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Chapter 1 The Living World
The living world is incredibly diverse and fascinating. The sheer variety of life forms found in diverse habitats, from cold mountains to hot springs, is astonishing. Observing the complexity of organisms, their interactions, and even the intricate processes within a single cell prompts us to ponder the fundamental question: what is life? While the philosophical aspect of this question is complex, scientists seek a technical understanding of what constitutes living as opposed to non-living.
Diversity In The Living World
When we look around, we encounter a vast array of living organisms – plants, animals, insects, birds, pets, and even microorganisms invisible to the naked eye. The variety increases significantly as we explore different regions and habitats, such as a dense forest.
Each different kind of plant, animal, or organism represents a **species**. The number of species that have been identified and described by scientists is estimated to be between **1.7 and 1.8 million**. This vast number and types of organisms on Earth constitute **biodiversity**.
With millions of species, using local names for organisms becomes impractical, as these names vary from place to place. This would lead to confusion when communicating about specific organisms across different regions or countries. To overcome this, there is a need for a standardized system of naming living organisms.
This process of assigning a standard name to an organism is called **nomenclature**. Nomenclature is possible only after the organism has been correctly described and identified. **Identification** is the process of correctly determining that a particular organism is the one being referred to or that it belongs to a specific known group.
To facilitate global study and communication among biologists, international procedures have been established for scientific naming. For plants, scientific names are based on the principles provided in the **International Code for Botanical Nomenclature (ICBN)**. For animals, it's the **International Code of Zoological Nomenclature (ICZN)**. These codes ensure that each organism has a unique scientific name that is accepted universally.
Biologists follow universally accepted principles for scientific naming, the most common system being **Binomial Nomenclature**. This system, proposed by **Carolus Linnaeus**, assigns a name with two components to each organism:
- The first component is the **Generic name** (Genus).
- The second component is the **specific epithet** (species).
Example: The scientific name of mango is *Mangifera indica*. Here, *Mangifera* is the genus name, and *indica* is the specific epithet.
Universal rules of nomenclature:
- Biological names are generally in **Latin** and are written in **italics**. They are Latinised or derived from Latin, regardless of their origin.
- The first word is the **Genus name**, starting with a **capital letter**.
- The second word is the **specific epithet** (species name), starting with a **small letter**.
- When handwritten, both words are **separately underlined**. When printed, they are in **italics**. This formatting indicates their Latin origin.
- The name of the author who first described the species is sometimes written in an abbreviated form after the specific epithet (e.g., *Mangifera indica* Linn. indicates it was first described by Linnaeus).
Since studying millions of individual organisms is impossible, organisms are grouped into convenient categories based on easily observable characteristics. This process is called **classification**. When we refer to a group like 'dogs', 'cats', 'mammals', or 'plants', we associate certain characteristics with the organisms in that group. These categories are called **taxa** (singular: taxon). Taxa represent groups at different levels (e.g., 'Animals', 'Mammals', 'Dogs' are taxa at different levels of classification).
The scientific study of classification, including characterization, identification, classification, and nomenclature of organisms, is known as **taxonomy**. Modern taxonomic studies are based on external and internal structure, cell structure, developmental processes, and ecological information. Systematics is a branch of study that deals with the systematic arrangement of organisms and also considers the evolutionary relationships between them.
Taxonomic Categories
Classification is not a single step but a process involving a **hierarchy of steps**, where each step represents a rank or **category**. All categories together form the **taxonomic hierarchy**. Each category is a unit of classification, also called a **taxon**.
Common taxonomic categories used in the classification of organisms, from lowest to highest rank, are:
- Species
- Genus
- Family
- Order
- Class
- Phylum (for animals) / Division (for plants)
- Kingdom
The basis for placing an organism in various categories is the knowledge of its characteristics, allowing comparisons of similarities and dissimilarities with other organisms.
Species
**Species** is the lowest taxonomic category. It is defined as a group of individual organisms with fundamental similarities. Organisms of different species are distinguished based on distinct morphological differences.
Example: *Mangifera indica* (mango), *Solanum tuberosum* (potato), *Panthera leo* (lion). *indica*, *tuberosum*, and *leo* are specific epithets (species names).
Human beings belong to the species *sapiens*, grouped under the genus *Homo*. The scientific name for humans is *Homo sapiens*.
