Q1. Why are living organisms classified?
Answer: Earth is home to a diverse array of flora, fauna, and microorganisms, which exhibit distinct differences in their physical attributes, habitats, and other features. Given the sheer number of living beings on the planet, it is impractical to study each one individually. As a result, scientists have developed systems to categorize all living organisms. These methods rely on established rules and principles to facilitate the identification, naming, and classification of each organism.
For instance, by applying specific principles, when a living being is recognized as an insect, it will receive a scientific name and be classified with other similar organisms. Consequently, diverse taxonomic groups are formed by categorizing organisms according to their similarities and differences. Therefore, biological classification enables the understanding of the relationships between different organisms and facilitates organized and streamlined study of them.
Q2. Why are the classification systems changing every now and then?
Answer: There exists a vast number of plants, animals, and microorganisms on Earth. While a portion of these have already been recognized by scientists, numerous newly discovered species continue to emerge worldwide. Consequently, the need to classify these fresh species necessitates the development of new classification systems periodically. As a result, this requirement results in changes to the existing classification systems.
Q3. What different criteria would you choose to classify people that you meet often?
Answer: Suppose we aim to classify a group of forty students. We can initiate the classification by differentiating the students based on their genders, leading to the creation of two major groups – boys and girls. Each of these groups can be further subcategorized based on the names of the students within each group. However, given the possibility of multiple students having the same name, we can create additional subcategories based on the surnames of the students. In the event that more than one student has the same surname, the final level of classification can be based on the roll numbers of each student.
Q4. What do we learn from identification of individuals and populations?
Answer: Comprehending the characteristics of an individual or an entire population is valuable in recognizing similarities and differences among individuals of the same species or between different types of organisms. This knowledge assists scientists in categorizing organisms into various classifications.
Q5. Given below is the scientific name of mango. Identify the correctly written name?
Mangifera Indica
Mangifera indica
Answer: The binomial system of nomenclature specifies that the generic name of a species should always begin with a capital letter, while the specific name must commence with a small letter. Consequently, the proper scientific name for Mango is Mangifera indica.
Q6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Answer: Each category or unit of classification is referred to as a taxon and represents a rank. The fundamental level of classification is the species, followed by genus, family, order, class, phylum or division in increasing order. The highest level of classification is recognized as the kingdom.
Q7. 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 accurate hierarchical sequence of taxonomic categories in ascending order is as follows:
Species –> Genus — > Family — > Order — > Class — > Phylum — > Kingdom
Hence, both (a), and (c) denote accurate sequences of taxonomic categories.
Sequence (b) is incorrect since after species, the correct category to follow is genus. Therefore, it does not represent the correct sequence of taxonomic categories.
Q8. 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: In biological terminology, species is the fundamental taxonomic rank. It can be defined as a cluster of similar organisms that have the ability to interbreed under natural conditions to produce fertile offspring. Consequently, a species consists of individuals that are relatively reproductively isolated from other groups.
Species can also be defined as a group of individuals that share the same gene pool.
Q9. Define and understand the following terms:
(i) Phylum (ii) class (iii) family (iv) order (v) genus
Answer:
- (i) Phylum: Phylum is the principal subdivision of a kingdom. It comprises one or more related classes of animals. In the context of plants, instead of phylum, the term ‘division’ is used.
- (ii) Class: A class is a taxonomic grouping that encompasses one or more related orders. For instance, the class Mammalia comprises numerous orders of mammals.
- (iii) Family: A family is a taxonomic grouping that includes one or more related genera. In the context of plants, families are classified based on their vegetative and reproductive characteristics.
- (iv) Order: An order is a taxonomic category that comprises one or more related families. For instance, the order Carnivora includes various families of carnivorous mammals.
- (v) Genus: The taxonomic group, genus, includes species that are closely related. For instance, the Solanum genus comprises numerous species like nigrum, melongena, and tuberosum.
Q10. How is a key helpful in the identification and classification of an organism?
Answer: Taxonomic keys are an important tool used for identifying plant and animal species based on similarities and differences in their characteristics. A key consists of a series of statements, known as leads, which typically appear in pairs called couplets. Different keys are used for categorizing each taxonomic rank, such as family, genus, species, etc. Taxonomic keys can be useful in identifying unknown organisms as well. There are two types of keys: indented and bracketed.
Indented keys provide a sequence of choices between two or more statements, while bracketed keys use a pair of contrasting characters.
Indented key is a type of identification key used to identify unknown organisms based on a series of choices. Here is an example of an indented key for identifying insects:
1. Wings absent or not well-developed … go to 2
Wings well-developed … go to 4
2. Body flattened, resembling a worm … Silverfish
Body cylindrical or slightly flattened, resembling a caterpillar … go to 3
3. Three pairs of well-developed legs … Millipede
Many pairs of poorly developed legs … Centipede
4. Body elongated and cylindrical, with a head and distinct segments … go to 5
Body broadly oval or circular, without distinct segments … go to 6
5. Antennae present, body covered in bristles or scales … Caterpillar
Antennae absent, body smooth or with few hairs … Earthworm
6. Body less than 1 cm in length, antennae present … Springtail
Body more than 1 cm in length, antennae absent … Pillbug
By following the choices in the key, an observer can narrow down the possibilities and eventually arrive at the correct identification of the insect they are trying to identify.
Bracketed key is a type of identification key used to identify unknown organisms based on a series of choices. Here is an example of a bracketed key for identifying trees based on leaf characteristics:
1. Leaves simple (unlobed) … 2
Leaves compound (lobed) … 5
2. Leaves alternate on stem … 3
Leaves opposite on stem … 4
3. Leaves toothed, oval-shaped … [White Oak]
Leaves smooth, oblong-shaped … [Red Oak]
4. Leaves with 3 leaflets, smooth-edged … [Boxelder]
Leaves with 5 leaflets, toothed … [Sugar Maple]
5. Leaves lobed with smooth edges … 6
Leaves lobed with toothed edges … 7
6. Leaves deeply lobed, with 3 or 5 lobes … [Redbud]
Leaves shallowly lobed, with 5 or more lobes … [Sweetgum]
7. Leaves with 3 lobes, hairy underneath … [Sassafras]
Leaves with more than 3 lobes, smooth underneath … [Black Cherry]
By following the choices in the key, an observer can narrow down the possibilities and eventually arrive at the correct identification of the tree they are trying to identify. The names of the trees are written in square brackets, which indicate the final identification.
Q11. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Answer: Taxonomic hierarchy is defined as the arrangement of various taxa in a hierarchial order. In this hierarchy, kingdom is the highest level and species is the lowest level. To remember this system, use the mnemonic – KEEP POT CLEAN OR FAMILY GETS SICK
KEEP – Kingdom
POT – Phylum
CLEAN – Class
OR – Order
FAMILY – Family
GETS – Genus
SICK – Species
Classification of Plant
As an example, let’s classify tomato (Solanum lycopersicum)
Kingdom – Plantae
Division – Angiospermae
Class – Dicotyledonae
Order – Solanales
Family – Solanceae
Genus – Solanum
Species – lycopersicum
Classification of an animal
As an example, let us classify tiger
Kingdom – Animalia
Phylum – Chordata
Class – Mammalia
Order – Carnivora
Family – Felidae
Genus – Panthera
Species: panther tigris