects of archaeal transcription and translation are more similar to those of eukaryotes than to those of Bacteria.

5. Describe the diagnostic characteristics of the four kingdoms within the domain Eukarya.

Answer:

Kingdom Protista:

Mostly unicellular, although some are simple multicellular organisms.
Includes autotrophs, such as many algae, and heterotrophs, such as protozoans.
Shows considerable diversity in structure and nutrition.

Kingdom Fungi:

Eukaryotic heterotrophs that absorb nutrients.
Usually multicellular, although yeasts are unicellular.
Possess cell walls made of chitin.
Many have bodies composed of hyphae.

Kingdom Plantae:

Multicellular eukaryotes.
Most prepare food through photosynthesis using chlorophyll.
Possess cell walls made of cellulose.
Generally retain food reserves in the form of starch.

Kingdom Animalia:

Multicellular eukaryotes.
Obtain food by ingestion.
Lack cell walls.
Most can move during at least one stage of their life cycle.
Many possess specialized tissues, organs, and nervous coordination.

6. Discuss the challenges of classifying viruses within the traditional three domains of life.

Answer: The traditional three-domain system classifies cellular organisms using characteristics such as cellular structure, ribosomal RNA sequences, and genetic relationships. Viruses present special challenges for the following reasons:

Acellular Structure: Viruses are not made of cells. They consist of genetic material (DNA or RNA) enclosed in a protein coat, and some also possess an outer envelope.
Lack of Ribosomes: Viruses lack ribosomes and do not possess the cellular ribosomal RNA machinery commonly used to determine evolutionary relationships among organisms.
Dependence on Host Cells: Viruses cannot reproduce independently and must use the machinery of host cells to make new virus particles.
Lack of Independent Metabolism: They do not carry out independent metabolic processes outside host cells.

For these reasons, viruses are not placed within the traditional three domains of cellular life.

7. Explain the rules and guidelines for assigning scientific names to organisms.

Answer: Scientific names are assigned according to internationally accepted nomenclature rules. The main guidelines for binomial nomenclature are:

Each species is given a two-part scientific name.
The first word is the genus name, which begins with a capital letter.
The second word is the specific epithet, which begins with a lowercase letter.
Both words are italicized when printed or typed.
When handwritten, the two words are underlined separately.
The genus name may be abbreviated to its initial letter after it has been written in full, provided the meaning remains clear. For example, Escherichia coli may be written as E. coli.
The name of the scientist who first described a species may sometimes be written after its scientific name according to the relevant nomenclature conventions.

Example: Homo sapiens

D. Inquisitive Questions

1. How might placing an organism in the incorrect taxonomic group affect our understanding of its evolutionary history, ecological role, and potential applications in medicine or agriculture?

Answer:

Evolutionary History: Misclassification can distort our understanding of evolutionary relationships and common ancestry. It may lead scientists to make incorrect assumptions about an organism’s genetic traits and evolutionary lineage.

Ecological Role: Placing an organism in the wrong group can lead to misunderstandings about its role in food webs, nutrient cycling, and symbiotic relationships within an ecosystem.

Potential Applications: In medicine and agriculture, scientists often investigate useful compounds, disease resistance, or pest-control properties in organisms related to species already known to have these benefits. Misclassification may cause researchers to overlook potentially valuable medicinal compounds or select unsuitable organisms for biological pest control.

Therefore, accurate classification is important for understanding biodiversity, evolutionary relationships, ecological interactions, and the practical applications of biological research.

Notes by Sir Dilawar

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