Genus
**Genus** is a higher taxonomic category comprising a group of related species. Species within the same genus share more common characters compared to species of other genera. Genera are essentially aggregates of closely related species.
Example: The genus *Solanum* includes different species like *Solanum tuberosum* (potato), *Solanum nigrum* (black nightshade), and *Solanum melongena* (brinjal). The genus *Panthera* includes species like *Panthera leo* (lion), *Panthera pardus* (leopard), and *Panthera tigris* (tiger). The genus *Panthera* is distinct from the genus *Felis* (which includes cats).
Family
**Family** is a higher category consisting of a group of related genera. Families have a smaller number of similarities compared to genera and species. Families are characterized based on both vegetative and reproductive features (especially in plants). The suffix '-aceae' is common for plant families (e.g., Solanaceae).
Example: In plants, the genera *Solanum*, *Petunia*, and *Datura* are placed in the Family **Solanaceae**. In animals, the genus *Panthera* (lion, tiger, leopard) and the genus *Felis* (cats) are placed together in the Family **Felidae**. Dogs belong to a different family, **Canidae**, showing similarities and differences with cats.
Order
**Order** is a higher category formed by an assemblage of related families. Orders are identified based on aggregates of characters. The number of similar characters is less compared to the families included in an order. The suffix '-ales' is common for plant orders (e.g., Polymoniales).
Example: Plant families like Convolvulaceae and Solanaceae are included in the Order **Polymoniales** based on floral characters. Animal families like Felidae (cats) and Canidae (dogs) are included in the Order **Carnivora**.
Class
**Class** is a higher category that includes related orders. The suffix '-ae' is common for plant classes, and '-lia' or '-a' for animal classes.
Example: Order Primata (comprising monkeys, gorillas, gibbons) is placed in the Class **Mammalia** along with the Order Carnivora (tiger, cat, dog). Class Mammalia includes other orders as well.
Phylum / Division
**Phylum** is a higher category in the classification of animals, including related classes. Based on common features like the presence of a notochord and a dorsal hollow neural system, classes like fishes, amphibians, reptiles, birds, and mammals are included in the Phylum **Chordata**. In the classification of plants, the equivalent category to Phylum is **Division**.
Kingdom
**Kingdom** is the highest taxonomic category in the classification system. All animals belonging to various phyla are assigned to the Kingdom **Animalia**. All plants from various divisions are assigned to the Kingdom **Plantae**. These are the broadest classification groups.
As we move up the taxonomic hierarchy from species to kingdom, the number of common characteristics shared by members within a taxon decreases. Conversely, lower the taxon, more specific and numerous are the shared characteristics. This makes classifying organisms into higher categories more complex due to fewer shared traits.
Example of Taxonomic Categories for Common Organisms:
| Common Name | Biological Name | Genus | Family | Order | Class | Phylum/Division | Kingdom |
|---|---|---|---|---|---|---|---|
| Man | Homo sapiens | Homo | Hominidae | Primata | Mammalia | Chordata | Animalia |
| Housefly | Musca domestica | Musca | Muscidae | Diptera | Insecta | Arthropoda | Animalia |
| Mango | Mangifera indica | Mangifera | Anacardiaceae | Sapindales | Dicotyledonae | Angiospermae | Plantae |
| Wheat | Triticum aestivum | Triticum | Poaceae | Poales | Monocotyledonae | Angiospermae | Plantae |
Question 1. Why are living organisms classified?
Answer:
Living organisms are classified for several reasons:
- **Facilitates Study:** With millions of diverse organisms, it is impossible to study each one individually. Classification groups organisms based on shared characteristics, making their study easier and more systematic.
- **Identification:** Classification helps in the identification of new organisms by comparing them with known groups.
- **Understanding Relationships:** Classification helps in understanding the relationships (similarities and differences) between different groups of organisms. Modern classification also reflects evolutionary relationships.
- **Communication:** Provides a universal system of naming (nomenclature) that is understood by biologists worldwide, facilitating communication and exchange of information.
- **Organisation of Information:** Organizes the vast amount of information about living organisms in a structured manner.
- **Practical Applications:** Knowledge of classification is useful in fields like agriculture, forestry, industry, and in conserving biodiversity.
Question 2. Why are the classification systems changing every now and then?
Answer:
Classification systems are not static; they change over time due to several factors:
- **Advances in Scientific Knowledge:** New discoveries about organisms' characteristics (e.g., molecular biology, genetics, biochemistry) provide more detailed information that leads to re-evaluation and refinement of existing classifications.
- **Improved Technology:** Technologies like electron microscopy and DNA sequencing provide deeper insights into the structure, function, and genetic makeup of organisms, revealing previously unknown relationships or differences.
- **New Organisms Discovered:** As new organisms are continuously discovered, they need to be incorporated into the existing classification system, sometimes requiring adjustments.
- **Better Understanding of Evolutionary Relationships:** Modern classification aims to reflect evolutionary history. As our understanding of evolutionary relationships improves (e.g., through fossil records, comparative anatomy, genetic studies), the classification system is updated to better represent the tree of life.
Question 3. What different criteria would you choose to classify people that you meet often?
Answer:
To classify people I meet often, I could use various criteria, depending on the context and purpose. Some possible criteria include:
- **Physical characteristics:** Gender, age group (child, teenager, adult, elder), height range, hair color, eye color.
- **Personal interests/hobbies:** Sports enthusiasts, book readers, music lovers, gamers, artists.
- **Profession/occupation:** Students, teachers, doctors, engineers, business people.
- **Location/Place of residence:** People from the same neighborhood, city, region.
- **Language spoken:** People speaking the same language or different languages.
- **Social groups/circles:** Friends, family members, colleagues, classmates.
- **Personality traits:** Introverts, extroverts, optimistic, cautious (more subjective).
Question 4. What do we learn from identification of individuals and populations?
Answer:
From the identification of individuals and populations, we learn several things:
- **Taxonomic Placement:** Identification helps determine the specific species (and higher taxonomic ranks) to which an individual or a population belongs.
- **Shared Characteristics:** We learn about the common characteristics shared by all individuals within that identified species or population.
- **Variations:** We learn about the variations that exist among individuals within the same population, which are important for adaptation and evolution.
- **Ecological Role:** Identification helps understand the ecological role (niche) of the organism/population in its environment, including its feeding habits, habitat, and interactions with other organisms.
- **Distribution:** We learn about the geographical distribution of the species or population.
- **Conservation Status:** Identification is essential for assessing the conservation status of a species (e.g., endangered, threatened).
Question 5. Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Mangifera indica
Answer:
According to the rules of binomial nomenclature, the genus name starts with a capital letter, and the specific epithet starts with a small letter. Both parts are underlined when handwritten or italicized when printed.
The correctly written name is: **Mangifera indica**
Question 6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Answer:
A **taxon** (plural: taxa) is a taxonomic group of any rank. It is a unit of classification that represents a distinct category of organisms based on shared characteristics.
Examples of taxa at different hierarchical levels:
- Kingdom: **Animalia** (includes all animals), **Plantae** (includes all plants)
- Phylum/Division: **Chordata** (animals with notochord), **Angiospermae** (flowering plants)
- Class: **Mammalia** (mammals), **Dicotyledonae** (dicot plants)
- Order: **Carnivora** (carnivorous mammals), **Poales** (grasses and related plants)
- Family: **Felidae** (cats), **Poaceae** (grass family)
- Genus: **Panthera** (lions, tigers, leopards), **Homo** (humans)
- Species: **sapiens** (humans), **leo** (lion)
Question 7. Can you identify the correct sequence of taxonomical categories?
(a) Species Order Phylum Kingdom
(b) Genus Species Order Kingdom
(c) Species Genus Order Phylum
Answer:
The correct sequence of taxonomical categories from lowest to highest is Species $\to$ Genus $\to$ Family $\to$ Order $\to$ Class $\to$ Phylum/Division $\to$ Kingdom.
Checking the given options:
(a) Species $\to$ Order $\to$ Phylum $\to$ Kingdom (Incorrect, Genus and Class are missing, and Order comes before Phylum)
(b) Genus $\to$ Species $\to$ Order $\to$ Kingdom (Incorrect, Species is lower than Genus, and Class/Phylum are missing)
(c) Species $\to$ Genus $\to$ Order $\to$ Phylum (Incorrect, Family and Class are missing, and Order comes before Phylum)
Looking closely at the options, they present partial sequences. We need to identify the one with categories in the correct relative order, even if intermediate categories are skipped.
Let's re-examine: (a) Species (lowest), Order, Phylum, Kingdom (highest). Relative order: Species is lowest, then Order, then Phylum, then Kingdom. This order is correct. (Family and Class are missing between Species/Order and Phylum/Order respectively).
(b) Genus, Species, Order, Kingdom. Relative order: Species is lower than Genus (Incorrect). Sequence starts wrong.
(c) Species, Genus, Order, Phylum. Relative order: Species is lowest, then Genus (correct). Then Order, then Phylum. This order is correct. (Family and Class are missing). Both (a) and (c) have correct relative order of the listed categories.
However, standard multiple-choice questions usually have only one correct option. Let's assume the question implies a sequence from lowest to highest *among the listed categories*. In that case, for (a), Species is lowest, then Order, then Phylum, then Kingdom. For (c), Species is lowest, then Genus, then Order, then Phylum. Genus is lower than Order and Phylum. The sequence in (a) has Order, then Phylum. The sequence in (c) has Order, then Phylum. Both (a) and (c) follow the general ascending trend.
Let's check if one sequence is more 'complete' or standard. (a) has Species, Order, Phylum, Kingdom. (c) has Species, Genus, Order, Phylum. The standard order starts with Species, then Genus. So (c) starts correctly with the two lowest categories. The standard order then goes Family, Order, Class, Phylum, Kingdom. (c) skips Family and Class but has Order then Phylum, which is the correct relative order. (a) skips Genus, Family, Class, but has Order then Phylum. Option (c) is the best fit for a *partial* correct sequence starting from the bottom.
Assuming the question is asking for a partial sequence in ascending order, option (c) represents categories in a correct relative order from lowest to highest.
The correct sequence of taxonomical categories shown is **(c) Species Genus Order Phylum** (although Family and Class are missing between Genus and Order and between Order and Phylum, respectively, the listed categories are in the correct relative order from lowest to highest).
Question 9. Define and understand the following terms: (i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Answer:
(i) **Phylum:** A major taxonomic rank in the classification of animals, above Class and below Kingdom. It groups together related classes that share some fundamental common characteristics (e.g., Phylum Chordata includes animals with a notochord). In plant classification, the equivalent rank is Division.
(ii) **Class:** A major taxonomic rank above Order and below Phylum (or Division). It groups together related orders that share a few similar characteristics (e.g., Class Mammalia includes warm-blooded vertebrates with hair/fur and mammary glands, grouping orders like Primata and Carnivora).
(iii) **Family:** A taxonomic rank above Genus and below Order. It groups together related genera that share some similarities, although fewer than species within a genus. Families are characterized based on vegetative and reproductive features (e.g., Family Felidae includes genera like Panthera and Felis).
(iv) **Order:** A taxonomic rank above Family and below Class. It groups together related families that share a few similar aggregate characters (e.g., Order Carnivora groups families like Felidae and Canidae).
(v) **Genus:** A taxonomic rank above Species and below Family. It comprises a group of closely related species that share more common characters compared to species of other genera (e.g., Genus Panthera includes the species leo, pardus, and tigris).
Question 10. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Answer:
Taxonomical hierarchy for **Man (Animal)**:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Primata
- Family: Hominidae
- Genus: Homo
- Species: sapiens
Taxonomical hierarchy for **Mango (Plant)**:
- Kingdom: Plantae
- Division: Angiospermae
- Class: Dicotyledonae
- Order: Sapindales
- Family: Anacardiaceae
- Genus: Mangifera
- Species: indica
Exercises
Question 1. Why are living organisms classified?
Answer:
Question 2. Why are the classification systems changing every now and then?
Answer:
Question 3. What different criteria would you choose to classify people that you meet often?
Answer:
Question 4. What do we learn from identification of individuals and populations?
Answer:
Question 5. Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Mangifera indica
Answer:
Question 6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Answer:
Question 7. Can you identify the correct sequence of taxonomical categories?
(a) Species $\rightarrow$ Order $\rightarrow$ Phylum $\rightarrow$ Kingdom
(b) Genus $\rightarrow$ Species $\rightarrow$ Order $\rightarrow$ Kingdom
(c) Species $\rightarrow$ Genus $\rightarrow$ Order $\rightarrow$ Phylum
Answer:
Question 8. Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand, and bacteria on the other hand.
Answer:
Question 9. Define and understand the following terms:
(i) Phylum
(ii) Class
(iii) Family
(iv) Order
(v) Genus
Answer:
Question 10. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Answer: